“The Coral Reef Micro-Canopy”: A New Concept in Coral Ecophysiology

Terrestrial plant canopies are highly optimised photosynthetic systems. The high photosynthetic efficiency is achieved on a systems level and is the result of two characteristic traits: 1) the incident irradiance is strongly diffused and redistributed by elements of the canopy and 2) the photosynthetic apparatus is photoacclimated to the local light environment. Our recent studies of coral tissue optics and in vivo photosynthesis have revealed that similar canopy characteristics occur on a microscale within the coral tissue. In the present talk we propose the “Coral Micro-Canopy” theory. We reveal new insight into the light handling strategies of coral tissues and then show how such light management can optimise photosynthesis, both on the algal cell level and on the tissue systems level. We propose that coral tissue optical properties and Symbiodinium photoadaptation in response to local light microgradients within the tissue work in concert to optimise energy acquisition of the coral tissue system. We argue that the evolution of flexible light scattering tissues is an important feature that enables highly efficient photosynthesis in symbiont-bearing corals. The coral micro-canopy theory is discussed with respect to our basic understanding of coral ecophysiology and stress physiology.