Spatial Environmental Correlates of Intertidal Recruitment: a Test Using Barnacles in Northern Chile

Nearshore circulation processes and local geomorphological patterns are thought to be important correlates of spatial variation in larval recruitment of benthic organisms. However, few studies have attempted to quantitatively separate their relative influences upon recruitment dynamics. Here we use 12 study sites spanning 250 km of the northern Chile upwelling ecosystem and the intertidal barnacles Jehlius cirratus and Notochthamalus scabrosus to examine the extent to which spatial variation in larval recruitment is related to environmental variability and how these relationships depend on spatial autocorrelation. We find that upwelling intensity and wind velocity are negatively related to larval recruitment while surface slicks showed a positive correlation. However, the pure effect of each environmental variable was lower than its combined effects. Taking spatial autocorrelation into account, we find that the spatially structured variation of upwelling dynamics, distance to upwelling fronts, wind velocity, and slick occurrence explained most of the variation in barnacle recruitment. Spatial variation in recruitment rates of barnacles showed a characteristic length scale of 60–70 km, similar to the scale estimated for the spatially structured variables (upwelling, wind velocity, and surface slicks). We find that conditions for the occurrence of surface slicks (as surrogates of internal waves activity) seem to operate across several sites, suggesting a mesoinstead local-scale influence over spatial variation in barnacle recruitment. Our results suggest that spatial variation in barnacle recruitment is modulated by the combined influence of several spatially structured nearshore processes operating at scales of 60–70 km and that spatial autocorrelation must be taken into account in the study of the recruitment–environment relationship. However, the influence of local and small-scale factors on recruitment dynamics of benthic invertebrates should be interpreted cautiously.