Understanding the causes of HABs and mitigating and preventing their consequences are national concerns. As a result, Congress passed the Harmful Algal Bloom and Hypoxia Research Act of 1998. The Act requires the formation of a federal multiagency task force to investigate the problem and report back to Congress with a plan and recommendations to address HAB and hypoxia. Amendments to the Act were introduced in both the House and the Senate in 2003. The House Science Committee, Subcommittee on Environment, Technology and Standards proposed that the amendment authorize the Coastal Ocean Science Program. The program is designed to focus on improving predictions of ecosystem trends, pollution, and coastal hazards. Congressman Brian Baird (Democrat of Washington) also introduced an amendment that requires the states and the president to develop and submit a plan "to protect the environment and public health from the impacts of harmful algal blooms" within one year of the date of enactment. As of April 2005 this legislation had made no headway in Congress.
What Are Harmful Algal Blooms?
Algae are microscopic, single-celled plants that live in the sea. The vast majorities of the thousands of algal species in U.S. coastal waters are not harmful and serve as the energy producers at the base of the food chain, without which higher life on earth would not exist. Occasionally the algae grow very fast or "bloom," creating dense, visible patches near the water surface. "Red tide" is a common name for events where certain algae containing reddish pigments "bloom" so that the water appears to be red. In most HAB events the rapidly developing algal bloom consumes all the oxygen in the water, resulting in hypoxia, which can have severe effects on local ecosystems. A small number of algal species produce potent neurotoxins that can be transferred through the food chain, where they affect and sometimes kill higher life forms such as shellfish, fish, birds, marine mammals, and humans that feed directly or indirectly on them.
Source of Harmful Algal Blooms
Most HABs are the result of the transport of offshore algal populations to inshore regions, that is, a naturally occurring physical relocation. For example, blooms of Gymnodinium breve, which causes neurotoxic shellfish poisoning, occur when algal cells from small offshore populations in the open Gulf of Mexico are blown into the west Florida shelf and into the coastal waters of other states bordering the Gulf of Mexico. This delivery of potentially harmful algal blooms from offshore to inshore regions in most areas of the world's coastal oceans occurs consistently but unpredictably. They occur even in areas that are unaffected by human activities. As a result, attempts to prevent HABs are somewhat impractical because people cannot control general oceanic circulation or even local coastal currents.
Increases in Harmful Algal Blooms
Harmful algal blooms are increasing in frequency and severity worldwide. Whether the increase is a direct result of cyclic or long-term variations in climate, other natural factors, or human activities is unclear. The frequency, duration, and intensity of algal blooms are related to a number of physical, biological, and chemical factors, the interaction of which is not clearly understood for many algal species.
Five possible reasons have been advanced for the increase in frequency and geographical extent of HAB events:
- Improved methods of detection and improved monitoring methods are detecting blooms that would previously have gone unreported.
- Introduction of new algal species into inshore areas through ship ballast water exchange or aquaculture.
- Reduction in populations of grazers (microscopic animals that eat the algae), resulting in their failure to control the algal population.
- Climate changes.
- Human activities that cause increases in nutrient levels or increased river discharge. (These are believed to be species-specific and not to apply to all HABs.)
All of these reasons are possible explanations and it is likely that it is a combination of one or more of these factors that causes HAB.
Effects on Human Health
The neurotoxins produced by some species of algae can be concentrated by bivalve mollusks (oysters, clams, and mussels) with no apparent ill effect to the bivalves. If bivalves with dangerous concentrations of neurotoxins are eaten by humans, severe illness or death can occur. In areas of the United States where HAB events occur, the densities of harmful algal species are heavily monitored in the water column by the coastal states as part of the NSSP. When the algal density exceeds certain levels, the areas are closed to bivalve harvesting until both the water column and the bivalve meat show the absence of neurotoxins.
Other human health effects from the neurotoxins include skin irritation from water contact and respiratory irritation from aerosols. Neurotoxin aerosols from sea spray have caused watery and stinging eyes, as well as breathing difficulties because the tiny acid droplets penetrate into and irritate the nasal passages and throat.
What Is Hypoxia?
Hypoxia (lack of oxygen) occurs when the dissolved oxygen level in the water column is less than two parts per million (ppm). It kills most of the bottom-dwelling life forms such as oysters and clams, and mobile marine organisms such as fish and shrimp either flee the area or die. For this reason, areas where hypoxic conditions exist are frequently referred to as "dead zones." Excess nutrient is the most frequent cause. Hypoxia is a worldwide problem that often occurs where rivers carrying large amounts of agricultural runoff empty into lakes, estuaries, oceans, and seas.
One location in the United States where hypoxia occurs is the Gulf of Mexico, off the Louisiana coast. The Gulf's hypoxic zone is comparable to the largest hypoxic areas in the world such as those in the Black and Baltic Seas. The Gulf of Mexico hypoxic zone, shown in Figure 6.10, is approximately 6,000–7,000 square miles of water where the oxygen level is below two ppm. Under normal conditions, dissolved oxygen levels would be five to six ppm.
The zone is caused by harmful algal blooms that are believed to be the result of the discharge of increased nutrients from the Mississippi River watershed into the Gulf of Mexico. The nutrients (nitrogen and phosphorus) come from fertilizers, animal wastes, and domestic sewage. The nitrate-nitrogen level in the main stem of the Mississippi River, which drains thirty-one states, has doubled since the 1950s. Figure 6.11 shows the Mississippi Basin watershed and the states whose rivers drain into it.
Correcting the problem requires a coordinated multi-state effort. The EPA, six other federal agencies, nine states, and two Native American tribes have developed an action plan to reduce nutrient loads reaching the Gulf. The Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (January 2000) was developed in response to the Congressional mandate in the Harmful Algal Bloom and Hypoxia Research Act of 1998. It has the goal of reducing the size of the hypoxic zone by 50% no later than 2015. The plan also called for implementation of nutrient management strategies to achieve a 30% reduction in the amount of nutrients reaching the Gulf of Mexico. Information generated through the research and monitoring portions of the plan will be used to modify future goals and actions as necessary.
The USGS has determined that about 25% of the nitrogen load in the Gulf comes from the Lower
FIGURE 6.10
Eutrophication, or excessive algae growth
Interior watershed of the Mississippi River Basin
Economic Consequences of Harmful Algal Blooms
Direct and indirect losses to local economies from HAB events are enormous. The amount of irretrievable revenue due to lost fish and shellfish production; impairment and loss of important ecosystems such as coral reefs; human illness and medical treatment; increased insurance rates for fisheries activities; unemployment and bankruptcy of seafood and recreational related businesses; loss of tourist dollars; and loss of sales for all seafood is staggering. For example, the 1991 outbreak of domoic acid in the state of Washington had a negative impact on the entire community, from the tourism industry to fisheries, with losses estimated between $15 million and $20 million.
During spring 2005 the New England region experienced the worst outbreak of the toxic alga Alexandrium fundyense in more than thirty years. The outbreak began in the Gulf of Maine in early May and spread into Massachusetts and Cape Cod Bays, resulting in the closing of coastal areas to shellfishing. In July 2005 the Woods Hole Oceanographic Institution estimated that the New England "red tide" was costing the local shellfish industry at least $3 million per week and had started a chain reaction of financial losses in the seafood processing and restaurant industries.
Even a nontoxic harmful algal bloom can have devastating consequences. In south Florida, blooms of macroalgae are overgrowing sections of coral reefs and seagrass beds. Coral reefs are a vital component of the Florida economy, attracting thousands of visitors each year. The seagrass beds are important to the survival of pink shrimp, spiney lobster, and finfish. Continued algae overgrowth could lead to severe economic losses for the local recreational, tourist, and seafood industries. In Washington state, Heterosigma akashiwo blooms have caused losses of $4 to $5 million per year to harvesters of wild and penned fish.
According to 2004 Economic Statistics for NOAA (April 2004), the economic impact of HABs in the United States averages $49 million per year. Individual outbreaks, however, can cause economic damage that exceeds the annual average. HAB outbreaks in Chesapeake Bay in 1997 cost the Maryland seafood and recreational fishing industries almost $50 million in just a few months. The report states that total public health effects resulting from shellfish poisoning by HABs averaged $22 million between 1987 and 1992. HAB events have also affected commercial fisheries. Losses of wild harvest and aquaculture average $18 million per year.
Preventing Harmful Algal Blooms
The U.S. Department of Commerce released a report, National Assessment of Harmful Algal Blooms in U.S. Waters (February 2001), which presents the findings of the federal multiagency task force created to investigate the problem of HABs. Because management options are limited, the focus for now remains on minimizing the impacts of HAB events.
Recommendations from the report include:
- Continue and enhance the state programs that regularly sample shellfish and shellfish harvest waters for presence of HABs and their toxins and have been effective for many years in reducing human illness and deaths.
- Develop communication programs that use educational and public health materials, electronic communication, and other techniques to educate and inform the public.
- Improve communication and information exchange among scientists; agencies; and federal, state, and local governments to increase cooperation and avoid duplicative effort.
- Improve sample collection techniques.
- Improve the laboratory and field detection methods for HABs, including rapid method development. Most of the standard laboratory tests take anywhere from four days to several weeks to provide a conclusive identification of the kind of algae causing the bloom. A rapid method would be one that could identify the organism and its concentration in the water within twenty-four to forty-eight hours. The level of toxicity is determined by injecting mice in the laboratory to see if they die. A rapid method would eliminate the mice and provide a chemical or other reaction that would give a definitive answer concerning toxicity levels within a few hours. Field methods that can be done easily at the site of the bloom do not exist.
- Establish long-term monitoring programs in areas currently affected by HABs and in areas that are likely to be affected in the future.
- Develop forecasting capabilities for the occurrence and impacts of HABs.
- Conduct basic research into the physiology, growth, and toxin production of HAB species; conditions that may stimulate blooms; and the toxin uptake, metabolism, and depuration in marine food webs, fisheries, and marine mammals.
These tools will allow states and local jurisdictions to prepare for the bloom events and communicate with the public in a timely manner, as well as provide data that can eventually be used in predictive models.
Some states that have the potential for HAB events have already established long-term monitoring programs, or are in the process of doing so, to gather information in advance of bloom situations. In addition, some research is being directed toward finding naturally occurring bacterial and viral populations that might be used in the biological control of HAB events.
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