The Northeast Shelf ecosystem is among the
more productive of the world's 64 Large Marine Ecosystems (LMEs).
The most recently measured ecosystem wide levels of zooplankton
and primary productivity are close to the long term mean (1986
- 2006) of 40 cc 100m-3 and 337 gC m-2 y-1, respectively. However,
spatial and temporal variability has been observed among subareas
and seasonal pulses of the LME in zooplankton, chlorophyll, and
primary productivity are described in this Advisory.
- Sea surface temperature and surface chlorophyll
data exhibit a large amount of within and between year variability,
but there is an indication in recent years of a warming trend
in shelf-wide SST during fall. Inter-annual variability in fall
levels of chlorophyll has been large, making it difficult to
discern a shelf-wide trend; however, the northern areas of the
shelf have had depressed chlorophyll levels in recent years,
whereas the southern areas of have shown an increase.
- There is also substantial inter-annual
variability in zooplankton biomass, as represented by a biovolume
measurement, yet a long-term trend is apparent. Zooplankton
biomass during fall is increasing in some areas and decreasing
- Long term trends (1854-2006) in SST show
that the NE Shelf Ecosystem is warming, both in terms of annual
mean and fall temperatures, but SST has been higher in the past.
These same analyses show that the summer to winter range in
temperature is at its highest level recorded, suggesting that
the ecosystem is experiencing extreme ranges in temperature
and rapid heating and cooling rates.
- Ship of opportunity data shows that in situ
chlorophyll trends in the Gulf of Maine match those observed
in the satellite data, suggesting a decline in fall phytoplankton.
The principal fall zooplankton species, Centropages typicus
and Oithonia, have also declined in recent years.
- Analysis of regional phytoplankton
cycles shows that there is a high degree of year to year variability
in seasonal bloom and phytoplankton concentrations. In the northern
part of the ecosystem, the fall bloom in the Gulf of Maine and
on Georges Bank has declined and even failed to develop in some
years. In the southern areas the trends are less well developed.