Several decades ago relatively few countries appeared to be affected by HABs, but now most coastal countries are threatened, in many cases over large geographic areas and by more than one harmful or toxic species. Many countries are now faced with disturbing trends of increasing bloom incidence, larger areas affected, more fisheries resources impacted, and higher economic losses. The causes behind this expansion are debated, with possible explanations ranging from natural mechanisms of species dispersal to a host of human-related phenomena such as nutrient inputs, coastal development, aquaculture development, and climatic shifts.
While HABs may appear to many to be a recent phenomenon, the phytoplankton species that cause HABs and their toxins are naturally occurring, and incidences of HABs and HAB-associated food poisoning are described in historical records dating back centuries. The recent associated with combined pressures of a growing world population, food production, aquaculture development, and coastal development.
Below is a timeline outlining some examples of historical records of HABs, as well as evidence of HAB impacts in the fossil record.
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