Algal resistance to herbivory on a Caribbean barrier reef |
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Authors: | Mark M Littler Phillip R Taylor Diane S Littler |
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Institution: | (1) Department of Botany, National Museum of Natural History, Smithsonian Institution, 20560 Washington, DC, USA;(2) Division of Science and Mathematics, College of the Virgin Islands, Charlotte Amalie, 00802 Saint Thomas, US Virgin Islands |
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Abstract: | Field and laboratory research at Carrie Bow Cay, Belize showed that macroalgae, grouped in functional-form units resisted
fish and urchin herbivory in the following order (from high to low resistance): Crustose-Group, Jointed Calcareous-Group,
Thick Leathery-Group, Coarsely Branched-Group, Filamentous-Group and Sheet-Group; thereby supporting the hypothesis that crustose,
calcareous and thick algae have evolved antipredator defenses and should show the greatest resistance to herbivory with a
gradation of increasing palatability towards filaments and sheets. Of the 21 species examined, several (e.g.,Dictyota cervicornis on grids,Laurencia obtusa andStypopodium zonale) had exceptionally low losses to fish grazing, probably due to chemical defences. The sea urchin,Diadema antillarum, was more inclined to feed on algae with known toxic secondary metabolites than were herbivorous fishes; hypothetically related
to the differences in mobility and concomitant modes of feeding. Tough leathery forms such asSargassum polyceratium andTurbinaria turbinata resisted grazing by bottom feeding parrotfishes (Scaridae) and surgeonfishes (Acanthuridae) but were susceptible when suspended
midway in the water column, possibly due to the presence of rudderfishes (Kyphosidae) which readily consume drift Sargassaceae.
The overall tendencies support our predicted relationship between grazer-resistance and algal morphology. In conjunction with
our previously reported findings concerning primary productivity, toughness and calorimetry for many of the same species,
these results lend credence to generalizations relating form with function in marine macroalgae. |
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