What is a Harmful Algae Bloom (HAB)?
The National Oceanic and Atmospheric Administration (NOAA) defines a harmful algal bloom as “Harmful algal blooms, or HABs, occur when colonies of algae — simple plants that live in the sea and freshwater — grow out of control and produce toxic or harmful effects on people, fish, shellfish, marine mammals and birds.”
This is certainly an adequate definition, but it does not take into account that, for the presence of some types of algae to be considered potentially harmful, they do not have to be present in large numbers or as “blooms”.
The broader explanation and definition of HABs preferred by Dalcon Environmental is that of the IOC Intergovernmental Panel on Harmful Algal Blooms (IPHAB) which is:
“Phytoplankton blooms, micro-algal blooms, toxic algae, red tides, or harmful algae, are all terms for naturally occurring phenomena. About 300 hundred species of micro algae are reported at times to form mass occurrence, so-called blooms. Nearly one-fourth of these species are known to produce toxins. The scientific community refers to these events with a generic term, ‘Harmful Algal Bloom’ (HAB), recognising that, because a wide range of organisms is involved and some species have toxic effects at low cell densities, not all HABs are ‘algal’ and not all occur as ‘blooms’.”
Although this Intergovernmental Oceanographic Commission (IOC) is, as its name suggests, focussed on marine systems, this definition also suits freshwater systems. It is the highlighted (bold) part of the last sentence in the above definition, which is the major difference between this and other definitions of what constitutes a harmful algal bloom.
For convenience, whenever algal blooms, harmful algae, toxic algae etc. are referred to herein, this includes both the cyanobacteria and the algae.