Stellwagen Bank Information
- Physical characteristics:
- Stellwagen Bank sanctuary = 628 square nautical miles
- Located in the Gulf of Maine.
- 26 miles from Boston , 6 north of Provincetown, Mass 7 miles
southeast of Gloucester, Mass.
- The bank is an underwater triangular plateau 18.5 mi. X 6.25
mi. X 2.5 mi.
- Shallowest point = 71.5 feet. Sides drop off steeply to depths
> 300 feet. These sides are steep on the landward side and
drop gradually on the seaward side.
- Geology:
- Throughout history the bank has been both above and below
sea level.
- The last glaciation (75,000 years ago) pushed debris in front
of it as it moved into present day Cape Cod.
- The weight of the glacier pushed the land below sea level.
- When the glacier retreated (18,000 years ago) it left behind
the sand and gravel debris which formed the plateau.
- The bank's ecosystem:
- "Stellwagen Bank is best described as a complex system
of plants and animals whose lives are interdependent, delicately
balanced, and sensitive to a myriad of constantly changing physical
and chemical processes." (Ward, pg. 34)
- Water currents and cycles move nutrients, pollutants, and
marine animals about the area.
- Nutrients:
- East / west currents caused by tides create areas of turbulence
as they move along the bottom and become uplifted by the bank.
- Nutrients are created by the decomposition of plants and animals
whose remains fall to the bottom.
- Upwelling currents send nutrients upward from the bottom to
serve as food for other marine animals.
- Nutrients are also created on land in salt marshes, and coastal
estuaries and carried outward by tides.
- Cold water from the northern Gulf of Maine moves southward
and brings along much nutrient rich water.
- Pollutants:
- The Gulf of Maine current collects run off from the land as
it pass river mouths in Maine, New Hampshire, and Massachusetts.
- Land pollutants can enter the ocean through this run off.
- Most of the banks pollutants come from this run off.
- Ocean pollutants such as oil and toxic chemicals from ships
or debris from ocean dumps moves with currents form all directions.
- Marine animals:
- Many species of animal such as barnacles, clams, and jelly
fish use the currents to disperse their young by releasing larvae
to drift about to new areas of colonization.
- Plankton
- Plankton forms a microscopic ecosystem. Millions of plants
and animals found in each gallon of sea water.
- Phytoplankton = plant life
- Primary producers
- 50 species.
- Use sunlight, water borne nutrients, and clean water to begin
photosynthesis.
- The first step in all food webs.
- Zooplankton = animal life
- First order consumers.
- 75 species.
- Some are miniature animals such as copepods
- Some are larval stages of animals such as snails, lobsters,
jellyfish, cod, flounder,...
- These animals eat phytoplankton.
- Seasonal Change and phytoplankton
- Summer:
- Phytoplankton (microscopic plants) gather energy through photosynthesis
from May to September. When they die and decompose, they sink
to the bottom.
- Warm surface water (up to 68 deg. F.) separates from cold
bottom water (50 deg. F.) by a boundary layer called the thermocline
(approximately 16 feet deep).
- The thermocline prevents decomposed nutrients from upwelling
to the surface where it could be used by other phytoplankton.
- Upwelling currents along the bank can become strong enough
to break through the thermocline.
- Fall
- Surface temperatures fall and the thermocline disappears allowing
upwelling to occur carrying many nutrients to the surface again.
- Photosynthesis declines throughout the fall as sunlight fades.
- Winter
- Very little photosynthesis occurs but great amounts of nutrients
rise from the bottom.
- Spring
- Nutrients from the bottom combined with increasing photosynthesis
(from increasing sunlight) create a "bloom" of phytoplankton.
The water can turn green.
- The marine food web
- Phytoplankton are consumed by zooplankton.
- Zooplankton are consumed by fish, sea birds, and filter feeders.
- Surface waters.
- Lots of plankton activity.
- Marine mammals such as sea turtles, whales, are most active.
- Sea birds prey on sand lances and herring.
- Mid water
- Sinking plankton consumed here.
- Herring, squid, jellyfish float throughout this layer.
- Humpback whales, and tuna drive schools of fish to surface
to catch.
- Benthos (Bottom) waters
- Detritus (decaying dead marine plants and animals) collects.
- Bottom feeders such as sculpins, lobsters, codfish, pollock,
and flounder feed here.
- Other animals include: sea anemones, sponges, clams, and scallops.