Comparison of the response of in hospite and ex hospite Symbiodinium to elevated temperature

ABSTRACT Corals exhibit different responses to increasing temperature but it remains unclear whether this is determined exclusively by symbiont type or by intrinsic properties of the host. Here, we investigated the response to elevated temperature of symbionts of the same ITS2 type from three acroporid species from Bolinao, northwestern Philippines. Maximum quantum yield (Fv/Fm) of PSII was measured in symbionts subjected to 26°C (average winter temperature) and 31°C (average summer temperature) for up to 48 hrs. Greater reduction in Fv/Fm was observed for ex hospite than for in hospite symbionts. However, no significant differences in response could be discerned for symbionts associated with or originating from the different acroporids. Thus, while these findings confirm that the coral host can protect in hospite symbionts from temperature perturbations, for the acroporids in this study, there is still no evidence that host type confers differential thermal susceptibility to the symbionts or to the coral holobiont.