C. B. Field, Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305, USA. M. J. Behrenfeld and P. Falkowski, Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901–8521, USA. J. T. Randerson, Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305, USA, and Department of Biological Sciences, Stanford University, Stanford, CA 94305, USA.