Date of Award

8-2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Robert S. Steneck

Second Committee Member

James M. Acheson

Third Committee Member

Les Kaufman

Abstract

Coral reefs worldwide are threatened by high algal abundance due to cumulative anthropogenic disturbances such as overfishing, climate change, and pollution. Scraping herbivore functional groups (particularly of the family Scaridae) can reduce algal biomass and improve coral reef condition by increasing recruitment and reducing mortality of corals. However, territorial damselfishes reduce herbivory and cultivate filamentous turf algae, thereby creating patches of elevated algal biomass. I examined the negative effects of damselfish aggression on the processes of herbivory. Research was conduced on Bonaire, Netherlands Antilles where damselfish abundance is high relative to a reef observed at Carrie Bow Caye, Belize. The negative interaction of damselfishes on grazing behavior by other herbivores and the resulting increases in turf algal abundance was shown to be highest in the center of a territory where defensive activity is greatest. The area of damselfish influence was mapped to determine the ecological effect based on damselfish body size, density, and spatial distribution. Damselfish territories occupy a considerable area of the reef substrate on Bonaire, with up to 25% of the reef covered by the highly defended territory centers. Compared to other reefs in the Caribbean with lower densities of damselfishes and lower live coral cover, this leaves little space available for potentially settling corals. However, due to the beneficial services of a robust population of parrotfishes (family: Scaridae) on Bonaire, algae abundance remains low on reef substrate outside damselfish territories and overall live coral cover is high. I also sought to quantify interaction strength of territorial damselfish aggression on the process of herbivory as it relates to sizes of the functionally important scarids. Bonaire's reefs have the lowest known algal biomass and an abundance of particularly large stoplight and queen parrotfishes and compared to more heavily fished reefs at Carrie Bow Caye, Belize. Bite rates made by the predominant herbivores (scarids) were differentially affected by damselfish aggression (identified by their bite and chase rates). While herbivory from the smallest scarids (i.e.,less than 20 cm, FL) was significantly depressed, the damselfish negative interaction strength was lower among larger size classes of scarids with the largest scarids being unaffected by damselfish aggression (p

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