Effects of Sedimentation Stress on Ultrastructure and Calcification in Montastraea cavernosa

Abstract

Montastraea cavernosa is an important scleractinian reef-building coral, commonly found throughout South Florida and the Caribbean. The proximity of Florida reef communities to the coast, particularly in Southeast Florida raises concern for the health of corals due to increased sedimentation from beach restoration, coastal development, dredging, and related activities. The effect of sedimentation on this species was investigated histologically in a series of laboratory experiments designed to assess cellular-level stress related to sanding. The purpose of this study was to investigate early assessment of stress in corals based on changes in ultrastructure and calcification. TEM examination of the coenosarc tissue from laboratory-sanded, control, and field-collected corals revealed ultrastructural changes, particularly in sanded corals. These included: 1. Vacuolization, cilia deterioration, and focal necrosis of epidermal cells congruent with histological observations; 2. Swelling and thickening of the gastrodermal layer, concomitant with increased numbers of zooxanthellae and mucocytes; 3. Deterioration and attenuation of the calicoblastic epithelium; 4. Appearance of spirocysts in atypical locations, including the gastrodermis and calicoblastic epithelium; and 5. Changes in zooxanthellae diameter, and variability in size of starch-filled vacuoles and accumulation bodies. Amoebocyte-type cells phagocytizing bacteria were observed in the epidermal tissue of several corals, including sanded, control, and field specimens. It is not known whether the bacteria are normal endosymbionts or represent a pathologic condition. SEM examination of the coral skeletal components revealed changes in septa morphology, septal ornamentation, and crystal morphology. Effects of sedimentation on calcification may be related to several factors including energy allocation and the relationship between the corals and their zooxanthellae symbionts. This methodology potentially provides a tool to assess stress in living corals before gross tissue changes occur. Changes in skeletal morphology in dead/fossil representatives may provide a useful indicator of past conditions. This study represents ongoing research directed at advancing our ability to detect and assess physiological stress in corals