Harmful algal blooms: Their ecophysiology and general relevance to phytoplankton blooms in the sea

Abstract

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...

Azadinium poporum from the Argentine Continental Shelf, Southwestern Atlantic, produces azaspiracid-2 and azaspiracid-2 phosphate

“…Such a seasonal stratification has been ascribed to heating of the superficial water during the Austral spring such that it reaches the inner zone (with only 30-40 m water depth) at 50 km from the coast (Lucas et al, 2005). It probably is responsible for creating environmental conditions that favour dinoflagellate blooms (Smayda, 1997).…”

Fluorescence patches in high-frequency internal waves

“…Nonetheless, even at this magnitude, predictable subsurface phytoplankton patchiness in internal waves might have a range of implications for planktonic organisms. For species of dinoflagellate with the ability to reproduce sexually, the success of their sexual reproductive phase could be enhanced within these small-scale patches (Smayda 1997). This small-scale patchiness may also confer benefits to fast-swimming grazers, such as some copepods, with the ability to utilize ephemeral resources.…”

Allelopathy of Aquatic Autotrophs

“…Angiosperms, macroalgae, and corals produce inhibitory compounds interfering with epiphytes and other epibionts, competing for light andlor space (Harrison and Chan, 1980;Harlin, 1987;Endean et al, 1997;Jeong et al, 2000). Allelochemical interactions among planktonic algae have been described, mainly when bloom-forming microalgae were involved (Smayda, 1997).…”

“…To counteract low nutrient uptake affinities compared with diatoms, four major adaptations, arnong them allelopathy and grazing deterrence, have evolved in harmful flagellates (Smayda, 1997). Dominance of harmful dinoflagellate blooms in marine phytoplankton communities is considered to be mediated by the production of poisoning toxins, okadaic acid (OA), and dinophysistoxin-1 (DTX-1) (Lewis and Holmes, 1993;Windust et al, 1996;Plumley, 1997).…”