Spatial pattern of Plicopurpura patula pansa, in rocky shores of Guerrero, México

Abstract

PLICOPURPURA PATULA PANSA IS A CARNIVORE SNAIL COMMON OF THE MEXICAN PACIFIC ROCKY SHORES. ITS HYPOBRANCHIAL GLAND PRODUCES A SECRETION THAT, IN THE PRESENCE OF OXYGEN AND SUNLIGHT, BECOMES PURPLE. WE DETERMINED THE SPATIAL DISTRIBUTION OF THE SNAIL ON BEACHES THAT DIFFER IN SUBSTRATUM, WAVE EXPOSURE, AND THE DEGREE SUBSTRATUM´S INCLINATION. THE AVERAGE SNAIL DENSITY WAS CALCULATED. USING THE MORISITA INDEX (ID) AND THE MORISITA STANDARDIZED INDEX (IP), WE FOUND THAT IN 96.3% OF THE SAMPLES TAKEN, THE SNAILS WERE DISTRIBUTED ACCORDING TO A PATCHY DISTRIBUTION. THE REST OF THE TIME, THEIR DISTRIBUTION WAS RANDOM. THE IP INDEX OSCILLATED BETWEEN 0.1522 AND 0.5435. SMALLER FL UCTUATIONS OF THE IP INDEX WERE OBSERVED IN 5 BEACHES WITH SUBSTRATA THAT WERE MORE STABLE AND HAD A LARGER NUMBER OF CRACKS AND CREVICES THAN THOSE ON BEACHES WITH MOBILE SUBSTRATA, SUCH AS ROLLED ROCKS.