We present the Cuban experience on employing descriptive ecological features of sessile marine communities as bio-monitors of environmental favorability and constancy. Using indices of heterogeneity (11') and equitability (J'), we interpret the environment at several reefs, taking into account the general requirements of each investigated taxon (sponges, gorgonians, and scleractinians). Dominant species indicate the primary physical factors influencing sessile communities. The range and the comparative intensity of the influence of pollution of Havana Bay on the neighboring reefs were inferred by the species-heterogeneity index. The classification of sampled stations with regard to their level of pollution was obtained by means of cluster analysis. The size- frequency distribution of Siderastrea radians also proved to be influenced by the degree of pollution. Variability with regard to depth has been obtalned for several indices from numerous stations. These graphs can be used to assess the environmental status of any sampled reef station. All of these methods, if used with caution and in combination, give deductive or predictive outputs that reflect the average conditions of the environment in some cases, while in others indicate the most recent strong events that have affected reef communities.
The inference of environmental quality by means of species or community composition and structure, or by observing the phenotypical adaptations of some species, is a comparatively simple and economical way to monitor and interpret environmental issues. Coral reefs are prQbably the most sensitive and vulnerable ecosystems in the sea, due to their past evolution under comparatively narrow ranges of environmental variability. For this reason, they are a promising reference choice for monitoring the changes in tropical marine biota. Being aware of this, The Institute of Oceanography of the Cuban Academy of Sciences has been dealing with the composition and structure of coral reef faunal and algal associations since the middie of the 1970's. The purpose of this paper is to offer a brief panorama of our experience in the research of coral reef sessile communities and their potential as bio-monitors.