BreveBusters optically detect Karenia brevis blooms by comparing light absorption by particles in ambient water to the light absorption fingerprint that is characteristic of K. brevis. That comparison yields a Similarity Index (SI) which is related to the fraction of phytoplankton community biomass contributed by K. brevis. Values of SI below 0.5 indicate less than 10% K. brevis, values over 0.8 indicate greater than 90% K. brevis.