Photoacclimation mechanisms of corallimorpharians on coral reefs: Photosynthetic parameters of zooxanthellae and host cellular responses to variation in irradiance

Baraka Kuguru, Yair Achituv, David F. Gruber, Dan Tchernov

Research output: Contribution to journalArticlepeer-review


Rhodactis rhodostoma and Discosoma unguja are the most common corallimorpharians on coral reefs in the northern Red Sea, where individuals of R. rhodostoma form large aggregations on intertidal reef flats and those of D. unguja occupy holes and crevices on the reef slope. Aside from these contrasting patterns of microhabitat, little is known concerning their mechanisms of photoacclimation to environmental conditions. We demonstrate here that different mechanisms of photoacclimation operate in both species and that these differences explain, in part, the contrasting patterns of distribution and abundance of these common corallimorpharians. Experimental exposure of the species' respective polyps to the synergistic effects of ultraviolet and photosynthetically active radiation revealed that endosymbiotic zooxanthellae protected the host R. rhodostoma from photooxidation damage. Zooxanthellae do so by reducing their chlorophyll pigment and cellular abundance, as well as by adjusting their efficiency of light absorption and utilization according to the level of irradiance. The host photoprotects its endosymbionts from harmful ultraviolet radiation (UVR) by synthesizing enzymatic antioxidants against oxygen radicals. In contrast, individuals of D. unguja utilize a behavioral mechanism of photoacclimation in which they physically migrate away from exposed areas and towards shaded habitats and thus avoid the damaging biological effects of UVR. We conclude that a combination of physiological and behavioral mechanisms appear to control microhabitat segregation between these corallimorpharian species on tropical reefs. These various mechanisms of local adaptation to environmental conditions may be largely responsible for the wide distributional ranges of some corallimorpharians, and may enable these common reef organisms to tolerate environments that are highly variable, both spatially and temporally.

Original languageEnglish
Pages (from-to)53-62
Number of pages10
JournalJournal of Experimental Marine Biology and Ecology
Issue number1-2
StatePublished - Oct 2010

Bibliographical note

Funding Information:
We gratefully acknowledge the staff and students of Dan Tchernov and Maoz Fine of the Interuniversity Institute for Marine Sciences in Eilat for technical assistance in various aspects of field and laboratory studies. We also thank Gal Dishon for spectral irradiance measurements and Beverly Goodman for assistance in manuscript preparation. This research was supported by funds from the Bar-Ilan University , Auburn University , City University of New York , Baruch College , the Interuniversity Institute for Marine Sciences in Eilat and Israel Science Foundation grant (# 981/05 ). We also wish to thank the US National Science Foundation grant (# 0920572 ). This research was submitted in partial fulfilment of the requirements for a doctoral degree by B.K. at Bar-Ilan University. Experiments performed in this study complied with the current laws of Israel. [SS]


  • Corallimorpharians
  • Microhabitat
  • Photoacclimation
  • Photosynthesis
  • Ultraviolet radiation
  • Zooxanthellae

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science


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