From 60 to 80 species of phytoplankton have been reported to be harmful; of thcsc, 90% are flagellates, notably dinoflagellates. The effects of turbulence on harmful algal bloom (HAB) taxa, their photoadaptive strategies, growth rate, and nutrient uptake aFlinity (K,) are considered. Flagellates, including HAB taxa, collectively have a lower nutrient uptake affinity than diatoms. Four major adaptations are suggested to have been evolved to offset the ecological disadvantages of their low nutrient affinity: nutrient retrieval migrations; mixotrophic tendencies; allelelochemically enhanced interspecific competition; and allelopathic, antipredation defense mechanisms. Motilitybased behavioral features of flagellates contributing to their blooms include: phototaxis, vertical migration, pattern swimming, and aggregation, which facilitate nutrient retrieval, trace metal detoxification, antipredation, depth-kceping, and turbulence avoidance. Neither a general physiological syndrome nor distinctive physiological profile distinguishes harmful flagellate species from nonharmful taxa. However, HAB tlagcllates exhibit significant ccophysiological differences when compared to diatoms, including greater biophysical vulnerability to turbulence, greater bloom dependence on water-mass stratification, grcatcr nutritional diversity involving mixotrophic tendencies, greater potential use of allelochemical mechanisms in interspecific competition and antipredation defenses, and unique bchaviorial consequences of their motility. Flagellates USC a "swim" strategy; diatoms a "sink" strategy.About 300 (7%) of the estimated 3,400-4,100 phytoplankton species have been reported to produce "red tides," including diatoms, dinoflagellates, silicoflagellates, prymnesiophytes, and raphidophytes (Sournia 1995). Excluding diatoms decreases this number to -200; moreover, most red tide spccics do not produce harmful blooms. Only 60-80 species (2%) of the 300 taxa are actually harmful or toxic as a result of their biotoxins, physical damage, anoxia, irradiance reduction, nutritional unsuitability, etc. Of these, flagellate species account for 90% and, among flagellates, dinoflagellates stand out as a particularly noxious group. They account for 75% (45-60 taxa) of all harmful algal bloom (HAB) species. The exceptional importance of dinoflagellates is further evident from their pm-eminence among the species, perhaps 10-12, primarily responsible for the current expansion and regional spreading of HAB outbreaks in the sea (Anderson 1989; Hallegraeff 1993;Smayda 1989a Smayda , 1990.Harmful algal taxa may be nonmotile or motile; pica-, nano-, or larger sized; photoautotrophic, mixotrophic, or obligate heterotrophs; siliceous or nonsiliceous species, etc., and have diverse modes of inimical action. The considerable physiological and phylogenetic diversity represented in the phytoplankton in general, and among HAB species in particular, prompt a basic question: what cellular processes and environmental mechanisms select for which HAB species, or s...

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Climate change pressures will influence marine planktonic systems globally, and it is conceivable that harmful algal blooms may increase in frequency and severity. These pressures will be manifest as alterations in temperature, stratification, light, ocean acidification, precipitation-induced nutrient inputs, and grazing, but absence of fundamental knowledge of the mechanisms driving harmful algal blooms frustrates most hope of forecasting their future prevalence. Summarized here is the consensus of a recent workshop held to address what currently is known and not known about the environmental conditions that favor initiation and maintenance of harmful algal blooms. There is expectation that harmful algal bloom (HAB) geographical domains should expand in some cases, as will seasonal windows of opportunity for harmful algal blooms at higher latitudes. Nonetheless there is only basic information to speculate upon which regions or habitats HAB species may be the most resilient or susceptible. Moreover, current research strategies are not well suited to inform these fundamental linkages. There is a critical absence of tenable hypotheses for how climate pressures mechanistically affect HAB species, and the lack of uniform experimental protocols limits the quantitative cross-investigation comparisons essential to advancement. A HAB “best practices” manual would help foster more uniform research strategies and protocols, and selection of a small target list of model HAB species or isolates for study would greatly promote the accumulation of knowledge. Despite the need to focus on keystone species, more studies need to address strain variability within species, their responses under multifactorial conditions, and the retrospective analyses of long-term plankton and cyst core data; research topics that are departures from the norm. Examples of some fundamental unknowns include how larger and more frequent extreme weather events may break down natural biogeographic barriers, how stratification may enhance or diminish HAB events, how trace nutrients (metals, vitamins) influence cell toxicity, and how grazing pressures may leverage, or mitigate HAB development. There is an absence of high quality time-series data in most regions currently experiencing HAB outbreaks, and little if any data from regions expected to develop HAB events in the future. A subset of observer sites is recommended to help develop stronger linkages among global, national, and regional climate change and HAB observation programs, providing fundamental datasets for investigating global changes in the prevalence of harmful algal blooms. Forecasting changes in HAB patterns over the next few decades will depend critically upon considering harmful algal blooms within the competitive context of plankton communities, and linking these insights to ecosystem, oceanographic and climate models. From a broader perspective, the nexus of HAB science and the social sciences of harmful algal blooms is inadequate and prevents quantitative assessment of impacts of futur...

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The importance of the benthic filter feeding community as a natural control on eutrophication is considered. The important environmental factors favorable for such a control are relatively shallow water depths and a dense benthic filter feeding commmunity of small animals. The criteria are summarized in the equivalence of the water recycling time, t, for the benthic community and the time constant, tp, for phytoplankton growth. The criteria are applied specifically to the conditions that exist in South San Francisco bay.