How physical and biotic factors affect brachiopods from the Patagonian Continental Shelf

Abstract

The Patagonian Continental Shelf (PCS) is a dynamic region characterized by the confluence of two western boundary currents (the Brazil and Malvinas currents) and the presence of several oceanographic fronts, giving rise to a large and rich biological area. In this study we analyze the distribution pattern of brachiopod assemblages along a latitudinal range between 39°S and 55°S, including the relationship with different physical factors of the benthic zone, either measured in situ (depth, sediment, water temperature, and salinity) or provided by the Bio-ORACLE database (water temperature, salinity, phosphate concentration, nitrate concentration, dissolved oxygen concentration, primary productivity, phytoplankton, and current velocity). Data show that articulate brachiopods were not homogeneous in terms of species composition, body size, relative abundance and taphonomic signatures along the latitudinal gradient, thus indicating environmental sensitivity. The brachiopod assemblages throughout the gradient are characterized by the dominance of Magellania venosa, especially in the internal sector of the platform, accompanied by Terebratella dorsata towards the slope, and Liothyrella uva in the southern sector. Based on all available information, it appears that the main physical factors that affect the distribution of articulate brachiopods from the PCS were sediment grain size and water flow velocities. Also, in M. venosa shells, sediment grain size is also associated with fragmentation, abrasion and encrusting by invertebrates. Finally, the larger sizes of M. venosa appear to be associated with higher productivity areas rich in phytoplankton and suitable environmental water energy.