Regional variation in oceanographic conditions influences intertidal fish assemblage structure

Abstract

I investigated the relationship between regional variation in habitat and oceanographic conditions and the population and assemblage structure of intertidal fishes (the sculpins Clinocottus globiceps, Clinocottus recalvus, and Oligocottus snyderi) throughout the spring and summer in 2001, 2002, and 2003. The assemblage structure of intertidal sculpins varied markedly with distance from an upwelling center: warmer sites in the northern Monterey Bay that were furthest from upwelling activity were dominated by C. recalvus, whereas cooler sites north of the bay closest to upwelling activity were dominated by O. snyderi and C. globiceps. Interestingly, species were spatially distributed according to temperature differences as would be predicted by the geographic distributions and temperature sensitivity of each species: C. recalvus is a more southerly species tolerant of warmer temperatures, whereas O. snyderi and C. globiceps have more northerly geographic distributions and are relatively less tolerant of warmer water conditions. Regional variation in adult and juvenile assemblage structure reflected differences in recruitment rates among species, suggesting that regional differences in assemblage structure of these intertidal fishes are influenced greatly by pre‐recruitment processes. In addition, possible limited larval exchange between the two regions — due to a combination of unique larval behavior of intertidal sculpins and the persistence of an upwelling front that acts as a barrier to larval dispersal — may serve to reinforce these patterns. The spatial differences in the assemblage structure of intertidal sculpins within this region are caused by a combined influence of variation in oceanographic conditions affecting both larval and benthic phases.