Etude morphométrique de deux espèces d’oursins réguliers, Paracentrotus lividus (Lamarck 1816) et Arbacia lixula (Linnaeus 1758), prélevées dans deux étagements paraliques de la côte de Mostaganem.

Abstract

A morphometric study of two species of regular sea urchin Paracentrotus lividus (Lamarck, 1816) and Arbacia lixula (Linnaeus, 1758) sampled from two paralic staging was carried out on the coast of Mostaganem. The sampling took place at three stations: Stidia, Salamandre and Sidi Mejdoub. The study examined the effect of two physical factors: "Difference in staggering" and "geographical distance" on the form of sample tests. After the taxonomic identification based on the morphology of the two species, we took two biometric measurements: height "H" and width "L", from which we calculated the geometric mean "MG" and the gibbosity "GIB" . It is on this last parameter that we have based our study. We performed a "z-test" on population of each station to test the effect of staging, then an ANOVA was performed on all samples of the same species at any station to analyze the effect of the distance between sites on individuals. A Principal Component Analysis (PCA) was performed on all specimens of the two species in order to observe the distribution of the individuals and the projection of the quantitative variables (H, L, MG and GIB). The results of the "z-test" give us very pertinent information about the sample of P. lividus from the Stidia station, where the mean gibbosity was high in the population of the mediolittoral staging in relation to the population of the infralittoral, which suggests that this phenomenon is a manifestation of parapatric speciation. The ANOVA shown us that allopatry caused by the effect of geographical distance between the three stations could have a considerable influence on the morphological disparity of populations of the two species studied along the direction of the marine currents along the coast of Mostaganem.