Photo-acclimation of the hermatypic coral Stylophora pistillata while subjected to either starvation or food provisioning

This study investigated the photo-acclimation capacity of the coral Styloph ora pistillata (Esper). Outer branches of coral colonies, taken from 2 m, w ere subjected to 90, 20, or 3% of incident surface photosynthetic active ra diation (PAR(0)), or kept in total darkness. The corals were maintained eit her in filtered seawater (i.e., under starvation), or in seawater that had daily additions of zooplankton (rotifers). The experiments were maintained for 31 days. Zooxanthellae population densities and chlorophyll concentrati ons increased in S. pistaillata fragments subjected to 20 and 3% PAR(0). Th e zooxanthellae densities decreased after 6 days in corals kept in total da rkness, although chlorophyll concentrations remained higher. Corals that we re fed and subjected to 90% PAR(0) showed lower degrading zooxanthellae fre quencies, higher photosynthetic and respiration rates, and higher chlorophy ll concentrations than corals in the same light regime under starvation. Co mplete acclimation to dim (20% PAR(0)) and low (3% PAR(0)) light was only a pparent for corals fed with zooplankton. Changes in zooxanthellae populatio n densities occurred through differential rates of zooxanthellae division a nd degradation. (C) 2001 Elsevier Science B.V. All rights reserved.