Stress Response in Montastraea cavernosa as a Result of Sediment Loading: Quantitative Histological and Ultrastructural Analysis

• Main Author: Miller, Aaron
• Format: Others
• Published: NSUWorks 2006
• Subjects: Marine Biology; Oceanography and Atmospheric Sciences and Meteorology
• Online Access: http://nsuworks.nova.edu/occ_stuetd/270; http://nsuworks.nova.edu/cgi/viewcontent.cgi?article=1126&context=occ_stuetd

This study investigates the effects of sediment stress on tissue and cellular structure in the cultured coral Monastraea cavernosa. The goal of this research is to quantify fine and ultrastructural data and examine potential correlation between sediment stress and changes in coral tissues and associated zooxanthellae dinoflagellate cells. An experiment in which colonies of this species were exposed to sediment stress provided the samples for this study (Vargas-Angel et al., in press). In that experiment, sediment stress was induced by the application of sediment (approximately 200-225 mg/cm2) twice daily over a four-week period. At the end of each week, a colony from each experimental tank was sacrificed and prepared for histological analysis. In the present study the paraffin blocks from this experiment were re-sectioned and stained for additional analysis. The sections were then examined for variability in the following stress parameters: 1) Symbiotic zooxanthellae and mucosecretory cell size (coenosarc, oral disk, and the middle polyp), 2) Epithelium thickness (coenosarc and oral disk), and 3) Zooxanthellae mitotic index (cell doublets) of cells (coenosarc and oral disk). Transmission electron microscopy (TEM) was also utilized for an ultrastructural study of coenosarc tissue and associated zooxanthellae. These included: 1) Zooxanthellae size comparisons with cells assessed using histological measurements, 2) Zooxanthellae accumulation vacuole size, and 3) Zooxanthellae nuclei chromosome bundle number. Significant differences were found in the tissues and cells examined from different areas of the polyp as well as with duration of sanding treatment. In sanded corals, zooxanthellae, mucosecretory cell sizes, and the mitotic index increased significantly through week three, and decreased significantly in week four. In addition, the epithelium thickness decreased significantly throughout the study and indicates that sedimentation causes atrophy (thinning) of the epithelium. Sediment stress related increase in mucosecretory cell (MSC) size indicates that coral mucus production increased under sediment stress. This increase in MSC cell size is correlated with subsequent increase in both zooxanthellae size and mitotic index. These effects may be a result of nutrient enrichment due to the chemistry of the mucus. In addition, this study also demonstrates that zooxanthellae sizes are distinct in different areas of the polyp and may respond differently to sanding stress. Therefore, current protocols for extracting zooxanthellae from corals, which results in combining cells from several sections of the polyp, may not discriminate tissue-specific zooxanthellae characteristics. Future culture-work in which examination of mucus related nutrient enrichment effects, and ultrastructural/ biochemical tissue-specific characteristics of the zooxanthellae are proposed.