Millions of microscopic plants (phytoplankton) thrive in nearly every drop of coastal seawater. In the presence of sunlight and sufficient nutrients, these plants photosynthesize and multiply, creating a “bloom.” Most species of algae or phytoplankton are not harmful and serve as the energy producers at the base of the food web, but some of these species produce potent toxins or have other detrimental environmental effects. While these have commonly been known as “Red Tides” scientists now prefer the term “Harmful Algal Bloom” (HAB). The term HAB is more accurate because not all toxic blooms produce visible water discoloration, while some non-harmful blooms can result in red or brown waters.

A HAB refers to any bloom phenomenon that causes negative impacts to people, fisheries, aquaculture, or ecosystems. Toxins from harmful algae accumulate in the shellfish and fish that consume them, and organisms that eat these contaminated seafoods can become sick. These toxic HABs can harm zooplankton, marine mammals, birds, fish, and even humans. Some non-toxic blooms can deplete oxygen from the water, causing anoxic conditions that lead to fish kills.

There are several species of harmful algae found in the Northeast United States, some of these blooms are well understood while others are emerging threats. The most well-studied HAB events are the seasonal blooms of Alexandrium catenella, the toxic dinoflagellate that causes paralytic shellfish poisoning (PSP). These blooms have occurred in New England on an annual basis since 1972. Toxic blooms of Pseudo-nitzschia, which produce domoic acid and cause amnesic shellfish poisoning, are a more recent phenomenon in New England waters. Other emerging HAB threats include Dinophysis, Margalefidinium, and Karenia mikimotoi.

State agencies are responsible for tracking HAB events and enacting fisheries closures when seafood consumption becomes unsafe. Scientists at Woods Hole Oceanographic Institution have been studying HABs for decades, and seasonal data collection is shared with managers and state officials responsible for making public health decisions. While rigorous monitoring and management have been implemented for PSP, scientists and managers must continue to work together closely to study emerging species and syndromes. WHOI researchers have received funding from NOAA’s National Center for Coastal Ocean Science to create an advanced multi-institutional observational network, (Link) HABON-NE, which will dramatically improve HAB surveillance in the region. Data collected through HABON-NE will be openly available, and will contribute to both early warning as well as future bloom forecasting.

See the timeline below for examples of notable HAB events in the Northeast United States: