THE SIGNIFICANCE OF MICROALGAL BLOOMS FOR FISHERIES AND FOR THE EXPORT OF PARTICULATE ORGANIC-CARBON IN OCEANS

Microalgal blooms are rapid increases in biomass, caused by locally enhanced primary production and resulting in abnormally high cell concentrations. Hydrodynamical processes may control blooms through the agency of irradiance and/or nutrients. In the oceans, phytoplankton blooms primarily governed by irradiance include the spring outburst, as well as the ice-edge, under-ice, winter, upwelling and estuarine blooms. Those primarily governed by nutrients comprise the tidal, summer, episodic and exceptional blooms. In addition, there are blooms of ice microalgae. Blooms reflect low recycling, and a large degree of uncoupling between increased primary production and grazing by zooplankton. As a consequence, they often result in high sedimentation of intact cells and faecal pellets. Microalgal blooms provide unique information on the potential fate (and not on the rate) of primary production in marine ecosystems. They have major effects on benthic and pelagic food webs, and are an essential condition for the great fisheries of temperate seas (Cushing, 1989). On the other hand, blooming systems have a high potential for exporting particulate organic matter from the euphotic layer, and thus provide unique information for the study of global fluxes of carbon in the marine environment. © 1990 Oxford University Press.