Soft-sediment community stability across years in San Francisco Bay

Abstract

Macrobenthos is used commonly in disturbance-related studies of coastal ecosystems, including those that evaluate invasions by non-native species (NIS), but still little is known about temporal variation in community characteristics, especially in bays and estuaries. In this study we investigated inter-annual changes in the soft-sediment benthic communities of San Francisco Bay over a period of five years, evaluating the contribution of NIS vs. native species to community attributes (species richness, abundance) and the efficacy of sampling (percent richness detected for each NIS and native species). Benthic macrofauna were collected, identified, and quantified from 10 stations (48–50 replicate samples) per year across the high salinity region of the Bay. A total of 36,872 individuals belonging to 126 morphospecies were collected; 61 species were native, accounting for 22% of total abundance, and 31 species were NIS, which reached 74% of total abundance. The other 34 species were either cryptogenic or unresolved taxa. Soft-sediment communities were mainly comprised of amphipods (Ampelisca abdita, Sinocorophium heteroceratum, Monocorophium acherusicum), polychaetes (Sabaco elongatus, Euchone limnicola) and bivalves (Venerupis philippinarum). Community structure and composition were stable across years during the period of the study, despite a major marine heat wave and a record-breaking drought that raised average salinity levels for several years. The sampling was effective, especially for NIS, detecting a higher proportion (94–100%) of estimated richness for NIS compared to native species (74–89%) across the five year period, suggesting NIS were more evenly distributed in space and time and many native species occurred more patchily and less frequently.