Simultaneous and sequential stress from increased temperature and copper on the metabolism of the hermatypic coral Porites cylindrica

Stressors arising from human activities may interact not only with each oth er, but also with natural disturbances. However, experimental studies on di sturbance complexity and physiological responses of corals to sublethal str esses, especially those due to human activities, are surprisingly few. In t his study we investigated the stress response of the scleractinian coral Po rites cylindrica after 24 h of exposure to copper (11 mug Cu 1(-1)) and inc reased temperature (following a 4 degreesC above-ambient curve), separately and in combination. We also investigated the effect of sequential stress w here corals pre-exposed to increased temperature for 24 h were exposed to c opper (for 24 h) after a 5-day recovery period. Changes in gross primary pr oduction (Pg: per milligram chlorophyll a per hour) and respiration (R:per square centimeter per hour) in terms of dissolved oxygen were used as indic ators of stress. The results show that heat and the combination of heat and copper significantly reduced production rate. However, corals er,posed to elevated temperature displayed a significantly higher production rate follo wing the 5-day recovery period. The combination of the two stressors showed no additive or synergistic effects. Copper alone had no effect on the prod uction rate. However, corals that were pre-exposed to increased temperature and again exposed to copper after 5 days displayed a significant reduction in production rate. The respiration rate was significantly reduced by all treatments, although no significant differences between treatments were det ected. The results presented here illustrate how a stressor that does not a ffect corals when acting in isolation may do so in sequential combination w ith other stressors.