Composition and Functional Diversity of Juvenile Groundfish Assemblages in the California Current

ABSTRACT Aim Long‐term monitoring data at the biogeographic scale are essential for developing baselines of biodiversity patterns and tools to diagnose natural cycles, trends, and anomalous events to assess threats from climate change. However, studies using these data often limit their analyses to relatively few metrics that may not adequately capture the breadth of biodiversity. Here, we calculate a suite of compositional and functional biodiversity metrics—collectively comprising ecoscapes—to better resolve assemblage‐level responses to environmental variability and test the spatiotemporal lability of faunal biogeographic provinces. Location California Current Large Marine Ecosystem (CCLME). Taxon Young‐of‐the‐year juvenile groundfish assemblages ( n = 45 taxa). Methods Species composition and abundance data from two long‐term fisheries‐independent surveys were collated with a functional trait database for pelagic taxa. Distinct assemblages were identified through cluster analysis. Compositional and functional alpha‐ and beta‐level biodiversity metrics were then calculated to characterise assemblage‐level biodiversity and to identify patterns of regional community composition and turnover in space and time. Results Ecoscapes revealed the assemblage structure, functional diversity, and turnover of juvenile groundfish from 1990 to 2023. Canonical CCLME biogeographic provinces were mostly supported, but with notable spatiotemporal variation and differences across compositional and functional diversity metrics. Highly productive (unproductive) years were associated with the widespread extent of assemblages characterised by high (low) biodiversity and abundance. Main Conclusions The differences between patterns of functional and compositional diversity of assemblages highlight the potential of ecoscapes to better resolve biogeographic patterns with promising applications for future studies. Ecoscapes may provide explicit links between biodiversity and ecosystem functioning and services, and additional insights into assemblage responses and resilience to environmental variability that can aid biodiversity monitoring and rapidly disseminate management‐relevant information in a changing climate.