Abstract
Detecting the long‐term impacts of global change in marine communities and ecosystem functioning is a major scientific challenge that requires long‐term time series. Despite their high biodiversity and functional importance, temperate coastal ecosystems remain comparatively under‐represented in long‐term assessments of global change. Because their functioning relies on tight interactions between pelagic and benthic compartments, approaches that analyze both components together are essential for a comprehensive understanding. Here, we use two decades of data obtained as mandatory monitoring of nuclear power plants to investigate temporal changes in phytoplankton, zooplankton, and benthic macrofauna. Specifically, we assessed shifts in taxonomic composition and trends in abundances of key functional groups and evaluated their relationships with abiotic drivers. Key results showed that both pelagic and benthic compartments exhibited significant inter‐annual changes in composition linked to water temperature. As species exhibit a diversity of ecological niches, differential responses to climate change can explain these patterns. While phytoplankton and benthic macrofaunal richness increased, zooplankton displayed strong taxonomic replacements with both losers and winners. These taxonomic changes translated into heterogeneous functional trends. For zooplankton, holoplanktonic filter‐feeding crustaceans declined whereas gelatinous filter‐feeders and meroplankton increased. As for the benthic assemblages, both suspension‐ and deposit‐feeders increased in abundance. Overall, these findings highlight an ecosystem‐wide restructuring, spanning pelagic and benthic compartments, coupled with an increase in benthic dominance. Convergence with studies from other European seas suggests that such complex, compartment‐specific responses are part of a wider pattern of coastal ecosystem adjustments to contemporary environmental change.