October 5, 2004
NMFS Northeast Fisheries Science Center
Plankton Boost Detected in Northern
Ocean Water off the U.S.
finmarchicus. Photo: C.B. Miller/K. Tande
1. 2004 Calanus numbers, sea surface salinity, and sea surface temperatures
across the northern Northeast Shelf LME plotted against 1961-1990
average (solid line=average; dashed line=variations from average;
stars=actual values from container ship data collected in 2004)
Narragansett, RI – This past summer,
a key zooplankton species on the northern U.S. continental shelf
was more than 14 times its 30-year average population size. The
boost meant plenty of food for haddock and Atlantic cod born this
year, and for endangered North Atlantic right whales in the area.
NOAA Fisheries scientists at the Northeast Fisheries
Science Center’s Narragansett Laboratory discovered the spike
after reviewing this summer’s field data. NOAA Fisheries
is the federal agency charged with studying and managing living
marine resources in U.S. waters.
Six species of copepods (tiny crustaceans) make up
most of the zooplankton population in the Gulf of Maine and on
Georges Bank. The very large zooplankton increase this year is
attributed almost entirely to one of those species, Calanus
which also grow to the largest size among the six species. The
increase in population was measured against the 1961-1990 average
(Figure 1, left).
The Calanus increase likely occurred throughout the
northern portion of the Northeast U.S. Continental Shelf large
marine ecosystem (LME), which includes waters from Maine to North
Carolina. An LME is a region of ocean space encompassing coastal
areas from river basins and estuaries to the seaward boundaries
of continental shelves and the outer margins of the major current
“We think that the big increase may have
happened because a mass of cold water from Labrador moved into
the northeast shelf waters during the Spring, which
up the chlorophyll level – meaning
lots of microscopic plant life, and that’s
what Calanus eat,” says Dr. Kenneth Sherman, who
has worked on plankton in the Northeast since the early 1970s.
These observations add support to analyses conducted by the
Narragansett Lab earlier this year that show phytoplankton and
zooplankton production on the shallower Northeast Continental
Shelf has been both robust and stable for nearly 25 years. This
means that the base of the food web, primary producers and prey
fields important to marine life, of the Northeastern Shelf LME
is in good condition.
Sherman and other scientists have been collecting
information on zooplankton abundance using commercial container
vessels operating between Boston,
Massachusetts and Halifax, Nova Scotia
2. Satellite imagery (AVHRR), Spring 2004, showing cooler than average
temperatures in the northern Northeast Shelf LME
3. Satellite imagery(SeaWiFs), Spring 2004, showing above average
in the northern Northeast Shelf LME
for the past 44 years. Zooplankton are collected on monthly transects
by these vessels, along with contemporaneous data on sea water
conditions during sampling. In recent years, the scientists have
been able to compare these data with other observations gathered
by NOAA and NASA satellite-bourne instrumentation that sense sea
temperature and chlorophyll levels.
Satellite-derived imagery for Spring 2004 indeed shows both lower
sea temperatures in Spring (Figure 2, above) and
broad-scale chlorophyll increases (Figure 3, left) over
the northern area of the Northeast Shelf large marine ecosystem.
Analyses of the longer time-series of data also suggest that this
year’s incursion of Labrador water is related to events further
north, affecting the Scotian Shelf and Newfoundland-Labrador LMEs.
In those systems, scientists have tracked increasing incursions
of cooler water, believed to be the result of the southward movement
of lower-salinity, colder waters introduced when Arctic ice melts.
The observations reported are based
on the multi-decadal Marine Resources Monitoring and Assessment
(MARMAP) Program conducted by the Narragansett Laboratory. The
MARMAP program is one of the ocean monitoring activities contributing
information to NOAA’s Earth Observing System.