Paper short abstract:

Harmful algal bloom (HAB) events occur since records begun. Rapid growth of HABs can be triggered by extreme weather events like floods or drought. This paper investigates historical HAB events, where and when they happened and how they affected livelihoods of coastal communities in past times.

Paper long abstract:

Commonly, the explosive growth in phytoplankton is an essential event for the marine food web that takes place in the spring/early summer. It is the food source for the marine pelagic ecosystem. By harnessing sunlight and nutrients phytoplankton turns inorganic material into organic matter which provides nourishment to all higher trophic levels. Only 2% of algae species are harmful or toxic capable of killing fish, other aquatic animals, mammals, birds and, rarely, humans.

These harmful algal bloom (HAB) events occur since records begun. The bible describes the “First Plague” of Egypt, that “turned the Nile River red” which is consistent with a red tide event. Frequently, we find anecdotal evidence of HABs and scientific journal articles on the topic start as early as 1672. Descriptions include the abnormal behaviour or deaths of dogs, cattle and birds after drinking water from lakes exhibiting a “hairy efflorescence”.

Rapid growth of harmful phytoplankton is a result of multiple factors, including high water temperatures, high light penetration and slow water movement. Extreme weather events can trigger HABs like cyclones, floods or drought usually when high nutrient concentrations are present. This paper identifies and investigates historical HAB events during the last two millennia, where and to what magnitude they happened, if they can be linked to extreme weather events and how they affected livelihoods of coastal fishing communities in past times.