Résumé:
This study, allowed us to put the light on marine invertebrate groups (echinoids, Holothuroidea, ophiuroids, Asteroidea and crinoids), rarely studied, in the Mediterranean sea. These echinoderms are studied in a shallow area of the coast of Mostaganem, at two sites (Salamander and Stidia).
In the present study the biodiversity have been analyzed in both sites and life traits of the three echinoderm species, Echinaster sepositus (Retzius, 1805) and Coscinasterias tenuispina (Lamarck, 1816) at the site of Salamander, and one species of brittle star Ophioderma longicauda (Retzius, 1789) at the Site of Stidia.
Sampling was carried out by scuba diving over six months (April to August 2014). For the determination of the biodiversity, we used the quadrat method. This method allowed us to use analytical methods for determining the following index: the Shannon index (H‟) and the equitability index (J'). The results, showed a dominance of Echinoid at both sites with Paracentrotus lividus (Lamarck, 1816) at the site of Stidia and Arbacia lixula (Lamarck, 1816) at the site of Salamander. Moreover, aspidochirote, Holothuroidea are represented by Holothuria Polii (Del Chiaje, 1823), Holothuria sanctori (Del Chiaje, 1823). A class of ophiuroids is also noted and is represented by a single species Ophioderma longicauda (Retzius, 1789). Moreover, the site of Stidia, showed a slightly higher ecological quality (H‟ = 1), and diversity with species richness of 5 compared to the site of Salamander. As for the analysis of equitability index (J), this one reflects a slight imbalance at the two sites with (J') <0.55.
Analysis of the life history of three species of echinoderm has shown that E. sepositus, has a disc diameter ranging from 1.75 to 2,75cm and a minorant allometric growth between the length of the arm and the diameter of the disc. As for the analysis of the physiological index two reproductive periods, are noted one in the spring (April) and the second in summer (in July). For the species C. tenuispina, demographic structure showed that 50 % of individuals have a disc diameter ranging from 0.8 to 1,00cm, marked by an isometric (allometric) relation between the length of the arm and the diameter of the disc. For the species O. longicauda, sampled in the site of Stidia, the population is represented by individuals with a disc diameter ranging from 2.00 to 2.50cm, and a minorante allometric growth.
In this work, the faunal inventory, realized at both sites (Salamandre and Stidia) has allowed us to point out the presence of endemic and invasive species; Maja crispate (Risso, 1827) and Lepadogaster lepadogaste (Bonnaterre, 1788), Tripterygion tripteronotum (Risso, 1810), Tripterygion melanurum (Guichenot, 1845), Libinia sp, Percnon gibbesi (H.milneEdxards, 1853) and Caulerpa racemosa (Forsskal).
