Theses and Dissertations

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Defense Date

12-17-2004

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Bernhard Riegl

Second Advisor

Curtis Burney

Third Advisor

Robert Van Woesik

Abstract

The processes structuring coral communities involve many factors including recruitment dynamics, competitive interactions, and acute and chronic disturbances. The shallow reef at Sunabe (Okinawa, Ryukyu Islands, Japan) was dominated by a dense cover of mainly Acropora spp. until the bleaching event in 1998, when most colonies died. Subsequent monitoring of the community showed that the number of juvenile colonies was high in 2000 and competition among these colonies may affect community dynamics. The aim of this study was to determine the possibility of predicting community change and recovery, using short-term observation data of size-specific mortality and growth rates of coral recruits. Predictions were made using a demographic model based on a Leslie-matrix approach with data collected on the shallow reefs of Sunabe in 2000. This existing data showed a tendency of high mortality of competing colonies, but with no significant difference among species. Over the period of 2000-2004 percent cover of Acropora sp. increased from 16% to 22% however the number of colonies decreased (from 6.5 per quadrat to 2.5 per quadrat). The prediction of size fraction derived from the matrix population model and the observed size fraction based on the 2004 data showed some agreement; however the model predicted a high number of colonies in the largest size class. There were no adult colonies in 2000. A known bleaching event in 2002, causing mortality of reproducing adult colonies (high mortality and low growth rates) is most probably the reason for the disagreement between is the matrix model-based prediction and the observed community structure. Therefore, it is suggested that one more size class is add to the model, representing reproducing colonies. It is also suggested that further improvement of the model is needed for disturbances (such as bleaching, typhoon, and mass predation events). Despite these suggested improvements, the model presented here shows that it is possible to use simple community data taken over the course of 1 year to predict short-term community size class dynamics and population growth on juvenile Acropora spp. dominated reefs. Thus, such investigations have practical value for the management of coral resources.

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