Community change in the algal endosymbionts of a scleractinian coral following a natural bleaching event on the Great Barrier Reef

The symbiont community of 460 randomly sampled colonies of Acropora millepora from a reef flat adjacent to Miall Island (Keppel Islands, Great Barrier Reef) were analysed after a natural bleaching event in early 2006.

To determine the Symbiodinium community composition, 460 colonies were tagged on the reef flat at Miall Island between September 2004 and March 2005. A combination of single-stranded conformation polymorphism (SSCP) analysis, cloning and DNA sequencing was used for symbiont identification. Symbionts were: the thermally sensitive Symbiodinium type C2, a tolerant Symbiodinium type belonging to clade D, mixtures of C2 and D, and C1. Background types were also recorded.

A subset of 79 colonies that survived the bleaching 3 and 6 months (May and August, respectively) after the bleaching event in January/February 2006 were examined for symbiont changes. These colonies were chosen haphazardly from surviving colonies and comprised 58 with predominantly C2-type, 15 with predominantly D-type and 6 with both C2 and D types present.

Mortality in the Acropora millepora population was assessed 6 months after the bleaching event in August 2006 by visually estimating the percentage (<10%, 11-50%, 51-99%, 100%,) of live and dead coral tissue on 159 haphazardly chosen tagged colonies using pre-bleaching photos of each colony as a reference.

To characterize the Symbiodinium community in an inshore population of Acropora millepora and compare the Symbiodinium community in the same tagged colonies before and after a natural bleaching that took place in 2006.

The first field study to follow changes in Symbiodinium genotypes in specific colonies over a 3 year period that includes a natural bleaching event.