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PRELIMINARY INVESTIGATION INTO DIEBACK OF MANGROVES INITIAL

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					   PRELIMINARY INVESTIGATION INTO
       DIEBACK OF MANGROVES
       IN THE MACKAY REGION:

INITIAL ASSESSMENT AND POSSIBLE CAUSES


           Norman C Duke, Chris Roelfsema,
            Dieter Tracey and Lloyd Godson
              Mangrove Ecosystem Research &
           Marine Botany Group, Botany Department
                The University of Queensland




                       Report to the
        Queensland Fisheries Service, Northern Region
                             and
             the Community of Mackay Region




                        15 May 2001
Mangrove Dieback around Mackay                      Duke, Roelfsema, Tracey & Godson 2001




Submitted for Review :   20 December 2000
Completed Final :        15 May 2001




Contact Details:         Dr Norman C Duke
                         Botany Department, Marine Botany Group
                         The University of Queensland, Brisbane QLD 4072
                         Telephone: (07) 3365-2729
                         Mobile: (04) 1967-3366 Fax: (07) 3365-7321
                         Email: n.duke@mailbox.uq.edu.au




Citation Reference:

Duke, NC, C Roelfsema, D Tracey and L Godson 2000. Preliminary investigation into dieback
of mangroves in the Mackay region. Report to Queensland Fisheries Service, Northern Region
(DPI) and the Community of Mackay Region. 15 May 2001. 81 pages.




COVER PAGE FIGURE. Aerial view of severe dieback of mangroves in Barnes Creek, Pioneer
River estuary, Mackay. South east view from Barnes Road Bridge, Mackay-Slade Point Road,
looking towards Cremorne, the Pioneer River and East Mackay. Most of the area seen is
mangrove with extensive areas of dead trees of Avicennia marina both along the waters edge and
throughout inner mangrove stands up to the highwater mark.




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Mangrove Dieback around Mackay                                                 Duke, Roelfsema, Tracey & Godson 2001




                                                          CONTENTS

Executive Summary............................................................................................. 4

Conclusions and Specific Recommendations.................................................... 5

Acknowledgments................................................................................................ 7

Introduction and Background.......................................................................... 10
!"First observations .............................................................................................................. 10
!"Comparable instances of dieback....................................................................................... 10
!"Possible causes of dieback in the Mackay region .............................................................. 12
!"Justification for this investigation ...................................................................................... 14
!"Objectives of the preliminary investigation ....................................................................... 15

Study Area and Methods Used......................................................................... 18
!"Study area........................................................................................................................... 18
!"Classification of dieback severity and assessment of extent ............................................. 18
!"Mangrove composition and condition................................................................................ 20
!"Measurement of plant photosynthesis ............................................................................... 22
!"Sample collection ............................................................................................................... 22
!"Sample analyses ................................................................................................................. 22

Results of the Investigation............................................................................... 27
!"Assessment of mangrove condition – spatial and temporal quantification........................ 27
!"Plant response parameters – Avicennia marina.................................................................. 35
!"Water and sediment conditions .......................................................................................... 43

Discussion of Findings....................................................................................... 50
!"Aspects of this investigation .............................................................................................. 50
!"Implications of current findings ......................................................................................... 50
!"Possible causes of dieback in the Mackay region .............................................................. 50
!"Conclusions ........................................................................................................................ 60

References........................................................................................................... 61

List of Table Legends ........................................................................................ 64
List of Figure Legends....................................................................................... 65

Appendices ......................................................................................................... 68




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Mangrove Dieback around Mackay                           Duke, Roelfsema, Tracey & Godson 2001



                                    Executive Summary
Early in 2000, mangrove trees were observed dying for no apparent reason in large numbers
across a wide area of the Mackay Region. This instance of dieback was considered the worst of its
kind in the world, so an urgent preliminary investigation was mounted in June 2000 to determine
the extent of dieback, to characterise dieback in the field, and to assess possible causative factors.
The investigation found: a) dieback was widespread along 30 km of coastline and centred in the
Pioneer River estuary; b) dieback was species-specific, apparently affecting only the common
mangrove, Avicennia marina; and c) herbicides, diuron and ametryn, were present in mangrove
sediments of the dieback area sampled.

Dieback of mangroves were assessed in the Pioneer River estuary, and north to Leila/Reliance
Creek, and south to Sandringham Bay and Alligator Creek. Within this area, enclosing around 53
   2
km of mangroves, ~58% were affected by moderate to severe dieback. Areas of most severe
dieback, comprising ~2 km2, were observed in the Pioneer River estuary, particularly in Bassett
Basin and around Barnes Creek, but not restricted to it.

There are serious long term implications of severe dieback of mangroves and the most serious
is the loss of habitat structure – irrespective of the cause of dieback. The stability of both physical
and biotic aspects of coastal environments in the region are threatened. Without seedling
recruitment also, there appears to be little to prevent permanent loss of significant portions of
mangrove habitat in the region. Erosion of once densely vegetated tidal mud banks appeared to
have begun, and this was expected to accelerate once more roots binding sediments had degraded.
Root degradation takes about 3-5 years from tree death. Such habitat loss is expected to reduce
water quality and increase turbidity in estuarine and coastal waters with consequential flow-on
effects manifest as declines in local fisheries, as well as deterioration of seagrass and coral reef
habitats offshore in the Great Barrier Reef Marine Park.

The most likely cause of dieback was determined through systematic deduction and elimination
based on known causes elsewhere, assessed in conjunction with characteristics of current dieback.
Herbicides were identified as the most likely cause based on the following evidence, including:
the wide extent of dieback throughout the region; the species-specific nature of dieback; the lack
of established recruitment in affected areas; the lack of any obvious direct effect on fauna; the
presence of herbicides diuron and ametryn in sediments of affected areas; reported high usage of
pesticides in sugarcane production in catchments upstream of affected mangroves; the
characteristic of herbicides to adhere to sediments and be transported downstream in muddy run-
off water during high rainfall incidents; recent evidence of toxic effects on tropical seagrasses
grown experimentally in concentrations of diuron comparable with levels measured during this
investigation of mangrove dieback; and, the lack of convincing alternate potential causes.

Specific recommendations of this preliminary investigation include, in brief:: additional aerial
and ground surveys to describe and map the full extent of dieback; regular monitoring of
estuarine water, sediments and biota to assess herbicide and other potential toxicant concentrations
in downstream habitats; an experimental study to assess toxic responses by mangrove plants to
herbicides; an investigation into the origin and progress of dieback using remote sensing
techniques; assessment of the regenerative capacity and status of damaged areas; an investigation
of impacts on key biota and food web linkages in both mangrove and neighbouring habitats; an
immediate re-evaluation of pesticide usage in the region, and revision of current monitoring
guidelines for toxic threshold limits for marine plants; and, adoption of coastal community
monitoring programs using mangroves as bio-indicators of ecosystem health.



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Mangrove Dieback around Mackay                        Duke, Roelfsema, Tracey & Godson 2001



Conclusions and Specific Recommendations of the Preliminary Investigation

CONCLUSION 1:

Significant mangrove dieback was observed in most estuaries surveyed along approximately
30 km of coastline around the Pioneer River estuary and Mackay.

RECOMMENDATION / ACTION:

!"Map the Full Extent of Dieback in the region. Accurately map the extent of damage, using
  remote sensing (airborne) techniques and where possible quantify mangrove health, with
  particular consideration of Avicennia marina, but not restricted to this species.

CONCLUSION 2:

Herbicides, diuron and ametryn, were detected in mangrove sediments collected from
mangrove areas of Barnes Creek area, Pioneer River estuary at concentrations toxic to
seagrasses.

RECOMMENDATION / ACTION:

!"Monitor Potential Contaminants of Coastal Habitats in the Region. Collect sediment and
  water samples for analysis of possible contaminants, particularly herbicides, from a specific
  selection of sites throughout dieback areas, beginning with those areas mapped during the
  preliminary investigation.

CONCLUSION 3:

Widespread dieback was characterised by death of trees of one species, Avicennia marina,
while approximately 20 other mangrove species in the area appeared unaffected.

RECOMMENDATION / ACTION:

!"Investigate Ecotoxicological Responses of Mangrove Plants. Investigate the physiological
  response of different mangrove plant species to the presence of toxic substances, particularly
  for the implicated herbicides, in water and sediment, in controlled tidal nursery experiments.

CONCLUSION 4:

Dieback began prior to 1998 in Bassett Basin, Pioneer River estuary, and it was worse in
2000, as shown by the relatively high proportion of unhealthy sick trees of Avicennia marina
compared with respective proportions of both dead and apparently healthy trees.

RECOMMENDATION / ACTION:

!"Map the Origin and Rate of Change of Dieback. Investigate the extent of dieback shown in
  earlier aerial, and possibly satellite, imagery in an effort to describe and map temporal change,
  the origin, and the rate of change of dieback in the region.




                                            5
Mangrove Dieback around Mackay                       Duke, Roelfsema, Tracey & Godson 2001




CONCLUSION 5:

Seedling recruitment and density of healthy young plants were noticeably lower in mangrove
areas affected by dieback.

RECOMMENDATION / ACTION:

!"Assess Recovery Potential of Dieback Areas. Determine recovery potential by investigating
  recruitment, species composition, and establishment success of mangrove seedlings in dieback
  areas. Conduct planting trials in worst affected areas and monitor their progress over several
  years.

CONCLUSION 6:

Faunal activity appeared normal but there were indications of fauna affected indirectly by
dieback. Loss of mangrove habitat had apparently resulted in changes to associated faunal
communities. Are the effects on fauna related directly or indirectly to the factor causing tree
death?

RECOMMENDATION / ACTION:

!"Study Impacts of Dieback on Ecosystem and Food Web Linkages. Determine effects of
  mangrove dieback on ecosystem tropho-dynamics by investigating presence, abundance and
  health of key associated fauna, including fishes and crustaceans, in the region.

CONCLUSION 7:

Although unproven, the agent most likely causing severe dieback of mangroves in the
Mackay Region are herbicides, diuron and ametryn, detected in tidal sediments during the
investigation.

RECOMMENDATION / ACTION:

!"Review Current Pesticide Usage in the Region and Elsewhere. Revise current guidelines
  for toxic threshold limits of marine plants based on new evidence of toxic effects of diuron on
  tropical seagrasses. Further inform pesticide users in the region of possible downstream effects
  of toxic chemicals in run-off on estuarine and coastal habitats, and review current land
  management practices concerning the use of environmentally toxic chemicals.

CONCLUSION 8:

Deterioration of mangrove health and diversity was indicative of severe habitat damage and
the presence of factors causing unintentional harm to protected tidal wetland areas.

RECOMMENDATION / ACTION:

!"Use Mangroves as Indicators of Ecosystem Health. Coastal managers and community
  groups might conduct regular status assessments of current condition and health of mangroves
  in their local areas, monitoring potential and known pressures on protected tidal wetland
  areas. Early detection of problems would contribute directly and significantly to minimising
  damage and the cost of restoration.

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Mangrove Dieback around Mackay                         Duke, Roelfsema, Tracey & Godson 2001




                                     Acknowledgments
Logistic support for field work and funding for analytical costs were provided by the Queensland
Fisheries Service, Northern Region. All other costs, including wages for personnel, were provided
by staff and students of the Marine Botany Group.

We acknowledge the support also provided by the Mackay region DPI Office, particularly for the
generous assistance of Kylie Dodd, Mackay Region Fisheries Officer. For support in the northern
region generally, we thank Peter Finglas and Dr Rob Coles (QFS Northern Region). The support
from DPI was integral to the successful conduct of this preliminary investigation.

Laurie Patterson and Ross Brown of DNR (Mackay) assisted by providing important background
data used during the investigation.

Generous support and local advice in the Mackay area were provided by Maureen Cooper (Bird
Observers Club of Australia) and Noel Whitehead (Sunfish).

Scientific advice and project support were provided by staff and student members of the Marine
Botany Group lead by Dr Bill Dennison. We are grateful also for the rigorous and constructive
discussions which take place regularly within the group. Gordon Moss (UQ Botany) conducted
analyses of nitrogen and carbon in mangrove leaves.

Dr Jochen Müller (NRCET) provided essential advice, assistance and coordination of laboratory
analyses undertaken by Queensland Health (QH). Specific analyses at QH were performed by: Dr
Henry Olszowy (heavy metals in sediments); Dr Mary Hodge (pesticides in sediments); Dr Ujang
Tinggi (major elements in leaves); and Dr Dan Wruck (nutrients in water).

Advice on mangrove photosynthesis and likely toxic effects of diuron and other herbicides on
mangrove plants was offered by Prof Christa Critchley (UQ Botany).

Advice on Halophytophthora (= ex Phytophthora) presence and its potential effects on mangrove
plants were provided in discussions with Prof John Irwin (UQ Botany), Dr Andre Drenth (UQ
CRC Plant Sciences), and Dr Ken Pegg (DPI Plant Pathology).

Advice on remote sensing considerations for assessments of mangrove health was provided by
Stuart Phinn (UQ Geographical Science and Planning) and Alex Held (CSIRO Land and Water).

Finally, but not least, the field work conducted in June 2000 would not have been possible without
the time and labour donated to this project by the enthusiastic field crew, including Fiona Manson
(PhD student UQ / CSIRO Marine) in collaboration with the authors. This commitment has been
an important factor in determining the success of this preliminary investigation.

We have sought as wide a range of comments and opinions as practical during the investigation,
however, it must be stated that the authors alone are responsible for the opinions expressed in this
report.




                                             7
Mangrove Dieback around Mackay                      Duke, Roelfsema, Tracey & Godson 2001




FIGURE 1. Map of the Mackay region showing mangrove areas assessed during the
investigation, extending south from Leila/Reliance Creeks to Sandringham Bay – Sandy/Alligator
Creeks. Note the three chief catchment areas, O’Connell, Pioneer and Plane, in the assessment
area. The mangroves in Bassett Basin comprise the majority of mangroves in the Pioneer
catchment while other catchments have multiple estuarine systems and mangrove areas.


                                          8
Mangrove Dieback around Mackay                      Duke, Roelfsema, Tracey & Godson 2001




FIGURE 2. Photographs of dieback of Avicennia marina in mangrove areas of Bassett Basin,
Pioneer River estuary. A. View from Mount Bassett Lookout looking across mangrove areas,
showing patches of dead Avicennia marina amongst other species in the middle ground. B. View
of Vines Creek upstream of Harbour Road Bridge, an area of moderate dieback both for channel
edge mangroves and inner stands. C. Sick and dead trees occurred commonly side by side; edge
trees along Vines Creek just downstream of Harbour Road Bridge. D. Sick trees were
characterised by yellow wilting leaves and sparse foliage; isolated emergent trees within mixed
stands dominated by Ceriops australis just downstream of Harbour Road Bridge. E. Dead
emergent trees in an inner stand; Vines Creek just downstream of Harbour Road Bridge. F. Young
trees with many sick and dead growing on an accreting bank in Vines Creek upstream of Harbour
Road Bridge; note algal growth on the surface of the bank.

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