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Liocarcinus depurator and Geryon longipes are two crab species which widely differ with regard to the marine depths they inhabit and their associated environmental characteristics. The bathymetric distributions and molecular diversity were studied along the Atlantic-Mediterranean transition for the two species. A fragment of the COI (Cytochrome Oxidase subunit I) mitochondrial gene was studied in both species. In the case of L. depurator, a large number of haplotypes were detected and could be classified in two large haplogroups. One was predominant in water masses of Atlantic origin, and the other in Mediterranean waters. Three main areas were observed concerning the relative distribution of these two haplogroups: Gulf of Cadiz, Alboran Sea, and Levantine/Catalan coasts. Only eight haplotypes were detected in G. longipes. In this species and according to its haplotype distribution, three regions could be described: Alboran Sea, Gulf of Vera (between Cape Gata and Cape Palos), and Levantine/Catalan coasts (the species is apparently absent from the Gulf of Cadiz). In L. depurator, the marine currents and oceanographic fronts affecting larval dispersion could explain the pattern of haplotype distribution. A similar, but not exact pattern is shown by G. longipes, despite its markedly different habitat and depth they inhabit. The similarities in genetic structure may be accounted for by the epipelagic habitat of the larvae, which are the life history phase where most of the geographic dispersion takes place

An interesting evolutionary question that still remains open is the connectivity between marine populations. Marine currents can favour the dispersal of larvae or adults, but they can also produce eddies and gyres generating oceanographic fronts, thus limiting gene flow. To address this subject, we selected the Atlantic-Mediterranean transition, where several fronts are located: Gibraltar Strait (GS), Almeria-Oran Front (AOF) and Ibiza Channel (IC). Seven populations of the marine crab Liocarcinus depurator (Cadiz, West and East Alboran, Alacant, Valencia, Ebro Delta and North Catalonia) located along this transition were analysed in six consecutive years (2014–2019) using a fragment of the COI (Cytochrome Oxidase subunit I) gene. All sequences (966) belonged to two well defined haplogroups: ATL (most abundant in Atlantic waters) and MED (predominant in Mediterranean waters). Following a geographic variation, the frequency of ATL decreased significantly from Cadiz to North Catalonia. However, this variation presented steps due to the effect of oceanographic restrictions/fronts. Significant effects were recorded for GS (2015, 2017, 2018 and 2019), AOF (all years except 2018) and IC (2016). The intensity and precise location of these fronts changed over time. Multivariate analyses distinguished three main population groups: Cadiz, Alboran Sea and the remaining Mediterranean populations. These findings could be relevant to properly define Marine Protected Areas and for conservation and fisheries policies

[EN] Liocarcinus depurator is a crab species of commercial interest that inhabits the muddy bottoms of the continental shelf of the Iberian Peninsula. The connectivity between seven populations of the Atlantic-Mediterranean transition was analyzed: Cádiz, Western Alboran Sea, Eastern Alboran Sea, Alicante, Valencia, Ebro Delta and North of Catalonia) in the period 2014-2019. To this aim, a 527 bp fragment of the COI (Cytochrome Oxidase subunit I) mitochondrial gene was sequenced. A total of 966 sequences were obtained. In general, the molecular variability was higher for the populations of the Alboran Sea than for the remaining populations. The haplotype network and the phylogenetic tree of the sequences showed two well-defined haplogroups: ATL (predominant in waters of Atlantic influence) and MED (predominant in those of Mediterranean influence). The frequency distribution of both haplotypes presented a gradient, but with a series of steps due to the presence of oceanographic barriers. In the study area these were: the Strait of Gibraltar (GS), the Almería-Oran Front (AOF) and the Ibiza Channel (IC). The first two were very important in reducing interpopulation gene flow, the second being a barrier that can vary over time in intensity and location. In 2016, a significant effect of the IC was also detected. All these results defined three areas of interest concerning Marine Protected Areas and policies for the conservation and management of fishery resources: the Gulf of Cádiz, the Alboran Sea and the Valencian/Catalan region, [ES] Liocarcinus depurator es una especie de cangrejo de interés comercial que habita los fondos fangosos de la plataforma continental de las costas peninsulares ibéricas. Se analizó la conectividad entre siete poblaciones de la transición atlanto-mediterránea: Cádiz, Oeste del mar de Alborán, Este del mar de Alborán, Alacant, València, Delta del Ebro y Norte de Catalunya) en el periodo 2014-2019. Para ello se secuenció un fragmento de 527 pb del gen mitocondrial COI (Citocromo Oxidasa subunidad I). Se obtuvieron un total de 966 secuencias. En general la variabilidad molecular fue más elevada para las poblaciones del Mar de Alborán que para el resto de poblaciones. La red de haplotipos y el árbol filogenético de las secuencias mostró dos haplogrupos bien definidos: ATL, dominante en aguas de influencia atlántica, y MED, en las de influencia mediterránea. La distribución de la frecuencia de ambos presentó un gradiente, pero con una serie de escalones debidos a la presencia de barreras oceanográficas. En la zona de estudio fueron: el Estrecho de Gibraltar (GS), el Frente Almería-Orán (AOF) y el Canal de Ibiza (IC). Los dos primeros se mostraron muy importantes en la reducción del flujo génico interpoblacional, siendo el segundo una barrera que puede variar a lo largo del tiempo en intensidad y localización. En 2016 también se detectó un efecto significativo del IC. Todos estos resultados definieron tres áreas de interés respecto a las Áreas Marinas Protegidas y las políticas de conservación y gestión de los recursos pesqueros: el Golfo de Cádiz, el Mar de Alborán y la región valenciana/catalana

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

We carried out a spatial and temporal genetic differentiation analysis using seven populations of the marine crab Liocarcinus depurator to elucidate the effect of three oceanographic discontinuities in the Atlanto-Mediterranean coast: Gibraltar Strait, Almeria-Oran Front and Ibiza Channel. To conduct this study, a 527 bp fragment of the mitochondrial COI gene was sequenced in individuals captured in the period 2014-2018 from the following Iberian coast populations: Cádiz, West Alboran, East Alboran, Alacant, Valencia, Ebro Delta and North Catalonia. Two haplogroups were detected; one characteristic of Atlantic waters and the other of Mediterranean, and their distribution allowed understanding the connectivity between populations. The effect of the oceanographic fronts on gene flow varied over time. Their effects were significant for the Gibraltar Strait (2014 and 2017), Almeria Oran Front (2013, 2014, 2015, 2016 and 2017) and Ibiza Channel (2015). Interestingly, the joint analysis of West Alboran, East Alboran and Alacant populations allowed detecting in a more precise scale the spatial location of the Almeria Oran Front. Finally, significant differences were observed in connectivity between Valencia and Ebro Delta in 2015, although there is not an oceanographic discontinuity between them. The main conclusion is that thegene flow is mediated by oceanographic fronts, but their intensity and effects change over time