MEPS prepress abstract  -  DOI:

Rhodolith structural loss decreases abundance, diversity, and stability of benthic communities at Santa Catalina Island, CA

Scott S. Gabara*, Scott L. Hamilton, Matthew S. Edwards, Diana L. Steller


ABSTRACT: Species that increase habitat structural complexity often have a disproportionate influence on their ecosystems. Rhodoliths are bed-forming unattached coralline algae, which increase benthic structural complexity and enhance biodiversity in coastal soft-bottomed ecosystems worldwide. Consequently, their degradation due to anthropogenic disturbance, such as crushing from boat mooring chains, may lead to reduced biodiversity and ecosystem functioning. To examine how anthropogenic disturbance impacts rhodolith community dynamics we used a comprehensive sampling and analytical approach to compare macroalgal, invertebrate (infauna and epifauna), and fish assemblages between rhodolith beds and adjacent mooring-disturbed crushed rhodolith sand. Sampling was conducted during two sampling times and across three sites at Catalina Island, CA, USA. Our results demonstrate that the more heterogeneous structure provided in undisturbed rhodolith beds supported greater community richness and abundances than crushed rhodolith sands. Specifically, disturbance related rhodolith structural loss was associated with significantly reduced richness of invertebrates and abundance of macroalgae, invertebrates, and fish. In particular, deposit feeding infaunal tanaids were far more abundant in rhodolith beds and drove much of the difference in invertebrate abundance between habitats. Further, spatiotemporal variation in the infaunal invertebrate assemblages was 54% lower within the rhodolith beds than crushed rhodolith sand, suggesting that rhodolith beds supported more stable communities. Our results suggest that structured rhodolith bed habitats support more abundant, diverse, and stable benthic communities than do disturbed rhodolith sand habitats. Better management of rhodolith ecosystems and the factors that disturb them could maintain coastal biodiversity and stability.