Community structure and height distribution of intertidal rockpool fish in Los Cóbanos, El Salvador

Tide cycles determine the ecological complexity and environmental dynamics observed in the intertidal habitats. Intertidal dwellers show particular patterns of distribution with abrupt changes even at distances of few meters. Tropical intertidal zones have seldom been studied; therefore the community structure and vertical distribution of the intertidal rockpool fish of Los Cóbanos was assessed. In the intertidal zone, a total of 18 rockpools were selected according to the shore height as low (3-39 cm), mid (40-75 cm) and high (76-110 cm), with 6 replicate rockpools per shore level. Physico-chemical variables (temperature, salinity, pH), substratum homogeneity (algal, sand and rock cover) and habitat complexity were measured and rockpools were sampled every three months for one year. Overall, the intertidal assemblage of rockpool fish was composed of 48 species and dominated in abundance and species richness by the families Gobiidae (4 species and 746 fish or 31.29%) and Pomacentridae (5 species, 546 fish or 22.90%). The most abundant species were Bathygobius ramosus (27.76%) and Stegastes acapulcoensis (11.07%). Juvenile fish (75%) were more abundant than adults and larvae. Opportunist fishes were more abundant than permanent residents and transients comprising 58.53%, 39.87% and 1.6% of the abundance, respectively. Intertidal height, volume and rock cover were the most important variables that determined changes in the community structure. Six species presented size class segregation among rockpools at shore heights in the intertidal zone