Windermere Science Project stakeholder meeting presentations. Grey on how invasive roach have caused changes to the dietary niche of native fish species, thereby altering the structure and functioning of the lake food web. Data derived from gut content and stable isotope analysis of contemporary & archived samples

1. Altered food web structure
Jonathan Grey1, Peter Smyntek1 & Ian Winfield2
1
Aquatic Ecology Group, School of Biological & Chemical
Sciences, Queen Mary University of London, UK
2
Lake Ecosystems Group, Centre for Ecology &
Hydrology, Lancaster, UK

2. Food web structure
Carnivores
Perch
Changes in
Pike diet
Planktivores
Increase in
roach
Reduction in
zooplankton
Zooplankton
Increase in
Phytoplankton
phytoplankton
Increased
internal Pload
Chemistry
Climate
change
Reduction in
Arctic charr
Warmer
water
Prolonged
stratification
Reduction
in oxygen
at depth
Physics

3. SIA samples
•
For stable isotope analyses:
•
980 individual fish
•
250 zooplankton samples
•
140 macroinvertebrate samples
•
Spanning 27 years (1985-2011)

4. Archives & isotopes
-12
A
-14
Acidified scale δ13C (‰)
-16
-18
-20
-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
Defatted muscle δ13C (‰)
eg Grey et al 2009

5. Hypotheses
•
Increase in roach caused: a change in pike diet through provision of
extra / alternative prey; and a shift in niche space for native
equivalents
•
Shift in routing of carbon through food web to top predator (pike)
from predominantly pelagic to littoral
•
Increased efficiency of food web via reduced trophic linkage

6. Recap from IJW
•
Diet changes alongside roach increase:
•
•
Arctic charr decreases in macroinvertebrates and Daphnia,
increase in zooplanktivores
•
•
Perch decreases in macroinvertebrates and Daphnia, increase
in zooplanktivores
Roach remarkably stable and dominated by macroinvertebrates
and predatory zooplankton
Roach impact upon perch and Arctic charr, forcing greater food
niche overlap between these native species

7. SI mixing models
11
10
9
δ15N (‰)
8
7
6
5
4
3
-32
-30
-28
-26
13
δ C (‰)
-24
-22
1.0
Predatory zooplankton
Macroinverts
Daphnia
Chironomids
0.8
0.6
0.4
0.2
0.0
1982
1987
Predatory zooplankton
1.0
0.8
1992
1997
Macroinverts
2002
Daphnia
2007
2012
Chironomids

8. SI-derived metrics
Layman et al 2007 a & b

9. SI-derived metrics
Grey & Jackson 2012

10. Diet shifts in isotope space
Pre-Roach
Expansion
(1986 – 87)
Post-Roach
Expansion
(2007 & 2009)
Pike
Charr
Perch
Zoopl.
Macroinv.
Roach
Pike
Charr
Perch
Zoopl.
Macroinv.
δ 15N (‰)
δ 13C (‰)
δ 13C (‰)

11. Diet shifts in isotope space
Early Roach
Period
(1993 – 95)
Recent Roach
Period
(2007 & 2009)
Pike
Charr
Perch
Zoopl.
Macroinv.
Roach
Pike
Charr
Perch
Zoopl.
Macroinv.
Roach
δ 15N (‰)
δ 13C (‰)
δ 13C (‰)

12. Samples for SIA

13. Pike GCA

14. Pike GCA

15. Pike diet

16. Carbon routing to pike
1.0
Pelagic carbon (%)
0.8
N Basin
S Basin
y = -0.011x + 22.569
0.6
0.4
0.2
0.0
1980
1990
2000
Year
2010

17. Food chain length
9.5
Food chain length (‰)
9.0
Zooplankton baseline
Macroinvertebrate baseline
8.5
8.0
7.5
7.0
6.5
6.0
5.5
1980
1990
2000
Year
2010

18. Summary
•
Distinct shifts in niche space of native fish following roach expansion
•
Changes to pike diet: reduction in charr; increase in perch + addition
of roach
•
Significant shift (SB) in routing of carbon from pelagic to littoral
•
Increase in overall food chain length post roach expansion; slight
but significant increase in efficiency if routed via littoral
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