Harmful Algal Blooms [HABs] naturally appear in cold temperate to tropical waters worldwide. They are caused by certain types of microscopic algaes, collectively known as phytoplankton. Normally, these tiny plants serve as the base food group for the marine food chain. When they accumulate in a higher-than-normal concentration, however, they produce a "bloom" that releases poisons into the water. The bloom may last for several weeks or months. The number of HAB incidents has been steadily increasing over the past few decades, causing concern among marine scientists, fishermen, and communities whose economic survival depends on the sea.
Scientists are still searching for the conditions that stimulate bloom production. Surveillance programs that monitor for marine toxins have significantly reduced the risk of HABs to human health. However, the costs associated with testing and the losses experienced by the tourism and fishing industries have struck a devastating economic blow to many coastal communities. To help reduce this impact, scientists are developing better detection methods and prediction models. The HABs are forcing some difficult decisions on policy makers; even if we understood how to rid coastlines of this nuisance, experts are divided about whether it would be a good policy to interfere with nature.
Are Red Tides always dangerous?
What about Yellow or Brown Tides? The most common type of HAB is referred to as a "Red Tide" because the bloom discolors the water, making it appear red. However, HABs may also be yellow, orange, brown, green, white, or pink, depending on which one of three primary types of phytoplankton are responsible for the problem; dinoflagellates, diatoms, or blue-green algaes. Of the more than 4,400 marine phytoplankton species, only 50 to 60 are believed to be toxic. What makes this problem more difficult, is that there are some NON-toxic species that will discolor of the water, and some toxic species that will NOT discolor the water. A Red Tide may or may not be a HAB, depending on the species that produced it. Because individual phytoplankton are so small, the only reliable method of identification is through laboratory analysis.
Is this problem caused by pollution?
Many people have questioned whether pollution is responsible for HABs.
There are several arguments against pollution as the primary cause:
- HABs tend to occur seasonally, with the predominant temporal pattern differing in each ocean region. Seasonal patterns typically suggest that the phenomenon occurs naturally.
- HABs usually begin 10-40 miles offshore, and are only brought near shore when currents and winds favor such a direction. Conversely, pollution levels would be higher closer to shore, where human activity is greater.
- HABs have been documented off the Florida coastline since the 1530s. This date precedes any significant sources of coastal pollution.
On the other hand, because of the strongly increasing trend in the variety and frequency of HAB incidences over the past few decades, we would be wise to consider the potential influence of pollution on this otherwise natural phenomenon:
- Global warming caused by pollution may raise ocean temperatures into a range favorable for HABs.
- The dumping of ballast water by international shipping vessels may enhance the transfer non-native algae species between habitats.
- The dumping of bilge waters by ships provides an enriched source of nutrients that may stimulate HABs. However, without more definitive evidence, the connection between HABs and pollution remains speculative.
What are the health risks to marine and human life?
HABs kill fish and other marine animals. Some species release poisons that enter marine animals when eaten or through their gills, where a paralysis ensues that leads to suffocation. Other species have spines that lodge in gill tissues, causing irritation, the overproduction of mucus, and eventually death. HABs kill fish and other marine animals.In high enough concentrations, even non-toxic species can reduce the amount of light and oxygen available in the water, resulting in plant and animal deaths.
One particularly insidious species is Pfiesteria. They swim towards fish prey and excrete toxins that make fish lethargic so that they wont swim away. The toxins also create bleeding sores in the skin, which eventually kill the fish. In the meantime, the Pfiesteria feed on the dead tissue, awaiting further feeding on the fish carcasses.
Humans are susceptible to the same hideous fate from exposure to these "cells from hell." Thirteen researchers learned this lesson the hard way after working with dilute solutions of Pfiesteria for 1-2 hours a day over a 5-6 week period. Their symptoms included narcosis, the development of sores (also on their face and chests, because of the unusual ability of many of these phytoplankton to aerosolize toxins), difficulty breathing, blurred vision, kidney and liver dysfunction, short-term memory loss, and cognitive impairment. These effects have recurred in these individuals up to six years after their exposure. Consequently, state and federal agencies require that all future work with Pfiesteria must be conducted in biohazard containment systems. It is obviously of a great human health concern to avoid eating seafood contaminated with these toxins. In the past, fish that remained alive and appeared healthy after exposure to HABs were assumed safe for human consumption. This is because scientists were able to demonstrate that the toxins did not accumulate in the flesh of these animals. Shellfish, who eat by filtering plant matter from water, would be transferred to uncontaminated waters for several weeks of filtering to purge themselves of any toxins before they would be considered safe for human consumption. Pfiesteria may be changing the rules. Because scientists have not yet chemically isolated the toxin, there are no methods to detect traces of the toxin in fish and shellfish. For now, seafood from Pfiesteria outbreak areas are to be avoided.
What are some common seafood illnesses?
Humans become ill with seafood poisoning within a few minutes to twenty-four hours after eating contaminated foods. Because the poisons are tasteless, odorless, and are not affected by heat or various preparation methods, they are not detected by normal screening methods. Laboratory analysis is required for an accurate identification of toxins.
|Human Illness ||Source ||Symptoms |
|Amnesic Shellfish Poisoning ||Clams, Mussels, Dungeness crabs ||Life-threatening; nausea, vomiting, abdominal cramps, diarrhea, chronic memory loss |
|Ciguaterra Fish Poisoning ||Barracuda, Grouper, Snapper, Amberjack, Kingfish, Mahi mahi ||Survivors usually recover, but it may take years; diarrhea, vomiting, abdominal pain, muscular aches, dizziness, sweating, numbness and tingling of mouth and digits |
|Diarrhetic Shellfish Poisoning ||Scallops, Mussels, Short-necked clams ||Recovery within three days, without medical treatment; diarrhea, nausea, vomiting, abdominal cramps, chills |
|Neurotoxic Shellfish Poisoning ||Clams, Scallops, Mussels, Oysters ||Recovery within a few days; diarrhea, vomiting, abdominal pain, muscular aches, dizziness, sweating, numbness and tingling of mouth and digits; asthma-like symptoms if aerosols are inhaled |
|Paralytic Shellfish Poisoning ||Clams, Scallops, Mussels, Oysters, some coral reef gastropods and crabs, lobster tomalley ||Life-threatening; tingling, numbness, ataxia, giddiness, drowsiness, fever, rash, staggering, possible respiratory arrest |
What are the economic costs associated with HABs?
One preliminary estimate suggests that HABs are a problem that costs the United States $40-100 million a year. Routine monitoring and human health care are sources of escalating expenses. Shellfish harvest restrictions, fish moralities, decreased tourism are sources of diminishing revenues. These costs are expected to rise; every coastal state is now threatened by HABs, whereas 25 years ago fewer regions were affected and the frequency of episodes was much lower. Because HAB occurrences are not recognized as natural disasters by federal and state agencies, the individual industries in the affected communities often bear the financial burden. With this much money at stake, some experts are in favor of developing a strategy to control the HABs. Developing a safe, cost-effective solution will not be easy. HABs are spread out over thousands of square miles of water and will therefore be difficult to treat or contain. In addition, it would be difficult to anticipate how the use of control agents may adversely affect other marine life.
How are scientists studying the problem?
Scientists have been using four different strategies to tackle the HABs problem:
- First, some scientists are trying to understand the basic biology of the dinoflagellates; what is the biological trigger that transform them to this toxic state?
- Second, some scientists are trying to develop less expensive, but more sensitive, methods for monitoring and detecting marine toxins.
- Third, some scientists are focused on developing prediction systems using satellite images like those used to predict the formation and movement of hurricanes.
- Fourth, some scientists have developed computer models to test theories of HAB development and migration in a virtual world.
Should we just let nature take her course?
Some experts believe that it is important to leave the HABs alone. They may be natures seemingly-backwards way of improving the productivity of the marine ecosystem. A similar philosophy is held by forest rangers who allow small, naturally occurring forest fires to burn themselves out. Afterwards, new seedlings and wildflowers can revitalize the forest ecosystem. Indeed, some fishermen report better catches of certain marine species after a period of HABs. It has been hypothesized that the HABs may "reset" the predator-prey balance or they may be a way of introducing more food into the marine system. It is also worth noting that phytoplankton are thought to play a significant role in controlling atmospheric carbon dioxide. Killing off a major source of oxygen production may be a dangerous game for the long-term survival of many other species, including humans.