Meeting Abstract
The effect of elevated temperature and illumination is examined in three species of alcyonacean octocorals, Phenganax parrini, Sarcothelia sp., and Sympodium sp. A microscopic analysis of symbiont (Symbiodinium spp.) location and counts demonstrated that the three host species generally responded similarly to perturbation, with decreased numbers of symbionts in the tissue and increased numbers in the gastrovascular system. Only a small proportion of symbionts were expelled, and variable mortality and retention was found (≈84.6, 0, and 52.7% of the initial number of Symbiodinium died and ≈15.4, 100, and 45.4% were retained by P. parrini, Sarcothelia sp., and Sympodium sp., respectively). The variation in the response to perturbation between the three species could be due to host and symbiont genetic differences, or host architectural differences, or both. Mitochondrial (mtMutS and COI) and nuclear (28S rDNA) gene sequences showed that Sympodium sp. and Sarcothelia sp. are closely related xeniids but are only distantly related to P. parrini. Sympodium sp. and Sarcothelia sp. host Symbiodinium type D1a, while P. parrini have type B1. Following considerable symbiont movement within the colonies, the three octocoral species retained high densities of symbionts (>2.07 x 105 per mm2) in the coenenchyme. This investigation is currently being extended to other species selected for their phylogenetic relevance, e.g. Briareum sp. and Stylophora sp.
