Variable fish habitat function in two open-coast eelgrass species

Abstract

Eelgrasses Zostera are foundation species that perform myriad ecosystem services, yet research into their habitat function is often focused on regions susceptible to intense anthropogenic disturbance. This trend has created a data gap on the role more remote eelgrass beds provide among the mosaic of other temperate marine habitats. In this study, we surveyed 15 Z. marina and Z. pacifica beds along Catalina Island and the Southern California Bight (SCB) mainland coast from 2018 to 2020 for areal coverage, structural components and fish assemblages, from which a relativized index of fish utilization was then created. We then evaluated the landscape and structural components that potentially drive fish utilization in Z. marina using the index as a response variable in a model selection procedure. Zostera beds ranged in size from 0.06 ha to >27.5 ha. Fish assemblages in Z. marina and Z. pacifica beds were significantly different, and in the case of fishes found in both, individuals were often below size at maturity in Z. marina and above size in Z. pacifica. Distance to the nearest reef and bed area, both positively related to the fish assemblage index, were the most important factors. The results suggest Z. marina beds function as a nursery habitat while Z. pacifica are used by mid-level predators for foraging. These data represent the first rigorous study of fish utilization of open-coast Z. marina and Z. pacifica beds, and are invaluable to marine spatial planning efforts that may incorporate a more holistic approach to habitat management in temperate regions.