Researchers with NOAA's National Centers for Coastal Ocean Science and the Woods Hole Oceanographic Institution are predicting a small, red tide for the Gulf of Maine this summer, continuing the pattern of smaller blooms observed in the region over the last few years.

Concentrations of Alexandrium cysts in Gulf of Maine bottom sediments, October 2018. Credit: NOAA's National Centers for Coastal Ocean Science.

Gulf of Maine red tide, caused by the algae Alexandrium catenella and fundyense, produces a toxin that can accumulate in shellfish, which can result in serious or even fatal illness in people who eat contaminated shellfish. The magnitude and severity of Alexandrium blooms, and the subsequent need for shellfish harvesting closures to protect human health, vary considerably from year to year and between decades. Shellfish toxicity was severe and widespread from 1978 to 1988 and again from 2003 to 2009, but has been lower since then. The causes of the decadal variations are the subject of ongoing research.

NCCOS and its partners produce a yearly red tide forecast for the Gulf of Maine that helps state shellfish managers gauge the severity of the season's harmful algal blooms before they occur. The forecast is based on data collected about Alexandrium’s dormant stage, when it exists as seed-like cysts in ocean sediments before growing in the spring into the swimming cells that can produce red tide. Scientists can predict the size of red tides in the spring and summer by counting the number of cysts in bottom sediments the preceding fall.

In October 2018, aboard NOAA Ship Nancy Foster, researchers collected the data needed to map the presence of red tide cysts in the gulf, and to predict the size of the red tide in 2019. Throughout this spring and summer, NOAA will provide coastal managers with weekly updates of modeled bloom extent, trajectory, and intensity to complement the seasonal forecast and guide states that will monitor Alexandrium cells and shellfish toxicity along the shore.

This marks the twelfth year that NOAA and its partners have issued the seasonal forecast, which enables proactive responses to protect coastal economies, making the region more resilient to red tide outbreaks.