Dennis McGillicuddy and Ruoying He have developed a computer model of the dynamics and dispersion of the harmful algae Alexandrium fundyense. (Photo by Mike Carlowicz, WHOI)
Related Multimedia
"Hindcast" model of 2005 red tide Oceanographers have developed a computer model to simulate last year's historic bloom of toxic algae. Data visualization by Ruoying He and Dennis McGillicuddy, WHOI
Model of 2006 Alexandrium season WHOI researchers have been running their model in real time this spring. Data visualization by Ruoying He and Dennis McGillicuddy, WHOI
The algae Alexandrium fundyense are notorious for producing a toxin
that accumulates in shellfish such as clams, mussels, and oysters, leading to
paralytic shellfish poisoning in humans. The microscopic plants are
naturally distributed in New England waters, but in some
years—2005, for example—a confluence of factors causes major blooms
that spread down the coast and force officials to close shellfish beds.
To protect consumers, and the livelihoods of
shellfishermen from Maine to Massachusetts, researchers would like to
able to forecast when and where Alexandrium will bloom and to explain
how and why. In a project sponsored by the Woods Hole Center for Oceans
and Human Health, scientists Dennis McGillicuddy and Ruoying He of
Woods Hole Oceanographic Institution have developed a mathematical
model of Alexandrium dynamics—a series of equations that captures the
physical and biological factors involved in harmful algal blooms in New
England.
Millions and millions of calculations Working with colleagues in the biology lab of WHOI
Senior Scientist Don Anderson, McGillicuddy and He entered a range of
factors into their model: the speeds and directions of ocean currents,
water temperature and salinity, winds, surface heat exchanges, tides,
river runoff, and the distribution and behavior of Alexandrium cells in
the water and in seafloor sediments. The team—aided by WHOI researchers
Valery Kosnyrev, Olga Kosnyreva, and Larry Anderson—also incorporated
other computer models that describe waterborne nutrients, solar
radiation, and large-scale motions in the North Atlantic Ocean.
“The beauty of a numerical model,” McGillicuddy said, “is that it can
be used to investigate extraordinarily complex systems by posing the
problem in terms of a few guiding principles expressed as mathematical
equations.”
Plug numbers into the equations, and the model develops a big picture
of how the algae spread as a result of the interactions of all those
variables. Using a 32-processor “mini-supercomputer,” as He calls it,
it can take two days to make all of the calculations necessary to
simulate three months of Alexandrium dynamics at more than a million
different points in the Gulf of Maine.
How does a bloom end? The project has been under way for several years,
but the work grew more intense and fruitful in 2005. A devastating
bloom provoked researchers from WHOI and a dozen federal and state
agencies to launch a substantial effort to gather observations of ocean
conditions during the event. That fieldwork has allowed He and
McGillicuddy to run an extensive “hindcast” of the 2005 bloom; that is,
they were able to plug real environmental data into their computer
model and see if it could reproduce what actually happened.
“We wanted to compare the model against new observations to see if we
really understood the system or if we were just fooling ourselves,”
said McGillicuddy.
The model successfully captured how intense spring northeasterly winds
and prodigious river runoff, coupled with a huge seed population of
Alexandrium cysts, blossomed
into a red tide that blanketed New England
waters from Canada’s Bay of Fundy to Martha’s Vineyard. The event had
an estimated $20 million impact on the seafood industry in New England,
according to researchers at the WHOI Marine Policy Center.
The principal flaw in the model’s 2005 projection is that it could not
replicate the end of the bloom, which occurred in July. “What processes
regulate the end of a bloom and make it shut down?” said He. “We just
don’t know enough yet about mortality in Alexandrium, and we are still
trying to improve the modeling of this process.”
But the team was encouraged enough to try to track the 2006 season as
it develops. Though they are not willing to make public predictions, He
and McGillicuddy have been plugging in field observations this spring,
letting their model run into the future, and then seeing how well it
did. So far, their computerized bloom seems to jibe with the milder blooming realities
of 2006.
This research is supported NOAA's Center for Sponsored Coastal Ocean
Research and by the National Science Foundation and the
National Institute of Environmental Health Sciences through the Woods
Hole Center for Oceans and Human Health.
Finding risks and remedies from the
sea
With a rising tide of harmful algal
blooms and waterborne pathogenic
microbes causing illnesses and closing beaches and shellfish beds,
policymakers recognized a growing need to examine links between the
oceans and human health. But few links existed between oceanogaphers
and scientists specializing in human health.
In
2004, two
federal scientific agencies that rarely interacted embarked on a
groundbreaking collaboration, which sparked a cascade of novel
partnerships. The National Science Foundation’s Division of Ocean
Sciences and the National Institute of Environmental Health Sciences
created four Centers for Oceans and Human Health (COHH) around the
country, including one in Woods Hole, Mass. Each center harnessed the
expertise and resources of scientists from several institutions and
disciplines to study “risks and remedies from the sea” (the remedies
being potential pharmaceuticals from marine
sources).
The Woods
Hole Center for Oceans and Human Health, for example, has brought
together physical oceanographers, biological oceanographers,
microbiologists, and genomics experts from Woods Hole Oceanographic
Institution (WHOI) , the Marine Biological Laboratory, and the
Massachusetts Institute of Technology, said John Stegeman, director of
the center and a WHOI biologist.
“The ocean is a
turbulent,
fluid medium that’s changing all the time,” said Dennis McGillicuddy, a
WHOI physical oceanographer and the center’s deputy director. “To make
significant progress in health concerns, we have to grapple with how
physics, biology, and chemistry intersect and interact. It’s really a
fundamentally new direction for this research.”
In its first two years, the Woods Hole COHH launched several
investigations on algae, bacteria, viruses, and other organisms that
threaten to compromise the safety of our seafood supply and the
commercial and recreational use of coastal waters.
