Why Sequence Reef-Building Corals and Dinoflagellate Symbionts?

Fluorescence micrograph of Acropora coral with algal symbiont

Endosymbiosis, in which a microbial partner lives within the cells of a larger host organism, has played a crucial role in shaping life on Earth from the evolution of eukaryotic organelles (mitochondria and chloroplasts), to the formation and regulation of ecosystems. In tropical marine environments, perhaps the most significant symbiosis is that between calcifying corals (scleractinian corals) and photosynthetic dinoflagellates. The presence of photosynthetic symbionts within the tissues of the host results in high levels of primary productivity as well as rapid deposition of CaCO3 that builds up to form the rock substrate of the coral reef. Thus not only are scleractinian corals key organisms in the formation of the most phylogenetically diverse of marine ecosystems, coral reefs, but they are a major component of the global carbon cycle. Gross primary productivity from coral reefs is among the highest in the tropical seas, between 300 and 5,000 gmC/m2/year (compared to 8-50 gmC/m2/year for non-reefal tropical marine environments).

The phenomenon of coral bleaching, caused by the loss of the endosymbiotic dinoflagellate, has been increasing over the past three decades, resulting in dramatic declines in coral cover and health of the reef. To address the effect of bleaching, it is essential that we begin to understand how the coral-dinoflagellate symbiosis is established and how it breaks down under conditions of environmental stress. This CSP project calls for sequencing a total of 128,000 ESTs from cDNA libraries constructed from Acropora palmata, Montastraea faveolata, Symbiodinium clade A that infects A. palmata, and Symbiodinium clade B that infects M. faveolata. The results will benefit researchers interested in a wide diversity of questions: symbiosis, disease, ecotoxicology, developmental genetics, comparative genomics, and the evolutionary biology of corals. A broader scope of scientists interested in basal metazoan genomics (several of these genomes are being sequenced at the JGI and by NIH) and in marine algal genomics (several also sequenced or being sequenced at the JGI -- diatoms, coccolithophores, and red and green algae) will also benefit from this sequencing effort.

Principal Investigators: Mónica Medina (Univ. of California, Merced), Alina Szmant, (Univ. of North Carolina, Wilmington), Mary Alice Coffroth (State Univ. of New York, Buffalo), and Jodi Schwartz (Vassar College).