Planktonic mollusks between the Reloncavi Fjord and the Corcovado Gulf, southern Chile: winter occurrence, distribution and abundance

Despite their important ecological functions, knowledge of planktonic mollusks in southern fjords of Chile is limited. Hence, the goals of this research were to determine the composition of the main groups of planktonic mollusks, their geographical distribution and abundance, between the Reloncavi Fjord and the Corcovado Gulf. Plankton samples were collected at 16 oceanographic stations during the CIMAR-19 Fiordos cruise, in July 2013. Oblique hauls were made in two water depth layers according to the pycnocline depth with a WP2 net (180 mu m mesh size). The organisms were removed manually from each sample, counted and assigned to the lowest possible taxonomic level. Mollusks were obtained in all stations: Bivalvia (39.68%), Gastropoda (60.31%) and Cephalopoda (0.01%). The total abundance of mollusks varied between 18.46 and 124.42 ind. m(-3). Among bivalves highlighted the abundance of Pholadidae, Teredinidae and Xylophagidae larvae. Among gastropods highlighted the abundance of Thecosomata and Nudibranchia. Among cephalopods, only Octopoda paralarvae were captured. The abundance of bivalve boring species and their larvae have an important role in the flow of allochthonous organic matter across the fjords. The water temperature and salinity may be the variables that mostly modulate the distribution of planktonic bivalves and gastropods in the Chilean fjords.