Although their impact is large, the causative "critters" are tiny. The longest dimension of these dinoflagellates and diatoms is 30-140 microns (human hair is about 80 microns wide); "Brown Tide" cells are at least ten times smaller! Typical dinoflagellates use two whip-like flagella to swim. Diatoms hold plant matter within glass shells, cannot swim, and often have spines that help them float. Like other organisms, plankton thrive in specific environments; thus scientists study which conditions favor Harmful Algal Bloom formation. NOTE that not all species which cause these illnesses are shown.
  • Toxic dinoflagellate lives on the red and brown seaweed associated with coral reefs
  • Optimal growth conditions: Shallow waters, 20-34°C, salinity of 25-40 PSU
  • CFP is one of the most reported food-borne illnesses
  • Although these DSP-producing algae have been found along the U.S. coast, there have been no reports of DSP-related illness
  • The U.S. Food and Drug Administration (FDA) limit of DSP toxins in shellfish is 0.2 parts okadaic acid per million
  • Optimal growth time: Late fall; Eastern Gulf of Mexico circulation determines bloom distribution
  • Researchers are working to discover the temperature, salinity & nutrient conditions that favor Karenia brevis's growth
  • The FDA limit of NSP toxins in shellfish is 0.8 parts brevetoxin per million
  • Unlike most dinoflagellates, Alexandrium catenella forms chains; its cells swim together in a snake-like fashion
  • Found along U.S. west coast
  • Highest toxicity in July and August; outbreaks occur when coastal upwelling decreases in intensity
  • A. tamarense and A. fundyense occur along U.S. northeast coast
  • Toxicity of cells increases from south to north; toxicity appears to be influenced by ratio of nitrogen to phosphorus in seawater; Gulf of Maine circulation and cyst distributions influence blooms
  • The FDA limit of PSP toxins in shellfish is 0.8 parts saxitoxin per million; amounts as low as 1.25 and 4.5 ppm have been shown to cause illness and death, respectively
  • P. multiseries was first identified as toxic in 1987 when 150 people became ill -- and three died -- after eating blue mussels on Prince Edward Island (Canada)
  • Optimal growth conditions: warm surface waters that are layered by temperature.
  • The FDA limit of ASP toxins in shellfish is 20 parts domoic acid per million
HARMFUL BLOOMS (non-toxic or toxicity under investigation*)
  • *Although no toxin has been isolated for P. piscicida; this dinoflagellate appears to be harmful only in the presence of fish
    • P. piscicida has amoeboid, encysted and flagellated (shown at left) stages; growth stage is influenced by nutrients
    • Optimal growth conditions: Poorly flushed upper estuarine tributaries, 26°C or warmer, salinity of 15 PSU
  • The raphidophyte H. akashiwo is a golden-colored algae with two flagella and numerous disk-shaped chloroplasts
    • Washington: Found in waters warmer than 15°C
    • Rhode Island: Tied to large-scale atmospheric patterns (i.e., the North Atlantic Oscillation) with seasonal pulses in late spring/early summer and mid-late fall
  • Although all species of Chaetoceros use "glass-like" siliceous spines to float, C. convolutus's numerous needle-like spines are particularly irritating to gills and contribute to massive fish kills
  • Mid-Atlantic Brown Tides are caused by very small (2-3 micrometers) plankton, Aureococcus anophagefferens
    • At left, Aureococcus are the bright "blobs" (seen under blue excitation); this sample has over 300,000 Aureococcus cells per milliliter
    • Aureococcus produces a substance called "mucopolysaccharide" that clogs gills of filter feeders, causing them to stop feeding and ultimately starve to death.
    • Brown tides caused the collapse of the scallop fishery in Long Island bays.
    • Optimal growth conditions: Poorly flushed estuaries, late spring/early summer, 20-25°C, salinity of 28 PSU or higher; can flourish in low light; thrive in high concentrations of organic nitrogen.
  • Texas Brown Tides are caused by slightly larger (4-5 micrometers) nanoplankton, Aureoumbra lagunensis
    • Optimal growth conditions: Shallow embayments; especially lagoons with miminal water transport and relatively high salinity