High densities of stalked barnacle larvae (Pollicipes pollicipes) inside a river plume

The pelagic phases of the commercially important stalked barnacle, Pollicipes pollicipes (Cirripedia: Scalpellomorpha), still remain a knowledge gap due to the extreme paucity of these larvae in the plankton. During four cruises at the Nalcn River mouth (Spain, Southern Bay of Biscay) high densities of these larvae were consistently found inside the river plume. Surface currents, hydrographic conditions and meroplankton distributions were measured during each cruise by means of several GPS-tracked drifters, a CTD probe and a surface floating bongo net. Surface abundance of P. pollicipes larvae reached densities over 300 individuals per cubic meter within the plume and only 24 outside, and were strongly and positively correlated with chlorophyll a concentrations. Larvae were probably gathered and entrained into the river plume by offshore convergent currents. We conclude that river plumes might act as nurseries for P. pollicipes larvae due to their enhanced food supply and their mechanistic effect of aggregation.