COMMUNITY STRUCTURE AND SEASONAL-VARIATION IN INTER-TIDAL PANAMANIAN SANDY BEACHES

Two Panamanian sandy beaches, one along each coast, were examined in 1973-1974 as a continuation of preliminary sampling in 1969-1970. Infaunal community structure for each beach is described in terms of species composition, density, biomass, diversity, and evenness. The influence of environmental factors on the zonation and abundance of the dominant species is discussed. The Caribbean beach is exposed to a marked wet versus dry season, while the major environmental feature of the Pacific beach is a strong upwelling of cool water during the dry season. Community'structure of the Caribbean beach is characterized by lower density, fewer species, higher diversity (H′), and greater fluctuation among faunal dominants. The Pacific beach fauna has higher density, greater number of species, and lower diversity due to the dominance by the isopod Excirolana braziliensis. Explanations for the major differences in community structure between the two beaches are presented. © 1979.