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2011 New England "Red Tide" Outlook and Management Response

Published on: 04/25/2011

In April 2011 scientists from the National Centers for Coastal Ocean Science-funded Gulf of Maine Toxicity (GOMTOX ) project issued an outlook for a moderate regional bloom of the toxic alga, Alexandrium fundyense, that can cause 'red tides' in the spring and summer of this year, threatening the New England shellfish industry. However, there are signs the bloom this year could be suppressed by recent changes in ocean conditions in the Gulf of Maine.

The 2011 forecast was based on runs of a biological-physical model, developed with ECOHAB and MERHAB support, using weather scenarios typical of the last few years. A critical component of the model is a map of Alexandrium 'resting' cysts on the seafloor, conducted every fall, as an indicator of bloom potential the next spring. The cysts of Alexandrium act as seeds and germinate every spring when conditions are right.

A cyst survey conducted in late 2010 showed a modest amount of cysts present in coastal sediments, not as high as the abundances prior to the major red tides of 2005 and 2008. The 2011 bloom could be an intermediate case, falling somewhere in between the large blooms of 2005 and 2008, and more mild outbreaks in 2006 and 2007.

The extent and severity of the bloom and the likelihood of it making landfall and affecting coastal resources will largely depend oceanographic and meteorological conditions during the spring and summer. Changing characteristics of water in the Gulf of Maine can have a direct effect on the growing conditions for Alexandrium. For example, in 2010 near-surface coastal waters were warmer, fresher, with lower in nutrients than usual. The GOMTOX team believes this suppressed what otherwise would have been a major regional bloom, which had in fact been forecast for that year. Similar conditions may be occurring again this year, which may reduce the overall severity of the bloom. In addition the extent to which any bloom causes shellfish toxicity depends on the wind patterns during the normal bloom season of May, June, and July.

Alexandrium blooms are one of several algal bloom types often called "red tides," but more correctly referred to as harmful algal blooms (HABs). Alexandrium produces a potent toxin that accumulates in shellfish and can cause illness in humans, Paralytic Shellfish Poisoning (PSP), who eat contaminated shellfish. States have well-established, rigorous shellfish monitoring programs to protect human health, so consumers are assured that shellfish are safe for consumption.

For more on the 2011 forecast, see the WHOI press release.

Management Response and Status

In southern Maine, toxicity was first reported on April 20, 2011 in mussels in the Harpswell area and the New Meadows River. Since then the closures have expanded and more species have been added. An area in eastern Maine was closed to mussel harvesting on May 13, but there have not been major changes since that time.

In Massachusetts some parts of the Nauset system on Cape Cod were closed to harvesting on April 2. The area was expanded on May 2 and the entire Nauset System was closed to harvest of all shellfish on May 6. Blooms in this area are thought to be isolated events that are not directly linked to blooms in the Gulf of Maine. On May 19, harvesting of all shellfish species along the north shore of Massachusetts was closed, with some exception areas. The area has subsequently been expanded.

On May 6 a bloom of Alexandrium fundyense in Shinnecock Bay triggered shellfish testing and closure of shellfish harvesting in Shinnecock Bay on Long Island in New York. This is the first time an area outside of the Northport/Huntington complex of bays and harbors on Long Island has been closed. On May 12 the entire Northport Bay/Huntington complex was closed to all shellfish harvesting. The ban was lifted for Shinnecock Bay and Huntington Bay on June 6, 2011, but the shellfish harvesting closure in Northport Bay, including Centerport Harbor, Duck Island Harbor remains in effect. The connection of these Long Island blooms to blooms in the Gulf of Maine is currently being investigated. NCCOS event response provided funding last year to assist the State of New York in maintaining its shellfish monitoring.

For up-to-date information on shellfish closures, visit the following:

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