Biological patterns and ecological indicators for Mediterranean fish and crustaceans below 1,000 m: a review

Abstract

The Mediterranean Sea is a relatively deep, closed sea with high rates of fisheries exploitation. In recent years fishing activity has tended to shift towards deeper depths. At the same time, the Mediterranean displays some rather special hydrographic and biogeographic conditions. The present paper reviews the present state of knowledge of the fisheries, biology, and ecology of the deep-sea fish and crustacean species in the Mediterranean dwelling below 1,000 m with potential economic interest, placing special emphasis on the western basin, for which more data are available, as a basis for future studies of the ecology, biodiversity, and effects of climate change and exploitation in this zone. This review reveals that mediterranean deep-sea fishes and crustaceans employ highly conservative ecological strategies, and hence the low fecundity and low metabolic rates in a stable environment like the deepsea make these populations highly vulnerable.Moreover, ripe females of the main species mentioned here concentrate in the deepest portions of their distribution ranges. Deep-sea fish and crustaceans have high trophic levels and low to medium omnivory index values. The ecological indices discussed here, in combination with the limited knowledge of deep-sea ecosystems, clearly call for an approach based on the Precautionary Principle.

Drivers of deep Mediterranean megabenthos communities along longitudinal and bathymetric gradients

“…The diversity differences found in the western basin between the 2 sampled communities suggest that the dynam-ics of strictly benthic species may be different from those of nektobenthic megafauna. In the deep Mediterranean, the biomass of nekto benthic fauna is known to decrease below 1500 m depth (Sardà et al 2009). Benthic invertebrates are more dependent on the organic matter found in the sediment than fishes and crustaceans, which could explain their significant decrease at the deeper station.…”

Diversity and bathymetric distribution of decapod crustaceans attracted to baited traps from the middle slope of the northern Aegean Sea

“…In addition, certain crustacean species are found only in the western Mediterranean and in the western region of the Ionian basin but not in the easternmost region. Also relative deepdwelling species abundance differences on geographic distribution occur with longitude (Sarda et al, 2009).…”

“…In the Mediterranean Sea, diversity and species richness decrease with depth in particular below 800 m and below 1500 m, where diversity and abundance suddenly decline (Cartes & Sarda, 1992;Company et al, 2004;Moranta et al, 2004;Sarda et al, 2004;Sarda et al, 2009;Fanelli et al, 2013). Crustacean diversity and species richness decrease considerably below 1000 m (Sarda et al, 2009).…”

“…Crustacean diversity and species richness decrease considerably below 1000 m (Sarda et al, 2009). Also, going to east and deeper, the number of taxonomic groups decrease (Tecchio etal., 2011b).…”

Structure, functioning, and cumulative stressors of Mediterranean deep-sea ecosystems

“…However, the Mediterranean Sea is unique in that below a depth of 1000 m trawl fishing is not permitted (EC Regulation 1967/2006. For this reason, and as suggested by recent works (Sardà et al, 2009;Ramírez-Llodra et al, 2011), the deep Mediterranean can be considered the last wild marine ecosystem.…”