|Monday, June 20, 2005
Red Tide Outbreak 2005
Through the last few weeks of late spring, eastern New England has experienced the worst red tide outbreak in decades. Red tide, which is the common name for a highly toxic algae called Alexandrium fundyense, can profoundly impact the harvesting of widely popular shellfish such as soft- and hardshell clams and oysters because these shellfish ingest the algae and make it unsafe for human consumption.
Shellfish beds are now closed throughout the coast of Maine and Massachusetts, prompting appeals for federal disaster assistance, which has just been granted. Governors of both states have declared state emergencies for economic losses due to the closures.
While officials and scientists struggle to keep up with the heavy workload the disaster has caused, the Provincetown Center for Coastal Studies (PCCS) has put together a team to help scientists at Woods Hole Oceanographic Institution (WHOI) monitor the red tide bloom. Since late May, weekly cruises have been conducted on the R/V Shearwater, sampling for red tide in Cape Cod Bay and at stations east of Cape Cod up to 20 miles offshore. Samples are taken to Woods Hole and immediately analyzed by WHOI scientists.
Red tide occurs naturally every few years in the Gulf of Maine, but this year as a result of an unusual combination of environmental conditions, it has spread rapidly along the coast of southern Massachusetts into Cape Cod Bay and waters east and south of Cape Cod.
Alexandrium fundyense, the predominant red tide algal species found in the Gulf of Maine, produces a potent neurotoxin known as saxitoxin that accumulates in shellfish feeding on these organisms and consequently causes food poisoning in animals that eat the shellfish. Humans are vulnerable to paralytic shellfish poisoning (PSP) only when they eat shellfish that have dangerously high concentrations of the toxin. The shellfish will flush the toxin from their systems within a couple of weeks after the red tide recedes. No one in New England has become ill or has died from red tide since it first appeared in the Gulf of Maine in 1972.
This year's exceptional red tide bloom is thought to have been caused by a combination of environmental factors and weather events that created the perfect conditions for the algae to thrive and spread. Phytoplankton, including red tide species, bloom in the spring after winter storms and cooler temperatures cause nutrient rich bottom water to mix with surface water. Algae favor water conditions such as low salinity and warmer temperatures, which often develop when springtime rains and snowmelt attend the warming atmosphere. In the spring, as more sunlight penetrates the nutrient- rich water, the algae begin to thrive. When the nutrients are depleted, the blooms naturally die off.
This year, cold weather and two nor'easters altered conditions enough to create this historical red tide event. Currents would normally have taken the algae out to sea, but two nor'easters in May pushed the Alexandrium cells into Massachusetts and Cape Cod Bays. Heavy rains from the two storms washed nutrients off the land into coastal waters, exacerbating the bloom. Finally, warm, sunny days following these events caused the algae to grow exponentially.
Similar conditions caused the first massive red tide bloom in 1972, when a slow-moving hurricane passed into the Gulf of Maine and encountered a large Alexandrium bloom in the Bay of Fundy. Strong winds blew the red tide to the Maine shore where coastal currents pulled the cells into the waters of Maine, New Hampshire and Massachusetts.
Like many species that fall under the loose category of red tide, Alexandrium fundyense is a dinoflagelette, an organism able to propel itself through the water using a tail-like appendage. These organisms are able to travel vertically through the water column feeding on nutrients below the photic zone where other algae cannot penetrate.
When sunlight and nutrients are plentiful, Alexandrium reproduces asexually by cell division. Toward the end of the bloom cycle, as nutrients dissipate and populations become dense enough, the organisms begin to reproduce sexually by forming cysts. These cysts sink to the ocean bottom and can lie dormant for years until conditions are favorable for another bloom.
WHOI scientists have found evidence that the Alexandrium cells are producing cysts that will sink and seed areas previously void of the organism. There is concern that this year's bloom may form large cyst fields with the potential to cause intense red tide blooms for years to come.
To learn more about the 2005 red tide outbreak:
Commonwealth of Massachusetts Department of Public Health
Public Health Fact Sheet: Information on Red Tide
Massachusetts Division of Marine Fisheries
Updates On Closures
Sponsored by Woods Hole Oceanographic Institution and the National Oceanographic and Atmospheric Administration
The Harmful Algae Page