Major Long-term Shifts in Spatial and Annual Plankton Biodiversity Patterns in the North Atlantic Ocean

Abstract Despite the fundamental role played by marine biodiversity within ecosystem functions and services, the impacts of climate on this key ecosystem property remain poorly documented. Here, we investigate long-term changes in spatial and annual biodiversity patterns for three key plankton groups (diatoms, dinoflagellates, and copepods) across the North Atlantic over ~ 6 decades (1958–2022) at a high spatio-temporal resolution. Over this period we show that biodiversity has generally increased polewards, with significant positive trends that cover ~ 30% [27; 38.9%] of the basin area for all three groups. Between the cold 1965–1985 and warm 2002–2022 periods, mean biodiversity has increased by ~ 8–17% [4.4; 22.2%] in cold-water regions, associated with significant expansions of high-biodiversity periods by up to 21 days [9.48; 25.33]. This pronounced change in species phenology is likely to desynchronise trophic interactions within the ecological networks and perturb energy transfer from primary producers to higher trophic levels.