Modelling crustacean larvae dispersal: Physical-ecological connectivity in the Gulf of Cadiz and across the Strait of Gibraltar

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Physical-ecological modelling of the transport, dispersal and connectivity of crustacean larvae in the Gulf of Cadiz and through the Strait of Gibraltar

Publication . Pires, Rita Filomena Teixeira; Santos, Antonina Maria de Melo dos; Peliz, Álvaro Júdice Ribeiro

The mechanisms of decapod larval dispersal were explored for the northeastern Atlantic‒western Mediterranean Sea region, a transition zone between temperate and tropical ecosystems where larval transport has been scarcely addressed. The main goal of this thesis was to understand the impact of the complex oceanic circulation and biological variables on transport and dispersal patterns. An ecological characterization of the decapod larval assemblages of each sub-basin was followed by the selection of benthic and demersal species to be used as biological references in modelling approaches. Combined oceanic simulations and particle-tracking Lagrangian experiments, developed according to in situ data on larvae, were used. Potential transport mechanisms, dispersal pathways, and the key physical and behavioural factors involved were identified, and connectivity metrics estimated. For the southern Portuguese margin, the larval transport, and the strategies of shelf exportation and return to the adult habitats were examined, focusing on the coastal crab Pachygrapsus marmoratus and the deep-water shrimp Parapenaeus longirostris. The connectivity with the western Alboran Sea through the Strait of Gibraltar and with the northwestern African margin was estimated, using larvae of Processa shrimps. Similar taxonomic composition of the larval assemblages was found, although dominated by distinct groups, linked to the ocean dynamics of each sub-basin. The simulations revealed distinct potential dispersal pathways in the region for larvae drifting from shelf or slope areas and following active or passive transport. High connectivity was simulated within the Alboran and along the northern margins in the Atlantic-Alboran direction, suggesting the retention of shelf-dwelling and epipelagic larvae in the sub-basin. The Alboran-Atlantic transport was enhanced in deep-water layers. In all exercises, the areas of particle release and the vertical positions defined the retention over or transport into productive shelf waters, dictating the transport direction and the connectivity throughout the region.

2022-01Doctoral thesis

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