Environmental Filtering Drives Widespread Trait Convergence in Marine Demersal Ray-Finned Fishes

Aim: Understanding the processes that shape the distribution of biodiversity in the oceans is central for predicting and conserving ecosystems under global change. Although a vast literature exists on drivers of species diversity, the geographical patterns and drivers of ecosystem functioning, and in particular the traits that shape this functioning, remain relatively unexplored. We address this gap by testing the effects of environment, fishing pressure and evolutionary history on fish trait compositions across continental shelf seas using scientific trawl surveys. Location: Northern Hemisphere shelf seas. Time Period: 1999–2021. Major Taxa Studied: Marine demersal ray-finned fishes. Methods: Here, we aggregate trawl and trait information (body size, habitat, reproduction, trophic ecology and growth) for 1164 demersal ray-finned fishes on continental shelf seas throughout the Northern Hemisphere to test the relative importance of environmental, evolutionary and anthropogenic drivers in shaping trait compositions. These patterns are tested across three different spatial scales (100 km2 to marine Ecoregions) using linear and non-linear models. We also compare trait compositions to expectations under null and neutral models. Results: Trait compositions throughout shelf seas are always positively related to environmental conditions but appear strongly associated with evolutionary history on the northeast Pacific shelves. Although fishing can alter individual traits and deplete populations, it shows no explanatory power in describing trait compositions. The majority (81%) of trait compositions are more similar than expected under neutral drift. Main Conclusions: We find that environmental filtering has strongly shaped the functional convergence of fish communities while, in contrast to expectations, phylogenetic conservatism across evolutionary lineages appears uniquely strong in the Pacific Ocean but less important in the Atlantic. The widespread role of environmental conditions in shaping fish traits highlights the potential sensitivity of community functioning to environmental and climate change and sheds new light on the potential for trait-based conservation strategies.