Are submarine groundwater discharges affecting the structure and physiological status of rocky intertidal communities?

This study evaluated the impacts of submarine groundwater discharges (SGD) on a rocky intertidal community of South Portugal, during April–November 2011. Chlorophyll-a concentration was higher at the SGD site in respect to the Reference site. Epibenthic community structure differed between sites, with an increase in Chthamalus spp. and a decrease in macroalgae coverage at the SGD site. The abundance and body size of Mytilus galloprovincialis were consistently higher at the SGD site. During mid-spring, under potentially higher SGD and less favorable conditions for coastal phytoplankton, the ecophysiological condition of M. galloprovincialis and G. umbilicalis was also higher at the SGD site. These beneficial effects on filter-feeders and herbivores probably resulted from local increases in prey availability, supported by SGD-driven nutrient inputs. Conversely, P. depressa was not favoured by SGD, probably due to a lower dependency on algae as food. The analysis of epibenthic community structure and ecophysiological condition represents a promising approach to disentangle the ecological impacts of SGD on intertidal ecosystems.This research was funded by FREEZE (PTDC/MAR/102030/2008) and PHYTOCLIMA (PTDC/AAC-CLI/114512/2009) projects, by public funds from FTC through project UID/Multi/04326/2013. L.A.K. was supported by a PhD scholarship from the Programme Science without Borders (Conselho Nacional de Desenvolvimento Científico e Tecnológico, of the Ministry of Science, Technology and Innovation of Brazil – 237998/2012-2). F.L. hold scholarship from FCT (SFRH/BPD/108949/2015). The authors would like to express their gratitude to NASA (SST data), ESA (Chl-a data), NOAA (wind data) and Agência Portuguesa do Ambiente (aquifer piezometric level and nutrient data) and every group that works hard to provide free and high quality products for the ocean sciences community. The authors thank Judite Fernandes, who kindly provided discriminated nutrient data for ARQ groundwater and Olhos de Água intertidal springs, collected in the framework of FREEZE project, as well as Dr. José Paulo Monteiro for sharing his knowledge on Algarve SGD. Special thanks are also due to Renata Gonçalves and Isa Máximo who helped in the laboratory work. The authors would also like to thank the reviewers and editor for their constructive comments that contributed for substantially improving an earlier version of the manuscript.Scopu