Eelgrass community dominated by native omnivores in Bodega Bay, California, USA

Abstract

Seagrass meadows are key nursery habitats for many important commercial and recreational fishes. This is due, in part, to high abundances of epifaunal invertebrate prey relative to other nearshore habitats. Despite this knowledge, baseline data for these invertebrate communities are scarce and limited in species-specific detail. Here we describe the results of a 16-mo survey of eelgrass, Zostera marina L., and its epifauna, conducted in Bodega Harbor, California, USA. In our study, we report several key ecological patterns: (1) this invertebrate assemblage comprises 39 identified taxa, mostly native detritivore-grazers; (2) this community is numerically dominated by three species, the polychaete worm Platynereis bicanaliculata (Baird, 1863), an undescribed porcellidiid copepod, and the native caprellid amphipod Caprella californica Stimpson, 1856; (3) both site and date significantly affected eelgrass and invertebrate abundances, (4) the effect of site upon invertebrate abundance is attributable to eelgrass habitat, namely leaf area and epiphyte load; and (5) our analysis suggests temperature explains the effect of date upon invertebrate abundance. finding of a few dominant species concurs with surveys conducted elsewhere globally; however, the abundance of native species in Bodega Bay starkly contrasts with nearby San Francisco Bay, where eelgrass beds are dominated by introduced species. Furthermore, declines in eelgrass and epifauna coincide with the onset of The Blob, an extreme warm water event that occurred along the California coastline. Our results support the importance of detritivore-grazers to seagrass ecology, as well as herald potential trophic effects of future extreme warm water events.