Availibility of Space for the Territorial Caribbean Damselfish Eupomacentrus Planifrons

Populations of coral reef fishes are often thought to saturate habitable space and to be limited by its availability, particularly those fishes that defend space. In Panama, individual adults of the common Caribbean damselfish Eupomacentrus planifrons defend permanent, all—purpose territories . A territory contains a mass of coral from which the fish derives required substrate—based resources: shelter from predators, a nest site (males only), and food (from a distinct mat of algae). Two experiments tested whether an excess of suitable substrate was present in two of the main habitats of E. planifrons. (1) Coral substrate that contained algal mats was removed from small areas (up to 45 m²) in habitats composed of Agaricia and Acropora corals. After 3 mo new algal mats were established on previously mat—free parts of the experimental areas, and the density of adult E. platnifrons increased in the experimental areas. (2) The area of habitat of three small patch—reefs was reduced by one—half through the removal of coral substrate. One year later, the density of E. planifrons adults had increased on the remaining halves of those reefs. The results of both experiments indicated that a surplus of suitable substrate existed in the experimental areas and that E. planifrons was not generally limited by the availability of habitable space. Compared to control fish of the same length, experimental E. planifrons were similar in mass, in the amounts of fat reserves, and, in the case of females, in activity of their ovaries. Both experimental and control fish were breeding at the end of the experiment. Thus the experimental increase in population density did not appear to be detrimental to the physiological condition or reproductive capacity of the fish. We conclude that E. planifrons is probably not at the carrying capacity of the habitats it occupies.