© google earth - wamsi · ©google earth hay river denmark river. pelagic bentho‐pelagic benthic...
TRANSCRIPT
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Trophic interactions in a seasonally‐open estuaryin south‐western Australia
byThea Linke, Janna Peters, Luke Twomey, Mike St John, Neil Loneragan
©go
ogle
ear
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Outline
• Seasonally‐open estuaries: Wilson Inlet
• Complementary methods to dietary analyses:guts, stable isotopes, fatty acids
• Implications of findings & managementrecommendations
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Introduction
Background
• Bar‐built estuaries
• Commercial fishery
• Recreational fishers
• Catchment modifications
• Eutrophication
• Management implicationsRuppia megacarpa
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Aims
• To characterise the food web in Wilson Inlet using threecomplementary techniques
• To identify markers of feeding mode
• To understand feeding niche separation betweenthree abundant species of teleost
Reflection of feeding history
Resolution ofprey species
Stomach contentsFatty acid markersStable isotopes
C. aequisetis
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Study area and sampling regime
©google earth
HayRiver
DenmarkRiver
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pelagicbentho‐pelagic
benthic
Acanthopagrus butcheri (Sparidae)Black Bream Pseudogobius olorum (Gobiidae)
Bluespot Goby
Leptatherina wallacei(Atherinidae)Wallace’s Hardyhead
The predators
Wilson Inlet
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• Similar δ15N similar trophic level
Stable Isotopes – trophic level
How do theypartition
their resources?
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• Similar δ15N similar trophic level
Stable Isotopes – trophic level
How do theypartition
their resources?
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• Similar δ15N similar trophic level
Stable Isotopes – trophic level
How do theypartition
their resources?
Crustaceans
AnnelidsMolluscs
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• Similar δ15N similar trophic level
Stable Isotopes – trophic level
How do theypartition
their resources?
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• Similar δ15N similar trophic levelPrimarilycarnivorous
Stable Isotopes – trophic level
How do theypartition
their resources?
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• Similar δ15N similar trophic level
Stable Isotopes – trophic level
How do theypartition
their resources?
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• Greater influence of pelagically‐derived carbon in the bentho‐pelagic and pelagic feeders
• Differences in the FA pattern?
Stable Isotopes – food source
pelagic (Hardyhead)
pelagic benthic
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Fatty acid markers – trophic niches
beee
16:0
16:1(n-7)
18:0
18:1(n-7)
18:1(n-9)
20:4(n-6)
20:5(n-3)
22:5(n-3)22:6(n-3) Unid3
R=0.554; 2D Stress: 0.19
pelagic(Hardyhead)
• Clearer separation than isotopes
• 3 feeding modes quite distinct
• Highest correlation is 20:4(n‐6) –produced by microalgae
benthic (Goby)
bentho‐pelagic(Bream)
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Fatty acid markers – trophic niches
•No typicalmarkers like16:1(n‐7) –Phytoplanktonor C18 PUFA’s –Dinoflagellates
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Fatty acid markers – trophic niches
EPA DHA
• Significant differences in20:5(n‐3) – EPA and 22:6(n‐3) – DHA
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DHA:EPA ratio – useful as marker?• Decrease inDHA:EPA ratio
• Both components of membrane lipids
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% V
0
20
40
60
80
100
DHA:EPA ratio – useful as marker?
Stomach contents
amphipodsamphipodsdecapodsdecapods
micro & macroalgaemicro & macroalgae
copepods & teleostscopepods & teleosts
annelidsannelidsmolluscsmolluscs
benthic
pelagicterr.
insectsinsects
n=108 n=78n=55
Stomach contents
• Species mainly differ incontribution of pelagic prey
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DHA:EPA ratio – useful as marker?
• DHA accumulateswith trophic level
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Conclusions ITrophic niche separation:
pelagic
bentho‐pelagic
benthic
Acanthopagrus butcheri Pseudogobius olorum
Leptatherinawallacei
Wilson Inlet
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Conclusions ITrophic niche separation:
• Stable isotopes: Similar trophic level: primarily carnivorous
• Fatty acids and stomach contents: Resource partitioning with overlaps reflected in both methods
pelagic
bentho‐pelagic
benthic
Acanthopagrus butcheri Pseudogobius olorum
Leptatherinawallacei
Wilson Inlet
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• No typical FA markers found – indicates diverse feeding modes
by all species, BUT
DHA:EPA ratio decreases from pelagic to benthic
predator and prey species
apparently related to food sources
• Accumulation of DHA with trophic level, BUT further research
is needed to determine whether this is a good trophic marker
Conclusions II
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Comparison between Swan and Wilson
pelagic/terrestrial benthic/aquatic
bentho‐pelagic(Bream)
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Comparisons between Swan and Wilson
• 18:2(n‐6): terrestrialmarker
• Higher influencein the Swan
• Carbon sourcediffers
• Higher influence ofaquatic sources inWilson Inlet
pelagic/terrestrial benthic/aquatic
bentho‐pelagic(Bream)
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This study provides the following:
•Trophic level of Black Bream in the food chain of the Swan Estuary and Wilson Inlet
•The main sources of organic material for the three species studied
• A basis for assessing environmental changes in the future
•Crucial data for quantitative and qualitative modelling of the two estuarine systems
Management value
photo: M. Wildsmith
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Acknowledgements
Murdoch University: Centre for Fish and Fisheries ResearchHamburg University: Centre for Hydrobiology and Fisheries SciencesWestern Australian Marine Science InstitutionFisheries Research and Development CorporationSwan River TrustFellow Fishgroup members