Feedback between physiological activity of Mytilus galloprovincialis and biogeochemistry of the water column

Abstract

We investigated the filter-feeding behaviour of individual Mytilus galloprovincialis Lmk in the Ría de Vigo (Galicia, northwest Iberian Peninsula) in order to assess changes in water column biogeochemistry due to mussel culture and the effect of seston organic content on mussel physiological rates. The study was carried out during 1 yr under different oceanographic scenarios by comparing data from a station located in a raft area (RaS) and from a reference site (ReS) with no direct effects of rafting culture activities. Results showed differences between stations in water column nutrient contents, mainly in ammonium levels, with a mean annual excess of 40% at RaS due to mussel feeding activities. We also observed a pronounced deficit of particulate matter at RaS, both in terms of chlorophyll a (chl a, -33%) and microbial plankton carbon (-34%), reflecting preferential grazing of mussels on living plankton carbon. Our investigation of the seston organic compound revealed that feeding and digestion of M. galloprovincialis are highly dependent on the quality of the organic composition of the available food. Mussel organic ingestion rate and absorption efficiency were more strongly correlated with microbial plankton carbon contents than with particulate organic carbon and chl a, illustrating the importance of considering not only autotrophic but also heterotrophic microbial plankton carbon as high-quality food for mussels in the Ría de Vigo.