Variation in the diversity of mollusks from the rocky intertidial of Playa Troncones, La Unión, Guerrero, México

Abstract

THIS WORK INTRODUCES A SPECIES INVENTORY GIVING THE DOMINANT SPECIES THEIR FREQUENCY OF OCCURRENCE, THEIR DIVERSITY AS WELL AS THE SPECIES” ACCUMULATED RELATIVE IMPORTANCE OF THE MOLLUSKS AT PLAYA TRONCONES IN GUERRERO STATE, MEXICO. IT ALSO ANALYZES CHANGES IN MOLLUSK DENSITY AND DIVERSITY IN COMPARISON TO THE ANNUAL RAINFALL CYCLE. BETWEEN DECEMBER 2000 AND DECEMBER 2001, FIVE THREE-MONTHLY SAMPLES WERE CARRIED OUT USING 20 X 1 M2 QUADRATS TAKEN RANDOMLY WITHIN A STRIP MEASURING 30 X 2 M TO GIVE A TOTAL SAMPLED AREA OF 20 M2. THE RICHNESS FOUND THERE WAS SIMILAR TO THAT REPORTED AT ANOTHER SITE IN THE STATE OF GUERRERO. THE REPRESENTATIVE SPECIES OF THIS COMMUNITY WERE BRACHIDONTES SEMILAEVIS, NERITA FUNICULATA, ISOGNOMON JANUS, PLICOPURPURA PANSA, NERITA SCABRICOSTA, PETALOCONCHUS COMPLICATUS AND NODILITTORINA ASPERA. BRACHIDONTES SEMILAEVIS AND P. PANSA WERE OF GREATEST IMPORTANCE DUE TO THEIR ABUNDANCE AND FREQUENCY OF APPEARANCE. THE DIVERSITY INDEX VALUES RECORDED IN THE STUDY AREA CORRESPOND TO THOSE FOUND IN TROPICAL REGIONS. IN THIS STUDY AREA, IT WAS OBSERVED THAT AN INCREASE IN RAINFALL PRODUCED A DECREASE IN THE AVERAGE DENSITY OF THE ORGANISMS, WHEREAS SUCH INCREASED PRECIPITATION PRODUCED AN INCREASE IN THE VALUE OF THE BIOLOGICAL DIVERSITY INDEX.