Scientists Build Model for Predicting Blooms

The end of April usually brings the first signs of harmful algae in New England waters, and this year, researchers from the Woods Hole Oceanographic Institution (WHOI) and North Carolina State University (NC State) are preparing for a potentially big bloom.

A combination of abundant beds of algal seeds and excess winter precipitation have set the stage for a harmful algal bloom similar to the historic "red tide" of 2005, according to researchers from WHOI and NC State. The 2005 bloom shut down shellfish beds from the Bay of Fundy to Martha's Vineyard for several months and caused an estimated $50 million in losses to the Massachusetts shellfish industry alone.

Weather patterns and ocean conditions over the next few months will determine whether this year's algal growth approaches the troubles of 2005.

The research team—led by WHOI senior scientists Don Anderson and Dennis McGillicuddy and physical oceanographer Ruoying He of NC State—is several years into the development of a computer model to predict the intensity and location of blooms of the toxic algae Alexandrium fundyense in the Gulf of Maine.

Though the scientists are reluctant to make an official "forecast" (because the bloom outcomes are directly dependent on episodic weather events that cannot be predicted months in advance), colleagues in coastal management and fisheries believe that seasonal forecasting can already serve as a useful tool for preparing the seafood industry for contingencies.

"With advance warning of a potentially troublesome year for algae, shellfish farmers and fishermen might shift the timing of their harvest or postpone plans for expansion of aquaculture beds," said Anderson, director of the WHOI Coastal Ocean Institute. "Restaurants might make contingency plans for supplies of seafood during the summer, and state agencies can ensure they have adequate staff for the significant monitoring efforts that might be required to protect public health and the shellfish industry."

Seeds or "cysts" of A. fundyense naturally germinate and turn into cells that swim up from the seafloor around April 1 of each year. By the end of April, cells usually begin to appear in large numbers in the waters off coastal Maine.

The algae are notorious for producing a toxin that accumulates in clams, mussels, and other shellfish and can cause paralytic shellfish poisoning in humans who consume them.

According to a seafloor survey conducted in the fall of 2007 by Anderson's team, the number of Alexandrium cysts—the dormant, seed-like stage of the algae's life-cycle—is more than 30 percent higher than what was observed in the sediments prior to the historic bloom of 2005. The seed beds were especially rich in mid-coast Maine, origin of many of the cells that affect western Maine, New Hampshire, and Massachusetts.

"Our hypothesis is that cyst abundance is an indicator of the magnitude of the bloom," said McGillicuddy, a biological oceanographer in the WHOI Department of Applied Ocean Physics and Engineering. "If there is a large bloom offshore, then wind patterns and ocean currents in the next few weeks will determine whether it will be transported onshore and have an effect on coastal shellfish resources."

The research team has run its computer model through four scenarios, using the predominant wind patterns and ocean conditions from each year since 2004. Toxicity levels during those years have ranged from relatively low in 2004 and 2007 to extremely high levels in 2005 and 2006.

Coastal exposure to the blooms is worst for scenarios in which the spring weather was dominated by strong northeast winds, which tend to drive /Alexandrium/ cells toward the southern New England coast. When southwesterlies dominated, the algae tend to stay offshore. Even when there are a lot of cells and toxicity, the effect can be confined to offshore waters.

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