Photosynthetic marine microalgae, particularly the relatively few species that form massive blooms, are responsible for half of total global carbon fixation on the order of 45-50 billion tons of production annually. The chlorophyll c-containing haptophyte alga genus Phaeocystis is distributed globally and forms massive blooms that structure planktonic ecosystems, export significant amounts of materials to the seafloor, and produce prodigious amounts of the important climate gas dimethylsulfoniopropionate (DMSP). Phaeocystis exhibits life cycle alternations between solitary cells and gelatinous colonies. These transitions caused by systems stresses, whether abiotic or biotic, restructure entire food webs and prompt adjustment of a variety of ecosystem characteristics ranging from nutrient utilization to trophic energy transfer to vertical export of salient elements. Because Phaeocystis can account for as much as 85% of total production, transitions into the colonial morphotype provoke substantial alterations in the flow of energy and nutrients away from food webs supporting fisheries to those fueling more regenerative detrital pathways. In addition to ecological considerations Phaeocystis occupies a supremely interesting and poorly understood position within the tree of life. This project will construct 10 ecologically and geochemically relevant cDNA libraries to which we will synergistically apply the strengths of traditional Sanger and powerful 454 FLX sequencing technology. The data will have immediate value in terms of uncovering unrecognized research directions as well as provide a firm foundation for complete genome sequencing and more advanced genome-enabled biology. Comparative analysis of genomic data provides a powerful tool for gaining insights about the biochemistry, physiology, evolution, and ecology of extant alga groups.