The aim of this study was to characterize and compare the population structure and dynamic of Microphrys bicornutus Latreille, 1825 on the phytal Halimeda opuntia (Halimedaceae) collected on the reef areas of Picãozinho (visited by tourists) and São Gonçalo (control area), in João Pessoa coast (Northeastern of Brazil), under the influence of environmental conditions and visitant numbers. In both study areas the populations analyzed were composed similarly of mature and immature males and females, with predominance of males and immature animals, and similar size frequency and reproductive period. Sex-ratio, size frequency distribution, and size of the biggest specimens differed from those estimated in others latitudes and habitats for this species. Sex ratio estimation has made evident that independently of maturation stage, males tended to predominate significantly and the proportion of females to decrease with sexual maturation. Without exhibiting influence of the alga biomass, and of the salinity and temperature of the water, significant population variations were associated to the increase of juvenile during rainy periods. The low population density and the largest disproportion of the relationship male: female in Picãozinho subarea with larger flow of people, are suggestive that the trampling of the alga might have induced this population variation.
Population composition; population density; sex ratio; algae trampling; seasonal effect
