Long-term stability of eelgrass fish assemblages in two highly developed coastal estuaries

Changes in fish assemblages were tracked in representative eelgrass (Zostera marina L.) beds within two estuaries on the urbanised coast of southern California, USA, San Diego Bay and Mission Bay, from 1987 to 2010. Assemblages were sampled twice yearly (spring and summer) at day and night using beach seines. Assemblage stability was examined over time along with changes in assemblage structure across time of day and season, including the influence of temporally variable abiotic variables. Only the occasionally occurring fish, those present in <70% of samples, in Mission Bay appeared to be shifting to a new assemblage. Although season and sampling time significantly affected assemblages, correlations with abiotic factors were low. Given the long history of urban development of these estuaries, community shifts may have occurred prior to the onset of sampling, giving the appearance of stability. Alternatively, eelgrass habitat may be providing a refuge from long-term disturbances.