Seasonal variations of the chiton community structure (Mollusca: Polyplacophora) in a rocky intertidal shore from the southern Gulf of Mexico

Abstract

Abstract.- The southern Gulf of Mexico is typically a coastal plain where rocky shores are scattered distributed. The goal of this study was to compare the chiton community structure of the rocky shore of Montepío during the dry and ‘nortes’ (stormy) weather periods, and to gather data on the relative growth of the dominant species. Sampling was carried out along a transect of 100 x 2 m in the intertidal zone and 83 individuals were collected. Six species were identified: Lepidochitona rosea, Chaetopleura apiculata, Ischnochiton kaasi, Lepidochitona pseudoliozonis, Lepidochitona liozonis and Acanthochitona andersoni. Species richness (S= 4) and Shannon diversity (1.36 and 1.29 bits ind^-1 in dry and stormy seasons) were very similar between the 2 seasons; however, only 2 species occurred in both periods, suggesting a strong seasonal exchange of species (50%). This seasonal dynamics could be due to the discontinuity of the rocky substrate, which would not allow a rapid recovery of the populations after the impact of storms. Density of individuals was low (< 2.50 ind. 10 m^-2) due to 2 factors: the diurnal tide, which induces the individuals to 12 h of air exposure, and the low salinity, due to the proximity of two rivers. The relative growth of the dominant species (L. rosea and C. apiculata) was isometric for the length vs. width relationship and negatively allometric for the length vs. height relationship. In the southern Gulf of Mexico, sites such as Montepío may function as marine oases for obligate inhabitants of hard substrates.