Geoscience Reference
In-Depth Information
holdfasts that glue the organism to the surface. Another so-called lichen that thrives in the spray zone is the
bryozoan Licheno-pora verrucaria, which grows in tarlike patches. Despite appearance, bryozoans are not
plants but colonial animals. Bryozoa literally means “moss animals,” and they are sometimes referred to as
“sea mats.” Individual colonies may cover several square centimeters, but it is difficult to know where one
colony ends and another begins.
A nor'easter spends its winter fury against the rocky shores of Acadia National Park in Maine.
The black zone is the highest of the intertidal zones and is only covered by the tide twice daily during the
highest course of spring tides. Nevertheless, unlike organisms in the spray zone, which are merely tolerant of
salt, those that live in the black zone are dependent upon periodic exposure to the tides. This zone takes its
name from the blue green algae that clothe the rocks in black, which Rachel Carson called “a dark inscription.”
The story they tell is of the evolution of organisms from the sea to the land.
Blue green algae are the most primitive of organisms. The most common species is Calothrix, a microscopic
filamentous organism that, like bacteria, has no nuclear membrane. The cells produce mucilage sheaths that
have a dual purpose, protecting the cells from drying out and, at the same time, glueing them to the rocks.
