1. Stable isotope evidence for mechanisms by which climate- driven variations in phytoplankton growth influence higher trophic levels Clive N Trueman, Kirsteen M MacKenzie

2. WESSEX SALMON and RIVERS TRUST Acknowledgements Particular thanks to Cathy Cole, Ed Westwood & Mike Bolshaw (UoS), Anton Ibbotson & Bill Beaumont (CEH/GWCT), Andy Moore, Bill Riley & Barry Bendall (Cefas), & Ian Davidson (EA)

3. Climate effects on high trophic levels Physiological mechanisms connecting SST and trophic cascades are less clear This hampers prediction of response of plankton and higher trophic levels to future warming (more or less production at higher SST?) Here we use high trophic level animals (Atlantic salmon) as natural samplers to probe connections between climate (SST), plankton and higher trophic levels

4. Stable isotopes in ecology  15 N  13 C Primary producer Primary consumer Secondary consumer  t-d Graham et al., 2009 Low growth High [CO 2 ] aq High growth Low [CO 2 ] aq Laws et al., 1995, Cassar et al., 2005

5. Atlantic salmon as natural autonomous samplers Feed in open ocean and return to natal river Occupy waters significantly cooler than growth optimum Cultural and economic interest – abundant archives

6. Apatite Collagen Scales as a target for isotope analysis Hutchinson & Trueman, 2006 © Guy Mawle W Last season of marine growth Fish sample the physiological status of plankton integrated over an 8 month feeding season

7. N = 235 N = 289 Todd et al 2008 Scales sampled from fish returning to two UK areas…..sampling marine conditions in feeding grounds

8. Frome 1SW Frome MSW NEC 1SW NEC MSW

9. SST  13 C SST  13 C Identifying Marine Location Time  13 C Time SST Time SST Time  13 C Unlikely Likely

10. Results: Feeding areas identified NECM NECG RFG RFM New method to identify location in migratory pelagic fish Use these results to investigate SST – plankton relationships in the areas sampled by the salmon

11. 1987 1988

12.  /[CO 2 ] aq  13 C org -ve +ve Low growth High [CO 2 ] aq High growth Low [CO 2 ] aq All significant relationships between SST and  13 C values are negative As the solubility of [CO 2 ] aq decreases with increasing SST, the negative slope implies either a reduction in mean plankton growth rates, or reduced removal of [CO 2 ] aq with increasing SST warmer years colder years Plankton growth rates and/or production fell with increasing SST in sub arctic N Atlantic

13. Possibility to predict magnitude of the resposnce of primary production to SST change in a region- specific fashion

14. Conclusions Across much of the sub- arctic NE Atlantic, increases in SST are linked with DECREASES in average phytoplankton growth rate Impacts on predictions of fish production in high latitudes under climate warming scenarios Fish tissue isotopes may provide an indirect proxy for plankton growth rates

15. Higher trophic level effects - Temporal (mass standardised)  15 N River Frome: 14 to 15 year cyclesNortheast Coast: 7 to 9 year cycles NECGNECM NECG Lag (Years) RFGRFM RFGRFM Lag (Years)

16. Results: Trophic variation and herring Salmon trophic level (δ 15 N values) vary with Scottish herring abundance (SSB) for both cohorts of the River Frome population.

17. ºC dependant Temporal  13 C variation NECG NECM NECG River Frome: 14 to 15 year cycles Northeast Coast: 7 to 9 year cycles RFM RFG RFM Lag (Years)

19. Salmon - temperature relationship Complex pattern of positive and negative correlations with SST Positive ResponsesNegative Responses Post smolt growth1SW growth Increased size R. Dee returnsDecreased size R. Esk Reduced condition of returns 1SW European returns2SW Scottish returns Suggesting differential response to SST in different stocks that likely feed in different regions Possible direct and indirect effects of changes in SST – indirect effects linked to bottom-up control through SST effects on primary production (Friedland et al 1993; 1998; 2005; Todd et al., 2008; ICES 2009)

20. Summary Spring-summer plankton growth rates appear to fall with increasing SST in the sub-arctic N Atlantic Suggests a mechanism for negative impacts of increased SST on salmon growth via bottom-up control Supported by a (weak) relationship between herring SSB and salmon d15N values Fish tissues can provide a good record of climate – plankton – ecosystem linkages providing location of feeding is well known