DOI 10.1007/s00227-007-0806-xRESEARCH ARTICLE Inter-polyp genetic and physiological characterisation of Symbiodinium in an Acropora valida colony

Abstract Corals harbouring genetically mixed communi-ties of endosymbiotic algae (Symbiodinium) often show distribution patterns in accordance with diVerences in light climate across an individual colony. However, the physiol-ogy of these genetically characterised communities is not well understood. Single stranded conformation polymor-phism (SSCP) and real time quantitative polymerase chain reaction (qPCR) analyses were used to examine the genetic diversity of the Symbiodinium community in hospite across an individual colony of Acropora valida at the spatial scale of single polyps. The physiological characteristics of the polyps were examined prior to sampling with a combined O2 microelectrode with a Wbre-optic microprobe (combined sensor diameter 50–100 m) enabling simultaneous measurements of O2 concentration, gross photosynthesis rate and photosystem II (PSII) quantum yield at the coral surface as a function of increasing irradiances. Both sun-and shade-adapted polyps were found to harbour either Symbiodinium clade C types alone or clades A and C simultaneously. Polyps were grouped in two categories according to (1) their orientation towardps light, or (2) their symbiont community composition. Physiological diVer-ences were not detected between sun- and shade-adapted polyps, but O2 concentration at 1,100 mol photons m¡2 s¡1 was higher in polyps that harboured both clades A and C symbionts than in polyps that harboured clade C only. These results suggest that the acclimatisation of zoo-xanthellae of individual polyps of an A. valida colony to ambient light levels may not be the only determinant of the photosynthetic capacity of zooxanthellae. Here, we found that photosynthetic capacity is also likely to have a strong genetic basis and diVers between genetically distinct Symbiodinium types