Sun and shade differences in productivity of reef corals

Abstract

REEF CORALS are mutualistic symbiotic associations between cnidarians and dinoflagellates. The algae photosynthesise and translocate photosynthate to the animal partner, although the animal is capable of heterotrophic nutrition^1–5. Some reef corals have wide bathymetric ranges^6,7 and the growth and survival of individuals in the deeper regions of the euphotic zone could result from an increase in the energy efficiency of the symbiotic complex. A number of reports document the laboratory-determined photosynthesis-radiation responses of corals^8–12 and zooxanthellae¹³, but because the details of the habitat or depth from which the animals were collected are rarely described, comparisons among results in the literature are difficult. Here we provide evidence for the existence of ‘sun’ (heliophytic) and ‘shade’ (sciophytic) differences in the net photosynthesis-radiant flux intensity response of individuals of one coral species from 10 and 25 m depth on the same reef in an atoll lagoon.