Theses and Dissertations

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Defense Date

12-2007

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Bernardo Vargas-Angel

Second Advisor

Bernhard Riegl

Third Advisor

Curtis Burney

Abstract

Traditional coral reef monitoring efforts lack assessment of coral health at tissue and cellular levels. This thesis investigated tissue, cellular, and gross morphological responses of the Caribbean staghorn coral, Acropora cervicornis, to elevated sedimentation and phosphate using state-of-the-art histological techniques. Branch fragments of A. cervicornis were collected offshore Broward County, FL, acclimated for 12 weeks, subjected to a 4-week experimental period, and given a 1-week recovery period in laboratory aquaria. Treatments consisted of high doses (200 mg cm-2 day-1) of sedimentation (S), phosphate (4 μM) (P), and a combination of these two (S + P), in addition to control conditions (C). Specimens were observed and photographed for gross morphological appearance. One specimen per tank was sacrificed for histological purposes weekly. Specimens were also sacrificed in the field and during acclimation for baseline comparison.

The following gross morphological changes were more common in treatments relative to acclimated and control specimens: polyp retraction, discoloration (including palor and/or bleaching), excess mucus, and loss of white apical tips. For sanded treatments, sediment-clearing rates declined from ≤ 2 hours to up to 24 hours after four weeks of daily exposure. After the recovery period, all remaining specimens showed slight improvement in gross morphological appearance.

Degenerative histopathological changes in the epidermis included attenuation, decreased abundance and atrophy of mucocytes, and loss of cellular architecture. In the gastrodermis, attenuation, mucocyte swelling followed by atrophy, compromised integrity and reduced densities of zooxanthellae, and necrosis were observed. In the calicoblastic epidermis, mucocyte swelling (S, S + P only) and an increase in eosinophilic granules were noted. In the mesenteries, changes included loss of gonad development, loss of basophilia, dissociation and/or necrosis of filaments and cnidoglandular bands.

Quantitative histological measurements in the oral epidermis revealed significantly different decreases in mucocyte abundance with exposure to treatments and additive or synergistic effects of sand and phosphate. Semi-quantitative results were obtained by separately ranking 16 histologic parameters within major coral tissue types. Ranks of each parameter were combined to give a histopathologic condition score for each specimen. Median condition scores for each treatment increased during Weeks 1 to 4, and significant differences were found between treatments in Weeks 1 to 3. Highest scores consistently appeared in S and/or S + P treatments throughout Weeks 1 to 4. Histopathological responses and severity of changes were similar for all treatments, without a clear additive or synergistic effect in the S + P treatment. During the recovery period, the P treatment continued to decline in overall tissue condition, while S and S + P treatments showed signs of tissue recovery. Acclimated and control corals also exhibited similar, yet less severe, patterns of gross morphologic and histopathologic alterations, indicating tank effects. Changes described at organismal, tissue, and cellular levels in this study were indicative of compromised health of coral specimens and may aid future health assessment and monitoring of critical populations of A. cervicornis in Florida and the greater Caribbean, with additional applications to the fields of coral stress and disease.

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