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Zooplankton responses to changing predation

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Windermere Science Project stakeholder meeting presentations.
Thackeray on changes in zooplankton abundance & community composition, especially with reference to fish biomass & predation

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Zooplankton responses to changing predation

  1. 1. Zooplankton responses to changing predation Stephen Thackeray Heidrun Feuchtmayr, Ian Jones, Alanna Moore, Peter Smyntek & Ian Winfield Lake Ecosystems Group, CEH Lancaster & Aquatic Ecology Group, Queen Mary University of London
  2. 2. The project hypotheses (revisited)...
  3. 3. Why are zooplankton important? • Occupy an important middle position in the aquatic food web • Graze upon bacteria/phytoplankton (and each other)……. …and are eaten by larger aquatic invertebrates and fish So…. • Affect water clarity and quality by consuming phytoplankton • Crucial for the transfer of energy and matter up the food web
  4. 4. The Windermere zooplankton community Cladocera Daphnia galeata Bosmina obtusirostris Calanoid copepods Eudiaptomus gracilis Arctodiaptomus laticeps Cyclopoid copepods Cyclops abyssorum Mesocyclops leuckarti
  5. 5. Changing predation in Windermere 6000 -1) 5000 4000 3000 h s i f ( e c a d n u b A 2000 1000 0 1990 1995 2000 2005 Year Expansion of non-native species 2010
  6. 6. Expectation 1
  7. 7. Expectation 1: reduced abundance
  8. 8. Data collection Water temperature • Fortnightly vertical profiles at the deepest point in the North Basin. Zooplankton abundance • Fortnightly net hauls (0-40m) at the deepest point. Fish predation • Monthly hydroacoustic surveys of fish populations (1991 – 2010).
  9. 9. A proxy for zooplanktivory 6000 12 -1) 5000 4000 10 3000 2000 8 h s i f ( e c a d n u b A Mean surface temperature (˚C) Mean surface temperature (oC) North Basin 1000 South Basin 6 1950 1970 1990 Year 2010 0 1990 1995 2000 Year 2005 2010 Maximum consumption rate = 0.016 x Weight (g)-0.16 x e0.133 x Temperature (˚C) Hölker & Haertel (2004) Journal of Applied Icthyology, 20, 548-550
  10. 10. Analysis 1995 2000 Year 2005 2010 1995 2000 2005 0.4 0.2 0.0 -0.2 -0.4 Adult Eudiaptomus abundance 0.6 0.4 0.2 0.0 -0.4 -0.2 Adult Eudiaptomus abundance 0.4 0.0 -0.4 Fish consumption 0.8 Key question: has the abundance of zooplankton decreased as a result of increasing predation pressure? 2010 Year 1.8 2.0 2.2 2.4 2.6 2.8 Fish consumption Correlation due to unmeasured (perhaps shared) drivers... ...or causal relationship?
  11. 11. Analysis 1995 2000 Year 2005 2010 1995 2000 Year 2005 2010 0.4 0.2 0.0 -0.2 -0.4 Adult Eudiaptomus abundance 0.6 0.4 0.2 0.0 -0.4 -0.2 Adult Eudiaptomus abundance 0.4 0.0 -0.4 Fish consumption 0.8 Key question: has the abundance of zooplankton decreased as a result of increasing predation pressure? 1.8 2.0 2.2 2.4 2.6 2.8 Fish consumption Are zooplanktivory and changes in zooplankton populations (significantly) related, after removing shared long-term trends? still
  12. 12. Long-term change in zooplanktivory Fish consumption 1.0 P<0.001 0.0 -0.5 -1.0 0 -1.5 200 400 600 800 -1 0.5 g wet weight prey ha day -1 1000 -1 g wet weight prey ha day -1 1200 1.5 Fish consumption 1991 1994 1997 2000 Year 2003 2006 2009 1995 2000 Year 2005 2010
  13. 13. Daphnia April-July Daphniaabundance, long-term 0.5 1.0 Numbers per litre 1.0 0.5 0.0 0.0 Numbers per litre 1.5 1.5 2.0 2.0 Daphnia abundance, seasonality 1 2 3 4 5 6 7 Month 8 9 10 11 12 1991 1994 1997 2000 Year 2003 2006 2009
  14. 14. Cyclops Adult Cyclops abundance, long-term 0.8 0.4 0.6 Numbers per litre 0.8 0.6 0.2 0.4 0.0 0.2 0.0 Numbers per litre 1.0 1.0 1.2 1.2 1.4 1.4 Adult Cyclops abundance, seasonality 1 2 3 4 5 6 7 Month 8 9 10 11 12 1991 1994 1997 2000 Year 2003 2006 2009
  15. 15. Eudiaptomus October-March Adult Eudiaptomus abundance, long-term 0.8 0.6 0.2 0.4 Numbers per litre 0.8 0.6 0.4 0.2 0.0 0.0 Numbers per litre 1.0 1.0 1.2 1.2 Adult Eudiaptomus abundance, seasonality 1 2 3 4 5 6 7 Month 8 9 10 11 12 1990 / 1991 1996 / 1997 2002 / 2003 Year 2008 / 2009
  16. 16. P=0.002 (autumn) 1.8 2.0 2.2 2.4 2.6 2.8 Fish consumption Adult Cyclops abundance -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 Correlation between decline and predation? P=0.23 (spring) P=0.31 (summer) Adult Eudiaptomus abundance -0.4 -0.2 0.0 0.2 0.4 Predation and zooplankton populations P=0.05 (summer) 1.5 2.0 Fish consumption 2.5
  17. 17. P=0.65 (spring) P=0.28 (summer) Likely causal relationship? Detrended Eudiaptomus abundance -0.5 0.0 0.5 Predation and zooplankton populations P=0.03 (autumn) -0.5 0.0 0.5 Detrended fish consumption P=0.81 (summer)
  18. 18. Expectation 2
  19. 19. Expectation 2: loss of the largest
  20. 20. Image analysis • Zooplankton samples scanned and images processed to estimate individual biovolume. • Each “target” categorised as Daphnia or copepods. • Average size structure analysed over time.
  21. 21. 0.6 m d r c t n e l a v i u q E Daphnia spp. 1.3 0.85 1.2 0.8 1.1 0.75 1 0.9 0.8 0.7 0.5 5 8 9 1 7 8 9 1 8 9 1 2 9 1 3 9 1 4 9 1 6 9 1 8 9 1 0 2 0 2 3 0 2 5 0 2 7 0 2 9 0 2 1 0 2 9 0 2 7 0 2 5 0 2 3 0 2 0 2 0 2 8 9 1 6 9 1 4 9 1 3 9 1 2 9 1 8 9 1 7 8 9 1 5 8 9 1 m d r c t n e l a v i u q E Changes in zooplankton size? Total Copepods 0.7 0.65 0.6 0.55 0.5
  22. 22. Summary • Predation pressure (from fish) has increased dramatically 1991-2010. • The zooplankton community has undergone a significant change: calanoid copepods vs. other species. • Only in the case of Eudiaptomus, is it likely that fish predation has caused an observed decline in abundance. • Complementary size-structure analysis does not strongly support the predation hypothesis (for the community as a whole). • Predation effect has likely been “selective”; acting on only some taxa.
  23. 23. Caveats and forward look Fish consumption 1000 -1 400 600 800 -1 200 Next steps  What about the role of larval fish in the spring? 0  We have a better understanding of fish predation pressure from the late summer onwards. g wet weight prey ha day  Larval (young-of-year) fish poorly detected until late summer. 1200 Accuracy of detection Hydroacoustic data give information on fish >4cm length. 1 2 3 4 5 6 7 8 9 10 Month  What is driving shared trends in fish populations and zooplankton e.g. Cyclops?  Process-based modelling of zooplankton 11 12

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