MEPS 508:149-162 (2014)  -  DOI: https://doi.org/10.3354/meps10836

ABSTRACT: Light availability is a major constraint on the growth and physiological energetics of photosynthetic organisms such as reef-building corals. Despite extensive research on the mechanisms of coral photoacclimation, the extent to which the depth distributions of different species are controlled by their capacity for physiological acclimation to light availability remains unclear. This study quantified the capacity for physiological acclimation to light intensity in 4 geographically widespread and locally abundant coral species (Acropora digitifera, A. nasuta, A. millepora and A. muricata). We aimed to determine the extent of physiological plasticity of these coral species, and how variation in different physiological traits (including photosynthesis, particle feeding and symbiont density) contributed to determining their depth ranges. The results demonstrated that the capacity for short-term (9 d) physiological acclimation was generally limited for the 4 Acropora coral species. Out of the 7 physiological traits that we measured, and which are known to contribute to photoacclimation in other species, 4 did not significantly vary with light under field and laboratory conditions. Collectively, this study indicates that light availability is unlikely to set the lower depth of occurrence for branching coral species that have relatively shallow depth distributions. Furthermore the capacity for reversible plasticity in these corals appears insufficient to cover the large changes in physiology that are required to enable corals to expand their depth distributions. This study suggests that processes such as selective recruitment, depth-dependent uptake of different types of Symbiodinium and inter-specific competition are important determinants of the habitat distribution of reef corals.

KEY WORDS: Photoacclimation · Reaction norm · Fluorometry · Symbiodinium · Vertical distribution · Coral physiology