Diversity, distribution, and habitat associations of deep-water echinoderms in the Central Mediterranean

Abstract

Limited research effort in the Central Mediterranean deep sea has reported a lower species diversity in this area than in adjacent regions. With the recent advent of remotely operated underwater vehicles (ROVs), the deep sea has become more accessible to surveys, especially rocky benthic areas such as canyons and escarpments. The aim of the present study was to assess diversity, spatial and bathymetric distribution, density, habitat, and microhabitat associations of echinoderms in deep waters around the Maltese Islands. Video data were acquired through ROV surveys as part of the LIFE BaĦAR for N2K project, at depths of 216 to 1031 m. In total, 25 echinoderm taxa were recorded, including the first Central Mediterranean records of the sea stars Marginaster capreensis (Gasco, 1876) and Sclerasterias neglecta (Perrier, 1891), and the first record of the holothuroid Mesothuria intestinalis (Ascanius, 1805) from Maltese waters. Six species were observed deeper than their currently accepted depth range in the Mediterranean. The most abundant species were the crinoids Antedon mediterranea (Lamarck, 1816) and Leptometra phalangium (Müller, 1841), which formed very dense aggregations of up to 2900 individuals/1000 m 2 in a small area to the south of Malta. This area also supports the only known Mediterranean population of the Atlantic sea star Coronaster briareus (Verrill, 1882). Bathymetric distribution varied for each species, and the overall echinoderm diversity seemed stable across the surveyed depths. Since previous deep-sea studies in the area were based on trawling surveys, many deep-sea echinoderm species are reported in the literature as occurring on sedimentary bottoms. However, the present study revealed that several occur more often on rocky substrata, corals, or anthropogenic objects than on sediments. Our study based on video footage also provided insights into the microhabitat of many deep-sea species, yielding information that is not obtainable through remote sampling.

The Bioactive Potential of Trawl Discard: Case Study from a Crinoid Bed Off Blanes (North-Western Mediterranean)

“…The methodology and results of this study could be used to discard species in other crinoid beds that are home to rich and diverse fish and invertebrate communities [ 11 , 13 , 69 ]. Additionally, these results could be applied to discard vulnerable habitats for which there is a need to find a balance between exploitation and conservation, such as muddy habitats on the continental shelf, which can also be highly diverse and productive [ 70 , 71 ].…”

“…Crinoid beds are located in a transition zone between the end of a continental shelf and the beginning of a slope; because of the orography of this zone, there are currents that transport a large amount of nutrients that are harvested by phytoplankton, leading to high primary production [ 9 , 10 , 11 ]. This habitat is characterized by a high density of the crinoid Leptometra phalangium , which feeds on suspended matter and fixes a large amount of nutrients from the water column to the substrate [ 12 , 13 ]. Due to the unusually large amount of food available, several species with high commercial value, such as European hake ( Merluccius merluccius ) or monkfish ( Lophius budegassa and L. piscatorius ), occupy this habitat, which is also used by these species as a nursery area [ 14 , 15 ].…”

“…Due to the unusually large amount of food available, several species with high commercial value, such as European hake ( Merluccius merluccius ) or monkfish ( Lophius budegassa and L. piscatorius ), occupy this habitat, which is also used by these species as a nursery area [ 14 , 15 ]. Despite its importance, this habitat does not have any special protections as other Mediterranean habitats, such as maerl beds or Posidonia oceanica meadows [ 16 , 17 , 18 ], both of which are included in Appendix A ( Table A1 ) of the Habitats Directive of the European Union, so that currently crinoid beds are exploited by trawling, which may cause irreparable environmental damage [ 13 , 15 , 19 , 20 ].…”

Diversity, structure and spatial distribution of megabenthic communities in Cap de Creus continental shelf and submarine canyon (NW Mediterranean)

“…Aggregations of the crinoid L. phalangium have long been regarded as characteristic of circalittoral and bathyal habitats of the Mediterranean Sea (Pérès & Picard, 1964), generally associated to flat areas of the shelf and shelf edge with muds, sands and gravels, where mid to strong bottom currents are common (Pérès, 1967). Dense patches of these crinoids have been reported from shelf and shelf break areas of the western (Grinyó et al, 2018), central (Colloca et al, 2003;Leonard et al, 2020) and eastern Mediterranean (Kallianiotis et al, 2000), where they can reach local densities of 15-30 ind⋅m − 2 . In Cap de Creus, L. phalangium had already been identified by Desbruyères et al (1972) as part of the sub-community of shelf detritic of the mid and outer continental shelf, which also includes the community of pennatulaceans and alcyonaceans and the brittle star aggregation identified in this work.…”

Outstanding Aggregation of the Atlantic Brisingid Hymenodiscus coronata (Sars, 1871) (Echinodermata: Asteroidea) in the Strait of Sicily

“…Mediterranean echinoderms represent 2.2% of the global echinoderm diversity, with 154 species recorded until 2010 [1]. Most of the known species reside in shallow environments, while there is still a substantial knowledge gap of deep-sea echinoderms species, especially in the southern and eastern regions of the basin [1][2][3]. The recent expansion in scientific interest and sampling efforts in deep-sea environments, coupled with advancements in the technologies involved in the explorations, has led to a continuous increase in our understanding of the biodiversity and ecology of deep-sea communities, including the echinoderm fauna [3,4].…”