Chemical communication

The settlement of coral larval is crucial to reef construction. While the origin of larval settlement cues is understood in a broad sense (it comes from chemicals emitted by crustose coralline algae and/or their associated bacteria) the details are unknown.

Just two years after establishing a small team to investigate this problem, including collaborators from the University of New South Wales, the group has identified and purified the first chemical signal from bacteria that induces larval metamorphosis of acroporid coral larvae.

The metamorphic cue was identified as tetrabromopyrrole (TBP) and was produced by just four Pseudoalteromonasstrains among a culture library of 225 bacterial isolates obtained from the surfaces of crustose coralline algae. The lowest density from one of the strains that induced metamorphosis was just 7,000 cells mm-2 in assays, which represents just 0.1-1 per cent of the total numbers of bacteria typically found on such surfaces; equivalent to finding "a needle in a haystack".

This break through result was published in the prestigious international journal, PLOS Onein 2011 but left the team with more work to do. While the potent chemical inducer caused coral larvae to transform into fully developed polyps in hours, only a small proportion of these polyps were successful in attaching to the substratum. As with all good stories, there is more to come.