Mesoscale patterns in barnacle reproduction are mediated by upwelling-driven thermal variability

Abstract

Environmental variables are known to regulate the reproductive output of marine intertidal organisms, but typically these variables are studied as averages and interpreted at a macroscale level. Along 200 km of coast in NW Iberia, great variability in the reproductive activity of the stalked barnacle Pollicipes pollicipes was found among 7 different locations. We found the highest number of broods reported to date in this species and suggest a more realistic method of predicting reproductive success that takes into account sea surface temperature (SST). At these same locations, we studied 13 yr of SST, thermal upwelling index (UI), ground skin temperature and chlorophyll a (chl a) satellite data, using spectral analyses to partition their temporal variability over ecologically relevant time scales. SST played the most relevant role as an environmental driver, explaining 48% of the variability in the proportion of breeding individuals (BI), but the SST-BI goodness-of-fit decreased sharply northwards. Variance-partitioning analyses indicated that cycles between 20 and 100 d in SST and UI were more important southwards, which is consistent with a latitudinal gradient in upwelling intensity and frequency along this coast. Thus, we found better biophysical coupling towards the south, where shorter fluctuation time scales in SST match the gonadal development period (around 1 mo). This pattern may explain the spatial variability in the strength of association between key environmental variables and the reproductive cycle of coastal species along their distribution range.