Harmful Algal Blooms (HABs) is a relatively new term used to describe a proliferation, or "bloom," of single-celled marine algae called phytoplankton. Once more commonly referred to as "red tides," these blooms occur when the algae photosynthesize and multiply. While there are thousands of phytoplankton species in existence, only a few dozen are known to be toxic. However, because phytoplankton serve as the base of the marine food web, the impact of these blooms can be devastating for consumers throughout the food web and for other marine flora or fauna in the affected ecosystem. Even blooms of non-toxic species can spell disaster for marine animals since the massive quantities of phytoplankton deplete the oxygen in the shallow waters where most phytoplankton blooms occur.
Recently, the world's coastal waters have experienced an increase in the number and type of HAB events. This is especially true in the United States, where virtually every coastal state is now threatened, in some cases by more than one species (refer to map, below, comparing known incidences of U.S. HABs, pre-1972 and present). As to the causes of this trend, scientists say the jury is still out. Possibilities range from natural causes (species dispersal) to human-related causes (nutrient enrichment, shifts in global climate, or transport of algal species by ship ballast water).
Harmful Algal Blooms
Causative Species: Gymnodinium breve (dinoflagellate)
Causative Species: Alexandrium (several species) (dinoflagellate)
Causative Species: Aureococcus anophagefferens Aureoumbra lagunensis
Causative Species: Pseudo-nitzschia (3 species) (diatom)
Causative Species: Pfiesteria piscicida (dinoflagellate)
Causative Species: Heterosigma (raphidophyte flagellate)
Causative Species: Chaetoceros convolutus Chaetoceros concavicorinus
Marine Phytoplankton Known to Cause HABs in the U.S.
Scientists categorize blooms by species, toxins produced, and the effect that such toxins have on consumers, namely humans. A brief description of each is listed in the table shown above.
Impacts of HABs
As evidenced by the table, the species of marine phytoplankton that cause HABs -- and their effects -- vary dramatically. While some are toxic only when concentrations reach high densities, others can be toxic at very low densities (only a few cells per liter). Whereas some blooms discolor the water (thus the terms "red tide" and "brown tide"), others are undetectable by even highly sensitive satellite imagery techniques designed to pick up color differences.
While the bloom charac-teristics of HABs are highly variable, the effects of HABs generally fall into two major categories, public health and ecosystem effects and economic impacts.
Public Health & Ecosystem Effects
Overall, preliminary estimates of the overall impact of HAB outbreaks on the U.S. economy, taking the above factors into accout, are over $40 million per year, or nearly $1 billion over a decade.
HAB Research Directions Now Underway
HAB research has been taking place for over two decades. One source of funding that has remained constant throughout the years -- even before the term HAB existed - is the National Sea Grant College Program. Sea Grant's research support, along with a recent influx of federal support from other NOAA agencies and NSF, has seen and will continue to see, better understanding of HABs. Unfortunately, due to the complexities of the individual species and the fact that identical species can behave differently region-to-region or under different environmental conditions, there remain many more questions than answers.
Sea Grant HAB research, to date, has focused primarily on the following:
In 1995, a national, multi-agency research agenda was initiated to increase the understanding of impacts and population dynamics of HABs. The program, called ECOHAB (ECology and Oceanography of Harmful Algal Blooms), is supported by the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), the Environmental Protection Agency (EPA), and the Office of Naval Research (ONR), and is administered by NOAA's Coastal Ocean Program and the National Sea Grant College Program.
What Do We Know?
Research over the past few decades has yielded a number of important results with respect to HABs. These include:
Where Do We Go From Here?
Three areas of HAB research that have gone largely unexplored, at least in the U.S., are now the focus of a NOAA initiative aimed at guiding federal, state, and local policy in dealing with the growing problem of HABs:
Support from Sea Grant and other funding sources is critical if researchers are to solve some of the many mysteries associated with HABs and to focus efforts on new areas such as those listed above. At the national level, a lot of attention has been given to the most recently discovered toxic dinoflagellate, Pfiesteria piscicida, (thus the term "Pfiesteria Hysteria"), but it is only one of many HABs that can have disastrous consequences for a region's economy, while threatening public health and safety.
As Donald Anderson, a Woods Hole Oceanographic Institution marine biologist and world-renowned expert on HABs, points out in a Nature Commentary: "One thing is certain -- there is a growing global problem at a time when human reliance on the coastal zones for food, recreation and com-merce is rapidly expanding." Today, more than ever before, research into HABs must continue.
For more information about the research or outreach projects profiled in Focal Points, contact WHOI Sea Grant at the address listed below.
Woods Hole Sea Grant 193 Oyster Pond Road, MS#2, Woods Hole, MA 02543 (508) 289-2665 email@example.com