The genetic connectivity between marine populations was traditionally thought to be limited only by distance. However, recent studies have disclosed that oceanographic discontinuities such as those originated by ocean currents constitute barriers thus interfering with the genetic flow between populations. The aim of this research was to conduct a spatial and temporal genetic differentiation analysis to elucidate the effect of three main oceanographic discontinuities on the Atlanto-Mediterranean coast: Gibraltar Strait, Almeria-Oran Front, and Ibiza Channel. In order to do so, we used different populations of the marine crab Liocarcinus depurator. A partial fragment of Cytochrome Oxidase I mitochondrial gene was sequenced in 194 individuals from 7 different populations (Cádiz, West Alboran, East Alboran, Alicante, Valencia, Ebro Delta and North Catalonia) captured in 2019. These sequences obtained from these individuals were used not just to determine the genetic composition in 2019 for each population, but to compare them with previous data from the period 2014-2018 thus completing the temporal study (2014-2019). According to our results, two haplogroups were clearly distinguishable: Atlantic and Mediterranean. The first one is mainly composed of individuals from Cádiz and West Alboran whereas the other one is mostly formed by specimens of the remaining populations. Significant genetic differentiation was found between Cádiz and West Alboran, which indicated that the Gibraltar Strait had the most important role in the separation of Atlantic and Mediterranean waters in 2019. Another significant genetic differentiation was observed between West Alboran and Alacant, suggesting that the Almeria-Oran Front could also have a certain effect on reducing the genetic flow between populations, but its effect is reduced compared with previous years. Finally, regarding the temporal analysis, it has revealed that oceanographic discontinuities are not stable, but dynamic and that both historical and short-term processes influence L. depurator genetic composition

Trabajo final presentado por Maria Sellés Altés para el grado en bioquímica de la Universitat de Barcelona (UB), realizado bajo la dirección del Dr. Francesc Mestres Naval de la Universitat de Barcelona (UB) y del Dr. Pere Abellò del Institut de Ciències del Mar (ICM-CSIC).-- 35 pages, 16 figures, 3 tables, 1 annexe