Geoscience Reference
In-Depth Information
right whale, with as few as three hundred to four hundred still in existence. Historically, they were hunted off
Cape Cod and adjoining waters, and the few that remain can still be found in the spring in the Great South
Channel region east of Cape Cod and Nantucket.
Satellite imagery demonstrates that the whales frequent very specific areas just to the north of a 100-meter
(300-foot) depth line, along the northern border of Georges Bank. South of this line, strong tidal currents keep
the water well mixed, and therefore colder, all year long. In spring, however, the surface water warms north of
this tidal mixing front. Along this front, where warm and cold waters meet, zooplankton concentrates into ex-
tremely dense patches, and it is here that right whales can be found in mid to late May. Whales also travel large
distances within the gulf itself in order to satisfy their energetic requirements. They are thus able to exploit the
patches of food on traditionally rich offshore fishing grounds as well as productive coastal areas, such as the
mouth of the Bay of Fundy.
Rocky Bands
The rocky shores that typify much of the coast of the Gulf of Maine north of Cape Elizabeth set it apart from
the coastal regions to the south, which are rimmed by sandy beaches backed by lagoons and salt marshes. In
northern New England, the glaciers scoured the shore of sediments, exposing the bedrock beneath. Daily, the
receding tide exposes a vast area where plants and animals have adapted to living on hard surfaces that cannot
be penetrated. Plants, such as the seaweeds, attach themselves to the substrate by holdfasts, and these gardens
of seaweeds provide cover and nutrients for a large array of marine vertebrates and invertebrates, and make a
significant contribution of energy to the coastal ecosystem.
The rocky shore, nevertheless, is an extremely stressful environment. Not only is it subject to the battering
energy of waves, but the rise and fall of tide exposes the plants and animals, alternately, to daily wetting and
drying. Furthermore, rainfall can cause dilution; sun, desiccation; and winter freezing and thawing cycles add
further stress. Lacking root systems, the plants cannot adapt by allowing their exposed parts to die back.
Neither can animals burrow to hide from these stressors as animals can in softer substrates like sand or mud.
But, for the plants that attach themselves to the rocky shore and for the animals that are able to cling to it, there
are certain advantages. Precisely because the environment is so stressful, there is little competition for the
rocky real estate from other plants, and for the animals there are fewer species of predators. As well, the turbu-
lent waters that ebb and flow over the rocky shores carry with them not only ample supplies of oxygen, carbon
dioxide, and dissolved nutrients, but food for passive filter feeders such as barnacles and blue mussels. As a
result, production along the rocky coast can be extremely high.
Along the rocky shorelines of the boreal coast, from Cape Cod north to Labrador, the intertidal habitat—the
area bracketed by the highest and lowest tides—is characterized by distinct biotic zones where a typical com-
munity of plants and animals has adapted to the rise and fall of the tide. These organisms align themselves in
more or less horizontal bands, which are examined below, in order, moving from the land toward the low-wa-
ter mark.
The spray or splash zone, as the name implies, occurs above the tide line but is subject to marine influence
when waves crash against the shore, sending their spray above the highest high tide mark. It is an ecotone—a
transitional zone between the terrestrial and marine zones that belongs wholly to neither one. It occurs in areas
exposed to the full brunt of the ocean swells, such as outer islands and rocky capes, rather than in more
sheltered places, such as coves. In the latter case, terrestrial plants may grow to the limit of the highest spring
tides. The plants that have adapted to the spray zone have a terrestrial origin but have evolved means to deal
with salt. In particular, a number of species of yellow lichens flourish there, painting the often dull rocks with
splashes of color. All lichen consist of two plant species, an alga and a fungus, functioning together in a symbi-
otic relationship. The fungus provides a moist protective environment for the alga by absorbing water, while
the alga produces organic compounds through photosynthesis to nourish the fungus. The alga also has little
