Growth of filter-feeding benthic invertebrates from a region with variable upwelling intensity

Abstract

Coastal upwelling is an ocean feature thought to have important impacts on benthic marine communities by enhancing planktonic productivity in the nearshore environment. In this study, growth rates of 3 species of filter-feeders were examined over a geographic region that includes sites where upwelling is typically weak (south of Point Conception, California, USA) and sites where upwelling is often strong and frequent (at and to the north of Point Conception). The growth of the mussel Mytilus californianus, the gooseneck barnacle Pollicipes polymerus and the acorn barnacle Balanus glandula, as well as the body condition of M. californianus, were all up to 3-6 times higher at sites furthest south of Point Conception, and decreased dramatically moving north around the point. Spatial variation in food availability (measured as chlorophyll a, particulate organic carbon and particulate organic nitrogen) and food quality (measured as C/N ratios) did not explain these patterns of growth. Tidal height of the organisms also failed to account for persistent spatial variation in growth rates. Water temperature varied in a pattern consistent with growth rates (i.e. mean temperatures were warmer in the south), and was the one factor most often selected in stepwise regressions for models contributing to patterns of filter-feeder growth. This study suggests that factors other than, or in conjunction with, productivity may drive large-scale differences in benthic filter-feeder growth rates.