Projected changes to tuna food webs in the

Projected changes to tuna food webs in the tropical Pacific

Based on……. .

Outline • Nature of food webs for tuna • Differences in food webs among provinces of the tropical Pacific Ocean • Effects of CC on provinces and their food webs • Uncertainties

Photo: Marc Taquet

Tuna food web Food webs are complex

Tuna food web

Oceanic provinces

Oceanic provinces • Warm pool Normal El Niño

Oceanic provinces • Equatorial divergence

Oceanic provinces • Northern and southern gyres

Impact of climate change present future Increased stratification • Decrease in nutrients reaching surface where photosynthesis occurs

Impact of climate change • Changes in surface area of provinces

Impact of climate change • Effect on phytoplankton and zooplankton Present present 2035 2050 2100

Impact of climate change Warm pool Equatorial upwelling W Northern gyre Southern gyre A = area P = phytoplankton

Impact of climate change • Effect on micronekton Midwater Dee micronekton Deep micronekton Image: Valerie Allain, SPC Shallow micronekton

Uncertainties Photo: Peter Sharples • Need to establish long-term observations for biological processes Image: Valerie Allain, SPC Image: Rudy Kloser, CSIRO micronekton zooplankton phytoplankton predators Photo: Valerie Allain

Conclusions • • Food webs are complex, based on phytoplankton 5 provinces have different food webs Production expected to decrease Long-term monitoring needed to reduce uncertainty