Coral-Zooxanthellae Symbiosis – Environment: Light & Water Depth

The productivity of the zooxanthellae is also largely dependent on environmental factors including, significantly, the amount of light penetrating the corals and reaching the dinoflagellates. Productivity is proportional to increasing light intensity, although it peaks when productivity becomes independent of light intensity. This explains why corals only inhabit relatively shallow coastal regions – light intensity in deep water is not great enough to permit photosynthesis within the zooxanthellae and in turn the corals themselves cannot be supported. However the depth that corals can survive is also dependent on the clarity of the water. Corals are found living at a depth of 100m in reefs in Jamaica for example, but only 12m in certain reefs in Puerto Rico. Different species of zooxanthellae are however adapted differently to cope with light intensities in varying habitats, for example zooxanthellae that specialise in slightly deeper water have more photosynthetic pigments in order to absorb more light for photosynthesis.