Résumé:
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.
