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Date of Award


Document Type


Degree Name

Master of Science (M.S.)


Graduate Studies

First Advisor

Steven Obrebski

First Committee Member

William B. Gladfetter

Second Committee Member

E. H. S[?]


Diadema antillarum (Philippi) is a common echinoid grazer in Caribbean reef areas. Field observations in st . Croix, u.s.v.r. an.d Disc. overy Bay, Jamaica and laboratory experiments demonstrate that these urchins have a strong feeding preference for algal turf. Seasonal variation in the abundance of this preferred food item results in increased incidences of live coral predation. Experimental manipulations demonstrate that over the short term food availability is more important than urchin density in determining prey item choice. Size and abundance data show an inverse relationship between urchin density and mean individual urchin size. There is also an inverse relationship between urchin density and algal turf abundance. This relationship is also shown experimentally as well as the effects of urchin grazing intensity on algal primary productivity and the numbers of algal species surviving. Tagging experiments demonstrate that homing behavior exists for these urchins. A simple model is presented to summarize factors regulating Diadema populations and their effects on the benthic algal community.



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