Abstract
A popular Guam beach experienced a temporary closure in May 1994 due to the simultaneous occurrence of a blue-green algal bloom and a massive die-off of juvenile rabbitfishes ( Siganus argenteus (Quoy and Gaimard) and Siganus spinus (Linnaeus). The microbial assemblage was composed primarily of the marine cyanobacterium Schizothrix calcicola (Ag.) Gomont with sparsely distributed strands of Lyngbya majuscula Gomont. Palatability of the crude organic extract of this mixed cyanobacterial assemblage was evaluated in feeding assays using the parrotfish Scarus schlegeli (Bleeker) and the sea urchin Echinometra mathaei (Blainville) in outdoor tanks on Guam. Bioassay-guided fractionation resulted in the isolation of ypaoamide, a new broadly-acting feeding deterrent compound. At natural concentrations, ypaoamide deters feeding by juvenile rabbitfishes ( S. spinus and S. argenteus), the parrotfish S. schlegeli, and the sea urchin E. mathaei. We propose that the production of deterrent secondary metabolites by this benthic cyanobacterial assemblage and other similar microbial assemblages facilitates the formation of cyanobacterial blooms on coral reefs surrounding Guam.
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