Surface phytoplankton populations, that persist for several weeks and over spatial scales > 100 km, can be monitored most effectively by satellite. We show how the Coastal Zone Color Scanner provides new information about the dynamics of dinoflagellate blooms, and discuss some problems with the application of the instrument. The estimated overall accuracy for measuring total chlorophyll, C (chlorophyll a + phaeopigment), by satellite was log C ±0.26.