Into the deep - Dispersal models for deep-water decapod shrimp larvae: the case of Parapenaeus longirostris

Abstract Deep-water shrimps remain some of the less understood decapod crustacean taxa, despite the high commercial and ecological importance. The lack of knowledge on adults and larval stages of many species results in an incomplete view of the biology, distribution, dispersal and connectivity, essential knowledge for conservation and stock management. In zooplankton samples, larvae of deep-water shrimps are usually found in low abundances. Here, we address the insufficiently studied topics of distribution and transport of deep-water shrimp larvae, providing information on potential pathways and mechanisms of dispersal. The work focuses on southern Portuguese waters, giving important indications for deep-water shrimp species worldwide. Physical-ecological modelling was used to examine the dispersal of larvae of the deep-water rose shrimp, Parapenaeus longirostris, that were found distributed over shelf waters in the study region. In situ spatial abundances were examined, and ontogenetic vertical distributions and sites of larval release were included in the models. The circulation in the vicinity of submarine canyons and deep moats promoted relatively shallower positions of simulated particles. Passive drifts were insufficient for larvae to reach the uppermost water layers, while the vertical distribution adopted, in the upper or lower water layers, was highly important, dictating the direction of the transport and the retention over shelf waters. Slope or shelf larval releases influenced the dispersal patterns and the concentration of particles over productive waters, suggesting that the onshore movement of females during spawning may benefit the larval retention over shelf waters.