The echinoderms of Northern Tunisiabiodiversity, biology, biogeography, phylogeny and valorisation

Abstract

Tunisia occupies a strategic biogeographic position in the Mediterranean Sea, between the eastern and western basins and close to the strait of Sicily which has been considered as a biogeographical boundary that separates the Mediterranean Sea in two different ecoregions. Despite its importance, studies on marine biodiversity in Tunisia and, in particular, in Echinodermata fauna are old and scarce. Besides, marine bioresources are suffering from overexploitation, pollution and climate change, leading to the ecosystem degradation and the biodiversity loss. A study of the phylum Echinodermata was carried out between 2012 and 2017 along the northern coast of Tunisia. It explores the ecology, biology and the classification of the echinoderms that occur in this area, in order to update the inventory of Echinodermata in Tunisia and to analyze their biogeographical affinities with neighbor regions and provinces. Furthermore, it studies the phylogenetic diversity of sea cucumber species from genus Holothuria with Atlanto-Mediterranean origin, by introducing the molecular tool "DNA Barcoding" as a molecular technique for sea cucumber and their genetic divergence identification. Sea cucumber spicules were also analyzed in order to test their morphometric and molecular similarity and to clarify their systematic identification since the genus Holothuria is, in many cases, under discussion and its literature is currently in confusion. A total of 45 echinoderm species were inventoried in northern Tunisia. They belong to the five living classes of Echinodermata and comprise 3 Crinoidea, 15 Asteroidea, 10 Ophiuroidea, 8 Echinoidea and 9 Holothuroidea. Amongst all, four species were first records for Tunisia. Two of them are exclusively Mediterranean species (Asterina pancerii (Gasco, 1876) and Leptopentacta tergestina (M. Sars, 1857)), one is an Atlantic species (Luidia atlantidea (Madsen, 1950)) and the last one is a cosmopolitan species (Ophiactis virens (M. Sars, 1857)). Otherwise, the sea cucumber genetic results showed a big similarity between spicule's morphometric and molecular results. While, the target species Holothuria (Roweothuria) poli (Delle Chiaje, 1824) showed a high phylogegraphic diversity on the Mediterranean Sea, in particular a large genetic connectivity between the central and the eastern Mediterranean basins it revealed a genetic differentiation between lagoon ecosystem and open sea. Eventually, the updated Echinodermata list from the available datasets provided 79 species in Tunisia. Also, the biogeographical patterns showed that species richness decreasing from the north to the south Tunisia and from the western to the eastern Mediterranean Sea with the dominance of cosmopolitan species in all the regions. The use of the DNA barcoding approach on Echinodermata species seems very reliable, fast and efficient method for species identification, and is very useful for biological knowledge of target species. Lack of information of the phylum Echinodermata in Tunisia is a knowledge gap for marine biodiversity. Consequently, amplifying the knowledge of its diversity and distribution will also allow its right fishery management and the valorization of its products, and ultimately its conservation and sustainability.