Evenness at the Edges: Transition Zones as Hotspots of Sea Anemone Diversity

Charlotte Benedict, Maanas Nukala, Mike Broe and Marymegan Daly. Diversity 2025, 17(11), 761; DOI: 10.3390/d17110761

Abstract

Global biodiversity assessments have traditionally emphasized species richness; however, a comprehensive understanding of marine biodiversity patterns requires incorporating measures of evenness to capture differences in dominance and rarity among species. In this study, we evaluate the evenness in diversity globally of sea anemones (Actiniaria), a cosmopolitan group of understudied marine invertebrates. We assembled a dataset of 247,542 occurrence records from GBIF (Global Biodiversity Information Facility), converted them into incidence data, and estimated diversity at multiple spatial scales using rarefaction, extrapolation, and coverage-standardized Shannon and Simpson indices. We find the highest evenness-based diversity in areas where marine provinces and current systems converge, notably the Philippines, Chile, South Africa, the eastern United States, and Haida Gwaii, British Columbia. Regions with high evenness globally only overlapped with regions of greatest species richness globally in one case, Haida Gwaii. Integration of evenness-based metrics alongside species richness improves the comprehensiveness of biodiversity assessments and points to regions and species in need of further exploration.