The global, complex phenomena of harmful algal blooms

Marine and fresh waters team with life,much of it microscopic, and most of itharmless; in fact, it is this microscopiclife on which all aquatic life ultimatelydepends for food. Microscopic algaealso play an important role in regulatingatmospheric CO2 by sequestering itduring production and transporting itto deeper waters. Yet some of the microscopic“algae” cause problems when theyaccumulate in sufficient numbers, dueeither to their production of endogenoustoxins, or to their sheer biomass or eventheir physical shape. These are known asthe harmful algae, or, when in sufficientnumbers, harmful algal blooms (HABs).These blooms were formerly called “redtides” because many were composed ofdinoflagellates containing red pigmentsthat in high densities colored the waterred, but blooms may also be green, yellow,or brown, depending on the typeof algae present and their pigmentation. As with all blooms, their proliferation results from a combination ofphysical, chemical, and biological mechanismsand their interactions with othercomponents of the food web that are forthe most part poorly understood. MostHABs are dinoflagellates or cyanobacteria,but other classes of algae, includingdiatoms, have members that may formHABs under some conditions. As statedby J. Ryther and co-workers many yearsago, “...there is no necessity to postulateobscure factors which would account fora prodigious growth of dinoflagellates toexplain red water. It is necessary only tohave conditions favoring the growth anddominance of a moderately large populationof a given species, and the properhydrographic and meteorological conditionsto permit the accumulation of organismsat the surface and to effect theirfuture concentrations in localized areas”(Ryther, 1955).

Author Posting. © Oceanography Society, 2005. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 18, 2 (2005): 136-147.

Funding for these activities has been provided byNSF, NOAA, and the European CommissionDG Research-EnvironmentDirectorate. GEOHAB is an initiative ofSCOR (Scientific Committee on OceanicResearch) and IOC (IntergovernmentalOceanographic Commission of UNESCO).P. Glibert and D. Anderson werefunded by the National Oceanic andAtmospheric Administration (NOAA),ECOHAB, MERHAB and NSF.