Jiménez-Marrero, Nilda M.

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    Fish, algae and coral dynamics from various reefs in southwest Puerto Rico
    (2009) Jiménez-Marrero, Nilda M.; Williams, Ernest H. Jr.; College of Arts and Sciences - Sciences; Bunkley-Williams, Lucy; Capella, Jorge; García, Jorge R.; Aponte, Nilda; Department of Marine Sciences; Ojeda, Edgardo
    A study composed of three experiments was conducted in 7 reef sites, at 5 and 10 m depth off the southwest coast of Puerto Rico, to examine fish, algae, and coral dynamics. The first experiment employed exclusion cages. Three exclusion cages (0.5 m x 0.5 m x 0.25 m) were placed at each site and depth. Algae and herbivores were removed from these cages to observe algae succession under no grazing pressure after algae removal. Control areas were established in the vicinity of each site to account for natural fluctuations on algae cover. A negative relation between cyanobacteria and coralline algae was observed. Algal development inside the exclusion cages suggests that algae interspecific competition dominates reef population dynamics. For the second experiment, five 1 m2 quadrats were marked per site and depth. Algae were removed from inside the quadrats to observe algae development under actual herbivore grazing pressure. The most abundant algae at the studied sites were Halimeda, Dyctiota, and turf. Algae interspecific competition was observed at most sites, in particular a negative relationship between macroalgae and turf. Shallow mid-shelf reefs and deep inshore reefs showed varying results, and possible explanations for the results are discussed. The third experiment consisted of fish surveys conducted at each site and depth contour on three different occasions using the stationary plot technique with discrete group sampling. Fish abundance was positively related to macroalgae cover. Turbidity and light intensity affected fish density, possibly because of the effect that these physical factors have on algal growth. Prevailing grazing pressure exerted by scarids, acanthurids, and probably sea urchins, in the midshelf at 5 m depth, promotes algal species diversity as predicted by the intermediate disturbance model. Major impact of herbivores on algal cover is thorough their apparent control over palatable algae. Algal cover is controlled by grazer density only in a spatial scale, since the effect of grazers was only observed at some sites and depths.