Exploring diversity and distribution of demersal fish species from the Northern Alboran Sea and Gulf of Vera (Western Mediterranean Sea)

The Alboran Sea is a transition region between the Mediterranean basin and the Atlantic Ocean containing a mix of Mediterranean and Atlantic species. The Strait of Gibraltar, at the west end of the Alboran Sea, connects the Mediterranean with the Atlantic Ocean. The Gulf of Vera also occupies a strategic location in the Western Mediterranean, representing a transition zone between the Alboran Sea and the rest of the basins with a more distinctive Mediterranean character. The Alboran Sea is one of the most productive areas of the Mediterranean, in contrast to the Gulf of Vera that displays a more oligotrophic character. Despite of the interest of the study area the information about the distribution of demersal fishes is scarce. In the present study, the main aim is to analyse diversity and distribution of demersal fish species of circalittoral and bathyal soft bottoms of the Alboran Sea (with a higher Atlantic influence and primary production) and the Gulf of Vera (with a higher Mediterranean influence and lower primary production). Sampling was carried out in the scientific trawl survey MEDITS (International bottom trawl survey in the Mediterranean) between 30 and 800 m depth. All samples were taken from Estepona and Cabo de Palos between 1994-2015 in the Alboran Sea and between 1995-2008 and 2014-2015 in the Gulf of Vera. (Figure 1). A total of 818 samples (687 from Alboran and 131 from Vera) were considered for this study. For each haul, the abundance and weight of individuals per fish species were standardised to 1 hour towing in order to calculate both species abundance (number of individuals per 1 hour towing) (ind•h−1) and biomass (g•h−1). In order to identify fish assemblages, ordination and classification multivariate methods using fish species abundance and biomass per haul matrices were applied. Prior to analyses, all data were logarithmically transformed using log(x + 1) to minimise the weighting of extreme abundance or biomass values of certain species. An analysis of similarities (ANOSIM) was carried out for statistical comparisons of groups of samples according to the different factors considered (depth, Alboran vs. Vera). Species rarefaction curves were used to compare the species richness values of each fish assemblage. In addition, for each group, Shannon-Wiener (H’) and Taxonomic distinctness (Δ*) diversity indices were calculated. For comparisons of the mean values of the considered variables (abundance, biomass and diversity indices) across the identified assemblages and years, we used a non-parametric Kruskal–Wallis test. A total of 231 fish species have been identified considering all samples, with 215 spp. collected from Alboran (3 classes, 25 orders and 75 families) and 160 spp.. from Vera (2 classes, 21 orders and 67 families), probably because the number of samples in the latter were lower. The number of occasional species, considering those that were captured only in 1 or 2 samples, were 56 in Alboran and 44 in Vera. The multivariate analyses (nMDS) indicated that depth is the main factor that determines the distribution of species in both areas, with four groups of samples displaying significant differences between them (ANOSIM-Alboran: R=0.85, p=0.001; ANOSIM-Vera: R=0.81, p=0.001). These groups were similar in both areas: Inner continental shelf (30-100 m), Outer continental shelf (101-200 m), Upper continental slope (201-500 m) and Middle continental slope (501-800 m) (Figures 2 and 3). Regarding the faunistic comparison between Alboran and Vera, the most acute differences were found between those samples from the Middle continental slope. These differences were evident for abundance (ANOSIM: R=0.81, p=0.001), biomass (ANOSIM: R=0.78, p=0.001) and species composition (presence-absence data) (ANOSIM: R=0.61, p=0.001). The trends for species rarefaction curves with depth was similar in both areas, with similar curves for the Inner and Outer continental shelf , a decrease of the species number for the Upper slope and finally the lowest number of species for the Middle slope. Likewise, the mean values of abundance, Shannon and Taxonomic indices also showed a similar pattern in both areas. Mean abundances differed significantly between assemblages increasing from the Inner shelf to Outer shelf and decreasing abruptly to the Upper and Lower slope (.minimum values). The Shannon diversity index showed significant differences in Alboran, but not in Vera, with minima in the Outer shelf in both areas. The taxonomic index also displayed significant differences in Alboran and Vera, with low values in the Inner shelf that increased abruptly to the Outer shelf and Upper slope, with a further acute increase in the Middle slope. Unlike for the other indexes, trends for mean the biomass values with depth were different in both areas. In Alboran biomass decreased from the Inner shelf to the Upper slope and increased to the Middle slope. Nevertheless, in Vera the biomass decreased with depth, with significant differences. In two sectors were evident significant differences. Regarding the interannual changes, the differences between years in Alboran were significant respect to species richness, abundance, biomass and Shannon diversity index. No clear increase or decrease trend was detected interannually. Unlike Alboran, in Vera, no significant interannual differences were detected. In conclusion: 1) Four main fish assemblages were detected on the continental shelf and slope in both areas that seem to be strongly linked to the depth gradient. 2) The middle slope showed the higher differences between both areas for abundance, biomass and presence-abundance data. 3) The species rarefaction curves, abundance, Shannon and Taxonomic diversity indices showed similar patterns with depth in both areas. Biomass index showed a different pattern, with maximum values in the Middle slope in Alboran and minimum ones in Vera

Detection of Red-spotted grouper nervous necrosis virus (RGNNV) in shrimp and squid of the Mediterranean Sea

The quest for sustainable fisheries and procurement of food supply has increased aquaculture production up to the world fisheries capture. Viral encephalopathy and retinopathy (VER), also known as viral nervous necrosis (VNN), is caused by nervous necrosis virus (NNV) and results in high mortality of larvae and juveniles of continuous increasing amount of fish species. The disease causes vacuolation and necrosis of the central nervous system. The virus has a nude capsid protecting a bipartite RNA genome that consists of positive stranded molecules RNA1 and RNA2. Four NNV genotype strains distributed worldwide are discriminated according to sequence homology of the capsid protein encoded by RNA2. Preventive treatments prioritize the RGNNV (Redspotted grouper nervous necrosis virus) genotype that has the highest optimum temperature for replication and the broadest range of susceptible species. A flow of NNV between wild and cultured fish had been demonstrated, and reservoirs of NNV have been reported in invertebrates, raising concern on the spreading of NNV in the mariculture industry through contaminated food. The present study aimed to contribute in the surveillance of reservoirs of NNV in invertebrates of the unexplored western Mediterranean Sea. We report the detection of the RGNNV strain in two species of squid (Alloteuthis media and Abralia veranyi), and in one shrimp (Plesionika heterocarpus) collected in 2015 in the Alboran Sea. According to RNA2 sequences obtained from invertebrates and reported to date in the Mediterranean Sea, the strain RGNNV is predominant in this semi-enclosed sea. Our results suggest that RGNNV distribution is apparently independent of host species and ecosystem, and similar between invertebrates and fish species that feed on invertebrates, calling for an increase in surveillance of NNV reservoirs in the wild.European Association of Fish Pathologists. PathoVe

Detection of Red-spotted grouper nervous necrosis virus (RGNNV) in shrimp and squid of the Mediterranean Sea

The quest for sustainable fisheries and procurement of food supply has increased aquaculture production up to the world fisheries capture. Viral encephalopathy and retinopathy (VER), also known as viral nervous necrosis (VNN), is caused by nervous necrosis virus (NNV) and results in high mortality of larvae and juveniles of continuous increasing amount of fish species. The disease causes vacuolation and necrosis of the central nervous system. The virus has a nude capsid protecting a bipartite RNA genome that consists of positive stranded molecules RNA1 and RNA2. Four NNV genotype strains distributed worldwide are discriminated according to sequence homology of the capsid protein encoded by RNA2. Preventive treatments prioritize the RGNNV (Redspotted grouper nervous necrosis virus) genotype that has the highest optimum temperature for replication and the broadest range of susceptible species. A flow of NNV between wild and cultured fish had been demonstrated, and reservoirs of NNV have been reported in invertebrates, raising concern on the spreading of NNV in the mariculture industry through contaminated food. The present study aimed to contribute in the surveillance of reservoirs of NNV in invertebrates of the unexplored western Mediterranean Sea. We report the detection of the RGNNV strain in two species of squid (Alloteuthis media and Abralia veranyi), and in one shrimp (Plesionika heterocarpus) collected in 2015 in the Alboran Sea. According to RNA2 sequences obtained from invertebrates and reported to date in the Mediterranean Sea, the strain RGNNV is predominant in this semi-enclosed sea. Our results suggest that RGNNV distribution is apparently independent of host species and ecosystem, and similar between invertebrates and fish species that feed on invertebrates, calling for an increase in surveillance of NNV reservoirs in the wild.European Association of Fish Pathologists. PathoVe

Molluscs collected with otter trawl on circalittoral and bathyal soft bottoms of the northern Alboran Sea

Molluscan assemblages of circalittoral and bathyal soft bottoms of the northern Alboran sea were studied from individuals collected with an otter trawl. Samples were collected in 191 hauls during four MEDITS-ES trawl surveys carried out in spring between 2012 and 2015. A total of 102 species, grouped in 55 families, was found at depths between 30-800 m. Abralia veranyi was the most abundant species, and Todarodes sagittatus and Illex coindetii were the most frequent ones. Multivariate analyses resulted in three faunistics assemblagea at different depth ranges: I) 30-200 m, II) 201-350 m, III) 351-800 m. The abundance, biomass and species richness decreased with depth. A clear difference is observed in the faunistic composition between the shelf and the continental slope with a sharp depletion from 350 m in the number of species as well as in the abundance and biomassVersión del edito

Demersal Resources

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Spatial distribution, inter-annual variability and influence of abiotic factors on molluscan assemblages collected with otter trawl in the northen Alborán Sea

Molluscs constitute one of the most diverse and best represented invertebrate groups in the marine environment. In the northern sectors of the Alborán Sea and Gulf of Cádiz 1200 spp. of the 1800 spp. occurring in the Mediterranean Sea, have been found so far highlighting the importance of this area for the european molluscan fauna (Gofas et al., 2011). Molluscs are also the second group in abundance and biomass in demersal fisheries and an important component of soft-bottom benthic communities, including ecologically important and/or commercial mollusc species that are also exposed to an increasing trawling impact (Snelgrove, 1998; Kaiser & De Groot, 1999). Previous studies on molluscs of the Alborán Sea has primarily focused on those from infralittoral habitats, with few studies focussing on the composition, structure and dynamics of circalittoral and bathyal molluscan assemblages ( Rueda et al., 2015). The study of soft bottom molluscan assemblages where trawling fishing fleet operates is important for improving the fisheries evaluation and management, as well as the implementation of ecosystemic and biodiversity conservation measures in the context of the new Marine Strategy Framework Directive. In the present study, the distribution and inter-annual variability of molluscan assemblages of circalittoral and bathyal soft bottoms of the Alborán Sea have been analyzed as well as the relationships of fauna with different environmental variables. Samples were collected in 190 otter trawl hauls performed between “Punta Europa” and “Cabo de Gata”, including the Alborán Ridge, at depths from 30 to 800 m during four MEDITS-ES trawl surveys in spring between 2012 and 2015. Several environmental variables from the water column (temperature and salinity) and sediment samples were taken where each haul was performed in order to elucidate their relationships with the molluscan assemblages. Abundances of each species (individuals . h-1) of each haul and trawl survey were pooled in a matrix for performing multivariate methods in order to contrast molluscan assemblages of different sites and years. The Bray-Curtis similarity index was then used to perform non-parametric multidimensional scaling ordinations (nMDS). A fourth root transformation pretreatment was applied on the quantitative data in order to minimize the contribution of the most abundant species to the analyses. Analyses of similarities (ANOSIM) were carried out for statistical comparisons of groups of samples according to different factors (e.g. year, location). Analyses of similitude percentage (SIMPER) were used to identify those species that contributed to the similarity and dissimilarity between groups of samples according to factors. These multivariate analyses were executed using the PRIMER v6 (Plymouth Routines in Multivariate Ecological Research). Average values of abundance of molluscs (N), species richness (S), Shannon-Wiener diversity index (H’: log2), evenness index (J’) and taxonomic distinctness index (Δ*) were calculated for each sample group. Statistical differences between these values were tested with the non-parametric Kruskal-Wallis using SPSS software. The relationships between environmental variables and molluscs abundance in the different hauls were only studied for the 2014 trawl survey using a correspondence canonical analysis (CCA). The statistical significance of the adjusted CCA was assessed using a Monte Carlo permutation test. Prior to this, the environmental variables were screened and those which presented a correlation higher than 0.9 (after a Spearman correlation analysis) were not further considered. These analyses were executed using the R software. Three main molluscan assemblages were detected and belonged to the: I) Continental Shelf (30-200 m); II) Upper Continental Slope (201-350 m), and III) Middle Continental Slope (351-800 m). The multivariate analyses revealed geographical differences within the Alborán Sea, being these differences more acute between the Alborán Island, mainly in the shallower assemblages (30-200 m and 201-350 m) and the remaining locations considered. These differences were due to a lower abundance in the island of species that were dominant in the continental margin, such as Alloteuthis media, Sepietta oweniana and Turritella communis and a higher abundance in the island of species that were less abundant in the continental margin, such as Neopycnodonte cochlear, Arca tetragona, Loligo forbesii and Sepia orbignyana. No significant differences of the abundance, biomass, species richness and diversity index were detected in the assemblages over the four years. Nevertheless, significant abundance declines of A. media, S. oweniana, and increases of N. cochlear were detected in the continental shelf over the years as well as abundance declines of Bathypolipus sponsalis and Galeodea rugosa in the slope assemblages. Regarding the environmental variables, the shallower assemblage (30-200 m) showed a significantly higher temperature, lower salinity and wider variety of sediment types than the others, with a predominance of sandy mud textures followed by muddy sand. As depth increases the sedimentary heterogeneity decreases, with dominant muddy sediments. Depth, temperature and mud percentage were the key variables that better explained the variability of the molluscan assemblage in the CCA. In conclusions: (1) Acute geographical differences occurred between the Alborán Island and the locations of the continental margin, due to its location far from the continental influence and, therefore, with lower fisheries activity and a less muddy and more bioclastic sediment, (2) Inter-annual trends in the abundance, biomass, species richness and diversity of assemblages were not detected, but some species displayed inter-annual changes due to biological aspects or accidental catch of gregarious species and (3) depth and some sedimentological variables displayed the most significant relationships with the molluscan assemblages, as previously observed for other invertebrate assemblages in the Alborán Sea

Decapod crustacean assemblages on trawlable grounds in the northern Alboran Sea and Gulf of Vera

This study analyses the samples collected annually (2012 to 2018) on circalittoral and bathyal soft bottoms (30 to 800 m) by the MEDITS surveys in the northern Alboran Sea (including Alboran Island) and the Gulf of Vera to determine the composition, structure and distribution of decapod crustacean assemblages. A total of 94 decapod crustacean species were identified. Non-metric multidimensional scaling showed depth to be the main factor for distinguishing four main decapod assemblages: the inner shelf (30-100 m depth), outer shelf (101-200 m), upper slope (201-500 m) and middle slope (501-800 m). PERMANOVA analyses revealed further significant depth-related differences between three established geographical sectors of the study area (northern Alboran Sea, Gulf of Vera and Alboran Island). Generalized additive model analyses were used to assess the bathymetrical, geographical and environmental effects on the ecological indices of each assemblage. Results showed that depth and the geographical effect were the main drivers in all cases. Decreases in abundance and increases in species richness, Shannon-Wiener diversity and Pielou’s evenness indices with depth were detected. This study shows the primacy of depth and geographical effect on the distribution of decapod species in the study area, in alignment with findings from other parts of the Mediterranean Sea.Versión del editor1,00

Contrasting molluscan fauna collected with beam trawl and otter trawl in circalittoral and bathyal soft bottoms of the northern Alboran Sea

The Alboran Sea display complex oceanographic, geological, ecological and biological processes, promoting a high biodiversity and complexity (Robles, 2010). On the other hand, molluscs constitute one of the most diverse and best represented invertebrate groups in this area, representing an important component of soft bottom communities, as well as the second group in abundance and biomass in demersal fisheries, with species of ecological and commercial importance worldwide (Gofas et all., 2011). The study of the molluscan assemblages is important where trawling fishing fleets operate, in order to improve fisheries assessment and move forward to an ecosystem based approach, which takes into account other components of the fishery than the target species such as non-target and protected species and habitats (Pikitch et al., 2004). Information collected on fisheries assemblages may introduce a bias depending on the fraction of the assemblage (e.g. demersal, epifaunal, infaunal) at which the sampling method is targeted, particularly in a group such as molluscs with a high variability in life strategies. The aims of this study are 1) to increase the scarce knowledge on the composition and structure of molluscan assemblages of circalittoral and bathyal soft bottoms of the Alboran Sea; and 2) to compare the information obtained on these assemblages by using two different types of sampling gears, the beam trawl and the otter trawl. During the MEDITS trawl surveys (springs 2014 and 2015) a beam trawl (BT) (horizontal opening 1.3 x vertical opening 1.2 m, mesh size 10 mm) and an otter trawl (OT)(GOC 73) (2.5 x 21.5 m , mesh size 20 mm) were used in 35 sampling stations at depths from 40 to 800 m in the Alboran Sea. Catches were sorted to species and their individuals counted and weighed. The molluscan assemblages and species were characterized according to their dominance (%Da) and frequency of occurrence (%F). Multivariate analyses using the Bray-Curtis index were performed with presence/absence species data and quantitative data obtained with each method were standardized to a similar sampling area. ANOSIM was used for testing the differences between groups of samples according to different factors (depth and sampling type) and SIMPER for the contribution of the different species to these factors using PRIMER v6. The characterization of the different types of sampling and assemblages was done with the species richness and statistical differences tested with Kruskal-Wallis using SPSS software. A total of 170 spp. have been collected, with 69 species collected in OT samples, mostly cephalopods (26 spp., 37.68%), followed by gastropods (25 spp., 36.23%) and bivalves (18 species, 26.10% total species of OT), being the latter the most abundant group. The top-dominant species were the bivalve Neopycnodonte cochlear and the cephalopod Alloteuthis media, whereas the most frequent ones were the cephalopods Octopus vulgaris, Todarodes sagittatus and Illex coindetii (Fig. 1 ). In beam trawl samples, 135 spp. of 6 classes were found, being gastropods the most diverse and abundant one (69 spp., 51.11% total species of BT), followed by bivalves (49 spp., 36.3%) and cephalopods (15 spp., 11.11%). The top-dominant species were the gastropods Turritella communis and Nassarius ovoideus and the bivalves Nucula sulcata and Abra longicallus, and the most frequent ones included Nucula sulcata, Nassarius ovoideus and the gastropod Euspira fusca (Figure 1). Contrasting both methods, only 20% (34 spp.) of the species were exclusively collected in OT samples (e.g. Alloteuthis spp., I. coindetii, Loligo spp., T. sagittatus) and 57% (97 spp.) in BT samples (e.g. N. ovoideus, Timoclea ovata, N. sulcata, Clelandella miliaris). Only 23% of the species (39 spp.) were collected with both methods (e.g. Venus nux, Turritella communis, N. cochlear). Figure 1. Some common and dominant mollusc of beam trawl (A-C, E-G) and otter trawl samples (D, H-J) collected in circalittoral and bathyal soft bottoms of the northern Alboran Sea. A) Turritella communis; B) Abra longicallus; C) Nassarius ovoideus; D) Illex coindeitii; E) Clelandella miliaris; F) Timoclea ovata; G) Nucula sulcata; H) Venus nux; I) Octopus vulgaris; J) Neopycnodonte cochlear. Multivariate analyses clearly separated two groups of samples, each one collected with a different sampling method, and in each grouping it revealed three main mollusks assemblages in relation to depth: I) Continental shelf (CS) (40-200 m), II) Upper slope (UCS) (201-400 m), and III) and Middle slope (MCS) (400-1800 m) (Fig. 2). Figure 2. MDS applied to presence-absence data of molluscs assemblages obtained from beam trawl and otter trawl samples collected in the northern Alboran Sea. BT: Beam trawl; OT: Otter trawl ; CS: Continental Shelf; UCS: Upper Continental Slope; MCS: Middle Continental Slope. The continental shelf assemblage in BT samples were characterized by T. ovata, N. cochlear, N. ovoideus and T. communis, whereas O. vulgaris, Eledone moschata and I. coindetii characterized the OT samples. For the upper and middle slope assemblages, E. fusca and A. longicallus characterized the BT samples, whereas T. sagittatus and Bathypolypus sponsalis characterized the OT samples. Mean values of species richness were significantly higher when using the BT. This study showed that OT nor BT samples can provide complete information on the whole molluscan assemblage, giving each sampling method complimentary information. The demersal and epi-benthic fractions of the community were better sampled using the otter trawl and the beam trawl, respectively. The estimates of infauna were higher using the beam trawl, but this information should be contrasted with data obtained from dredges in order to assess whether the beam trawl yield acceptable estimates of the abundance of these molluscs

Macroscopic and microscopic maturity stages. living working document for small tuna species.

Maturity ogives are usually estimated using different methods, including macroscopical and microscopical maturity data. Differences in maturity ogives estimations are found for species and by area/stock. So those differences may be a consequence of the use of different methodological techniques (criteria) or due to different spawning tactics. Taking this into account is essential to guarantee that the maturity criteria for each species are consistent across the laboratories and countries involved in stock assessment. The objective of this document is to show a large amount of detailed photos (macro and microphotographs) of the different gonad stages of Auxis rochei, Sarda sarda and Euthynnus alletteratus, for females and males, which will be an enhancement to the descriptions of maturity stages given in the maturity tables