DIEL, LUNAR AND SEASONAL-CHANGES IN A MANGROVE FISH ASSEMBLAGE OFF SOUTHWESTERN PUERTO-RICO

Visual censusing was used to investigate diel, lunar, and seasonal variations in abundance and composition of a fish assemblage inhabiting a mangrove key off the southwest coast of Puerto Rico. Forty-one species were visually identified among the mangrove prop-roots duing designated census periods: 0700, 1200, 1700, 2200. Statistical analysis indicated distinct trends in diurnal, day versus night, and seasonal abundances. Although diurnal variability was evident, the most pronounced feature was nighttime declines in species abundance. All species present during the day showed marked reduction in numbers or complete absence at night. Unlike coral reef habitats, there was no evidence for a diurnal-nocturnal changeover of species assemblages in the mangroves. Low nighttime abundance was partly due to twilight migrational activities. Movements away from the mangrove prop-root habitat at dusk were observed for a variety of fishes, particularly haemulids. Predictable, well ordered migrations were observed for juvenile French grunts (Haemulon flavolineatum) and sub-adult bluestriped grunts (H. sciurus). Timing, duration, and pre- and post-migratory behaviors differed among species. Seventy-six % of species examined showed significant (P < 0.05) seasonal differences between Oct/Nov 86 (rainy season) and Apr/May 87 (dry season). Lunar periodicity had no obvious effect on species abundance in this mangrove fish assemblage.