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Community structure and faunal composition of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean) were investigated. Samples were collected during 32 hauls between 793 and 1598 m in depth over the 2003–2007 period. A total of 1900 decapod specimens belonging to 23 species were collected. Multivariate analysis revealed the occurrence of three faunistic assemblages related to depth: (i) an upper slope community at depths of 793–1002 m; (ii) a middle slope community at depths of 1007–1212 m and (iii) a lower slope community at depths greater 1420 m. In the upper and middle slopes the benthic ( Polycheles typhlops) and epibenthic–endobenthic feeders (mainly Aristeus antennatus and Geryon longipes), which eat infaunal prey, were dominant, followed by the macroplankton–epibenthic feeders such as Acanthephyra eximia and Plesionika acanthonotus. In the deepest stratum, the most remarkable feature was the prevalence of macroplankton–epibenthic feeders ( A. eximia and P. acanthonotus). A small percentage of the benthic deep-sea lobster Polycheles sculptus was also present. The biomass presented higher values in the middle slope and declined strongly in the lower slope. There was no general pattern of mean individual weight/size versus depth among decapods, and the changes seemed to be species-specific with different trends. [ABSTRACT FROM AUTHOR]

This study compiles information on the size distribution and reproductive patterns of five chondrichthyans and 10 bony species dwelling on the continental slope of the Central-Western Mediterranean (south-eastern Sardinian waters, depth 720–1890 m). The abundance of the relatively less numerous chondrichthyans was found to decrease with depth. Almost all chondrichthyan species had a long reproductive period throughout the year at all depths. In bony fishes, the upper bathymetric stratum (<1100 m) was dominated by species with continuous and seasonal (autumn-winter) spawning cycles. At intermediate and lower depths (>1100 m), continuous reproduction was the most common pattern. Both chondrichthyans and bony fishes exhibited large sizes at maturity and at first maturity (>75% and >60% of their maximum body length, respectively), supporting the hypothesis that most deep-sea fish populations are characterized by a delayed maturity, which makes them highly vulnerable to fishing pressure and over-exploitation. In some sharks, population partitioning was observed, according to life stage as a function of depth: adult/mature females occupied deeper habitats than males and juveniles. Conversely, Dipturus nidarosiensis female and male juveniles (>1100 m) were segregated from the adult/mature population, dwelling between 1000 and 1100 m. In four of the 10 bony fishes examined, we found a clear and significant predominance of females, particularly pronounced in Alepocephalus rostratus , which is clearly related to their K-reproductive strategy. The four key-selected species (Galeus melastomus , A. rostratus , Bathypterois mediterraneus and Trachyrincus scabrus), characterized by different reproductive strategies/modalities and feeding behaviours, were differently affected by depth and fluxes of organic matter (Particulate Organic Carbon concentration) from the photic zone towards the sea-bottom as a function of sex and life -stage. • The numbers and densities of chondrichthyans were lower than those of bony fishes and decreased with depth. • A continuous breeding cycle in chondrichthyans and a spawning duration increasing with depth in bony fishes were observed. • The seasonal reproduction in autumn and winter was related to POC concentration at surface. • A delayed size at maturity, in chondrichthyans >75% and in bony fishes >60% of their maximum length, was reported. • Population partitioning according to sex and life stage was showed both in chondrichthyans and bony fishes. [ABSTRACT FROM AUTHOR]