MAPPING THE BLOOM—These maps of coastal New England waters reveal the distribution of the harmful algae Alexandrium as surveyed by scientists from May 10-16 on their way north, and again on May 16-18 as they were cruising south. (The ship did not survey below the latitude of Boston.) Bright reds and oranges depict areas with the highest concentrations of algae; blues show area of minimal concentration. The evenly spaced white dots mark the locations where WHOI scientists collected water samples on the May 9-18 expedition. (Woods Hole Oceanographic Institution illustration)
WHOI researchers attach hooks to retrieve a CTD rosette, which collects water samples and measures conductivity, temperature, salinity, and other water properties. The research team raised and lowered the CTD 160 times on an nine-day expedition, collecting nearly 500 samples. (Photo by Clindor Cacho, WHOI)
Coastal resource managers shut down shellfish beds in three New
England states in mid-May—including rare closures of Massachusetts Bay
and Cape Cod Bay—because of an intense bloom of the toxic algae Alexandrium fundyense. Researchers from the Woods Hole Oceanographic Institution saw the “red tide” coming before its toxic effects reached the shore.
The bloom of Alexandrium—the worst since 1972—began just as biologists and oceanographers departed Woods Hole on May 9 on R/V Oceanus
for a long-planned research expedition to study the harmful algae.
Within hours of reaching open waters east of Boston and Cape Ann, the
team led by physical oceanographer Dennis McGillicuddy and marine
biologists Deana Erdner and Bruce Keafer found hundreds to thousands of
algal cells in every liter of water sampled from the ocean.
McGillicuddy
and Keafer traded daily cell phone and e-mail messages with their
counterparts on land, including WHOI Senior Scientist Don Anderson and
colleagues from several fishery and water resource agencies in
Massachusetts, New Hampshire, and Maine. Though some shellfish beds in
Maine and New Hampshire were closed just before the cruise, managers in
Massachusetts had not yet detected toxic algae within the Bay. It was
just a matter of time.
Sailing right into the bloom
On an expedition that took them from edge of Boston Harbor to the
middle of the Bay of Fundy, the WHOI researchers worked around the
clock for eight days. They collected nearly 500 water samples from 160
locations in the Gulf of Maine as they surveyed and mapped the location
of Alexandrium
cells. Using novel genetic probe techniques developed at WHOI and the
Monterey Bay Aquarium Research Institute, the shipboard scientists were
able to rapidly detect and quantify the amount of harmful algae in
offshore waters. At the same time, researchers on the ship and at
Dartmouth College provided oceanographic models of where ocean currents
were likely to carry the cells.
The researchers detected a mother lode of Alexandrium
on the western edge of the Gulf of Maine and in Massachusetts Bay. The
algae are notorious for producing a toxin that accumulates in clams,
mussels, and other shellfish and can cause paralytic shellfish
poisoning (PSP) in humans who consume them. Alexandrium is
naturally distributed throughout New England waters, though it
typically develops into large-scale blooms only in waters off Maine and
Canada, with intensities varying from year to year.
The
research expedition was the first ever for the Woods Hole Center for
Oceans and Human Health, a new center funded by the National Science
Foundation and the National Institute of Environmental Health Sciences.
(See “Risks and Remedies from the Sea.”)
The purpose of the research cruise was to analyze and model how
physical, chemical, and biological factors combine to distribute and
disperse Alexandrium throughout New England waters.
Researchers also hoped to discern how those factors can naturally
select for certain strains of the organism—which vary widely in their
toxicity—to favor blooms at different times.
An assortment of possible causes In
most years, natural current and wind patterns keep the cells from
flowing into the coastal waters of southern New England. But during a
spring marked by unusual amounts of rain and snowmelt and steady stream
of northerly and easterly winds—capped by nor’easters on May 7-8 and
May 24—ocean conditions developed almost perfectly for a massive bloom.
Anderson
and McGillicuddy offered several possible explanations for the
widespread algae bloom. The first is that the unusual weather patterns
this spring—particularly the wind-driven currents from the north—pushed
an abundance of Alexandrium cells south into Massachusetts
Bay and Cape Cod Bay. Another idea is that there was a larger source of
cells in the Gulf of Maine, following an intense bloom off western
Maine in autumn 2004. Or perhaps the record-setting precipitation of
this winter and spring flushed more fresh water and nutrients into the
coastal region, creating better conditions for the cells to grow and
reproduce. Finally, ocean conditions this year may have favored a
particular strain, or genotype, of Alexandrium in the western Gulf of Maine.
In
response to the large-scale bloom, WHOI researchers have been granted
“rapid response” funds from the Center for Sponsored Coastal Ocean
Research at the National Ocean Service to follow up and extend their studies of this bloom for several more weeks. Using WHOI’s coastal research vessel Tioga, McGillicuddy and Keafer will conduct at least two more surveys of Massachusetts Bay and Cape Cod Bay in June.
In
the coming months, marine biologists will examine the genetic makeup of
the cells they collected to decipher the diversity of the Alexandrium
population. Chemists will analyze dissolved nutrients in water samples
to find the natural blends that promote or hamper the algae’s growth.
Physical oceanographers at WHOI, Dartmouth, and the Northeast Fisheries
Science Center will refine their models of how ocean currents and North
Atlantic weather patterns affect the distribution and intensity of Alexandrium blooms. Together they will sort out the confluence of factors that produce harmful algal blooms in New England waters.
