Sampling of deep sea fish Sampling of Deep sea fishes from German research

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					Sampling of Deep-sea fishes from German research cruises and Deep-sea fish parasitology – an overview
Sven Klimpel and Uwe Piatkowski, IFM-GEOMAR, Germany

It is difficult to delimit the deep-sea from other ocean habitats. Neither temperature nor depth or geomorphological features (edge of the continental shelf) are universally correlated with the distribution of organisms. At low latitudes, the typical shelf fauna may inhabit the continental slope to a depth of more than 1.000 m, and characteristic deep-sea taxa are found in the polar region at depths of a few hundred meters. The transition from the shelf to the deep-sea is formed by the archibenthal (bathyal) region (Fig. 1a). At high latitudes the archibenthal fauna has strong affinities to both, the shelf and the deep-sea fauna, constituting the so-called archibenthal transition zone. At lower latitudes this zone is situated between 1.000 and 3.000 m (tropical submergence), and it has few species in common with the fauna of the neighbouring shelf and abyssal regions. It is thus difficult to clearly define the conditions that determine the distribution of deep-sea organisms (Ott 1996). Environmental conditions in the deep-sea are characterized by an absence of sunlight and by low water temperature, high hydrostatic pressure, weak water currents, and scarcity of food. Due to the absence of light and the constant environmental conditions, the principal factors determining the settlement of organisms are food availability and water movement. However, little is known about the influence of direct biotic interactions (Competition, predator-prey relationships) on the distribution and structure of deep-sea communities (Hureau et al. 1979). Deep-sea fishes are perfectly adapted to the conditions in deep-sea layers. For example, mesopelagic fish species spend the day at depths of 400 to 600 m and migrate to the surface at night. They feed on zooplankton and fish. Benthic fish species often are eel-like and belong to the Macrouridae, Ophidiidae and Brotulidae. An ability to find food items with a patchy distribution is of particular importance for predatory fish, because continuous searching activity is impossible under these environmental conditions. Therefore, many deep-sea predators have low mobility, drifting motionless in the water and attracting their prey by means of luminescent organs. Benthic predators and scavengers are able to detect prey over great distance with the help of olfactory organs (Fiedler 1991). The initially rare finds of deep-sea animals at first created the impression that the fauna was poor in species. It has become clear, however, that the diversity of the deep-sea, and that of the upper abyssal zone in particular, surpasses that of some shallow water habitats. This realisation was one of the principal foundations of the “Time-Stability Hypothesis” by Sanders, which assumes that environmental stability and prolonged lack of habitat disturbance result in high species diversity. This supposedly requires an apportionment of resources and a construction of small niches, thus being at odds with the apparently low structural complexity and scarcity of food in the deep-sea, which should make any specialisation disadvantageous. In terms of deep-sea fish parasites, a low specialisation might be reflected by low host specificity, the ability of the parasites to occur in a wide range of different host organisms. The origins of the deep-sea fauna are unclear. It is neither ancient, nor a refuge of ancient species. Almost all species and genera are less than 100 million years old, and most of them younger than 20 million years old (Ott 1996). In the Cretaceous Period, the deep-sea had water temperatures of about 15 °C and was probably anoxic periodically. The ocean circulation that today provides the deep basins with cold water rich in oxygen did not begin until the Eocene, and present day conditions were attained around the Pleistocene. The colonisation of the deepsea was probably achieved by shallow-water species that underwent a great amount of adaptive radiation and speciation as they penetrated to greater depths (Ott 1996).

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Parasites are an essential part of each aquatic community. Their presence becomes evident after a massive development, causing diseases and sometimes even leading to the mass mortality of infested host. Such events are often combined with biotic changes in the environment. There is increasing evidence that parasites are an important element of marine biodiversity. In fisheries biology, parasitological studies have increasing importance, because parasites may serve as natural markers for the identification of fish stocks. Moreover, parasites can help to analyse the diet of fish species, serving as biological indicators of the prey species and their origin. Whereas stomach analyses may provide detailed information on the immediate trophic relationship at the time of sampling, parasitological studies make it possible to infer previous trophic interactions, thus integrating short-term variability in the food web to make wider relationships more apparent. Helminths, such as cestodes and nematodes, are particularly useful for such studies, because the different stages in their life cycle are passed through the marine food web until they reach their definitive host. Finally, parasites provide information on habitats and trophic status of the studied fish species within the marine ecosystem. Parasitological studies on deep-sea fish species are scarce, compared to studies on commercially important fish and on fish from the shallow coastal and shelf regions. One of the main obstacles is the difficult access to deep-sea organism, which necessitates expensive research expeditions or deep-water fisheries. Even then, only a few of the abundant species are available for parasitological examination, as parasitologists compete with scientists of other disciplines for the material. The first comprehensive survey of helminths of deep-sea fishes was conducted by Manter (1934), who examined 721 fish species (Tortugas) of which 37% were infested by digenea (Fig. 1b), 25% by cestoda (Fig. 1c), 18% by nematoda and 2% by acanthocephala (Fig. 1d). To date, deep-sea parasitology has mainly been concerned with describing new species of parasites, and with quantitative studies on the parasites of Atlantic and Pacific deep-sea fishes. Campbell et al. (1980) investigated 52 fish species from the deep-sea (New York Bight) and found the following infestation rates (prevalences): 48% digenea, 13% monogenea (Fig. 1e), 22% cestoda, 55% nematoda and 4% acanthocephala. In Korsfjorden (Norway) Noble et al. (1972) studied the parasites of 48 individual Macrourus rupestris, finding infestation rates ,of 52% nematoda and 6% cestoda; no other helminths were found. Houston & Haedrich (1986) studied the parasites in the digestive tracts of 471 deep-sea fishes (Newfoundland), and found 7% of them infested by digenea, 37% by nematoda and 21% by acanthocephala. Zubchenko (1981) investigated 353 specimens of three macrourid species (North Atlantic), finding a total of 21 parasite species (48% digenea, 10% monogenea, 19% cestoda, 19% nematoda, 5% acanthocephala). Gartner & Zwerner (1989) recently studied the parasite fauna of 668 deep-sea fishes (Norfolk Submarine Canyon) and found them infested by 5% digenea, 23% cestoda, 6% nematoda and 1% acanthocephala. Almost all of these studies have been carried out in the northern hemisphere. Comprehensive studies on the parasite fauna of deep-sea fishes from the southern hemisphere, Mid Atlantic Ridge and Seamounts (e.g. Great Meteor Seamount) are rare. One exception is the study by Heath (1989) on 1.308 fish specimens from south-east Australia; he found that 21% of the fishes were infested by digenea, 26% by cestoda, 24% by nematoda and 2% by acanthocephala. The deep-sea parasite fauna studied to date is mainly characterised by digenea, cestoda and nematoda (Klimpel et al. 2001). The major digenean families present in deep-sea fishes are the Lepocreadiidae, Hemiuridae, and Derogenidae; in addition, Fellodistomidae, Opecoelidae and Zoogonidae have been found fairly frequent (Klimpel et al. 2001). The most frequent genera are Lepidapedon and Steringophorus (Campbell 1983). Two of the predominant monogenean families are Diclidophoridae and Microcotylidae. Three orders of cestodes predominate in deepsea fishes: the Tetraphyllidae, Trypanorhyncha and Pseudophyllidea (Campbell 1983, Gartner & Zwerner 1989). Furthermore the two principal parasitic nematode families are the Anisakidae 2

and Rhabdochonidae, which may have deep-sea fish as both final and intermediate hosts (Gartner & Zwerner 1989, Noble 1973). Acanthocephalans are the most rare helminth parasites of deep-sea fishes (Campbell et al. 1980). The parasitic copepods (Fig. 1f) reported most often in deep-sea fishes are from the families Sphyriidae, Lernaeopodidae, and Chondracanthidae (Boxshall 1998); copepods of the family Chondracanthidae, especially the genus Chondracanthodes are the most frequent (Boxshall 1998). Other genera commonly found on deep-sea fish are Clavella and Lernaeopodina. The genus Lophoura, a member of the Sphyriidae, is the most diverse among the deep-sea genera (Boxshall 1998). In conclusion, the diversity of parasites in deep-water fishes is dependent on the specific feeding behaviour of hosts, the availability of intermediate and final hosts, depth distribution and host migrations. Similarities in diet and habitat of potential host species may result in similar parasite faunas. In contrast, hosts with different food preferences may have large differences in their parasite faunas. In conclusion, a combination of different factors, especially the feeding ecology and habitat preferences of the hosts, can be seen as the reason for the observed infestation patterns. This outline clearly demonstrates the urgent need to investigate the parasite fauna of the deep-sea fishes which will be collected during the forthcoming MAR-ECO cruise of RV G.O. Sars. We consider this task as a highly valuable contribution to the envisaged food web studies and to general biodiversity studies of the MAR-ECO project.

Background Since 2001 we have regularly sampled deep-sea fishes that have been collected during German research cruises to East/West Greenland and the Irminger Sea. These cruises have been conducted by the FRV Walther Herwig III. They were embedded into international ICES and NAFO surveys to study the population dynamics of Atlantic cod and redfish in the target areas. The sampling of deep-sea fishes from the by-catch were performed by Sven Klimpel et al. Basic data on the fish specimens and their parasite load has been examined and is in study. The following sample material is available and can be used for the tasks of the MAR-ECO project, for more details see also Table 1: 2001: WH 229 – 17.06. – 12.07.2001 WH 233 – 12.10. – 23.11.2001 Number of analyzed fishes: 203 2002: WH 244 – 11.10. – 22.11.2002 Number of analyzed fishes: 231 2003: WH 252 – 27.05. – 22.06.2003 WH 257 – 20.10. – 27.11.2003 Number of analyzed fishes: 395 Total number: 829 Sampling depth range: 250 – 950 m The continuation of sampling deep-sea fishes from the Atlantic cod and redfish surveys is ensured for the years 2004 and 2005.

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Table 1. Summary of analyzed fishes from German fishery surveys to East/West Greenland and the Irminger Sea. Greenland Sea/ Irminger Sea year Research cruises 2001 WH 229/233 n 10 35 10 20 25 45 8 30 10 10 203 2002 WH 244 n 17 68 10 23 7 38 3 45 10 10 231 2003 WH 252/257 n 20 40 20 40 20 115 25 40 35 40 395

Fish species 1. Arctozenus risso (Bonaparte, 1840) 2. Bathylagus euryops Goode & Bean, 1896 3. Borostomias antarcticus (Lönnberg, 1905) 4. Chauliodus sloani Bloch & Schneider, 1801 5. Lampadena speculigera Goode & Bean, 1896 6. Coryphaenoides rupestris Gunnerus, 1765 7. Malacosteus niger Ayres, 1848 8. Lampanyctus macdonaldi (Goode & Bean, 1896) 9. Scopelogadus beanii (Günther, 1887) 10. Serrivomer beanii Gill & Ryder, 1883 ∑

Additionally, various other deep-sea fishes were sampled, partly in low numbers: Family Caristiidae – Caristius groenlandicus Families Oneirodidae, Chaulophrynidae, Ceratiidae, Anotopteridae, Platytroctidae – Lophodolos acanthognathus, Ceratias holboelli, Anotopterus pharao etc. Useful definitions for parasite investigations: Ectoparasite - lives on surface. Endoparasite - live inside host. Mesoparasite - penetrates external openings - buccal cavity, cloaca, external ear. Definitive host - where parasite reaches sexual maturity. Intermediate host - required by parasite to complete its life cycle. Usually undergoes morphological or physiological change in it. Paratenic host - optional transport host - no detectable morphological change in parasite Vector - host that plays an active role in transmission, can be a definitive or an intermediate host.

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