Molluscs collected with otter trawl in the northern Alboran Sea: main assemblages, spatial distribution and environmental linkage

Abstract

Molluscan assemblages of circalittoral and bathyal soft bottoms of the northern Alboran Sea were studied using an experimental otter trawl. Samples of fauna were collected from 190 hauls during four MEDITS surveys carried out in spring between 2012 and 2015 at depths ranging from 30 to 800 m. Measurements of water column variables (temperature and salinity) and sediment samples were taken in the same locations where faunistic sampling was carried out. A total of 101 species grouped in 55 families were recorded. Cephalopods were the most abundant group, with Abralia veranyi dominating in abundance, Octopus vulgaris in biomass and Illex coindetii and Todarodes sagittatus being the most frequently collected species. Multivariate analyses carried out separately with abundance data of demersal species, benthic species, bivalves, gastropods and cephalopods as well as of all molluscs, generally resulted in three main molluscan assemblages corresponding to a shelf assemblage (30-200 m depth), an upper slope assemblage (201-350 m depth), and a middle slope assemblage (351-800 m depth). PERMANOVA test revealed that significant differences of different groups of molluscs in relation to depth were more acute than to geographical sectors of the Alboran Sea (eastern, central, eastern and insular sectors). Abundance, biomass and species richness decreased with depth with a clear dominance of cephalopods in the slope. Significant geographical differences were mainly detected for demersal and benthic species as well as for gastropods and cephalopods between the insular sector (Alboran Island) and the western and eastern continental sectors. Both depth and temperature were the most influencing variables in the different CCA analyses using datasets of molluscs with different life styles and from different classes, but sedimentological variables displayed a more acute significant relationship with the benthic molluscs than with the demersal ones.

Ecological Gradients of Epimegafaunal Distribution along The Sectors of Gulf of İzmir, Aegean Sea

“…In general, only mega-molluscans (retained in mesh-size of 5 mm of a benthic sledge) had a peak number of species at the shallowest waters as observed in Mersin Bay (Mutlu and Ergev, 2008). This could be attributed to the higher heterogeneity of bottom types on the shallow waters since some molluscan species were related to specific sedimentary habitats (Gofas et al, 2011;Ciércoles et al, 2018). The shallow waters was ascribed "fine, well-sorted sand", SFBC and the deep zone "the Muddy-Detritic community", DE (Peres, 1982), being composed mainly of mud, sand and detritus dwelling species at depth greater than 100 m in Cretan shelf (Karakassis and Eleftheriou, 1998).…”

“…Abundance of the fish species (N≤100000 ind/km 2 ) was fluctuated with the seasons and seafloor depths in similarity to the molluscans, echinoderms and arthropods (N≤100000 ind/km 2 for each). The molluscs were the second most abundant faunal group in terms of density after the crustaceans, and other less represented faunal groups included echinoderms, annelids, and cnidarians in Alboran Sea (Ciércoles et al, 2018). The echinoderms were predominated abundantly in summer and winter, followed by mollusks and tunicates in the Catalan Sea (DeLaHoz et al, 2018).…”

“…Similar to the echinoderms, fish had the highest number in a depth range of 25-45 m. The number of arthropods was the highest at 45 m. Only molluscans had a peak number of species at the shallowest waters as observed in Mersin Bay (Mutlu and Ergev, 2008). This could be attributed to the higher heterogeneity of bottom types on the shelf since some mollusc species were related to specific sedimentary habitats (Gofas et al, 2011;Ciércoles et al, 2018).…”

A review of recent studies on the life history and ecology of European cephalopods with emphasis on species with the greatest commercial fishery and culture potential

“…In the Alboran Sea, S. elegans is more abundant on the continental part of the shelf, while in the island area at these depths (30− 200 m) S. orbignyana is more common. At greater depths, only S. orbignyana is present (Ciércoles et al, 2018). In the Catalan Sea, S. elegans and S. orbignyana were generally the most abundant cuttlefish species, with the former most abundant at 30− 100 m and the latter at 200− 400 m. However, in winter, S. officinalis was more abundant than either of these species (DeLaHoz et al, 2018).…”

“…The spatial distribution and abundance of a common cuttlefish were addressed in a series of survey-based studies. Results from surveys in the Alboran Sea and Catalan Sea (Ciércoles et al, 2018;DeLaHoz et al, 2018) and in the Mediterranean Sea in general (Quetglas et al, 2019) indicate that S. officinalis inhabits shallower and more inshore waters than S. elegans and S. orbignyana. In the Catalan Sea, S. officinalis was generally the least abundant cuttlefish species except in winter, when it was most abundant and its abundance reached a peak in the 30− 100 m depth range (DeLaHoz et al, 2018).…”