Preliminary characterization of echinoderm assemblages in circalittoral and bathyal soft bottoms of the northern Alboran Sea

Echinoderms, with 7.272 species described so far (based on WORMS), provide an ecosystemic role which can be important depending on their habitat, and including tag species (Manjón-Cabeza et al., 2014; Palma-Sevilla 2015) or even dominant ones (Iken et al., 2010; Hughes et al., 2012). Despite the increasing knowledge on their taxonomy, studies on ecological and assemblage composition and structure of echinoderms are very scarce compared to those for other invertebrate groups, being this information essential for improving the knowledge on Mediterranean ecosystems (Coll et al., 2010). The Alboran Sea, in the junction of the Atlantic Ocean and the Mediterranean Sea and the European and African continental margins, represents a biodiversity hotspot due to the overlapping of species from those basins and continents, including some endemic components (Coll et al., 2010). Regarding echinoderms of the Alboran Sea, most previous studies focussed on infralittoral bottoms, with very few for circalittoral and bathyal ones (Manjón-Cabeza et al, 2014; Sibuet, 1974). Nevertheless, these studies generally included faunistic lists (Ocaña & Pérez-Ruzafa, 2004; Manjón-Cabeza et al., 2014), sometimes with identification keys, ecological and distributional data of some species and rarely on the assemblage composition and structure (Palma-Sevilla, 2015), which represent the main aim of this study on echinoderm assemblages of circalittoral and bathyal soft bottoms of the Alboran Sea. During the MEDITS survey expeditions (April-May 2014-2015) on board the R/V Miguel Oliver (Fig. 1), 35 samples were collected using a beam trawl (horizontal and vertical openings of 1.3 and 1.2 m, respectively, and a mesh size of 10 mm in the codend) at depths from 40 to 774 m in the Alboran Sea (Fig. 1). Hauls were done at a speed of ca. 2 knots during 5-10 (shelf stations) and 15 minutes (slope stations). Echinoderms were separated, identified to the lowest possible taxonomic leveland specimens counted and weighed to the nearest 0.5 g. Abundance and biomass data were standardized to 1000 m2 according to the sampling area of each haul. Echinoderm assemblages were characterized according to the dominance and frequency of occurrence of species in the samples and considering different ecological indexes. Multivariate methods (CLUSTER, nMDS, SIMPER, ANOSIM) were applied, based on the Bray & Curtis similarity index, for detecting and contrastingassemblages in relation to depth and 4 geographic areas of the Alboran Sea with different influence of Atlantic waters (Occidental-Esteponato Málaga, Central-Málaga to Motril, Oriental-Motril to Almería and Alboran Island). Fig. 1. Location of beam-trawl samples (dots) collected during 2014 and 2015 MEDITS expeditions in the northern Alboran Sea. At present 39 taxa have been detected, mostly belonging to Ophiuroidea and Asteroidea (28.2 and 25.6% of all species, respectively), followed by Holothuroidea (23.1%), Echinoidea (17.9%) and Crinoidea (5.1%). Regarding abundance, a total of 54689 individuals have been collected, being Ophiuroidea (98.6% of all individuals), Holothuroidea (0.6%) and Crinoidea (0.4%) the top-dominant classes. Regarding biomass, ophiuroids also dominated (52.8%), followed by asteroids (16.1%) and holothuroids (15.0%). Considering other faunistic groups, echinoderms were the most abundant phyllum in the samples (60.7%) and the fifth one in biomass (7.6%). The dominant (for both abundance and biomass) and frequent genera included Ophiocten (displaying dominances >90%) Hymenodiscus, Luidia and Astropecten for asteroids, Antedon and Leptometra for crinoids, Dendrochirotida and Molpadidae for holothuroids, and Brissopsis and Echinocyamus for echinoids (Fig. 2). Fig. 2. Some echinodermscollected in circalittoral and bathyal soft bottoms of the Alboran Sea using beam-trawl during the MEDITS expeditions. A: Ophiocten; B: Dendrochirotida sp.; C: Brissopsis; D: Anseropoda; E: Luidia. Multivariate analyses indicated groupings of samples and significantly different echinoderm assemblages in relation to depth (RANOSIM=0.22, p0.05). Shelf assemblages displayed lower intra-group similarities (<20% similarity in SIMPER) than the slope ones (ca. 40%). Species characterizing the shelf assemblages belonged to the genera Astropecten, Antedon, Ophiothrix among others, whereas those of the slope belonged to the genera Luidia (L. sarsi), Hymenodiscus, Ophiocten, Leptometra and Amphiura

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

Asociaciones de moluscos de fondos sedimentarios circalitorales y batiales del norte del mar de Alborán

Molluscan assemblages from shelf and slope soft bottoms of the Alboran Sea have been sampled with a beam trawl during 2014 and 2015 MEDITS expeditions. A total of 134 spp. of molluscs (shell size > 3 mm) were identified, being gastropods the most diverse and dominant group. Four main depth related assemblages were detected in multivariate analyses and characterized by (1) Turritella communis, Chamelea striatula and Nucula sulcata for the inner shelf, (2) Timoclea ovata, Clelandella miliaris and Neopycnodonte cochlear for the outer shelf, (3) Nassarius ovoideus, Calumbonella suturale and N. sulcata for the upper slope and (4) Abra longicallus, Euspira fusca and Aporrhais serresianus for the middle slope. Species richness and abundance decreased with depth, unlike evenness and Shannon-Wiener diversity which displayed an opposite pattern. A higher spatial variability was detected for the shelf, indicating that more assemblages may occur at this level and further sampling is needed for covering all sedimentary habitat types of the Alboran Sea.Versión del edito

El patrimonio natural de la bahía de Málaga

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Biodiversity and spatio-temporal changes of benthic and demersal assemblages of circalittoral soft bottoms of the bay of Málaga (northern Alboran Sea)

The Bay of Málaga is located in a high biodiversity and productivity area that harbours a wide variety of commercial species exploited by different fishing fleets. Benthic and demersal fauna from circalittoral soft bottoms have been studied using a benthic dredge (BD) (8 sampling stations) and an otter trawl (OT) (8 sampling stations on a seasonal basis). Some sediment and water column variables, as well as the trawling activity, have also been studied and used for analysing their linkage with the fauna. A total of 287 species have been found in these bottoms and fish, molluscs and crustaceans represented the most diverse and abundant faunistic groups. A new record of the decapod Hippolyte leptometrae for Spanish waters is also included in this study. Some multivariate analyses using BD samples indicated the presence of three assemblages, but these seem to represent different facies of a single benthic community due to the absence of acute sediment changes and significant differences in the fauna. OT samples only displayed differences related to seasons but not to sediment types or depth. These seasonal differences seem to be linked to biological and ecological features of both dominant and/or commercial species. Mud and organic matter contents (%OM) in sediment, as well as the temperature, were the main variables linked to the spatial distribution of the benthic community identified with BD, whereas medium and coarse sand as well as gravel contents were the main variables linked to the changes of the epibenthic and demersal assemblage resulting from OT samples. The information of this study is of importance for improving the knowledge on the biodiversity of circalittoral soft bottoms of the Mediterranean and Alboran Sea as well as for the potential creation of a Marine Fisheries Reserve in the Bay of Málaga

Preliminary characterization of Vulnerable Marine Ecosystems and associated communities of Chella Bank (Alboran Sea, W Mediterranean)

Poster presentation at ATLAS 3rd General Assembly. Seamounts may promote the presence of vulnerable marine ecosystems (VMEs) worldwide. In the Alboran Sea (W Mediterranean Sea), the Chella Bank (locally known as “Seco de los Olivos”) is a seamount that covers ca. 100 km2 and is under the influence of different water masses in this important Atlanto-Mediterranean biogeographical transition zone. During the MEDWAVES expedition (September-October 2016) within the frame of the H2020 ATLAS project, biological and sediment samples collected with Van Veen dredge and ROV underwater videos were obtained in sedimentary and coral rubble bottoms of Chella Bank. The analyses have revealed a diverse invertebrate community associated with these bottoms containing abundant cold-water coral (CWC) remains (mainly Madrepora oculata and Lophelia pertusa), which provide complex heterogeneous microhabitats to many different taxa. The community associated with the coral rubble bottoms is mainly composed of different genera of bivalves (Mendicula, Limopsis, Asperarca), gastropods (Gibberula, Epitonium), small crustaceans (class Malacostraca), polychaetes (Eunice), ophiuroideans (Ophiothrix), bryozoans (order Cyclostomata), hydrozoans (Cryptolaria), poriferans (Terpios, Haliclona) and brachiopods (Megathiris, Megerlia), among other taxa. Furthermore, the megafauna include cnidarians (Bebryce, Acanthogorgia, Dendrophyllia), sponges (Pachastrella) and dense shoals of the carangid fish Caranx rhonchus. Unlike coral rubble bottoms, macro- and micro-fauna inhabiting close sandy, muddy or hemipelagic muddy habitats seems less diverse (up to four times in terms of abundance and species richness). These communities are mainly composed of polychaetes, small crustaceans and bivalves (Abra, Ennucula, Yoldiella), together with shoals of the ammodytid fish Gymnammodytes cicerelus. Coral rubble bottoms of Chella Bank may therefore represent an interesting habitat for conservation, harboring a good representation of the biodiversity linked to CWC communities. This study increases the scarce information on biodiversity and biogeography (WP3) for this area that probably favors the connectivity of CWC associated fauna (WP4) between the Atlantic and Mediterranean basins