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New niches for larger phytoplankton in a warmer, more resource-limited ocean

Leles, S. G.; Breithaupt, L.; Krinos, A.; Alexander, H.; Moeller, H. V.; Flanjak, L.; Laufkoetter, C.; Litchman, E.; Aranguren-Gassis, M.; Levine, N. M.

2025-08-18 ecology
10.1101/2025.06.22.660956 bioRxiv
Show abstract

Warming and nutrient limitation are major stressors that affect primary production in the ocean, with cascading impacts on the food web. Yet, we lack a mechanistic understanding of how phytoplankton manage the combined stress of heat-damage and nutrient-limitation and the implications of these responses for phytoplankton biogeography. By combining theory, proteome allocation modeling, and climate projections, we identified two potential competing strategies for multi-stressor growth: (1) increase growth temperature optima through higher nutrient uptake efficiency and smaller cells, or (2) invest in heat-mitigation mechanisms achieving higher thermal tolerance at the cost of growth and larger cells. By simulating the optimal metabolic strategies of different phytoplankton functional types across a latitudinal gradient, we found that Prochlorococcus are more vulnerable in warmer, heat-stressed, tropical regions due to greater heat sensitivity and lower storage capacity, indicating a potential ecological niche for larger phytoplankton with lower sensitivity to oxidative stress, such as Synechococcus and picoeukaryotes. Our findings advocate for the inclusion of phytoplankton heat-stress responses in global models to more accurately predict their ecological niches as the climate warms.

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