Archives and isotopes: changes afoot in the food web of Windermere
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1) Long-term research on fish populations in Lake Windermere using archived samples has allowed reconstruction of the food web using stable isotope analysis. 2) Isotope analysis shows roach rely mostly on littoral prey while perch have shifted to pelagic and profundal resources due to trophic overlap with roach. Arctic charr also appear to now rely more on profundal resources. 3) Pike diet has shifted from Arctic charr to roach, changing the routing of energy in the food web from pelagic to littoral zones. There has also been a subtle increase in trophic efficiency within the web.
Archives and isotopes: changes afoot in the food web of Windermere
- 1. Archives and isotopes: changes afoot in the food web of Windermere Jonathan Grey, P Smyntek, S Maberly & I Winfield et al j.grey@qmul.ac.uk
- 2. Long term research on the fish of Windermere 1940+ Arctic charr gill net survey 1943+ Perch traps 1944+ Pike gill nets 1966+ Arctic charr fishery record scheme 1990+ hydroacoustic survey 1995+ Roach gill nets
- 3. Long term fish abundance General increase since late 1990s, especially in the south basin data from Winfield et al 6000 5000 Abundance (fish ha-1) 4000 3000 2000 1000 0 1990 1995 2000 2005 2010 Year
- 4. Decrease in Arctic charr Marked decline since 2000; 2010 CPUE lowest recorded data from Winfield et al 6 5 CPUE (fish h-1) 4 3 2 1 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Year
- 5. Increase in roach data from Winfield et al 50 CPUE (Fish 100 m 2 net-1 day-1) 40 30 20 10 0 1995 2000 2005 2010 Year
- 6. Fishy Conflict English Lake District
- 8. Isotopes and archives -12 -14 A -16 C (‰) -18 13 -20 Acidified scale -22 -24 -26 y = 0.99x + 0.64; r2 = 0.92; P<0.0001 -28 -30 -30 -28 -26 -24 -22 -20 -18 -16 -14 -12 13 Defatted muscle C (‰) Grey et al 2009
- 9. Hypotheses testable using SIA 1. Roach populations have increased as a result of warming surface water 2. The recent reduction in summer zooplankton is causally linked to increased predation pressure by planktivorous fish 3. The increased abundance of summer phytoplankton, and associated changes in the lake such as increased ratio of phytoplankton chlorophyll a to total phosphorus, is causally linked to the reduction in grazing pressure 4. The decline in Arctic charr in the lake is causally linked to competition for food with other planktivorous fish, particularly the introduced roach in recent years 5. Invasion by a generalist consumer (roach) has also affected the top predator in the lake (the pike) by shortening the food chain, further influencing food- web interactions.
- 10. Windermere isotopic food web…. then Trophic Level Indicator ? 15N (‰) 15N Offshore (Pelagic) 13C (‰) Near shore (Littoral)
- 11. Isotope mixing model of dietary contribution Importance of littoral prey; greater importance of primary consumers 1 Cyclops 0.9 0.8 Proportion in Diet 0.7 Daphnia 0.6 0.5 0.4 Macroinverts 0.3 0.2 0.1 Chironomids 0 2000 2005 2009 2010
- 12. Isotope mixing model of dietary contribution Increase in pelagic and possibly profundal prey 1 0.9 Cyclops 0.8 Proportion in Diet 0.7 0.6 Daphnia 0.5 0.4 Macroinverts 0.3 0.2 0.1 Chironomids 0 2000 2005 2009 2010
- 13. Isotope mixing model of dietary contribution Slight shift from littoral toward profundal prey 1 Cyclops 0.9 0.8 Proportion in Diet 0.7 Daphnia 0.6 0.5 0.4 Macroinverts 0.3 0.2 0.1 Chironomids 0 1985-1987 1992-1994 2000-2002 2003-2005 2009-2010
- 14. Isotope mixing model of dietary contribution Shift from charr to roach 1 0.9 Roach 0.8 Proportion in Diet 0.7 0.6 0.5 Perch 0.4 0.3 0.2 Charr 0.1 0 2000 2005 2009 2010
- 15. Windermere isotopic food web….. now Trophic Level Indicator 15N (‰) 15N Offshore (Pelagic) 13C (‰) Near shore (Littoral)
- 16. Change in trophic position? Shift from charr to roach 1.4 N data 1.2 Pike 15 Charr Pike Change in trophic position from 1.0 0.8 P-zoop Roach 0.6 H-zoop M-inverts 0.4 Basal Res Pike - Roach Pike - Charr 0.2 2000 2010 2000 2002 2004 2006 2008 2010 Year
- 17. Summary • Long term collections and archived tissues / samples from the FBA / CEH has provided material for food web reconstruction • Stable isotope analysis of carbon and nitrogen can be conducted on such material with confidence • Roach diet comprises mostly littoral prey; trophic overlap with perch appears to have pushed perch toward reliance on pelagic and profundal resources • Knock on effect to charr pushing them toward reliance on more profundal resource. Cautionary note: we do not know what YOY fish are doing • Shift in pike diet from charr to roach and consequent shift in ‘routing’ of energy through the foodweb from the pelagic to the littoral zone • Subtle shift in trophic position – increasing efficiency within food web? http://www.windermere-science.org.uk/home j.grey@qmul.ac.uk