Fig. 8.2.

Typical characteristics of photosynthetic processes occurring in marine organisms. (A) Typical photosynthetic curve showing how the rate of photosynthesis increases with light intensity until it matches the respiratory rate at the compensation irradiance (IC) and eventually saturates at the net maximum rate of photosynthesis (PN max). At this point, the maximal gross photosynthetic rate (PG max) can be calculated from the sum of PN max and the respiration rate (R). The saturation irradiance (Ik) is a measure of the irradiance at which the photosynthetic rate is maximised. The efficiency with which light is converted into photosynthetic production is measured by the photosynthetic efficiency (α). If light levels continue to increase, the net rate of photosynthesis may decrease due to photoinhibition. (B) Organisms may acclimate or adjust physiologically to different light environments. In high light acclimated organisms, maximum rates of photosynthesis will be higher, while photosynthetic efficiencies will be lower. The opposite is true in organisms that have acclimated to living in low light conditions. (C) A typical pattern over time associated with the activity of a photosynthetic organism on a reef (net photosynthetic rate per hour). At night time, respiration dominates. At dawn, photosynthetic activity begins to increase as light levels rise until they achieve maximum levels of both light and photosynthetic activity at midday (Figure: D. Kleine and O. Hoegh-Guldberg).