New Maps Provide Clues to the Historic 2005 Red Tide Outbreak in New England And Hints for 2006


April 13, 2006

Scientists at the Woods Hole Oceanographic Institution (WHOI) have
completed two extensive survey and mapping efforts to better understand
why the 2005 New England red tide was so severe and to suggest what
might lie ahead.  WHOI Senior Scientist Don Anderson
and colleagues mapped the distribution of Alexandrium fundyense cysts
in seafloor sediments immediately before and after the historic harmful
algal bloom of 2005. The first of these analyses shows unusually large
numbers of cysts of Alexandrium fundyense in bottom sediments of the
Gulf of Maine in late 2004, compared to previous survey results from
1997. The hardy, seed-like cysts lie dormant in ocean sediments until
growing conditions are favorable for a bloom of this toxic alga. 
A subsequent survey conducted last fall, after the 2005 outbreak, shows
slightly fewer cysts in the sediments than there were in 2004, with the
abundance and distribution of those cysts giving a hint of what might
be in store for 2006.

“This is partially good news since the 2005 cyst distribution shows
that the species did not create a new southern ‘seedbed’ within
Massachusetts Bay and southern waters, as we had feared. The cyst
abundance we found there may be too low to initiate blooms in the bay
proper, although we don’t know if there are cysts in harbors or
embayments that might lead to localized toxicity,” said Anderson,
director of the National
Office for Marine Biotoxins and Harmful Algal Blooms, based at WHOI.
“On the other hand, there are still five times as many cysts off
western Maine as there were in 1997 and only slightly less than in
2004, so there is certainly the potential for another regional
event.”

The presence of large numbers of cysts does not guarantee that 2006
will bring another widespread bloom in southern New England.  The
large seedbed that has just been mapped supports the likelihood of a
significant bloom for the region as a whole.  Cells germinated off
the coast of Maine tend to be transported south and west by
regional-scale ocean currents.  Whether or not those cells make
landfall in Massachusetts and Cape Cod Bays depends on the wind. 
“If we have persistent winds from the northeast this spring and early
summer, there is a higher probability for a bloom and shellfish
closures within the bay, whereas if we get winds from the southwest,
which is more common for those months, that scenario is less likely,”
Anderson said.

These inferences are based on knowledge gained from a decade or more of research on Alexandrium and its blooms in the Gulf of Maine. The distribution and transport of Alexandrium
cells has been documented through numerous blooms, and sophisticated
computer models have been developed that allow the WHOI researchers to
evaluate the relative importance of the cyst seedbeds, weather
patterns, and other factors. Coupled with real-time oceanographic
observations, such as those provided by the Gulf of Maine Ocean
Observing System (GoMOOS), the prospect for bloom forecasts is
brightening.

Looking at the longer term, Anderson and colleagues are wondering if
southern New England may be entering a period of more frequent and
extensive toxicity. Another massive Alexandrium fundyense bloom in 1972 was
followed by two decades of heightened toxicity in Massachusetts Bay
that did not slacken until the early 1990s.  In western Maine and
northern Massachusetts, the toxicity that began in 1972 has not
relented.

The outbreak of Alexandrium fundyense in 2005 was the most widespread
and intense in New England since 1972, with concentrations of toxic
algae growing to 40 – 100 times the normal number and spreading to
regions usually unaffected by the species. Toxins from this toxic algae
can cause paralytic shellfish poisoning in humans who eat shellfish
that have ingested the toxic algae as they feed.   

From May to December 2005, a group from Anderson’s laboratory made a
dozen trips to track the bloom and then to map out its cyst “footprint”
on the WHOI-operated research vessels Oceanus and Tioga, as well as the
Environmental Protection Agency’s (EPA) ocean survey vessel Bold.
The effort
was made possible by  “event response” funds from the National
Oceanic and Atmospheric Administration’s National Ocean Service, Center
for Sponsored Coastal Ocean Research (NOS/CSCOR), and a major research grant
from the National Science Foundation and the National Institute of
Environmental
Health Sciences to  the Woods Hole
Center for Oceans and Human Health. Ship time on the Bold was provided
by the EPA.  

With prior support from NOAA’s National Centers for Coastal Ocean
Science, Anderson’s group had previously conducted an extensive
cyst survey in
the fall of 2004, unaware that a massive bloom was coming a few months
later in 2005.  That survey revealed a substantial seed population
waiting for the favorable growing conditions that developed in the
spring
of 2005. The cyst population in New England waters at the end of 2004
was
10 times larger than when it was last mapped in 1997, with the bulk of
this increase occurring off western Maine.

 “We believe the very high abundance of cysts off western Maine
was a critical factor in the 2005 bloom,” said Anderson. “We don’t know
when they were laid down between 1997 and 2004, but we do know that
they were in place immediately prior to the historic bloom.” An unusual
late-season bloom of Alexandrium in that region in the fall of 2004 may
have deposited the cysts.

As they now work to analyze the cyst map produced
after the 2005 bloom, Anderson’s group is puzzled by the low abundance of
cysts in Massachusetts Bay and the waters to the south of
Cape Cod.  They expected to find more cysts because the bloom had
very high cell abundances in those bays, and spread as far south as
Martha’s Vineyard and Nantucket.  “We thought we would have much
higher numbers down there,” Anderson said. “Frankly, we are scratching
our heads trying to figure out why we don’t have more.”
 
One theory is that marine animals such as microscopic zooplankton may
have eaten the Alexandrium
cells, terminating the bloom before the
cells were able to go through the process to make cysts and settle into
the sediments. Another line of thinking suggests that the cells were
dispersed naturally by winds and currents before they could aggregate
into the concentrated populations needed for cyst formation. Lastly, it
may be that the sandy, coarse-grained sediments characteristic of many
areas offshore of southern New England may not be favorable to
retention of cysts deposited on the bottom.

In parallel with the mapping efforts, researchers in Anderson’s lab are
also exploring the genetics of the 2005 bloom.  They have isolated
and cultured the cells from that bloom, analyzing the genetic and
physiological makeup of Alexandrium communities from various locations.

The study is focused on the idea that, as with humans, a single
population of algae is actually composed of different “races” or
genotypes. For Alexandrium, each genotype varies in the types and
amounts of toxins it produces, so knowing the distribution of genotypes
and their preferred environmental conditions could help researchers
someday predict the extent and toxicity of blooms.

WHOI Research Associate Bruce Keafer, who led many of the 2005 surveys
for Anderson’s team, has scheduled at least eight surveys of New
England waters this spring to observe the development of the toxic
algae.  Cruises began this week, again with support from
NOAA’s CSCOR program.