Rui Ying, Fanny M. Monteiro, Jamie D. Wilson, Daniela N. Schmidt

Climate changes have threatened marine organisms causing migrations, biomass reduction and extinctions. However, the capacity of marine species to adapt or acclimate to these changes remains poorly constrained in both geological and anthropogenic timescales. Such uncertainty makes modelling past and future ocean biodiversity and ecosystem functions challenging, particularly for the plankton community transferring energy to the whole ocean food web. Here, we use both fossil record observations and a global trait-based plankton model to show that spinose (symbiont and non-symbiont) foraminifera ecogroups acclimated to the slow deglacial transition from the Last Glacial Maximum (LGM, 21 ka) to the pre-industrial period. Non-spinose (non-symbiont) foraminifera kept the same thermal preference. Our study thus provides the first evidence that marine plankton can acclimate during the last deglacial warming, which we confirm by re-analyzing a longer-term global fossil observation (600 ka). However, when forcing the trait-based plankton model with rapid transient warming to next century, our model suggests that the acclimation capacity of these ecogroups is saturating. Foraminifera are projected to migrate poleward, dropping their global biomass by 2.5-12.2% by 2100 relative to 2022 (depending on the warming scenarios). Our study highlights the impact of warming timescale on determining plankton acclimation and migration. Anthropogenic warming is modifying the long-term acclimation pattern of marine zooplankton and causing species distributional change, biodiversity loss, and decreasing fishery production, which could worsen considering the effects of ocean acidification and symbiont bleaching.