Biomass and taxonomic richness of epilithic cyanobacteria in a tropical intertidal rocky habitat

Abstract

The epilithic biofilms colonizing the intertidal and splash zones of a rocky shore in the southern Gulf of Mexico were studied by phase contrast and scanning electron microscopy (SEM), along with phytopigment analyses. These biofilm communities comprised a mixed assemblage of phototrophs, dominated by cyanobacteria, with occasional diatoms and other eukaryotic microalgae. Eight out of nine cyanobacterial genera identified were filamentous. A Stigonema species, a cyanobacterium that rarely occurs in marine habitats, was found in low intertidal samples. Microscopy analysis (phase contrast and SEM) showed that more diverse cyanobacterial populations (morphotypes) occurred on intertidal rocks than in splash zone biofilms, probably owing to the desiccation and thermal stress to which the latter are exposed. However, the phycobiliprotein content, as indicative of cyanobacterial biomass, was similar at both tidal levels. The numerical dominance of Pleurocapsa species and its wide distribution among intertidal and splash zone rocks may be related to its ability to withstand environmental stress by producing moisture-retaining external capsules.