Geoscience Reference
In-Depth Information
The hardy community of plants and animals that cling to the rocky coast have adapted to the daily rise and fall of tides
and relentless battering of waves.
As Mark D. Bertness points out in Atlantic Shorelines: Natural History and Ecology, “the critical feature of
tidal flats that differentiates them from rocky shores is that many of the conspicuous organisms living in soft
substrates are much larger than the particles they live in.” The organisms furthermore act as “ecosystem engin-
eers,” the worm tubes, grass stems, and mussel beds helping to stabilize the sediments. In other words, they
shore up their own houses by the act of living in them.
Rocky shores form a large part of the Atlantic coastline north of Cape Cod, where the glaciers stripped away
much of the sediment. What most distinguishes the rocky shores, besides the size of the substrate, is the clearly
visible vertical zonation of organisms, an expression of the strong physical stresses on these exposed, wave-
battered shorelines. Typical animals and plants have adapted to the environmental stresses at each level of the
intertidal zone: lichens in the spray or splash zone above extreme high water; blue green algae and rough peri-
winkles in the black zone, which is covered only by the highest tides. Below this high-water mark, in descend-
ing order, are the barnacle zone, a blazing white due to the limestone shells of the dominant barnacles; the
brown algae zone, where knotted wrack and bladder wrack clothe the rocks with luxuriant growth; and finally,
in the low intertidal zone, the Irish moss zone, the realm of the red algae. These zones and the organisms are
discussed in greater depth in Chapter 5, on the Gulf of Maine, where they have been intensively studied.
Offshore, many islands serve as nesting grounds for seabirds, such as gulls, auks, terns, and petrels, as well
as breeding and birthing grounds for seals. Far offshore, we encounter the fishing banks, notably Georges
Bank in the Gulf of Maine and the Grand Banks off Newfoundland. The banks stand out from the rest of the
continental shelf as shallow areas where sunlight penetrates into the water column and nutrients are found near
the surface, a combination that kick-starts the classic marine food web: salts, diatoms, copepods, shrimp, her-
ring—and ultimately, whales, seabirds, and humans. Finally, deep canyons project into the margins of the con-
tinental shelf and are home to rarely seen denizens of the deep.
