1. Vulnerability of open ocean food webs in the tropical Pacific to climate change
Presented by
Valerie Allain

2. Authors
This presentation is based on Chapter 4 ‘Vulnerability of open ocean food webs in the tropical Pacific to climate change’ in the book Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change, edited by JD Bell, JE Johnson and AJ Hobday and published by SPC in
The authors of Chapter 4 are: Robert Le Borgne, Valerie Allain, Shane P Griffiths, Richard J Matear, A David McKinnon, Anthony J Richardson and Jock Young

3. Photo: Marc Taquet, FADIO, IRD/IFREMER
Photo: Photoshot/Superstock

4. The tuna food web
Food webs are complex

5. The tuna food web Light Nutrients
Phytoplankton at the base of the food web require light and nutrients to develop

6. Photo: Gustaaf Hallegraeff
Phytoplankton

7. The five oceanic provinces

8. The five oceanic provinces
Warm Pool
Normal El Niño

9. The five oceanic provinces
North and South Gyres (Case 3) and equatorial divergence (Case 4)

10. Impact of climate change
Surface area of the provinces
Present day

11. The impact of climate change
Surface area of the provinces
2035
↘ rich equatorial divergence
↗ poorer gyres and warm pool

12. Impact of climate change
Surface area of the provinces
2050
↘ rich equatorial divergence
↗ poorer gyres and warm pool

13. Impact of climate change
Surface area of the provinces
2100
↘ rich equatorial divergence
↗ poorer gyres and warm pool

14. Impact of climate change
present
future
GYRES
Exchanges between deep rich water and surface poorer waters
↘ of nutrients reaching the surface where photosynthesis can occur

15. Impact of climate change
present
future
Equatorial upwelling
Exchanges between deep rich water and surface poorer waters
↘ nutrients reaching the surface where photosynthesis can occur

16. Impact of climate change
Effect on phytoplankton and zooplankton
Today
2050
2035
present

17. Impact of climate change
Effect on phytoplankton and zooplankton
2035
2035
2050
present
↘ of phytoplankton and zooplankton

18. Impact of climate change
Effect on phytoplankton and zooplankton
2050
2035
2050
present
↘ of phytoplankton and zooplankton

19. Impact of climate change
Effect on phytoplankton and zooplankton
2100
2035
2050
present
↘ of phytoplankton and zooplankton

20. Impact of climate change
Effect on micronekton
Image: Valerie Allain, SPC
↘ micronekton

21. Uncertainties and adaptation
Need to establish long-term observations for biological processes
Phytoplankton
Image: Valerie Allain, SPC

22. Uncertainties and adaptation
Need to establish long-term observations for biological processes
Zooplankton

23. Uncertainties and adaptation
Need to establish long-term observations for biological processes
Micronekton
Image: Rudy Kloser, CSIRO
Image: Valerie Allain, SPC
Image: Valerie Allain, SPC

24. Uncertainties and adaptation
Need to establish long-term observations for biological processes
Predators
Photo: Peter Sharples

25. Uncertainties and adaptation
Global reduction of greenhouse gas emissions
Appropriate tuna fisheries management measures can help maintain healthy food webs and fisheries giving better chances to food webs and tuna to adapt to climate change

26. Conclusions Food webs are complex, based on phytoplankton
5 provinces and food webs in the Pacific
Reduction of the production
Long-term monitoring is needed
Reducing greenhouse gas emissions and managing tuna fisheries