Harmful algal bloom
Harmful Algal Blooms, or HABs, are algal blooms composed of phytoplankton known to naturally produce biotoxins. The term red tide is sometimes used to describe some harmful algal blooms comprising specific species that give the water a red colour.
Certain algal blooms are of special concern because some species of algae produce toxins. At the high cell concentrations reached during some blooms, these toxins may have severe biological impacts on wildlife. These harmful algal blooms (HABs) cause severe economical and ecological damage in many European waters. They cause large economic losses every year in aquaculture throughout Europe, due to shellfish toxicity and mass fish mortality. Furthermore some harmful algal blooms lead to closure of beaches to tourists and have devastating effects on aquatic ecosystems.
The frequency and intensity of recorded harmful algal blooms has increased worldwide over the past decades. The reason for this is often assumed to be eutrophication. However, many other explanations are possible, for example increased transport of algae with ship ballast water or increased monitoring efforts. For management purposes it is important to understand which are the main factors controlling the risk of harmful algal blooms. Although many researchers have investigated various aspects of harmful algal blooms, the results are too scattered to get a clear understanding of the human impact on harmful algal blooms in comparison with natural variability. For a long time, a link was made between high nutrient concentrations and harmful algal blooms. More recently, researchers point out the importance of interacting biological and physical processes, including effects of wind, currents and water temperature.
Harmful algal species
Examples of phytoplankton species typically associated with harmful algal blooms in Europe are:
- Nodularia spumigena
- Phaeocystis globosa
- Dinophysis acuminata and D. acuta
- Karenia mikimotoi
- Alexandrium minutum
- Alexandrium tamarense
These species are associated with problems such as nuisance scum layers, nuisance foam, mussel toxicity and fish mortality.