Riverine discharges impact physiological traits and carbon sources for shell carbonate in the marine intertidal mussel Perumytilus purpuratus

Abstract

Anthropogenic modification watersheds and climate change have altered export from fluvial systems causing changes to the carbonate chemistry of river-influenced near shore environments. To determine the possible effects of riverine discharges on the mussel Perumytilus purpuratus, we performed in situ transplant experiments between river-influenced and open coastal habitats with contrasting seawater carbonate chemistries (i.e., pCO2, pH, Ωar) across four regions covering a wide latitudinal range (32°55'S-40°10'S). The river-influenced habitats selected for transplant experiments were different than open coastal habitats; with higher pCO2 (354-1313 μatm), lower pH (7.6-7.9) and Ωar values (0.4-1.4) than in open coastal area. Growth, calcification, metabolism were measured in a reciprocal transplant experiment to determine physiological responses associated with river-influenced sites and non-influenced control sites. Growth and calcification rates were higher in river-influenced habitats; however the organisms in this area also had lower metabolic rates, possibly due to enhanced food supply from river systems. Further analysis of carbon isotopic composition (δ13C) indicated that the relative contribution of seawater dissolved inorganic carbon (DIC) to the carbonate shells of P. purpuratus was much higher than respiratory carbon. Nevertheless, P. purpuratus incorporated between 7% and 26% of metabolic carbon in the shell depending on season. There was a strong, significant relationship between δ13CPOC and δ13CTissue, which likely influenced the isotopic composition of the shell carbon.