Mismatched seasonal patterns of larval production and quality in subtropical barnacle populations along a coastal trophic gradient

Abstract

The seasonal breeding patterns of a wide array of marine invertebrates are shaped by strong and deterministic environmental factors over their geographic distribution range, such as temperature or photoperiod. Whether or not such patterns will remain adaptive at more localized scales may depend on how consistent are secondary drivers controlling resource supply to parents and offspring. We address this question by examining the seasonal patterns of both the trophic state of coastal waters, and larval production and quality produced by a filter-feeding invertebrate, the intertidal barnacle Chthamalus bisinuatus, along a 150 km long trophic gradient in Southeastern Brazil. Results are consistent to previous remote sensing work showing strong seasonal variation of chlorophyll-a and particulate organic carbon concentrations, increasing 2 to 2.5 times from summer – early autumn to winter, compatible to enhanced production through vertical mixing caused by passing cold fronts. The spatial gradient was also verified and found to be consistent between seasons, but contrasts were of smaller magnitude (coefficients of variations between 15 and 35%). All reproductive parameters showed important seasonal but no spatial trends. Larval production was much higher in summer-early autumn, agreeing with previous results based on gonad development and early recruitment rate for this same species and published results for other chthamalids. However, per capita parental transfer of neutral fatty acids to larvae and larval survival without exogenous food increased 2 and 1.4 times from the breeding to the non-breeding season, respectively, indicating that coastal oceanographic processes favor larval quality when reproductive activity is lower. Given that food limitation is likely frequent in the study region, shifting from oligotrophic to mesotrophic, and that effects of larval nourishing can be carried over to benthic barnacle stages, results also suggest that the contribution of out-of-season offspring to overall recruitment may be disproportionately higher.