The cyanobacterium Trichodesium erythraeum forms filaments (top) made up of many cylindrical cells, each about 9 micrometers (10-6 meters) wide. Hundreds of filaments form a raft-shaped colony of Trichodesium erythraeum several millimeters (10-4 meters) long (bottom). The raft is colored red because the cyanobacteria contain the red light-harvesting pigment, phycoerythrin. In calm weather, buoyant colonies rise to the surface in massive blooms that can cover thousands of square kilometers. These blooms gave the Red Sea its name. (Photos by John Waterbury, WHOI)[back]
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