Unraveling bivalve larvae density patterns in a semi-enclosed shallow gulf in northern Patagonia, Argentina.

The planktonic larval phase serves as the dispersive component in bivalve species, since larvae are transported by marine currents, making this phase a key determinant of population connectivity in marine ecosystems. Cross-shore and along-shore currents are key features in coastal areas that drive oceanographic processes. This study examines the relationship between environmental variables (wind, temperature, tides, and thermal stratification) and both the density of bivalve larvae and the proportion of the pediveliger stage, with the aim of inferring larval transport/retention patterns relevant to population dynamics in San José Gulf, Patagonia, Argentina. Bivalve larvae were sampled from December to March. Larval density was highest during rising and slack tides and was positively influenced by water-column stratification. However, it was negatively associated with temperature and wind 3 h prior to sampling. The proportion of pediveliger larvae was higher during periods of low or near-zero tidal changes, higher temperatures, and stronger north, east, and west winds intensity 3 h before sampling. The proportion of pediveliger larvae was influenced by the Day/Night cycle and moonlight, which negatively impacting their vertical distribution during the night. The increased larval density and proportion of pediveliger larvae associated with slack tides, stratification, and prevailing northwest winds in this area may play a crucial role in larval retention. Larval distribution and its interaction with environmental variables provided deeper insights into dispersal and recruitment patterns, as well as the mechanisms driving larval transport and retention in coastal waters.