NCCOS and its partners produce an annual red tide forecast for the Gulf of Maine that helps state shellfish managers gauge the severity of the season’s Alexandrium catenella bloom before it occurs. A low-to-moderate Gulf-wide bloom is projected for the Gulf of Maine this spring and summer, continuing the pattern of smaller blooms observed in the region for over a decade.
The Gulf of Maine red tide is caused by the algae Alexandrium catenella. A. catenella produces a potent neurotoxin that can accumulate in filter-feeding animals, including shellfish, which can result in serious or even fatal illness in people who eat contaminated shellfish. Red tides can pose a public health threat, jeopardize state shellfish industries, and negatively impact the tourism industry in the Gulf of Maine.
The forecast is based on data collected from Alexandrium’s dormant stage, when it exists as seed-like cysts in ocean sediments before growing into the swimming cells that can produce red tide in the spring. Scientists can predict the size of the red tide in the Gulf of Maine by counting the number of cysts in bottom sediments the preceding fall or winter. The Alexandrium cyst abundance for the 2026 sampling cruise ranked 15 out of 23 years of the cyst sampling record.
The actual timing of the bloom depends on atmospheric weather and hydrodynamic conditions, including nutrients, wind speed and direction, and currents. NOAA will provide coastal stakeholders with weekly updates of modeled bloom spatial extent, trajectory, and intensity throughout the spring and summer, and guidance to states monitoring harmful algae and shellfish toxicity along the shore.
In addition to the seasonal forecast, weekly forecasts will be produced and available online throughout the bloom season.
This work is authorized under the Harmful Algal Bloom and Hypoxia Research and Control Act (33 U.S.C. §§ 4001 et seq.).