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The English Channel has protected the Brits since time immemorial. On friday, daredevil Swiss Yves Rossy made history by crossing the channel from France to England on a home-made jet-powered wing.

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									A review of long-term research in the western English Channel
O Langmead1, Southward, AJ1, Hardman-Mountford, NJ2, Aiken, J.2, Boalch, GT1, Joint, I2, Kendall, M2, Halliday, NC1, Harris, RP2, Leaper, R1, Mieszkowska, N1, Pingree, RD1, Richardson, AJ3, Sims, DW1, Smith, T2, Walne, AW3 and Hawkins, SJ1
1. Marine Biological Association of the UK, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK. 2. Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth, PL1 3DH, UK. 3. Sir Alister Hardy Foundation for Ocean Science The Laboratory, Citadel Hill, Plymouth, PL1 2PB, UK.

1.Executive Summary
This review aims to outline long-term research from the western English Channel undertaken by the laboratories in Plymouth. Data held at Plymouth are described, and details of survey methods, sites, and time-series are given. Major findings from long-term studies are summarized, and their limitations outlined. Current research, with recent resurgence and expansion of many sampling programmes, is presented, along with future approaches, illustrating how these important and unique data, as well as providing an environmental baseline, can aid in understanding and predicting complex ecological responses to a changing environment. Between 1888 and the present date, investigations have been carried out into the physical, chemical and biological components (from plankton and fish to benthic and intertidal assemblages) of the western English Channel ecosystem. The Marine Biological Association of the UK has collected the main body of these observations, with more recent contributions from the Continuous Plankton Recorder Survey (from 1957) and Plymouth Marine Laboratory (from 1988). Together, these constitute a unique data series, in terms of the long time span and comprehensive sampling of biological and environmental parameters of the western English Channel ecosystem. Since the termination of many of these time-series in 1987, there has been a resurgence of interest in long-term environmental change. Many programmes have been restarted and expanded with the support of DEFRA and other agencies. Key findings from these long-term research programmes are as follows: 1. Observations span significant periods of warming (1926-36; 1985-present) and cooling (1961-79). During these periods of change, the abundance of key species has undergone dramatic shifts. The first period saw changes in pelagic assemblages (zooplankton and larval fish) that culminated with the collapse of the local herring fishery. During later periods of change, shifts in species abundances have been reflected in other assemblages, such as the intertidal and benthic fauna. 2. Many of these changes are related to climate, manifest as temperature change. This hypothesis is widely supported today and has been reinforced by recent studies that show responses of marine organisms to climatic attributes such as NAO strength. 3. Long-term data yield important insights on the impacts of anthropogenic disturbances (fisheries exploitation, pollution). Comparison of demersal fish hauls over time highlights fisheries impacts, not only on commercially important species, but the entire demersal community. The impacts of acute (Torrey Canyon oil spill) and chronic (TBT antifoulants) pollution are clearly seen in intertidal records. 4. Significant advances in diverse scientific disciplines have been generated from research undertaken using these long-term data series. Many textbook models of ecological processes have originated from this work (e.g. seasonal cycle of plankton, cycling of nutrients, pelagic food web trophic interactions and the influence of hydrography on pelagic communities). Today, associated projects range from studies on marine viruses and bacterial ecology to zooplankton feeding dynamics and validation of ocean colour satellite sensors. Recent advances in technology mean these long-term programmes are more valuable than ever before. Future directions being pursued include the continued development of coupled physical-ecosystem models using western English Channel time-series data to expand relationships between surface and subsurface properties with ecosystem-wide responses to predict future changes. It also would be highly beneficial to provide more spatial and high-resolution temporal context to these data, which is fundamental to capture processes that operate at multiple scales and understand how they operate within the marine environment. This can be achieved through employment of technologies such as satellite-derived information and advanced telemetered instruments that provide real-time in situ profile data from the water column.

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Table of Contents
1. Executive Summary ........................................................................................................... 1 2. Historical Background........................................................................................................ 3 3. Marine Biological Association (MBA) .............................................................................. 4 3.1. ICES stations: E1, L5 and the Channel Grid............................................................... 4 3.1.1 Temperature and Salinity ...................................................................................... 5 3.1.2 Currents and circulation ........................................................................................ 5 3.1.3 Nutrients ................................................................................................................ 6 3.1.4 Phytoplankton and productivity ............................................................................ 7 3.1.5 Zooplankton and post-larval stages of fish ........................................................... 9 3.2. Intertidal .................................................................................................................... 10 3.3. Demersal fish............................................................................................................. 11 3.4. Benthos...................................................................................................................... 12 4. Plymouth Marine Laboratory (PML) ............................................................................... 12 4.1. L4 .............................................................................................................................. 12 4.2. Bio-optics and photosynthesis................................................................................... 14 5. Sir Alister Hardy Foundation for Ocean Science (SAHFOS).......................................... 14 5.1. Phytoplankton............................................................................................................ 16 5.2. Routinely identified species ...................................................................................... 17 5.3. Species not routinely identified................................................................................. 17 5.4. Plankton and mesocale hydrography......................................................................... 18 6. Discussion ........................................................................................................................ 18 7. Tables ............................................................................................................................... 22 8. Figures.............................................................................................................................. 27 9. References ........................................................................................................................ 39

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2. Historical Background Investigations of the western English Channel began in Plymouth in 1888 when the laboratory of the Marine Biological Association (MBA) was opened. A condition attached to financial aid in the foundation years of the MBA stated that researchers should “aim at practical results with regard to the breeding and management of food fishes” (Southward, 1995). Hence as soon as the laboratory was completed in 1888 studies of eggs and larval stages of many fish species began (Cunningham, 1892a, b, c, d, e, f; Lankester et al., 1900; Garstang, 1903). Systematic collection of data on zooplankton, including fish eggs and larvae, only became possible when the MBA obtained reliable sea-going vessels: first ‘Oithona’ in 1902 then ‘Huxley’ in 1903 (Garstang, 1903). These vessels were used to carry out exploratory surveys of the Channel and continental shelf west of Plymouth and represented the UK’s contribution to the International Council for the Exploration of the Seas (ICES). Cruises were instigated upon the early recognition that continental shelf waters influenced hydrography and biological communities of the English Channel (Lankester et al., 1900). Results of this work were never published completely, although cruises continued until 1909 and provided the foundation for later studies (Southward & Roberts, 1987). Early interest by Allen (1922) regarding ‘natural fluctuations… and the conditions which influence them’, coupled with the belief that ‘life of the sea must be studied as a whole’ led to establishment of some time-series (notably by repeat sampling of ICES stations). Other studies were not designed to be the basis for long-term datasets; series evolved after early scientists recorded sampling locations, methods and findings, which were used for comparison by later workers. The benthic dataset originated in this way, with historic baseline surveys (Allen, 1899; Smith, 1932) revisited three decades later (Holme, 1961, 1966). The demersal fish surveys carried out in 1913-14 and 1921-22 with detailed records of catches and sizes also provided an accurate baseline for later work (Clark, 1914, 1920). The detection of large changes in marine communities during the 1930s (Russell, 1935a, b), followed by the failure of the herring fishery in the Channel and the replacement of the herring stock by pilchard (Cushing, 1961), led to the importance of continuing these programmes being recognised. During the First World War (1914-1918), sampling was interrupted when research vessels were requisitioned for the Royal Navy. After 1918, increased funding from the UK Government Development Commission allowed programmes to be greatly expanded when restarted. Work ceased again during World War II (1940-45) as vessels were again requisitioned. Systematic sampling was continued with relatively little disruption, with several expansions related to advances in technology, throughout the next 30 years. For example, in the 1970s continuous profiling instruments for temperature, salinity, chlorophyll a fluorescence, water transparency and inorganic nutrients of phosphate, nitrate and silicate were introduced, as well as underway measurements of all properties along the transect from Plymouth to E1. This period also saw an increase in the number of marine science organisations in Plymouth. The NERC Institute of Marine Environmental Research (IMER) had been created in 1970 through the merger of a number of units, the largest of which was the Edinburgh Oceanographic Laboratory, with a vision to satisfy a national need for coastal and marine research consolidated on one site in Plymouth. The Continuous Plankton Recorder (CPR) survey had been in operation since 1932 and started sampling in the English Channel in 1957, although operated from Edinburgh by the Scottish Marine Biological Association. It moved to Plymouth in 1976 where it was run by IMER (for a full history of the CPR survey see Reid et al. (in press). 3

In 1987 there was a major change in NERC funding priorities and all current MBA long-term series were terminated, with the exception of intertidal studies, which were maintained on a reduced scale. This coincided with formation of the Plymouth Marine Laboratory (PML) in 1988 by a merger of IMER and the laboratory of the Marine Biological Association (MBA), although the MBA also retained its identity. With the termination of the MBA long-term series, sampling was initiated at the historic coastal station L4 by PML. Initially no formal time-series was proposed; rather the L4 time-series was developed and maintained through a combination of different research projects, notably zooplankton and phytoplankton species composition. Shortly after these changes, international support for the CPR survey was found and in 1990 the Sir Alister Hardy Foundation for Ocean Science (SAHFOS) was formed as a charity to continue the CPR survey. Since 2001 most of the original Plymouth time-series have been restarted with funding from a variety of sources, but the period between 1987 and the restarts remains the longest interruption in most of the western English Channel long-term series. This review aims to outline the long-term research that has been conducted in the western English Channel by the three laboratories in Plymouth: MBA, PML and SAHFOS. Data held at Plymouth are described, and details of survey methods, sites, and time-series are given. Major findings from long-term studies are summarized, and their limitations outlined. Current research, with recent resurgence and expansion of many sampling programmes, is presented, along with future approaches, illustrating how these important and unique data can aid in understanding and predicting complex ecological responses to a changing environment. 3. Marine Biological Association (MBA) 3.1. ICES stations: E1, L5 and the Channel Grid These stations were established when the MBA undertook the initial investigations on behalf of the UK following the establishment of ICES, between 1902 and 1909 both from Plymouth and its laboratory at Lowestoft (Fig. 1, Fig. 2). E1 is situated about 22 miles southwest of Plymouth on a transect that passes through the ‘L’ stations (Fig. 1). It is well stratified in summer (Harvey, 1923, 1925; Pingree & Griffiths, 1978). The earliest records from E1 date back to 1902 (temperature and salinity; Matthews, 1905, 1906, 1911). This pioneering work was also the first to quantify changes in phosphate in the English Channel, documenting high levels in winter that decreased in spring and were related to changes in plankton abundance. Since then sampling has generally been maintained on a monthly basis, except during the gaps described above (Fig. 3). L5, two nautical miles west of the Eddystone, is less strongly stratified in summer than E1 (Armstrong et al., 1970, 1972, 1974), but its close proximity to Plymouth means regular sampling is possible. This site was favoured historically as, being close to the Eddystone, it could be easily and reliably located. L5 has been primarily used for sampling zooplankton and planktonic fish stages. The earliest records for zooplankton date back to the beginning of the last century, although not all from this site (Gough, 1905, 1907; Bygrave, 1911). There were also many early studies of planktonic fish larval (Cunningham, 1892b; Holt & Scott, 1898; Browne, 1903; Hefford, 1910; Clark, 1914, 1920; Allen, 1917; Fig. 3). In 1924, regular sampling of zooplankton and planktonic fish larvae began and samples were taken at weekly intervals 2 nm east of the Eddystone reef at Station A (Russell 1925; 1930; 1933; 1935a). Sampling was relocated later to L5 to maximise ship time, as this was en route to E1 (Southward, 1970; Southward & Boalch, 1986; Fig. 1, Table 1).

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The Channel Grid was established in 1959 (Armstrong et al., 1970) following concerns that station E1 was not typical of conditions in the western Channel (Cooper, 1958b). This constituted a grid of 42 stations covering an area of 30 x 45 nautical miles around E1 (Armstrong & Butler, 1962). Nutrient and hydrographic conditions varied considerably from station to station, so this grid was extended to cover the full extent of the mouth of the English Channel in 1961 (Armstrong et al., 1970, 1972, 1974). Findings from this work are presented in section 3.1.4. 3.1.1 Temperature and Salinity Early analyses of temperature data at E1 did not detect inter-annual changes (Atkins & Jenkins, 1952; Cooper, 1958a), although this apparent absence of variability may have been due to analyses using the integral mean for the whole water column (Southward, 1960). However, a later study that only included surface temperatures found a rise of 0.5 °C between 1921 and 1959 (Southward, 1960). Subsequent analyses of the period from 1900 until 1970 showed increasing temperature until 1945 followed by a period of cooling (Southward & Butler, 1972). The most comprehensive analysis examined these data in conjunction with data from within Plymouth Sound as well as air temperature and rainfall (Maddock & Swann, 1977). The authors concluded that although long-term temperature trends appeared small when compared with seasonal cycles. Such changes can be highly significant for species distributions (Russell et al., 1971; Southward et al., 1975, 1988). Annual time-series and seasonal variations of salinity at E1 have been described and discussed in detail by Pingree (1980). Seasonal changes in salinity reflect the total fresh water flux from river run-off and precipitation minus evaporation, and water movement. Water movement has relatively more affect on salinity changes than on temperature change and therefore more readily reflects circulation changes. The historical data set of salinity measurements has allowed quantitative estimates to be made of the mean flow through the English Channel and a value of 0.14Sv was determined. In the winter, the mean flow provides a significant warming contribution to the monthly heat budget (~20% in the eastern English Channel). The causes of interannual variability in the western English Channel have been linked to several climatic factors. Records from 1925-1974 show cyclical patterns synchronized with the 11-year sunspot index (Southward et al., 1975), however this relationship was not apparent in later years (Southward, 1980). More recent studies have shown that the strength of the North Atlantic Oscillation (NAO) also influences temperature (Alheit & Hagen, 1997; Sims et al., 2001). There are likely to be opposing tendencies between NAO and salinity change since positive winter NAO is associated with both an increase in rainfall and an increase in westerly wind strength, which will force saltier surface water into the region. 3.1.2 Currents and circulation A programme of in situ current measurements coupled with modelling studies for the South West Approaches was started in 1973, and moorings for continuous measurement of currents and temperature were deployed at E1 and E2 in 1974 (Pingree & Griffiths, 1977). The funding for the programme was jointly between MBA and National Institute Oceanography. These studies led to the tidal environment and circulation for the region being established (Pingree, 1980; Pingree & Le Cann, 1989). Mean northerly to northwesterly currents to the west of the mouth of the English Channel (i.e. Rennell Current) were found to be less than 3

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cms-1, but through a combination of Eulerian and Lagrangian1 methods, a significant northerly coastal current was found to flow near the Isles of Scilly to Lundy Island (Pingree et al., 1999) before being directed southwestward along the Irish coast and then northwest in a strengthening Valencia coastal current. Thus, flow at the mouth of the English channel was shown to have a much broader influence than previously realised. Later studies showed these currents to be related to flow in the West European Continental Slope Current. By relating these measurements to modelling studies, an in depth understanding of circulation in the western English Channel has been developed. Model responses (Pingree & Griffiths, 1980) showed that, for a given wind strength, westerly winds were least effective in driving a net transport of water through the straights of Dover and that a southerly wind gave the maximum transport of water from the English Channel into the southern North Sea. Water driven along the English Coast by west and westsouthwest wind fields in Eddystone Bay and Lyme Bay tends to have a more northern origin, whereas southerly winds collect water in the entrance to the Channel that has originated from the Armorican shelf region. On balance, there are opposing coastal circulation tendencies between southwesterly winds, which drive eastward flow along the Irish coast and western English Channel coast (Eddystone Bay and Lyme Bay), and buoyancy or density effects resulting from low salinity in coastal regions, which tend to produce cyclonic conditions in the coastal regions of the South West Approaches. Lagrangian measurements from buoys deployed in the English Channel during the winter of 1995/96 showed that a marked poleward continental slope flow, with warmer than average temperature on the outer shelf, occurred under negative NAO conditions (Pingree, 2002). Negative winter NAO conditions are associated with southerly or southeasterly winds in the region, although warmer winter sea temperatures in the Channel are also expected with westerly winds. 3.1.3 Nutrients The nature of the nutrient data collected at E1 reflects the evolution of quantitative measurement techniques in marine chemistry. The earliest phosphate measurements were made in 1916 (Matthews, 1917a, b) and regular inorganic phosphate measurement began in 1924 when quick and reliable techniques were developed (Atkins, 1923, 1925, 1926a, 1928, 1930). During this early period, a combination of phosphate and pH measurements was used as a proxy for plankton productivity, with the first estimate being 1.4 kg of diatoms m-2 integrated through the 70 m water column at E1 between March and July (Atkins, 1923). Nitrate was sampled sporadically from 1925 (Harvey, 1926), but was not routinely measured until 1974. Measurement methods changed several times throughout the series as new and more reliable techniques were developed (reviewed by Joint et al. 1997; Table 2). With the introduction of the photocombustion technique (Armstrong & Tibbitts, 1968), dissolved organic nutrients could be quantified, greatly enhancing understanding of nutrient dynamics (Butler et al., 1979). Seminal early publications resulting from nutrient research at station E1 include that of Harvey (1927) who demonstrated that the winter ratio of nitrate to phosphate in the English Channel was very similar to that in deep water in the Atlantic. Later, a ratio of 15:1 was proposed as the constant and suggested that ‘the anomaly of the nitrate-phosphate ratio’ be defined as the amount by which the nitrate:phosphate ratio differed from 15 (Cooper, 1938a, b, c). This ratio is very close to the now widely accepted Redfield ratio of 16:1 (Redfield et al., 1963). Jordan & Joint (1998) re-examined the historical E1 data highlighting the high
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While most time series studies reviewed here are Eulerian (fixed point) in nature, Lagrangian (drifting) studies also represent important time series with an added spatial dimension.

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degree of variability in nitrate:phosphate ratios, particularly during mid-summer when, in a significant number of years, mid-summer values of phosphate increased for short periods of time while nitrate concentrations remained low. While these changes were discussed in relation to phytoplankton assimilation and nutrient regeneration, no clear explanation has been determined. Much effort was made to understand nutrient dynamics in context with hydrography and biological activity (Pingree et al., 1977a). Early work by Atkins (1926b) recognised the relationship between the spring diatom bloom and silica content in seawater. This was later developed by Atkins & Jenkins (1956). Once the seasonal cycle of phytoplankton was understood (see section 3.1.4), the characteristic hydrographic conditions promoting bloom onset could be predicted using an analysis of temperature and nutrient vertical distributions from E1 (Pingree & Pennycuick, 1975). The distinctive nutrient signals from each period of the plankton cycle could be determined, together with the degree to which the composition of phytoplankton (dinoflagellate/diatom) in turn mediates nutrient signals (Pingree et al., 1977a, b). 3.1.4 Phytoplankton and productivity Phytoplankton samples from tow-nets were first analysed for species presence in 1903 (Fig. 3). Early records were semi-quantitative (Cleve, 1900; Gough, 1905, 1907; Bullen, 1908; Bygrave, 1911), and included frequent samples from Plymouth Sound and the Plymouth fishing grounds (Fig. 1) as well as less frequently visited stations in the western Channel. However, little work was published between 1911 and the 1964 Channel Grid project (see below). The most important work to come from this early period was a complete study of the seasonal changes in phytoplankton by Lebour (1917). This was followed by a study of phytoplankton dynamics in conjunction with zooplankton, hydrography and some nutrient measurements at L4 (Harvey et al., 1935). The seasonal cycle they first described is the basis of many textbook accounts (e.g. Tait, 1981). This innovative, multidisciplinary study showed that zooplankton grazers limited the spring bloom of diatoms, while the autumn bloom appeared to be controlled primarily by light, and provided a basis for the emerging study of marine productivity measurements. This work was extended in 1939 and additional measurements were taken at the Western Approaches; findings indicated high productivity which was related to vertical mixing of surface with deep oceanic water (Mare, 1940). At this time chlorophyll measurements were also beginning to be used to estimate phytoplankton biomass (Harvey, 1934a, b; Atkins & Parke, 1951; Atkins & Jenkins, 1953). Characterisation of marine optical properties was another important area for early work. It was quickly recognised that light attenuation of sea water was caused by a combination of absorption and scattering (Atkins, 1926c), with the latter occurring in a predominately forward direction (Atkins & Poole, 1940, 1952). Optical properties of the sea were related to phytoplankton seasonality and depth distribution, and the role of plankton pigments in mediating transmission of blue wavelength light was identified (Atkins & Poole, 1958). The majority of this work was carried out at E1, although inshore waters were also investigated (L4, L5). This important work provided the foundation for subsequent marine optics research. After the establishment of the Channel Grid in 1961, phytoplankton studies (counts, measurements of primary production) were added in 1964 to ongoing sampling of nutrient and hydrographic parameters (Boalch et al., 1969). The number of stations was reduced from 42 to 16 in 1967, but as intensive studies were not feasible at all stations, three stations: 4, 7 and E1 were selected for detailed study because of their contrasting hydrography: frontal, stratified and mixed respectively (Fig. 5; Pingree, 1978). Clear seasonal cycles were found in phytoplankton population structure, and differences between stations were related to 7

hydrography (Fig. 6). It was not possible to determine long-term trends with these data (Maddock et al., 1981) but productivity varied greatly from year to year, with timing of maximum growth depending on hydrographic and meteorological conditions (Boalch et al., 1978). Primary production increased after 1966 (Boalch, 1987), which corresponded with measurements of zooplankton biomass from farther inshore (L5; Russell et al., 1971). This also reflected with changes in inorganic nutrient levels (Armstrong et al., 1974) and temperature (Southward & Butler, 1972). Phytoplankton coastal sampling also picked up trends and pinpointed two occasions when changes were most marked: 1968-1970 and 198385 (Maddock et al., 1989). These patterns could be related to changes in weather patterns, and were similar to those found in other marine taxa (Southward, 1967, 1974, 1983; Russell et al., 1971). Complete characterisation of the seasonal succession of phytoplankton using continuous vertical chlorophyll ‘a’ measurements was an important step and provided the foundation for further work relating biological activity to nutrient chemistry and hydrography (Pingree et al., 1976; Holligan & Harbour, 1977). Three distinct periods were defined: 1) a near-surface spring bloom (<4 mg chl m-3 at 0-15m in April); 2) a summer subsurface bloom in the thermocline (2-4 mg chl m-3 at 20-25m in May-September, and fuelled by regenerated NH4); and 3) a near-surface autumn bloom (<2 mg chl m-3 at 0-15 m in late September to October). The spring bloom was dominated by diatoms, abundant in the subsurface bloom until May, when dinoflagellates and flagellates began to replace them, in a process completed by midsummer. In the autumn bloom, diatoms again became important. The spring bloom of diatoms usually develops faster than herbivores can increase their consumption rates by population buildup; consequently, much of the plant biomass sediments to the sea floor to provide at least a part of the regenerated nitrogen utilized by the microalgae of the summer phytoplankton. Once this cycle was characterised, it could be related to the differing physical stabilities encountered in the region, and the importance of frontal boundaries as sites of phytoplankton blooms was demonstrated (Pingree et al., 1976; Pingree & Griffiths, 1978; Pingree et al., 1978). Hydrographic conditions across the English Channel vary from stratified near the English coast, through a transitional region to the Ushant frontal boundary in the centre of the Channel and then to vertically well-mixed water near the French coast (Pingree, 1978). These conditions, particularly vertical stability of the water column, appear to play an important role in the development of dense dinoflagellates blooms in this region (Holligan & Harbour, 1977; Pingree et al., 1977b; Holligan et al., 1980). The introduction of remotely sensed information aided understanding of spatial patterns in productivity in the western English Channel, putting in situ measurements in context. Infrared and visible images of the E1 region and the South Western Approaches have been provided by the University of Dundee for MBA since 1975. Ocean colour studies were enhanced with the introduction of CZCS imagery in 1979 and SeaWiFS coverage from 1997. The data were not used for validation but rather for planning measurement cruises from Plymouth and observing near real-time development of plankton blooms in the region. There were several papers issuing from this NERC remote sensing support both for the local studies and the extended programme to the shelf break and Bay of Biscay. Notable papers that used the imagery coupled with in situ measurements include Pingree et al. (1982) and GarciaSoto & Pingree (1998). These papers defined the seasonal distribution and abundance of chlorophyll a at the mouth of the English Channel and in adjacent shelf and ocean margin environments. Further studies have involved monitoring coccolithophore blooms and a large bloom passing through E1 in June 1992 that impacted on the Isles of Scilly was studied using 8

simultaneous in situ measurements from RV Squilla and a NERC aircraft flight (Sinha & Pingree, 1994). Additional remote sensing data, for sea level and climate change studies were introduced in 1992 with altimeter data from the ERS1/2 and TOPEX/Poseidon satellite sensors. 3.1.5 Zooplankton and post-larval stages of fish Methods for sampling zooplankton and planktonic fish stages are outlined in Table 1. Thirty zooplankton species were regularly recorded (Table 3), corresponding to observations between 1924 and 1930 (Russell, 1933, 1935a, 1936), with some later amendments (Digby, 1950; Southward, 1962). These species were chosen as they were: 1) reasonably common in samples, 2) not able to reproduce rapidly, 3) distinctive and 4) typical of particular water masses. Attention was initially concentrated on longitudinal distributions of zooplankton from oceanic through western to Channel species (W to E) (Russell, 1935a, 1936). Further sampling led to the detection of relationships with latitude and climate (Southward, 1962) confirmed by later analyses (Southward, 1980; Southward et al., 1995). This work showed that original indicator species included north-south species pairings, so factors explaining their occurrence were expanded to include effects of climate change (Southward, 1962, 1963, 1980; Russell et al., 1971; Russell, 1973). Between 1924 and 1940 there was a decline in the chaetognath Sagitta elegans and associated cold-water plankton (Fig. 7). These were replaced by S. setosa together with a warm-water assemblage, and this shift in community composition was accompanied by a decline in planktonic fish and decapod larvae (Fig. 7) and demersal fish catches of cold-water species (Corbin, 1948, 1949, 1950; Russell, 1973; Southward, 1983; Southward & Boalch, 1994). Further reductions were apparent in Calanus helgolandicus and euphausids leading to a reduction in the diversity of intermediate trophic levels (Fig. 7). Non-clupeid larval species declined to very low levels between 1930-39, and herring (Clupea harengus), the most commercially important local species, was replaced by pilchard (Sardina pilchardus) (Cushing, 1961; Russell et al., 1971; Fig. 7). At the time this switch (later known as the ‘Russell Cycle’; Cushing & Dickson, 1976) was attributed to reduced Atlantic flow into the English Channel. This was suggested to cause a reduced influx of ‘new’ inorganic nutrients, with concurrent effects of decreased primary production and phytoplankton abundance leading to decreases in all higher trophic levels (Russell, 1933, 1935a; Kemp, 1938). Later work indicated that inorganic nutrient availability was not the primary factor driving these changes since nutrient levels in a subsequent cold- to warm-water community shift were higher than average (Boalch et al., 1978; Southward, 1980; Southward & Boalch, 1986; Southward et al., 1988). Furthermore, early data have been re-examined and little evidence found to support the role of phosphate in the Russell Cycle (Joint et al., 1997). The warm-water plankton community persisted until the early 1960s. From this point there was increasing abundance of Calanus and fish larvae (Russell, 1973), cold-water species characterised by Sagitta elegans began to return, reaching a peak in 1979, by which time there was reduced spawning of pilchard off Plymouth (Southward, 1974, 1995). Additionally after 1961, pilchard peak spawning timing switched from spring and autumn to mostly autumn, coinciding with cooler conditions. After 1985 the balance began to switch again from coldwater species to warm-water species, and pilchard spawning increased (Southward et al., 1988). These trends in pelagic fish are reflected on a regional scale, with large herring catches on the Swedish coast (Bohuslän) and in the Bay of Biscay coinciding with those at Plymouth, and also corresponding with severe winters in western Europe and the negative phase of the NAO (Alheit & Hagen, 1997).

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3.2. Intertidal The first MBA records of selected intertidal organisms on rocky shores were surveys at five sites around Plymouth in 1934 (Moore, 1936). Subsequently, annual records were taken from 1951, primarily to assess the abundance of barnacles for 19 stations (Southward & Crisp, 1956; Fig. 8). As funding decreased stations were reduced over the course of time to three and then to one critical site (Cellar Beach) in 1988 (Southward, 1991). A further series exists, over a wider geographical area originally surveyed in 1931-4 (Fischer-Piette, 1936) and including a larger number of intertidal species. This was continued from 1954-1987 at sites around the south west peninsula (Crisp & Southward, 1958; Southward, 1967). There are further series monitoring intertidal organism abundance spanning more than 20 years; 1) from 1980 collected by SJ Hawkins focussing primarily on Patella spp. (Southward et al., 1995) and 2) a trochid series (1978-1985 with resurveys in 2002) collected by M Kendall and N. Mieszkowska. Striking patterns in barnacle abundance can be seen in the data (Fig. 9); Chthamalus spp., with a “southern” or warm-water distribution dominated shores in the 1950s (Southward, 1991). In the 1960s and 1970s Semibalanus balanoides, the “northern” coldwater species became more prevalent, increasing rapidly after the cold winter of 1962-3, which severely affected Chthamalus populations (Southward, 1967). Since the late 1980s Chthamalus have increased again, but have not yet reached levels recorded during the 1950s. The displacement of S. balanoides by Chthamalus in warmer periods is thought to occur through increased competition, as Chthamalus produces more and earlier broods of larvae, together with increased mortality of S. balanoides related to high temperatures (Southward & Crisp, 1954, 1956; Burrows, 1992). The ratio of these species has been used as an index, and shows good correspondence with sea temperature, notably with a 2-year time lag (Southward, 1967; Southward et al., 1995). This time lag represents the average interval between reproduction in successive generations. The relationship between events in the Channel and further offshore (best correspondence was found with Bay of Biscay sea surface temperature) suggests a general forcing function from the ocean. Most sites showed this pattern but local factors such as topography and currents, as well as chance events, also have a strong influence. Similar effects have been seen in other intertidal organisms such as limpets (Southward et al., 1995), though gaps in these data preclude detailed analyses. The most rapid decline in Patella depressa (a warm-water species) followed the cold winter of 1962-3 (Crisp, 1964). It had been abundant prior to this, and during colder periods it was displaced by P. vulgata. From the mid-1980s P. depressa increased again. Changes in limpet abundance are not as clear as barnacles as a result of life history differences (Southward et al., 1995). Particularly an extensive juvenile phase in a different habitat (rock pools in the case of P. depressa, rock pools and damp places in the case of P. vulgata) can dampen signals generated by climate. Changes in trochid (Osilinus lineatus and Gibbula umbilicalis) population structure and distribution have also been recorded (Kendall et al., submitted). The significance of long-term intertidal records became apparent in the wake of the 1967 “Torrey Canyon” oil spill and subsequent excessive application of toxic dispersants. Longterm studies of recovery were made at one of the worst affected sites, Porthleven (Southward & Southward, 1978; Hawkins et al., 1983; Hawkins & Southward, 1992). These data were vital to separate pollution-induced changes from natural effects (Smith, 1968; Southward & Southward, 1978; Hawkins & Southward, 1992). Recovery at dispersant treated sites occurred as a series of damped oscillations (periodic collapses in destabilized key species populations such as limpets and fucoids) until normal levels of small-scale patchiness were reached after 10-15 years (Hawkins et al., 2002). By contrast, areas where dispersants had not been applied recovered after 2-3 years (Southward & Southward, 1978). 10

During the mid-1980s the toxic effects of the antifoulant tributyl tin (TBT) on a variety of non-target organisms were demonstrated (review by Bryan & Gibbs, 1991). In the UK, the dogwhelk Nucella lapillus proved to be highly sensitive to TBT pollution, and a useful bioindicator of coastal ecosystem recovery (Hawkins et al., 2002). In 1987 TBT was banned in the UK on vessels less than 25m. Sites monitored near Plymouth (1986-2000) showed that recovery was initially rapid but has levelled out in recent years, suggesting there is still some contamination from large ships or sediments (Evans et al., 1991). 3.3. Demersal fish The demersal fish assemblage off Plymouth has been sampled intermittently between 1913 and 2003 (Fig. 3). A total of 92 species have been recorded within 784 otter trawls (mean duration, 52 min) during 24 years. The number of individual fish were counted and length and weight recorded. Trawls were undertaken at 30-50 m depth over an area covering 42 x 19 km (Fig. 10). Throughout the series six vessels were used, ranging in overall length from 18.3 to 39.0 m. The trawl gears used were of comparable dimensions and trawling was carried out at similar speeds during the time series. An important aspect of this continuity in method has been the usage of the same net and vessel from 1976 to the present day. This ‘Standard Haul’ time series was complemented by a high-temporal resolution trawl series undertaken with the MBA ship RV Sarsia between 1953 and 1972. Over 1,550 trawls each of 2.4 h (mean) duration were undertaken in four trawling areas off Plymouth (the inshore stations: Looe Grounds, latitude 50o16′ N, longitude 04o24′ W, and Middle Grounds, L4, 50o15.5′ N, 04o13′ W; the deeper water grounds, Eddystone (inner) Channel Grounds, 50o08.5′ N, 04o15′ W, and the Eddystone (outer) Channel Grounds 50o02′ N, 04o20′ W). The inshore areas were trawled during both ‘Sarsia’ and ‘Standard Haul’ series, but the deeper water grounds were sampled only during the shorter ‘Sarsia’ series. These long-term datasets indicate both short and long-term trends in the responses of fish and squid to both natural fluctuations in climate and human-induced changes associated with commercial exploitation of stocks. Interannual changes in the timing of migration of veined squid (Loligo forbesi) were linked to climate forced changes in sea bottom temperature, with migration occurring earlier in warmer years when the NAO was more positive (Sims et al., 2001). In contrast, the spawning migration of flounder (Platichthys flesus) from their overwintering estuarine habitat to spawning grounds at sea started earlier in years that were up to 2oC cooler (Sims et al., in press). Flounder responded to low winter temperatures in the estuary with early migration to the relatively warmer sea, thermal changes that were mediated by the cold, negative phase of the NAO. These studies indicate that climate-forced fluctuations in sea temperatures affect the timing and location of peak population abundance of fish and cephalopods. Long-term data on the annual abundance of fish off Plymouth clearly show major changes in the composition of the demersal fish assemblage (Fig. 11). Analyses show that these longterm changes are driven in part by climate-linked trends in sea temperature. The southwest region has been subjected to major climate shifts over the last century (Russell et al., 1971; Southward, 1980; Southward et al., 1995), namely warming in the 1950s to the present day, following relatively cooler periods in the 1900s and 1970s. It is thought that these changes resulted in increasing observations of rare warm-water fish in the 1930s, such as Clupea finta, Polyprion americanum, Naucrates ductor, Seriola dumerili, Pagellus erythrinus, Pagrus vulgaris, Lepidopus cuadatas, Scomber colias, Pelamys sarda, Euthynnus pelamys, Balistes capriscus and Tetrodon lagocephalus (Russell, 1953). By the early 1950s there had been an increase in proportion of warm-water demersal fish in hauls (Southward, 1963; Southward & 11

Boalch, 1992), a trend that has continued and is reflected at other locations in the South West UK (Stebbing et al., 2002). The continued effect of rising sea temperature from 1990 to present day has resulted in the increased abundance of a subset of dominant (common) species with a southern geographical distribution (e.g. dragonet, Callionymus lyra). These species have no commercial importance in the region, however, changes of some species in the assemblage in the last 25 years show that major, ecosystem-level impacts of fishing have occurred (Genner et al., 2001). Mean fish length has declined, as has mean maximum length and mean length of maturity for the assemblage. This suggests a species level shift to taxa that grow to, or mature at smaller sizes. These declines are most striking in commercially exploited species, notably skates and rays (Hawkins et al., 2003). Taken with other criteria, evidence is consistent with patterns expected from the selective, unsustainable harvesting of large, commercially valuable species (Genner et al., 2001). 3.4. Benthos The benthic invertebrate fauna of the English Channel were sampled intermittently from 1899 to 1985 (Fig. 3). The longest continuous dataset are those collected by Holme (1959-1985) (Table 4), that have been assessed for quality of the data and potential for resurvey (Genner et al., 2001). Holme made a point of resurveying historic sites, e.g. Eddystone Grounds (Fig. 1), which had been originally surveyed between 1895 and 1898 (Allen, 1899) and again from 1931 to 1932 (Smith, 1932). Three datasets were produced: 1) survey of seabed species, 2) brittlestar survey and 3) death assemblages, there is also an extensive archive of videotapes, videocassettes and photographic transparencies. The seabed species dataset constitutes a qualitative faunal record of echinoderms and molluscs for 324 stations distributed throughout the English Channel. In addition Holme compiled reference lists from comparable historic MBA surveys as far back as 1895. The brittlestar survey used a different methodology to the seabed species survey (mini-Agassiz trawl and anchor dredge, respectively), and provides a quantitative record of all echinoderms from 329 stations on the south coast of England. Death assemblages are a record of all dead-shell material retained in anchor dredges. Fluctuations in benthos have been related to sea temperature, notably exceptionally cold winters, immigrant species, dinoflagellate blooms, and, increasingly, heavy fishing gear (Holme, 1983). Fluctuations in western species (cold water) are likely to relate to temperature (e.g. Munida bamffica - anomuran crustacean, Echinus acutus - sea urchin and Dentalium entalis - scaphopod mollusc), as are fluctuations in Sarnian species (warm water), (e.g. Octopus vulgaris, common octopus, Venus verrucosa and Dentalium vulgare) (Holme, 1966). However, the increased use of toothed scallop dredges and heavy chains on trawls to catch sole were recognised as increasingly important factors in determining benthic communities (Holme, 1983). In 1998 selected benthic communities were resurveyed to test hypotheses regarding resilience of megabenthic species (Glycymeris glycymeris and Paphia rhomboids) to fishing disturbance (Kaiser & Spence, 2002). Most sites showed temporal changes in bivalve and echinoderm communities, as would be expected over a 40-year period, although two out of ten did not, suggesting that a few areas of the seabed exist with a similar community composition to that before the general increase in bottom-fishing disturbance. These results reflect the patchy nature of benthic communities and highlight the need for further work in this area to interpret such spatial and temporal inconsistencies. 4. Plymouth Marine Laboratory (PML) 4.1. L4 L4 is situated about ten nautical miles SW of Plymouth (Fig. 1) in water about 55 m deep and is influenced by seasonally stratified and transitional-mixed waters (Pingree & Griffiths, 12

1978). Zooplankton monitoring data have been collected at station L4 on a near weekly basis since 1988, together with a range of physical, chemical and biological measurements (see Table 5 for methods), notably zooplankton and phytoplankton species composition (Fig. 12). This sampling was initiated when the other long-term records were terminated in 1987 (Fig. 3). The majority of the work has been carried out by PML staff, visiting workers and students over the years. This is reflected in the variety of publications which have been based on particular elements of the L4 programme: Appendicularian and copepod population dynamics (Green et al., 1993; Acuna et al., 1995; Lopez-Urrutia et al., in press); copepod feeding (Bautista & Harris, 1992; Bautista et al., 1992; Irigoien et al., 2000c); copepod egg production (Bautista et al., 1994; Guisande & Harris, 1995; Pond et al., 1996; Laabir et al., 1998; Irigoien et al., 2000a; Irigoien et al., 2002), and the testing of new in situ techniques (Biegala & Harris, 1999). The L4 sampling has also been compared with the Continuous Plankton Recorder data for the area (John et al., 2001). The complete L4 dataset is available online at: www.pml.ac.uk/L4. One of the strengths of the L4 time-series is that it covers microbial elements of the planktonic food-web. For example Rodriguez et al. (2000) describe parallel changes in viruses, bacteria, phytoplankton and zooplankton at this station. Over the time series Pseudocalanus has been the most abundant copepod making up 12% of the total population. Abundance of Calanus helgolandicus at L4 shows a decreasing trend from 1988 to 1995. Similar trends were seen in total zooplankton; low spring abundances of Pseudocalanus and Acartia spp. were characteristic of the years of overall low zooplankton abundance (1988-1995), as was a high abundance of Cirripede nauplii (Harris, 2003). Recovery of zooplankton populations between 1995 and 1999 was mainly due to two autumndeveloping copepods, Euterpina sp. and Oncaea sp., as well as Paracalanus parvus. Seasonal and interannual variability in environmental variables, egg production rates and abundance of Calanus helgolandicus at L4 have been analysed in detail (Irigoien & Harris, 2003). The results (for example, Fig. 13) show a mismatch between the timing of maximum egg production and timing of the abundance peaks. However, except for the year 1996, there was a significant relation between the initiation of the thermocline and the timing of the maximum female abundance. Advection and egg mortality due to sinking were suggested as the main factors controlling the timing of the C. helgolandicus abundance peaks in the English Channel at station L4. The seasonal phytoplankton cycle is characterised by a spring diatom and a summer dinoflagellate bloom. The spring bloom assemblage, dominated by diatoms differs from year to year, e.g. Chaetoceros socialis was dominant in 1993 whereas in 1994 Rhizosolenia delicatula was dominant. The dominance of diatoms within the spring bloom phytoplankton has been related to the North Atlantic Oscillation (Irigoien et al., 2000b). Spring diatom concentration (both abundance and percentage of diatoms) showed a positive relation with the winter NAO index when the average for the April-May period was considered (Fig. 14). In contrast the average amount of total phytoplankton carbon during the spring was not related to the NAO. Positive NAO conditions in the NE Atlantic imply increased westerly wind stress and increased precipitation. Stronger mixing (increased winds) and nutrient levels (increased river run off) should favour diatoms to the detriment of flagellates. Phytoplankton composition has important consequences for ecosystems in terms of both energy transfer efficiency and nutritional value for upper trophic levels. The dinoflagellate bloom in summer is intense at L4 and is usually dominated by Gyrodinium aureolum, which usually comprises >95% of phytoplankton carbon at peak production.

13

4.2. Bio-optics and photosynthesis From the early 1980s, phytoplankton fluorescence and optical measurements have been acquired throughout the western English Channel (Aiken, 1981a, 1985; Aiken & Bellan, 1986b, 1990). From this work came significant advances in instrumentation and methodology for quantifying chlorophyll fluorescence (Aiken, 1981b), chlorophyll adsorption (Aiken, 1985), bioluminescence (Aiken & Kelly, 1984) and photosynthetically active radiation (PAR) (Aiken & Bellan, 1986a). Particularly notable are the development of hemispherical logarithmic PAR and multiband light sensors (Aiken & Bellan, 1986a). Between 1979 and 1984, chlorophyll fluorescence, salinity, temperature, depth and zooplankton abundance were measured with the Undulating Oceanographic Recorder (UOR) in conjunction with the CPR along the Plymouth-Roscoff ship-of-opportunity route (MV Cornouallies) used by the CPR survey (Robinson et al., 1986). The bio-optical work in Plymouth has been of utmost importance in the validation of satellite ocean colour measurements. Measurements of downwelling and upwelling hemispherical irradiance in four wavebands (443, 520, 560 and 620 nm) were recorded on some UOR tows as validation of measurements from space by the Coastal Zone Color Scanner (CZCS) (Holligan et al., 1983). Throughout the late 1990s, profiled optical data were acquired occasionally at L4, E1 and other stations in the western English Channel (Zibordi et al., 1998), combined with a buoy designed to provide calibration and validation of SeaWiFS satellite ocean colour sensor in a shelf sea location in temperate waters, far removed from NASA’s principal site off Hawaii. The Plymouth Marine Bio-optical Data Buoy (PlyMBODy) was originally sited at L4, but after collision with a merchant ship, it was moved to a new site nearby with similar oceanographic and optical characteristics. PlyMBODy was deployed through the spring to autumn periods of 1998, 1999 and 2000 and supporting optical data were acquired by profiled systems alongside the buoy site. PlyMBODy showed that a small low-cost data buoy could provide accurate calibration and validation of SeaWiFS and reported the calibration errors in the SeaWiFS visible channels in the location of the western English Channel. A regular weekly schedule of sampling optical properties and photosynthetic parameters (with Fast Repetitition Rate Fluorometer, FRRF) at L4 was implemented in 2001 and has continued to the present date (Table 5). These data are currently being used to validate the MERIS ocean colour sensor on ENVISAT. Occasional sorties were made to E1 prior to 2002, but it was only through the E1 restart in 2002 that regular monthly sampling of optical properties was established there (Table 8). Aiken et al. (in press) reported the seasonal succession of phytoplankton quantum efficiency (PQE), pigment composition and optical properties at L4 and E1. These measurements show that there may be a functional link between these properties, suggesting that chlorophyll a is synthesised preferentially when plants are in active growth, providing a pigment and optical proxy for PQE and the possibility of detecting these in remotely sensed ocean colour spectra. 5.Sir Alister Hardy Foundation for Ocean Science (SAHFOS) CPR background The CPR is a towed body, approximately 1 m long, that filters seawater onto a continuously moving band of filtering silk. Samples are taken at a depth of about 10 m (Batten et al., in press). Organisms captured on the CPR silk (270 µm mesh) are preserved in borax-buffered formalin within the CPR immediately on collection. Samples are then returned to the laboratory where they are counted in a four-stage process (Table 6; for more details see Colebrook, 1960; Warner & Hays, 1994). A list of the taxa identified can be found in Warner & Hays (1994) or at the SAHFOS website (www.sahfos.org), along with access to the CPR 14

database. Methods of analysis have remained relatively unchanged since 1948, although a different method for counting phytoplankton was used from 1948-1957 (Table 7). The western English Channel was first sampled by the CPR in January 1952, and a total of 4768 samples have been collected and counted up to 2001 (see Fig. 12 for sample locations). Two routes have been sampled consistently on a monthly basis (Warner & Hays, 1994). The first runs approximately east-west, from Portsmouth through the English Channel and then across the Bay of Biscay (Fig. 15). This route was first towed in April 1957 and remained in operation until May 2000, although other routes now sample this area. Fourteen ships have towed this route and a total of 2548 samples have been collected. The second route that has been well sampled runs north-south across the English Channel from Plymouth to Roscoff (Fig. 15). This route has been sampled monthly from April 1974 until May 1994, and will resume again in 2004. A total of 1778 samples have been collected and counted. Consistency issues As with other long-term time series, there are issues regarding the consistency of the data. The survey has tried to maintain the methodological consistency in terms of equipment and counting procedures as far as is possible. There have only been minor modifications to the CPR itself since 1929. These include the attachment of a box tail that was phased in from 1977-1980 to increase stability at faster ship speeds, and an elongated tail end that was introduced in 1985 to carry additional electronic instruments (see Reid et al., in press), for more details). However, the synoptic coverage of the survey means that there are additional consistency issues encountered, different from those facing long-term time series at a single location. The synoptic coverage is only possible because the CPR is voluntarily towed behind ships of opportunity on their normal routes of passage, making it difficult for the Survey to maintain consistent sampling in space and time. One issue related to the use of ships of opportunity is that ship speed has generally increased over the period that the CPR Survey has operated (Fig. 16a). On particular routes this increase has been stepped because of ship changes. For the route from Southampton to Spain, ship speed remained remarkably constant at ~12.5 knots from 1958-1985, after which speed increased gradually to ~14 knots. The passenger ferries on the Plymouth to Roscoff route are considerably faster than the cargo vessels to Spain, with speeds from 1974 to the mid-1980s averaging ~16 knots, and these increasing to ~18 knots by 1995 with some routes being towed at speeds >20 knots. Some consistency issues related to using ships of opportunity manifest spatially. Large spatial changes over the years (Fig. 16) are often a consequence of the availability of ships willing to tow CPRs, as well as the effect of vagaries of funding. There are also variations in the mean latitude and longitude of sampling each month in a region such as the western English Channel, which can influence the plankton community observed. In terms of latitude, there has been very little change in the average sampling position, but there have been greater changes in longitude. The average sampling position in the Channel was ~4ºW until the mid1970s, and is now ~2.8ºW. Other consistency issues can manifest on various time scales from annual to diel scales. On an annual scale, the actual number of samples collected has varied considerably: ~60 samples were collected each year from 1957-1973, whereas ~150 samples per year were collected from 1974-1994 when the Plymouth to Roscoff route was operating. On a monthly scale, sampling can be reduced or absent in a particular month because of the jamming of the internal cassette that contains the silk, although this is relatively infrequent (success of CPR tows is ~95%). Data for a month can also be lost because a ship is out of service or when the 15

sea state is too rough for safe deployment of CPRs, a condition more frequent in winter. On a diel scale, the time of day that sampling is carried out can change as schedules and ships change. As the CPR is a near-surface sampler, this temporal bias needs to be considered when investigating zooplankton species that undergo diel vertical migration. For the western English Channel, the proportion of samples during daylight is quite variable each month (Fig. 16b), although there has also been a clear tendency toward collecting a greater proportion of samples during the night. This change in sampling in the mid-1970s was a result of the start of the daytime Plymouth to Roscoff route in 1974. 5.1. Phytoplankton Considerable work has been undertaken on the seasonal dynamics of phytoplankton blooms in the region. Diatom blooms are mainly found in the western English Channel in May and July, and Ceratium blooms (a dinoflagellate) in July (Reid et al., 1987). Colebrook (1979) reports that the seasonal phytoplankton cycle in the western English Channel had a large spring peak with a very small autumn peak. This seasonal cycle resembled most closely that of the southern North Sea. The spring bloom occurs earlier in the western English Channel and North Sea and was more readily exploited by copepods than blooms off the continental shelf (Colebrook, 1979). Robinson et al. (1986) report that the seasonal cycle of phytoplankton species was earlier in the northern areas of the Channel than off the French coast, concluding that this was in response to the stability of the water column. This was also found by Boach & Harbour (1977). Interannual changes in phytoplankton in the region have been described by Robinson & Hunt (1986). They analysed a series spanning 1967-1983 covering the area where the Portsmouth to Spain and Plymouth to Roscoff routes intersect (49°-50° N and 3°-5° W). Sixteen phytoplankton species were used to identify long-term trends, and these (together with the zooplankton) fell into four groups of species with similar trends in their annual abundance. The strongest trend was an increase in phytoplankton, notably the dinoflagellates Prorocentrum, Ceratium lineatum, C. furca, C. tripos, C. fusus and the diatoms Thalassiosira spp. and Rizosolenia shrubsolei. Complex relationships were found between the plankton and environmental factors (salinity, sea surface temperature, radiation, atmospheric pressure patterns, wind speed and current strength), suggesting that long-term changes are mediated through the interaction between plankton and climate (Robinson, 1985; Robinson & Hunt, 1986). They conclude that changes in the western Channel were responding to climate changes over a much wider area. More recently, Edwards et al. (2001) reported that there has been little change in the phytoplankton colour (see Table 7) in the western English Channel for the period 1981-1995, although there has been substantial increases elsewhere in the North East Atlantic. One of the most dramatic changes to the phytoplankton community in the North East Atlantic appears to have emanated in the western English Channel. This was the site of an introduction of the non-indigenous diatom species Coscinodiscus wailesii, a large centric diatom (175-500 µm) that was originally only known from the North Pacific Ocean. It was first recorded in the North Atlantic Ocean off Plymouth in January 1977 (Boach & Harbour, 1977), probably having arrived via ballast water or by the importation of oysters from the North Pacific. It was first seen in CPR samples of spring the same year off Plymouth, and spread over the next decade throughout the English Channel, North Sea and Irish Sea (Edwards et al., 2001). C. wailesii has become established in European continental shelf seas, becoming a significant member of the phytoplankton community in spring and autumn. During spring this species can comprise up to 90% of the phytoplankton biomass in some areas (Edwards et al., 2001). Interestingly, C. wailesii in the western English Channel has been scarce in recent years (Fig. 17). 16

5.2. Routinely identified species The seasonal cycle of copepods in the western English Channel has been described by Robinson et al. (1986). Although the timing of the seasonal cycle may be slightly earlier off the English than the French coasts, the most marked difference is the longer seasonal cycle of zooplankton in the Central Channel. Some key species in the region, however, do not have only one peak in their abundance: the seasonal cycle of Calanus helgolandicus is generally bimodal, with a peak in spring and autumn (Planque & Fromentin, 1996). Interannual trends in 20 zooplankton species were reported by Robinson & Hunt (1986). They found that there had been a general decrease in many species, particularly Acartia clausi, Centropages typicus and Euphausiacea. This decline has reversed since 1983, although abundance of these species was low during 2001 (Fig. 17, updated from Robinson & Hunt, 1986). More recently, a comparison of CPR data for the English Channel, Bay of Biscay and Celtic Sea between 1979 and 1995 was conducted, exploring factors that influence the relationship between climate and plankton (Beaugrand et al., 2000). Results showed that negative NAO strongly influences the copepod community in the Channel (Acartia spp., Calanus helgolandicus, Centropages typicus, Oithona spp. and Para-pseudocalanus spp.) through a number of mechanisms including turbulence, though this relationship could not be extended to other areas. It was concluded that the local physical environment and biological composition appear to modify the relationship between winter climatic conditions and interannual fluctuations in the plankton community. New insights into the dynamics of the copepod community in the western English Channel have been provided by analysing changes in spatial extent of assemblages in the North Atlantic based on diversity. Copepod diversity in the western English Channel is generally higher than in the North Sea but lower than the Bay of Biscay to the south (Beaugrand et al., 2000). Seasonally, diversity is highest from May to September in the western English Channel (Beaugrand & Ibañez, 2002). The spatial extent of the regime shift that has been reported in the North Sea by Reid et al. (2001) was investigated by Beaugrand & Ibañez (2002). They found that the regime shift affected copepod diversity in the central and northern North Sea, Bay of Biscay, and off the European shelf, but that there was no significant effect in the western English Channel or southern North Sea. The most dramatic change, however, has been the movement of warm water copepod assemblages northward, with a southward retraction of cold-water assemblages. This has resulted in fewer cold water species in the western English Channel and an increase in the generally warm water pseudo-oceanic temperate species assemblage comprising Rhincalanus nasutus, Eucalanus crassus, Centropages typicus, Candacia armata, Calanus helgolandicus (Beaugrand et al., 2002). 5.3. Species not routinely identified Although many taxa in the CPR survey are not routinely speciated and are reported as a combined entity, specific studies are sometimes undertaken. These have been published in Bulletins of Marine Ecology throughout the history of the Survey. Common species in the western English Channel for the following groups can be found: chaetognaths (Wood et al., 1967), cirripede larvae (Roskell, 1975), Clausocalanus (Williams & Wallace, 1975), gastropods (Vane, 1961), ostracods (Williams, 1975), the pteropod Pneumodermopsis (Cooper & Forsyth, 1963), thaliaceans (Barnes, 1961), tintinnids (Lindley, 1975) and young fish (Henderson, 1961; Coombs, 1975). A detailed study of the distribution and seasonal cycle of decapod larvae from the CPR throughout the North East Atlantic from 1981-1983 was conducted by Lindley (1975). The most common species in the western English Channel were Atelecyclus rotundatus, Galathea intermedia, Hippolyte varians, Liocarcinus puber, Pandalina brevirostris, Pilumnus hirtellus, 17

Pisidia longicornis, Total Polyblinae and Upogebia deltaura. Both the timing of the appearance of decapod larvae and their distribution were highly correlated with water temperature. These taxa are expected to be good barometers of climate change. Coombs (1975) described inter-annual and seasonal changes of selective fish larvae from the CPR survey. He noted that the northern limit of the distribution of Stomias boa ferox (dragonfish) shifted much further south between 1968-72 and extended into the Channel, compared to 1948-67 when larvae were only found over deep water beyond the continental shelf (Coombs, 1975). Other fish also showed a southerly shift in their distributions e.g. Melanogrammus aeglefinus (haddock), Micromesistius poutassou (blue whiting), Scomber scombrus (mackerel) and Hippoglossoides platessoides (long rough dab). This occurred over the same period that similar changes in geographical distributions have been reported in fish and other marine animals indicating an increased boreal influence from about 1965 (Southward, 1967; Russell et al., 1971; Russell, 1973). Furthermore, the seasonal period during which most Stomias larvae are found in the Western Approaches has shifted from March-April (1948-1961) to April-June (1968-1972). This was coincident with a shift in pilchard egg seasonality in the Channel to later in the year (Russell et al., 1971). This adds to evidence already available (Southward, 1980) that many marine organisms underwent a marked change around 1965-1967 (Russell et al., 1971; Russell, 1973). 5.4. Plankton and mesocale hydrography The most detailed study of mesoscale relationships between plankton and hydrography in the region was conducted by Robinson et al. (1986). The distribution of 21 phyto- and 24 zooplankton taxa in relation to temperature (from the Undulating Oceanographic Recorder) and fronts was described along the Plymouth to Roscoff route. CPR samples yielded similar phytoplankton species to those recorded by Maddock et al. (1981). Three areas could be identified according to their planktonic and hydrographic properties; 1) French coastal area where the water column is mixed throughout the year, the abundance of phytoplankton and zooplankton is low and the productive season is short; 2) a central area with strong stratification in summer and high zooplankton (particularly copepod) abundance, and 3) British coastal waters where the spring outbreak of phytoplankton is earliest, numbers of phytoplankton are high, zooplankton numbers are low and there is a long productive season. Inter-annual variability in plankton distribution could be related to changing position of fronts at the northern and southern ends of the route (Robinson et al., 1986). 6. Discussion The importance of long-term records is progressively being recognised as anthropogenically driven climate change, together with more direct disturbances such as fishing and pollution, are increasingly identified as major influences on marine ecosystems (Hawkins et al., 2003). This recognition is coupled with an urgent need to understand the mechanisms by which these influences act on the marine environment. This is of primary importance in order to interpret current changes and predict future impacts, thereby enabling effective management and conservation of marine biodiversity and resources. Furthermore, research emphasis will undoubtedly shift in future with different problems becoming apparent; thus records of today could help resolve future problems. Records from the western English Channel presented in this review have exceptional significance due to a combination of factors, namely 1) the location of Plymouth at the edge of many species distributions (Boreal-Lusitanian boundary), 2) the situation of long-term monitoring stations reflecting both oceanic and coastal water properties, 3) the wide range of environmental and biological parameters that have been systematically recorded and 4) the 18

long temporal scale over which these observations extend, from the onset of large-scale fisheries exploitation and encompassing several periods of temperature change including periods of warming, cooling and warming again. There are, however, significant limitations to the data. First, the data are not complete; there are gaps in all datasets, notably during wars and funding crises. Secondly, methods are not necessarily consistent throughout the series. This results from a variety of factors, such as the development of new and increasingly accurate techniques (e.g. measurement of inorganic and organic nutrients) and the use of different equipment (e.g. replacement of stramin mesozooplankton nets with terylene ones; the replacement of vessels incurring changes in towspeeds and, in some cases, reductions in net size). Sampling frequency has also varied during the course of the series, and even for the most well represented sites such as E1, data require careful treatment during analysis to account for this (Southward, 1960; Maddock & Swann, 1977). Additionally, long-term records are difficult and costly to maintain and continue. By their very nature, they cannot be funded on a short-term basis and past hiatuses in funding have led to gaps in data sets during key periods. Major findings from this work include the dramatic changes in ecology of the western English Channel ecosystem. Three periods characterised by large shifts in the abundance of key species have been identified: 1926-36, 1961-79 and 1985 onwards. The first was a period of warming that culminated with the collapse of the herring fishery, while the second period of change was a cooling following the severe winter of 1962-3. The current period is characterised by warming becoming more rapid and reaching greater maxima than during any other period of the twentieth century (Hawkins et al., 2003). These periods of change are separated by relatively stable periods where marine organism abundances have remained constant (Southward, 1980). While these changes have been collectively termed the “Russell Cycle” (Cushing & Dickson, 1976), it is now apparent that the changes are not a straightforward periodic shift in species occurring at predictable frequencies and rates. Early workers who interpreted these signals based their hypotheses on what was effectively half a cycle, and did not have the benefit of the three transitional periods that are now recorded. Hypotheses regarding the cause of these shifts have attributed a range of factors (Southward, 1980). Initially depleted nutrients was considered the major cause, particularly inorganic phosphate, that appeared to have resulted in decreased productivity at a regional scale (Russell, 1933; Harvey, 1955). Fluctuations in nutrients are now understood to be a symptom rather than a cause of changes (Southward, 1963; Joint et al., 1997). Competition between similar pelagic fish species, specifically pilchards with herring, was subsequently proposed as a possible mechanism for driving changes in the pelagic food web (Cushing, 1961). While this may account for changes in pelagic systems, it does not explain all trends in demersal fish, intertidal organisms and benthic communities (Southward, 1963, 1980). The overarching influence of climate, manifest as temperature change, is widely supported today and has been reinforced by recent studies. Marine organisms have clear responses to climatic features such as NAO strength (Alheit & Hagen, 1997; Beaugrand et al., 2000; Irigoien et al., 2000b; Sims et al., 2001). It is most likely that interaction between low amplitude climatic effects plays a strong role in forcing changes. Work from the intertidal zone has shown time lags between changes in temperature and organism abundance that can be related to individual species life histories (Southward, 1967, 1995). Furthermore, interactions between climatic influences and physiological (e.g. reproduction, survival) and ecological (e.g. competition, altered physicochemical environment) factors generate complex patterns for individual species responses. 19

Other significant findings from these data relate to commercial marine exploitation. Demersal fish hauls strongly reflect fishing disturbance since many of these data pre-date increases in commercial effort during the last three decades (section 3.3). This is significant since climatic effects on fish behaviour, that are masked by effects of fishing in contemporary data, can be detected in historic records e.g. influences of NAO strength on the timing of squid and flatfish migration (Sims et al., 2001; Sims, in press). Secondly, these data represent an entire demersal assemblage, and hence include both commercially important and non-commercial species. Such a comprehensive dataset is rare since most studies are directed at monitoring a single high-value species. Extended re-sampling and re-analysis of historic data are likely to aid in the interpretation of the wider ecological effects of fisheries exploitation and will shed light on long-term dynamics of these important communities by identifying the effect on fish populations of the interplay between climate change and fishing pressure. The value of long-term research lies not only in the records themselves; significant advances in understanding have come about indirectly from these long-term research programmes. Many widely accepted models concerning areas such as cycling of nutrients in the sea (Atkins, 1925; Cooper, 1933, 1937, 1958b; Atkins & Jenkins, 1956), trophic interactions within pelagic food webs (Lebour, 1919, 1920, 1921), diurnal vertical migratory behaviour of plankton (Russell, 1925, 1926a, b, c, 1927a, b, 1928a, b, c, 1930, 1931a, b, 1934) and the influence of hydrographic properties on pelagic systems (Pingree & Pennycuick, 1975; Pingree et al., 1975, 1976, 1977a, b, 1978; Pingree, 1978; Pingree & Griffiths, 1978), originated from work in Plymouth. Furthermore, work initiated during the 1920s into marine optics (Atkins, 1926c; Atkins & Poole, 1952, 1958) provided the foundation for later work aiding the development of algorithms to estimate phytoplankton biomass from contemporary satellite ocean-colour sensors (Moore et al., 1999). In a similar way, the L4 data series, besides studies of interannual variability and climatic linkages (Fig. 13 and Fig. 14), is currently providing the foundation for many related studies e.g. zooplankton molecular biology, microbial and virus ecology, research into release of biogases (carbon dioxide, methane and dimethyl-sulphide) and provides validation for satellite ocean-colour sensors. The current resurgence of interest in long-term change has led to many of the Plymouth programmes being restarted (methods are given in Table 8). Demersal fish collection and intertidal surveys were restarted by the MBA in January 2001 (with support from MAFF/DEFRA and within the framework of the Marine Biodiversity and Climate Change (MarClim) consortium2, respectively). The establishment of a Marine Environmental Change Network (MECN) in 2002 (coordinated by the MBA, with DEFRA support) has restored full water column measurements at E1 and plankton studies (young fish and mesozooplankton hauls, 53µm and 200µm WP2 net hauls and phytoplankton sampling), together with inorganic nutrients at L4. In addition, the Plymouth-Roscoff route is being restarted by SAHFOS in 2004. A key part of MBA time-series work is the preservation of historic data. This can mean extraction from notebooks or obsolete electronic formats. Infaunal and epifaunal benthos data have been archived from the MBA with MAFF/DEFRA support and funding is currently being sought to restart this series. Other ongoing work involves the use of remotely sensed data to provide a spatial framework within which to interpret ongoing in situ measurements. Recent advances in technology mean these long-term programmes are more valuable than ever before. Future directions being pursued include the continued development of coupled
MarClim Consortium: EN, Crown Estates, DEFRA, SNH, Scottish Executive, CCN, EA, States of Jersey, WWF and JNCC
2

20

physical-ecosystem models (e.g. POLCOMS-ERSEM3) using western English Channel timeseries data to expand relationships between surface and subsurface properties with ecosystemwide responses and predict future changes. Understanding processes regulating marine ecosystems can require sampling over varied temporal scales. Recent technologies such as advanced telemetered instruments, e.g. SMART buoy system developed by CEFAS, can enhance ongoing core research as well as focus sampling strategies by providing real-time data. Importantly, such instruments yield in situ profile data from the water column, thus together with satellite-derived information, can greatly extend the spatial and temporal extent of measurements. This is fundamental in order to capture processes that occur at multiple scales and understand how they operate within the marine environment. Further goals are to determine the major controls structuring this system, and crucially, to determine the strength of those acting in a top down direction (such as fishing) or are driven from the bottom up (climate/nutrients). Data from the western English Channel include records of all the key biological components within the ecosystem, along with physical and chemical environmental parameters through several periods of significant change. This global perspective of the system is fundamental to address these increasingly important questions. Advances into these areas are expected to generate tangible support for management and conservation policies. In conclusion, these unique western English Channel time series started by the MBA and continued through collaboration of the MBA, PML and SAHFOS in Plymouth, are increasingly valuable for the detection of ecological responses to environmental change and their future predictions. The legacy of observations collected throughout warming and cooling periods during the last century have clearly demonstrated the importance of this work in contributing to our understanding of the coastal marine environment. In the face of current unprecedented rates of change, it is vital that the lessons of the past are learnt and these programmes are fully supported and maintained for the future.

3

Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS), European Regional Seas Ecosystem Model (ERSEM)

21

7. Tables
Table 1. Sampling methods for zooplankton in the MBA long-term data series. Stations (see Fig. 1) Tow speed and time pre-1958 post-1958 pre-1958 1958 – 1978 1978 onwards post-1958 pre 1962 post 1962 pre-1981 post-1981 post-1985 all years A (Russell, 1933) L5 30 minutes at 2 knots 20 minutes at 4 knots 20 minutes at 2 knots Scripps depressor (Southward, 1970) "stramin" - irregular holes c. 0.8mm "terylene" - regular holes c. 0.7mm 2 m diameter - round 1m diameter - round 0.9m2 - square (Southward, 1984) counts adjusted to nominal 4000 m3 water filtered (Russell, 1976; Southward & Boalch, 1986)

Tow stabilisation Net mesh Net aperture dimension

Counting/identification techniques

Table 2. Hydrographic and chemical sampling methods employed at E1 (1902-1987). Parameter Inorganic phosphate Year ranges pre-1938 1948-c.1965 c.1965-1987 Dissolved organic phosphate Nitrate Dissolved organic nitrate Sea surface temperature 1950s-c.1962 c.1962-1987 pre-1938 1966-1987 c. 1962-1987 pre-1984 post-1984 Subsurface sea temperature profile pre-1984 post-1984 Method tin (II) chloride method (Atkins, 1923) tin (II) chloride method (Harvey, 1948) ascorbic acid method (Murphy & Riley, 1962 in Butler, 1979) Harvey’s method (Harvey, 1955) photocombustion technique (Armstrong & Tibbitts, 1968) reduced strychnine method (Cooper, 1932) cadmium copper reduction to nitrite (Wood et al., 1967 in Butler, 1979) photocombustion technique (Armstrong & Tibbitts, 1968) Insulated water bottle, then Lumby sampler Electronic thermometers fitted vessels, CTD vertical profile NIO bottle samples CTD vertical profile on research

22

Table 3 List of plankton species used as indicators of water conditions in the Channel at stations L5 and E1. The species list was originally drawn up by Russell (1935a). It has been reviewed and modified by Southward (1962). Group Medusae and siphonphores Species Aglantha digitalis Lirope tetraphylla Muggiaea atlantica Nanomia ‘floats’ Tomopteris helgolandica Sagitta setosa Sagitta elegans Sagitta friderici Calanus helgolandicus Candacia armata Eucalanus crassus Eucalancus elongatus Euchaeta hebes Centropages typicus Podon polyphemoides Evadne nordmanii Thermisto gracilipes Nyctiphanes couchii Meganyctiphanes norvegica Limacina retroversa Bivalve larvae Clione limacina Luidia sarsi larvae Echinoderm larvae and post-larvae Salpa fusiformis Doliolidae Appendicularia Water body association north western south western south western north western north western Channel north western south western western southern western/southwestern western north western western north western north western coastal western north western coastal western/south western oceanic south western

Polychaetes Chaetognaths Copepods

Cladocerans Amphipods Euphausids Molluscs Echinoderms Tunicates

Table 4. Benthic surveys of the Plymouth area (after Holme, 1983) Survey date 1895-1898 1906 1922-1923 1928-1929 1931 1939 1949-1951 1950 1958-1962 1970-1981 1972-1982 Ground Eddystone grounds Outside Eddystone Plymouth area Inside Eddystone Eddystone gravels Rame mud Plymouth area Plymouth area English Channel W English Channel Lizard-Start Point Sampling gear Dredge; trawl Dredge; trawl Grab Grab; trawl Conical dredge Corer; grab Camera Grab Anchor-dredge Dredge TV sledge Reference Allen, 1899 Crawshay, 1912 Ford, 1923 Steven, 1930 Smith, 1932 Mare, 1942 Vevers, 1951, 1952 Holme, 1953 Holme, 1961, 1966 Holme, 1984 Wilson et al., 1977; Franklin et al., 1980

23

Table 5 Sampling techniques for L4, sampled on a weekly basis. Sample type Zooplankton Equipment WP2 net (200 µm) WP2 net (50 µm)* Methods Vertical haul from 50 m to the surface Samples stored in 5% formalin Identification to genera/species level under dissecting microscope, completed within a week of sampling Collected at 10 m depth Samples stored in 2% Lugol’s iodine (Holligan & Harbour, 1977) 10-100 ml of sample is settled and species abundance determined using an inverted microscope. Determined on 90% acetone extracts of GF/F filtered samples, using a Turner Designs fluorometer. 250 ml aliquots are prefiltered through a 200 µm mesh, then filtered onto 25 mm ashed glass fibre filters (GF/F). CN samples are washed with phosphate buffered saline before storage at -25°C. All analyses use a Carlo-Erba Elemental Analyser Model NA1500. Autoanalyser, Bran & Luebbe AA3, Unfiltered and 0.2µm Nuclepore, Frozen –20°C (Brewer & Riley, 1965; Grasshoff, 1976; Mantoura & Woodward, 1983; Kirkwood, 1989) CTD haul to 50 m

Phytoplankton

Bottle samples

Chlorophyll Particulate carbon and nitrogen

Bottle samples Bottle samples

Nutrients* nitrate, nitrite, ammonium, phosphate, silicate Temperature and salinity

Bottle samples

CTD (fitted with a fast repetition fluorometer and transmissometer) * Samples collected since May 2002

Table 6 Methods used to analyse CPR samples (SAHFOS). Stage 1: Phytoplankton colour Stage 2: Phytoplankton analysis The intensity of the green colouration of CPR filtering silk is assigned to 4 categories (which can be converted to chlorophyll equivalents). Phytoplankton are identified from 20 fields centred on the mesh and traversed diagonally from corner to corner under x450 magnification. The number of fields where each taxa is seen is counted (1/8000 of the silk is covered). Small zooplankton (<2mm) are identified and counted on a stepwise traverse across both the filtering and covering silks under x48 magnification (1/40 of the silk is covered). All larger zooplankton (>2mm) are removed from the silk, identified and counted.

Stage 3: Zooplankton traverse Stage 4: Zooplankton eyecount

24

Table 7 Continuous Plankton Recorder. Recording methods for different taxa. Taxon Coccolithaceae Cosinodiscus wailesii Dinoflagellate cysts Gonyaulax spp. Navicula planamembranacea2 Noctiluca scintillans Phaeocystis pouchetii1 Polykrikos schwartzii cysts1 Scripsiella spp.1 Silicoflagellatae2 Caprellids Copepod eggs Echinoderm larvae Euphausiids Parafavella gigantea2 Ptychocylis spp. Sergestes larvae Tintinnids Explanation Invasive First recorded as a species Only presence/absence recorded Presence recorded 1965 1977 1974 1965 March 1962 1981 1958 Abundance recorded 1993 1977 1993 1965 March 1962 1981 _ 1975 1982 1993 1962 1993 1949 1960 1966 1996 1993 1996 1993 1993 2004

Eggs counted individually Total euphausiids (juveniles and adults)

? 1948 1948 1946? 1996 1948-1957?, 19581991? 1996 ? 1964 1958?

Tintinnopsis spp. Umrindeten cysts Zoothamnium pelagicum Dinophysis caudata, D. Previously only Dinophysis spp. norvegica, D. tripos recorded 1 Edwards (2000), 2 Batten et al. (in press).

25

Table 8 Current sampling methods for E1 and L5, sampled at monthly intervals. Sample type Mesozooplankton and young fish Equipment 0.9 m2 Young Fish Trawl (YFT) fitted with a 700µm Terylene net, partial filtering cod-end and a Scripps depressor. Methods Double-oblique profile haul to ~5m depth above the seabed Depth and temperature profiles are recorded using a MINILOG recorder. Volume of water filtered is calculated using flow data recorded by a GO flowmeter fitted across the net mouth. 2 x 1 litre sample jars c/w preservative (20% borax- buffered formalin . 10 litre water samples from 60, 40, 30, 20, 10m and surface Autoanalyser (Bran and Luebbe AA3) 10m water sample (rosette sampler) 4 x vertical hauls to 50m, (2 x 200µm and 2 x53µm) 1 x horizontal 10m WP2 net (53µm) haul Samples preserved in Lugol’s iodine and live All pigments measured using HPLC Vertical profile to 65m

Nutrients NO3, NO2, NH4, PO4, SiO2 Phytoplankton, zooplankton and pigments

Rosette sampler + Niskin Rosette sampler 53µm WP2 net 200µm WP2 net

Temperature, salinity, optical properties

2 x CTDs (SeaBird & Valeport) Optics rig (FRRF, transmissometer, multispectral downwelling irradiance, upwelling radiance, attenuation, scattering and back-scattering)

26

8. Figures

Fig. 1 Map of major sampling stations, both historic and current, for long-term data series.

27

(a)

ICES Surveys (1902-10)

(b)

Channel Grid (1964-87)

Fig. 2 Examples of the scope of serial observations made by the Plymouth staff and research vessels. (a) ICES surveys (1902-1910); the ‘E’ stations, (b) 1964-1987; numbered stations indicate the position of the western Channel Grid (1964-1974) while the large open circles are E1, L5 and L4, where most sampling has occurred.

28

Temperature & salinity Larval fish stages Zooplankton Phytoplankton Productivity Intertidal Infaunal/epifaunal benthos Demersal fish CPR* L4**
1900 1925 1950 1975 2000

Fig. 3 Long-term data series from the western English Channel held at MBA, PML and SAHFOS, Plymouth, UK. Black bars indicate existing data, grey indicates lost records and white denotes gaps when surveys were not taken. * Continuous Plankton Recorder (operated by SAHFOS) ** see Fig. 12 for more detail.

1 0.8 0.6 0.4 0.2

°C

0 -0.2 -0.4 -0.6 -0.8 -1 1900

1920

1940

1960

1980

Fig. 4 E1 annual sea surface temperature anomaly (grey line) and 5-year running mean (black line).

29

Fig. 5 Mixing properties of the western English Channel. Source: Maddock et al. (1981). The numbers correspond to stations in Fig 5; 1 = E1.

Fig. 6 Phytoplankton productivity. Mean monthly rates of carbon fixation (g C under 1 m2 day-1) for 3 stations (see Fig. 4) in the western English Channel for the years 1964-1974. Broken lines show results with the values for 1966 omitted. Source: Boalch (1987).

30

260 240 (a) 220 200 180 160 140 120 100 80 60 40 20 0 1920
120

monthly mean per haul (x 103)

1930

1940

1950

1960

1970

1980

1990

2000

Monthly mean per haul (x 103)

100 80 60 40 20 0 1920
35

(b)

1930

1940

1950

1960

1970

1980

1990

2000

monthly mean per haul (x 103)

30 25 20 15 10 5 0 1920

(c)

1930

1940

1950

1960

1970

1980

1990

2000

12

S. elegans (no. per haul, x 103)

10 8 6 4 2 0 1920

40 30 20 10 0 2000

1930

1940

1950

1960

1970

1980

1990

Fig. 7 Mesozooplankton. (a) Calanus helgolandicus, (b) larval stages of decapod crustaceans (c) eggs of Sardina pilchardus and (d) the chaetognaths Sagitta elegans (cold water species) and S. setosa (intermediate and warm water species). Monthly mean abundance at L5. Sources: a) Southward et al., (1995) c) and d) Hawkins et al. (2003).

31

S. setosa ( no. per haul, x 103)

(d)

elegans

setosa

50

Lynmouth Woolacombe

51.0°

Hartland Quay Bude Lyme Regis

Latitude

Swanage

50.5°

Trevone Newquay West Looe Wembury/Cellar St. Ives Cape Cornwall Porthleven Sennen Prawle Brixham

Portland Bill

50.0°

Lizard

-5.5°

-4.5°

-3.5° Longitude

-2.5°

-1.5°

Fig. 8 Intertidal organisms. survey sites for barnacle abundance

5.0 4.5 4.0 3.5
Chthamalus S. balanoides

no. per cm 2

3.0 2.5 2.0 1.5 1.0 0.5 0.0 1950 1960 1970 1980 1990 2000

Fig. 9 Intertidal organisms. Annual abundance of barnacles (mean of all tide levels), Cellar Beach. After Southward (1991).

32

4°30’ W

4°15’ W

≥ 100 trawls ≥ 10 trawls ≥ 1 trawls
Looe

Plymouth

Polperro

50°20’ N

R Q P O N

Rame Hd Yealm Hd

50°15’ N

M L K J I
50°10’ N

96

97

98

99

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

Fig. 10 Demersal fish. Distribution of historic MBA trawls 1913-1986. Most trawls have taken place at ICES station L4 (grid square N12). Source: Genner et al. (2001).

c)
1953 1913 1921 1920 1919 1985 1983 1979 1978 1977 1976 Stress: 0.13 1986 1984 1956 1954 1957 1950 1955 1952 1951 1958 2001

1922 1914

Fig. 11 Demersal fish. MDS plot using annual frequency of occurrence within hauls. Distance between years represents degree of similarity. Source: Genner et al. (2001).

33

Fig. 12 Summary of the long-term data sets from Station L4 held by PML, Plymouth, UK. Black indicates periods during which samples have been taken and data are available. All L4 data can be downloaded from http://www.pml.ac.uk/l4/.

100 80
Females m-3

a) No data

20 18 16 14
Temperature (oC)
EPR (eggs fem-1 d-1)

60 40 20 0 1992 1993 1994 1995 1996 1997 1998 1999 2000 200

12 10 8

100 80
Females m-3

250 No data No data 200 150 100 50 0 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
800 600 500 400 300 200 100 0 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

60 40 20 0

100 80
Females m-3

c) No data

60 40 20 0

100 80
Females m-3

d)

70 60 50 40 30 20 10 0 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

60 40 20 0

Fig. 13 Station L4. Seasonal variation of: a) abundance of C. helgolandicus females (grey line) and surface temperature (black line), b) abundance of C. helgolandicus females (grey line) and phytoplankton concentration (black line), c) abundance of C. helgolandicus females (grey line) and concentration of the dinoflagellate Gyrodinium aureolum (black line), d) abundance of C. helgolandicus females (grey line) and egg production rate of Calanus helgolandicus (black line). Source: Irigoien & Harris (2003).

G. aureolum ( mg C m-3)

700

Phytoplankton (mg C m-3)

b)

300

34

Log concentration diatoms

2 a) 1.5 1 0.5

y = 0.18x + 1.16 R = 0.85 p<0.05
2

Average diatom concentration April - May 0 -4 -2 0 2 4 6 Winter NAO

Log concentration total carbon

2.5 2 1.5 1 0.5 0 -4

b)

y = 0.02x + 1.88 2 R = 0.20 p>0.05 Average phytoplankton carbon April - May -2 0 2 4 6

Winter NAO
Fig. 14 Station L4. Relation between the winter NAO index and different aspects of the spring phytoplankton bloom: a) logarithm of the average diatom concentration during the April-May period, b) relation between winter NAO and the logarithm of phytoplanktonic carbon concentration at the spring carbon maximum Source: Irigoien et al. (2000b).

35

1950s

1960s

1970s

1980s

1990s

2000-1

Fig. 15 Continuous Plankton Recorder tows in the 1950s, 1960s, 1970s, 1980s, 1990s and 2000-1 in the western English Channel and approaches.

36

(a)

22 20 18

Portsmout-Spain route Plymouth-Roscoff route

Speed (knots)

16 14 12 10 8 6

1960

1970

1980

1990

2000

Year (b)
1.0

Proportion of samples during daytime

0.8

0.6

0.4

0.2

0.0 1960 1970 1980 1990 2000

Year

Fig. 16 Continuous Plankton Recorder. Routes in the western English Channel showing (a) the average ship speed each month for the Portsmouth to Spain and Plymouth to Roscoff routes and (b) the proportion of samples collected during the day each month.

37

Coscinodiscus wailesii
2500 2000 1500 1000 500 0 1955
450 400 350 300 250 200 150 100 50 0 1955

Acartia spp

1965

1975

1985

1995

2005

1965

1975

1985

1995

2005

Euphausiacea Total
4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 1955 1965 1975 1985 1995 2005
160 140 120 100 80 60 40 20 0 1955

Centropages typicus

1965

1975

1985

1995

2005

Fig. 17 Continuous Plankton Recorder. Long-term mean abundances for selected plankton in the western English Channel (updated from Robinson & Hunt, 1986).

38

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