Meso-scale spatial variation in settlement and recruitment of intertidal barnacles along the coast of central Chile

Spatial and temporal variation in recruitment can be the leading determinant of population fluctuations in species with pelagic larval stages. Characterizing and identifying the causes of such variation is, therefore, necessary to understand population dynamics, and to develop conservation and management strategies. We examined spatial patterns in settlement and recruitment of the intertidal barnaclesJehlius cirratus,Notochthamalus scabrosusandNotobalanus flosculus, and their relationships with environmental variables operating at meso- (sea surface temperature, SST) and small (local topography) scales. Settlement and recruitment were studied over 6 mo at biweekly intervals at 16 sites along 120 km of coastline in central Chile. All species showed similar temporal patterns, with a peak in settlement and recruitment during austral spring. We decomposed the spatial patterns into their corresponding meso-scale trend (from a few to 10s of kilometers) and into their small-scale (site) residual variation. Recruitment of chthamaloid species was highly and positively correlated at meso- and small-scales, and the among-site rankings showed consistency of the spatial structure throughout the recruitment season. SST explained a significant fraction of the variance in recruitment of the chthamaloids at the meso-scale, and spatial analysis showed coincident decorrelation scales of about 35 km for SST and recruitment. In contrast, recruitment of balanoid species did not show a clear spatial structure, was not associated with meso-scale variation in SST, and local topography seemed to play a significant role in their settlement. Topographically modified upwelling dynamics over scales of 10s of kilometers is the most plausible factor shaping meso-scale variation in recruitment of chthamaloid barnacles, whereas settlement and recruitment of balanoid species seem more strongly influenced by processes acting at local scales. The spatial scale and structure of recruitment provide guidelines for the placement and spacing of protected areas in the region.