A critical habitat for Mediterranean fish resources: shelf-break areas with Leptometra phalangium (Echinodermata: Crinoidea)

Abstract

This paper considers the potential role of the crinoid Leptometra phalangium as an indicator of highly productive areas along the shelf break that can sustain large biomasses of benthopelagic fish and recruits. The structure of fish assemblages in the central Mediterranean Sea (central-western coast of Italy), analysed on the basis of surveys carried out in summer and autumn from 1997 to 2001, revealed the presence of a well-defined group of species on the shelf break. This area, occurring at a depth of between 120 and 170 m, is characterised by detritic organogenic sediments colonised by the crinoid L. phalangium, a suspension-feeding macro-epibenthic species confined in the Mediterranean to the shelf-break area. Its abundance in the studied area can reach 12-15 ind. m )2 . A total of 121 species belonging to 66 families of demersal organisms (crustacean decapods and stomatopods, cephalopods, selaceens and teleosteens) were caught at shelf-break stations from September to October. The species which typified the assemblage were the fishes Trisopterus minutus capelanus, Merluccius merluccius, Glossanodon leioglossus, Argentina sphyraena, Capros aper, Macroramphos scolopax and Lepidotrigla cavillone, the crustacean decapod Parapenaeus longirostris and the cephalopods Illex coindetii and Todaropsis eblanae. Detritic shelf-break stations showed a higher abundance of demersal organisms than stations distributed on muddy bottoms in the same depth range (100-200 m). Such differences appeared to be significant in September-October, when a clear increase in benthopelagic zooplanktivorus species, such as Glossanodon leioglossus, Trachurus trachurus, Trachurus picturatus, was found. The length structure of species occurring on the shelf break showed that for some of them the selection of this area is related to specific phases of their life cycle. Significant highest abundance of recruits and juveniles was observed for Merluccius merluccius, Helicolenus dactylopterus, Phycis blennoides, Parapenaeus longirostris and Capros aper in at least one of the two seasons. Similarly, an increased abundance of spawners of red mullet Mullus barbatus and four-spotted megrim Lepidorhombus boscii was observed on the shelf break. Results of this study may have important consequences for management of fish stocks and assemblages in the central Mediterranean. The cooccurrence of high densities of L. phalangium and benthopelagic fish, occurring mainly with juveniles and spawners, strongly indicates a potential role of L. phalangium as an indicator of highly productive areas around the shelf break. Such areas appear to play a major role in the production of some of the most abundant and commercially important fish species, such as the Mediterranean hake and red mullet.

Biology, Feeding, and Habitat Preferences of Cadenat's Rockfish, <I>Scorpaena Loppei</I> (Actinopterygii: Scorpaeniformes: Scorpaenidae), in the Balearic Islands (Western Mediterranean)

“…In the Mediterranean these beds are considered to be indicators of highly productive areas of the deep shelf and shelf break that sustain large biomasses of benthopelagic fish (Colloca et al 2004). Similarly to the coastal small scorpenid species which have been linked to structurally complex vegetated bottoms (Edgar and Shaw 1995), S. loppei seems to prefer the most structurally complex bottoms on the deep shelf, which in the area of study are represented by crinoid beds with high abundance of macro-epibenthic species.…”

Harvest Strategies for an Ecosystem Approach to Fisheries Management in Western Mediterranean Demersal Fisheries

“…The fishing grounds traditionally exploited by the BTF overlap with red algae beds including maërl and Peyssonnelia beds , respectively. The crinoid beds, also considered an EFH (Colloca et al, 2004;Ardizzone, 2006), dominate certain areas of the deep shelf, primarily between 120 and 200 m depth. Studies carried out in the Balearic Islands confirm the importance of these habitats in structuring demersal resources assemblages .…”

Mollusca from a species-rich deep-water <em>Leptometra</em> community in the Alboran Sea

“…García-Muñoz et al (2012) indicated the presence of low hydrodynamic conditions and a high incidence of pelagic sedimentation at the summit of Algarrobo and Herradura banks based on sedimentological characteristics and this may benefit the vertical influx of larvae. Moreover, the dense population of Leptometra phalangium at the summit, as suspension feeders, benefit from a highly productive environment due to a high amount of particles from surficial levels (Colloca et al 2004, Gil et al 2010.…”

“…Mediterranean communities of the offshore "detritic" bottoms have also attracted interest elsewhere and qualify as a "reservoir" of biodiversity (Colloca et al 2004(Colloca et al , 2006.…”

“…The outstanding species richness may be favoured because the crinoid increases heterogeneity, but above all its presence is an indicator of favourable resources and it has been explicitly put forward as a species deserving a protection status (Colloca et al 2004, De Ranieri et al 2006, Angeletti et al 2010 Colloca et al 2006). This culminated in having Leptometra beds (along with Posidonia beds 1120, a priority habitat in Europe's Habitat Directive, and along with maërl beds) as one of the 14 habitats selected by the Scientific Advisory Committee of the General Fisheries Commission for the Mediterranean as criteria for identifying Essential Marine Habitats (EMH) of relevance for the management of priority species (General Fisheries Commission for the Mediterranean 2009).…”