Please note cell densities of the bloom forming dinoflagellate Noctiluca scintillans have been observed to be increasing in multiple inshore locations in the South (Kinsale, Youghal, Oysterhaven) and Southwest (Bantry, Dunmanus Kenmare, Sherkin, Roaringwater bays) this week (w/c 10-08-26) and last week, in samples submitted for the Phytoplankton National Monitoring Program. This organism is notable as it is a species that results in bioluminescence which can be observed when the water is disturbed at night, and also an orange seawater surface discolouration during the day.

While this species is non-toxic, it may cause mortalities among marine organisms, particularly as the bloom decays and depletes oxygen in the water column. It may also cause an unpleasant smell as the bloom breaks down due to the release of ammonia.

It is a naturally occurring bloom which happens annually around the coast of Ireland along South and Southwest coasts, and historically has also been observed off western coasts.

Please report any mortalities and seawater discolouration’s to HABS Team Marine Institute (habs@marine.ie)

Karenia mikimotoi bloom event – Southwest Coast
Updated 14-08-26

Please note cell densities of the bloom forming dinoflagellate Karenia mikimotoi have been observed to be further decreasing in multiple inshore locations along the Southwest and West Southwest this week in samples submitted for the Phytoplankton National Monitoring Program and BIM Southwest Mussel Larvae programme. There have been no observatiobs of water discolouration or mortalities reported during this week (w/c 10-8-26).

Along the South coast this week (w/c 10-08-26) low cell densities have been observed and have decreased since last week.

Please beware previous Karenia mikimotoi blooms in Ireland have also been associated with mortalities of marine organisms including flatfish, benthic invertebrates, as well as farmed shellfish and finfish. It is thought that these mortalities are as a result of depleted or low oxygen levels that can occur when the bloom begins to decay.

Please report any mortalities and seawater discolouration’s to HABS Team Marine Institute (habs@marine.ie)

Diarrhetic Shellfish Toxin Event – Offshore Southeast Coast
Updated 14-08-26

Please note quantifiable levels of Diarrhetic Shellfish Toxin (DST)have been detected in whole tissues of king scallops in non-classified offshore harvesting grounds of the Southeast coast since w/c 03-08-26.

Affected harvesting grounds are ICES Rectangles: 32E2 Mine Head, 32E3 Saltees and 31E2 South of Minehead, with DST concentrations ranging from 0.10 µg/g to 0.28 µg/g.

Quantifiable concentrations of Diarrhetic Shellfish Toxin (DST’s) concentrations have been observed in a number of mussel and oyster sites in various production areas in Castlemaine, Kenmare, Bantry and Dunmanus bays, below the regulatory limit (0.16µg/g) during w/c 10-08-26.

However, a moderate to high risk of further increases in DST concentrations still exists as the occurrence of the causative toxin producing phytoplankton species Dinophysis is still being observed in multiple locations this week, and have been continually observed on a weekly basis in some areas since mid-June. Please also be aware that due to the recent DST intoxifications observed in the southwest, there maybe potential variability of DST concentrations within shellfish from these areas.

Please note quantifiable levels of Paralytic Shellfish Toxins (PST) have not been detected in mussels and oysters in Castlemaine Harbour or oysters from Cork Harbour. Over the last three weeks there has been a decreasing trend of PST concentrations in both areas, where with this weeks results (w/c 10-08-26), no PST’s were not detected in any shellfish species from either area.

However, a moderate risk of potential PST concentrations in being further observed over the coming week in Oysters from Cork Harbour potentially exists due to the high cell density of Alexandrium >880,000 cells/l reported this week.