An examination of the effects of environmental stresses on stony corals
Lewis, Sarah Kathryn
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Understanding threats to a resource may allow development of management techniques to limit resource degradation. I chose to examine the impact of four threats on stony corals; elevated ultraviolet radiation, elevated visible irradiance, elevated salinity, and elevated temperature. Colonies of the Pacific stony coral Montipora verrucosa were exposed to elevated ultraviolet radiation and elevated visible irradiance by transplanting them from 10m depth to an in-situ respirometer at 0.5m depth. The corals were exposed to full sun or 30% sun, with and without elevated ultraviolet radiation. Corals exposed to elevated ultraviolet radiation exhibited decreased photosynthesis and chlorophyll levels, but no change in respiration, suggesting that ultraviolet radiation may be more damaging to photosynthetic algae than coral tissue. No change was seen in the UV absorbing compounds, mycosporine-like amino acids, suggesting that longer exposure times to elevated ultraviolet radiation are necessary before changes occur. Stony corals that were photoadapted to low visible light levels exhibited decreased maximum photosynthesis rates, respiration rates, and photosynthetic efficiency following acute exposure to dramatically increased visible irradiance. These results suggest that increased visible irradiance was detrimental to both the photosynthetic algae and to the coral tissue. Colonies of the Atlantic stony coral Montastrea annularis were monitored during exposure to elevated salinities of 40‰, 45‰, and 60‰. As salinity levels increased, algal photosynthesis decreased but coral respiration increased. Chlorophyll concentration was also reduced by exposure to elevated salinities. These effects were more pronounced the higher the salinity and the longer the exposure. Furthermore, this study revealed a threshold lethal salinity, since corals exposed to 40‰ or lower survived, while corals exposed to 45‰ or higher all eventually died. Montastrea annularis was also exposed to elevated temperatures of 33 o C and 36 o C while metabolic measurements were collected. These corals showed decreased photosynthesis and photosynthesis to respiration ratios. Chlorophyll levels were also lower in corals exposed to elevated temperatures. These effects were more pronounced the higher the temperature and the longer the exposure. These results indicate that corals respond dramatically to short-term exposures to these environmental stressors, suggesting that these conditions do not need to persist for long before damage occurs.