Algal blooms reported along South-West coast

Water samples from the South coast analysed by Marine Institute laboratories last week identified a bloom of Phytoplankton called Noctiluca scintillans, which is non-toxic to shellfish. This species of phytoplankton has no impact on human health and is not uncommon at this time of year when water temperatures increase. The algal bloom is red/orange in colour and can appear quite dense in bays where there is not much movement in the water.

Further reports of similar red/orange algal blooms along the South-West Coast were received this week. The Marine Institute has requested further water samples from affected beaches in order to identify the species of Phytoplankton.  Based on eyewitness reports and photographic evidence to date, it appears likely that the Noctiluca scintillans bloom, identified last week on the South coast, has spread to other beaches along the South–West, and therefore poses no threat to human health.

Noctiluca scintillans is one of the "bioluminescent" phytoplankton, which emits a naturally occuring greenish light when disturbed. This accounts for the flashes of light often seen along the shoreline at night when blooms of Noctiluca are in the area. This bioluminescence is created by the mixing of two naturally occuring compounds in the body of Noctiluca and is thought to be a defence mechanism aimed at making potential predators more vulnerable to attack.

Like Noctiluca itself, this bioluminesence is harmless to human beings.

Algal blooms are naturally occurring plankton and are seen almost every year during the summer months. The Marine Institute routinely analyses water samples from around the coast of Ireland to identify harmful or nuisance phytoplankton, and their impact on shellfish & finfish in particular. The results of the Marine Institute's Phytoplankton Monitoring Programme can be seen on These results are also circulated to shellfish producers, the Department of Communications, Marine and Natural Resources, and the Food Safety Authority of Ireland.