"The surveys of cyst abundance gives us an indication of the potential extent of the bloom, but whether or not that potential is realized depends on the growing conditions," said McGillicuddy. "In 2010 we forecast a large bloom but we got it wrong. That spring, an unusual mass of warm, fresh water that was low in nutrients changed the growing conditions."
Wind direction imposes another uncertainty to the forecast. For example, strong northeast winds in the spring and early summer drive the bloom inland toward coastal shellfish beds. In contrast, when southwesterlies dominate, the algae tend to stay offshore.
"Each year, we add another set of environmental conditions to our archive of model runs. In the future, a winter that is warmer and drier than normal can be represented by 2012, but right now, we have no similar year in that archive," said Anderson.
In order to protect public health, shellfish beds are closed when toxicities rise above a quarantine level, often during the peak harvesting season. Due to effective monitoring by state agencies, there have been no illnesses from legally harvested shellfish in recent years, despite some severe blooms during that time period. There have been, however, several severe poisonings of individuals who ignored closure signs.
The economic impacts of PSP toxicity are significant in the region. Direct and indirect costs of the extensive Alexandrium bloom in 2005 were estimated at nearly $50 million for Massachusetts and $23 million for Maine.
The 2012 designation of a "moderate" bloom now has a specific, quantifiable meaning, thanks to a complementary research effort by Anderson and his colleagues to develop forecast terminology to describe a bloom's potential impact. As part of that work, Judy Kleindinst, a member of Anderson's team,
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Woods Hole Oceanographic Institution