Harmful Algal Blooms
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A minority of HABs consist of one of the small subset of toxic phytoplankton, single-celled organisms that can be fatal to the local marine life, or humans, that ingest them. At almost any time of the year, a local fishery in the United States is shut down because of a HAB outbreak.
Increasing HABs and fisheries closures have prompted research into their causes and effects. Considering the fact that algal blooms flourish under conditions of warm water and an adequate food source, two interrelated causes of increased HAB outbreaks are being explored, climate change and ocean nutrient loading resulting from large scale agricultural runoff. (see Global Warming and Cyanobacterial Harmful Algal Blooms).
While scientists can not accurately predict toxic algal bloom outbreaks or duration, technology improvements are leading to the institution of a state of the art West Coast monitoring system that provides almost instantaneous sampling, reporting, and when necessary, public health warnings.
Five organisms are known to cause problems on the West Coast. Four of the most common fall into one of two phytoplankton categories, diatoms (tailess single-celled organisms) or dinoflagellates (tailed single-cell organisms).
Pseudo-nitzschia, the only diatom representatives on the list, have both plant and animal characteristics. Their blooms, present on both the East and West Coasts of the United States, can be tracked using ocean current data. Their lack of tail means they are built to go with the flow.
The most recent Pseudo-nitzschia research, Harmful Algae (2007) shows a strong correlation of blooms with high surface salinity levels. Researchers also documented the existence of Pseudo-nitzschia and the toxin domoic acid (DA) at ocean depths of 550m one week after a surface bloom.
These facts initially suggest that blooms exhibit self-reinforcing behavior. The organisms live on the ocean floor, returning to the surface as blooms under specified environmental conditions. The exact parameters of those conditions is still under investigation. Within a week of blooming, the organisms fall to the ocean bottom, waiting for the next appropriate set of conditions to resurface.
A spring 2007 bloom along the California coast caused significant sea bird and marine mammal mortalities. Pseudo-nitzschia blooms are also present on the East Coast, and in 2003 NOAA documented a humpback whale fatality linked to Pseudo-nitzschia ingestion.
Toxic species of the dinoflagellate Alexandrium, can also be found on the East and West Coasts. They are problematic because they secrete a potentially fatal neurotoxin that accumulates in shellfish. Coastal New England residents have been facing risks posed by the blooms for a couple of decades. The 2005 Alexandrium blooms were the largest on record to date, causing sustained fisheries closures.
Further south, Mid-Atlantic residents have been dealing with Pfiesteria Outbreaks for the better part of the past two decades. Pfiesteria, also a dinoflagellate (tailed organism), live in brackish waters. Recent research suggests that the action of Pfiesteria feeding on fish, rather than poisoning them, is the cause of fish mortality.
Finally, for centuries, the dinoflagellate called Karenia brevis has been know to cause what Gulf of Mexico residents call Red Tides. The name stands for the color the algal blooms assume when fully formed. Scientists are unsure of the underlying causal mechanisms associated with these Red Tide outbreaks, however, like other toxic algal blooms, coastal water monitoring programs, along with satellite data are used for early bloom detection. Karenia brevis Red Tides are also known to occur along the South Atlantic Coast of the United States.
© 2007-2009 Patricia A. Michaels