From plankton to fish: 21st-century redistribution of marine biodiversity and the changing role of rare species.

Predictions of climate-driven marine biodiversity change typically overlook noncommercial and rare taxa, leading to an incomplete and potentially biased understanding of change. We address this gap by quantifying α-, β-, and γ-diversity using Hill numbers consistently across co-occurring phytoplankton, zooplankton, benthos, and fish taxonomic groups. Using Bayesian additive regression trees and extensive survey data, we project climate-driven biodiversity change in the northeast Atlantic until 2100. We show that climate change could redistribute biodiversity both within taxonomic groups, altering the contribution of rare species, and across the food web. Widespread increases in fish and benthos species richness, reflecting poleward migration, often coincided with declines in zooplankton and phytoplankton richness, potentially disrupting energy transfer from lower to higher trophic levels. By identifying areas with high biodiversity across taxonomic groups and predicting how these could change in the future, we provide a framework to support proactive conservation actions to help achieve global biodiversity targets in a changing climate.