HAB's sometimes take the form of dense patches of algae that form near the surface of the water. These patches can often be coloured, depending on the type of algae or organisms present. Sometimes, however the algae causes harm, even when their cell concentrations are so low that the water colouration does not change.
Although some algal blooms are not toxic, some can become harmful if they are comprised of species that contain harmful toxins.
The harmful toxins produced by some of these species can affect fish, marine animals and humans.
Due to the toxic nature of some blooms, HAB's have a devastating impact on the fishing industry. Fisheries are often closed as shellfish become contaminated with the toxins which are a serious health risk to consumers, often causing a suite of poisoning syndromes called Diarrhetic, Amnesic, Paralytic, Neurotoxic and Azaspiracid shellfish poisoning, OR DSP, ASP, PSP, NSP, AND AZP respectively. HAB's can also cause wild and farmed fish by the millions.
In response to the impact that HAB's have on the fishing industry and ocean life, many scientists are trying to find out if there is a driving cause of these HAB's, if they are increasing in occurrence and size and how the impact to fishermen can be minimised.
Work by Donald Anderson on HAB's of Woods Hole Oceanographic Institution has suggested that HAB's are now threatening more countries across the world than they were several decades ago.
HAB's are currently having a serious impact across the world and a recent International Conference on HAB'z in Korea was attended by scientists and managers from over 60 countries.
In his work, Dr Anderson has highlighted a variety of possible causes for the expansion of HAB's including, natural dispersal of species by currents and storms, dispersal through human activities such as ballast water discharge and shellfish trans-location and increased water pollution from human activities (eutrophication).
The addition of various wastes to water through human activities may have caused nutrient changes which in turn have triggered increased harmful algae growth in some regions.
DR Anderson notes that some aspects of the global expansion of HAB's could also be simply due to improved detection of HAB's and their toxins, as in many places that are newly experiencing HAB's, the toxic species have always been present and were not stimulated or introduced by the activities of man. Improved communication among scientists or even climate change are also thought to be involved in the expansion.
Can HAB's be Managed?
At present, HAB's are managed through routine monitoring of bloom presence and of toxins in shellfish.
There has been some progress in bloom control, mainly in countries such as Korea, China and Japan, where HAB's are having a serious economic impact on fish and shellfish aquaculture industries.
In Korea and China, the spraying of clay has proved effective at stopping HAB's from taking place as it causes the algae to combine with the clay and fall to the sea floor. Although some believe that clay can have other environmental impacts, the use in these areas is justified by the reduction in the impacts caused by HAB's.
There is a call for more research in this topic area, as of yet, not enough is known about the environmental impacts of HAB's control strategies to make bloom mitigation acceptable to society.
Chemical use and genetic engineering have also been studied as ways to prevent HAB's but again, these have both raised environmental issues over the possible effects on other parts of the ecosystem. Despite the possible impacts, these avenues should be subject to further research, stated Dr Anderson.
"By analogy, many chemical and biological methods are used to protect crops on land from insect pests, but it will take a major change in the mind set of environmentalists and managers to allow the same level of applications and interventions to protect fisheries and aquaculture from HAB's", said Dr Anderson.
Despite the need for more research, some advances have already been made. Thanks to research by scientists involved in the Gulf of Maine Toxicity (GOMTOX) project, fishermen in Georges Bank, which has been closed for over 20 years to the harvest or surf clams and ocean quahoga due to HAB's, are now able to harvest shellfish for the first time in more than two decades.