Theses and Dissertations

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Defense Date

2004

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Bernhard Riegl

Second Advisor

Andrew Rogerson

Third Advisor

Roy Houston

Abstract

Long term monitoring of coral reefs on the northwest coast of Roatán, Honduras, has documented significant changes in coral cover over a seven-year period. Twenty photographic quadrats were permanently installed at approximately 12 m depth at each of three study sites located on the northwest coast of Roatán. Photographs were taken at six or twelve month intervals from 1996 through 2003. This observation period included a massive bleaching event which began in late-September of 1998, and Hurricane Mitch which struck in October of the same year. A measurement of projected surface area (PSA, cm2) was used to estimate total coral coverage. Changes in colony number, percent cover, species diversity and recruitment of all scleractinian corals were monitored within the quadrats. During the seven-year period, living coral cover decreased significantly from 30-34% to 17-20%. This represents net losses ranging between 32% and 50%. The greatest loss occurred in the year following the bleaching event and Hurricane Mitch and was largely due to the decline of the dominant reef building species Montastrea annularis, M. faveolata, and M. franksi. These three species accounted for 56% of total hard coral cover in 1996 and only 32% at the conclusion of the observation period. A sharp reduction in the total number of living colonies in the quadrats was observed with 217 of the 532 original colonies (41%) suffering complete mortality. While 117 coral recruits were identified during this period, recruitment mortality was high (40%) with only two cases of the massive frame building Montastrea species recruiting into the photostations. A combination of at least three factors have contributed to changes in the benthic community observed during this investigation: (1) the massive coral bleaching event in the fall of 1998 which disproportionately affected Montastrea spp.; (2) a category 5 hurricane; and (3) increased anthropogenic stress in the form of sedimentation and nutrient enrichment as the result of new and unregulated development.

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