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


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 m2 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.

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We thank the crew of the Oceana Ranger for their assistance with the ROV surveys. We are also grateful to Prof. Rocío Pérez-Portela for assistance with the identification of Ophiothrix fragilis and to Dr. Andreas Kroh for supplying us with the identification key for Cidaridae. The present work was undertaken as part of the LIFE BaĦAR for N2K (LIFE12 NAT/MT/000845) Project, which was 50% co-financed by the EU LIFE+ Funding Programme and implemented by the Maltese Environment and Resources Authority (ERA), the University of Malta, Fundación Oceana, the Ministry for the Environment, Sustainable Development, and Climate Change (MESDC), and the Department for Fisheries and Aquaculture within MESDC. We are also grateful to ERA and to the Continental Shelf Department within the Ministry for Transport and Infrastructure (Malta) for granting us the necessary permits to undertake the marine surveys. We also thank two anonymous reviewers for their helpful comments.


This study was funded by the EU LIFE+ Funding Programme (grant number LIFE12 NAT/MT/000845, awarded to LIFE BaĦAR for N2K Consortium).

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Correspondence to Camille Leonard.

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This article does not contain any studies with animals performed by any of the authors.

Sampling and field studies

All necessary permits for sampling and observational field studies have been obtained by the authors from the competent authorities and are mentioned in the acknowledgements, if applicable.

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All data generated or analysed during this study are included in this published article (and its supplementary information files). The conclusions of this paper do not rely on any publicly available data.

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PJS, JAB, and RA conceived and designed the research. RA led the offshore research cruises supported by SG and HA; JE and LK also contributed to the field sampling. CL extracted and analysed the data and wrote the manuscript together with JE. All authors reviewed and approved the manuscript.

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Leonard, C., Evans, J., Knittweis, L. et al. Diversity, distribution, and habitat associations of deep-water echinoderms in the Central Mediterranean. Mar. Biodivers. 50, 69 (2020).

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