Population dynamics and resource utilization by the dusky damselfish, Stegastes adustus (Troschel, 1865)

Coral reef fishes depend upon the reef substrate for the duration of their lives. Consequently, patterns of distribution and abundance of reef fishes may be influenced by this relationship. The spatial and temporal abundance variability of the dusky damselfish, Stegastes adustus was studied in the coral reef ecosystem of La Parguera, southwestern Puerto Rico. Monthly surveys were conducted over one year at permanent transects established in the fore reef areas of five reefs. Microhabitat association was evaluated by correlating the quantified available substrate in transects and within territories to fish abundance and the number of fish with territories respectively, and by multi-factorial manipulative experiments combining the presence and absence of refuge and food. An increased abundance of S. adustus was noted when compared to that recorded prior to the decline of Acropora spp. and Diadema antillarum. Significantly higher abundance was observed in one relatively shallower reef and a seasonal peak in abundance was recorded for two reefs. These results corresponded with observations elsewhere in the Caribbean. Juveniles and adults showed significant differences in abundance between and within ontogenetic stages. The amount of dusky damselfish territories was similar among reefs and was correlated to mean fish abundance, except in the shallower reef. Turf colonized pavement dominated the reef substrate at all sites. Fish abundance was not correlated to this particular substrate type but to lesser substrate categories. Regardless of the higher cover by boulder star coral, Montastraea annularis no correlation was found between the coral species and fish abundance. The number of established territories was related to substrate cover by dead coral. Rugosity was similar between reefs but did not influence abundance. Choice of microhabitat during recruitment may explain abundance and distribution of juveniles and adults once a substrate section is occupied by the fish. This study suggests that S. adustus is an opportunistic generalist that settles and recruits to a specific habitat but that juveniles and adults may further benefit from modifying their surroundings. Setting aside variability in settlement, environmental factors and other biological and ecological processes may explain the observed differences in the abundance and distribution of S. adustus.