An assessment of soft coral community (Octocorallia; Alcyonacea) around Mauritius and Rodrigues Islands — New records of soft corals

Abstract This study aims to assess the soft corals community around Mauritius and Rodrigues Island due to the limited research on the abundance and diversity of soft corals in the area. Seven soft corals species are newly reported from Mauritian waters. Triplicates of 5-metreline transect were used to survey soft corals at twelve different monitoring sites. Of the sites monitored for soft coral occurrence, the highest Margalef richness index and Shannon index (H’) values were obtained at Port Mathurin for Rodrigues Island and at Les Salines for Mauritius. Identification was carried out using both morphological characters and a DNA-based marker. The morphological identification process was based on the external form and colouration, type of colony growth; the type of polyps and colonies and sclerites analysis. 41 different species showed dissimilar characteristics, and results grouped the colonies to three different families; 32 colonies of Alcyoniidae, 3 of Nephtheidae and 6 of Xeniidae were obtained. To ascertain morphological classification, the longest non-coding region of the mitochondrial COI-COII intergenic spacer (IGS) (consisting of 122 nucleotides) was used to construct a molecular phylogeny that included 21 species of octocorals. The COI-COII IGS phylogeny recovered 5 well supported clades, which did not tally with the cladogram based on morphological characters. Three dendrograms based on morphological characters were constructed where the first one involved mapping of all the morphological characters onto the tree, the second one was based mainly on the type of sclerites present and the third one based on the collection depth of the samples. The dendrogram based on morphological markers clustered all the soft corals from the Alcyoniidae family aside from the other families. The second dendrogram clustered all the soft corals from the genus Sinularia, Lobophytum, Sarcophyton as well as Cladiella kashmani together, away from the soft corals with distinct sclerite form. Furthermore, the third dendrogram clustered the soft corals into 2 major clades, one clade clustering the soft corals which are ubiquitous and a larger clade including all soft corals collected from a depth of 0 m to above 20 m. As documented by other studies on octocorals, construction of the phylogenetic tree has led to an appreciation of the importance of genetic work which has been overlooked while using traditional morphological characters.