Harmful algae are microscopic, single-celled plants that live in the sea. These algae are usually associated with the blue-green
algae. "Blue-green algae” is the common name for several different types of algae. They are actually bacteria, which live in shallow, warm, slow moving or still water and use sunlight to create food and support life. Algae can range in colour from olive-green to red. Most species of algae or
phytoplankton are not
harmful and serve as the energy producers at the base of the food web, without which higher life on this planet would not exist.
A mass of algae in a body of water is called a “bloom.” The term "harmful algal blooms" or HABs is used to describe a diverse array of blooms of both microscopic and macroscopic marine algae which produce toxic effects on humans as well as other organisms. "Red Tide" is a common name for such a phenomenon where certain phytoplankton species contain reddish pigments and "bloom" such that the water appears to be coloured red. These blooms are potentially toxic and may pose a direct threat to human and animal health. In order to bloom, the phytoplankton or “Blue-green algae” need warm temperatures, sunlight, phosphorus and nitrogen to grow.
Basically, there are two types of phytoplankton that causes harmful algae bloom. One of which is the group that produces toxin and the other which causes bloom in high densities or through massive multiplication. Phytoplankton that produces toxin is reported to be responsible in contaminating sea food and it is even capable at killing fish at very low concentration. Apart from this, the toxin produced by phytoplankton is subjected to accumulation in food chains, eventually causing gastrointestinal and neurological illness as well as other toxic effects to human.
On the other hand, phytoplankton that blooms in high density results in discolouration of the seawater. Though the bloom formed by this group of phytoplankton is non-toxic, it is still harmful to marine flora and fauna due to the low dissolved oxygen level in the water as the bloom decays. This happens because the phytoplankton has used most of the available oxygen in the water for respiration. As a result of this issue, there would be a major reduction of fish or shellfish due to mortality. Eventually, even the economy of the country will be affected with poor fisheries dumping. Besides this, such bloom may bring about damages even to non-commercial marine resources and wildlife. In other words, there will be a loss of natural and cultural seafood resources in the country affected. Apart from this, massive bloom of phytoplankton leaves behind bad odour which may bring about a negative impact on the tourism sector of a particular country. The occurrence of harmful algae bloom in high densities may be risky to human health too if at all they are exposed to it for a long duration of time. Consequently a harmful algal bloom may have economic and social impacts because it results in a significant increase in water supply treatment costs or need to use alternate supplies as well as various health problems and high medical treatment related to it. When the bloom of phytoplankton worsens, the aquaculture industry may suffer lots of losses in form of income. For instance, shellfish farms may be forced to close due to high mortality rates. Sooner or later, there will be great fear among investors whether or not to invest in the aquaculture business. Even in the seafood business, consumer will have the fear of purchasing seafood to avoid various health problems and in the worse case, death. As mentioned earlier, the tourism sector will be badly affected as well. The occurrence of such phytoplankton bloom will result in dead fish being washed ashore. Then, apart from making the water discoloured, an unpleasant odour will come along. This problem is not only limited to the water as the toxins from the phytoplankton can be released into the air and bring about human respiratory problems. So, in relation to all of these issues, the total medical cost and lost productivity of workers poisoned by HAB toxin will be extremely high.
In the ecosystem context, the toxins or any other compounds released are capable in killing marine fauna directly. Filter feeders like clams, mussels, oysters and scallops have the ability to accumulate algal toxins at level that are potentially lethal to human or fish, invertebrate and marine mammal. In other words, the toxins released by the phytoplankton can be accumulated throughout the food chain, therefore poisoning the whole ecosystem. Next, HABs decreases the light penetration into the water which is an important consideration for many organisms especially those relying on it to produce food through photosynthesis. There will also be low dissolved oxygen levels in the water as the bloom decays because most of the oxygen would have been used by the phytoplankton for respiration purposes and this would be most critical for aquaculture organisms that are in captivity. To sum, the whole phenomenon of HAB is harmful to the whole marine ecosystem.