An introduction to primary producers in the sea. who they are, what they do, and when they evolved.

This chapter examines the molecular biological issue of how water came to be oxidized and the ecological and evolutionary issues of this process, once evolved, that were appropriated and perpetuated by a wide variety of organisms living in the oceans. The chapter provides insight into what is primary production. A discussion on how photosynthesis is distributed in the oceans and the evolutionary history of primary production in the oceans are presented. Photosynthesis uses the energy of the sun to catalyze a redox reaction. The process requires an electron donor/acceptor pair. The machinery that evolved to use water as a source of reductant is the most complex energy transduction system in nature. On land, photosynthesis is dominated by a single clade derived from the charophyte green algae, the embryophytic land plants. About half of known dinoflagellate species are photosynthetic, and most of these also contain plastids derived from the red algal line. The chapter provides access to a new understanding of the organisms responsible for half of the primary production on the planet. The understanding of evolution of marine photoautotrophs has been greatly enriched in recent years as information in the fields of molecular biology, algal physiology and biophysics, paleontology, genomics, and Earth systems history have been more integrated.