Geoscience Reference
In-Depth Information
The rocky coast at low tide reveals the bold banding typical of the Gulf of Maine and outer Bay of Fundy.
Its reproductive strategies further demonstrate the adaptability of this creature, which is one of the few crus-
taceans that is hermaphroditic—each individual possesses both male and female sexual organs. Each barnacle
has a remarkably long penis, which can reach into the mantle cavity of a neighboring animal and fertilize it.
The fertilized eggs are brooded in the mantle cavity until they are released as larvae and drift with the tide in
search of a site to anchor themselves. Once they find a suitable site, they undergo a remarkable metamorphosis
within a period of twelve hours: from a relatively shapeless larval form, the head and appendages emerge, and
the cone of the shell is formed, replete with plates. During its three-to-five-year life cycle, the barnacle will
have to molt its chitinous skin to grow, enlarging its shell to accommodate its growing body, leaving behind
what Rachel Carson described in The Edge of the Sea as “semitransparent objects . . . like the discarded gar-
ments of some very small fairy creature.” The molting process is usually triggered when the waters reach a
particular temperature in the early spring, and all the barnacles in the region molt at about the same time.
Because of their remarkable hardiness, barnacles dominate the upper levels of the intertidal zone, where
conditions are harshest. They do have predators, however, and, at the lower end of the intertidal zone, compet-
itors.
AS WE MOVE
farther down the rocky intertidal seashore, we enter the brown algae zone, which normally ex-
tends from the lower edge of the barnacle zone to the mean low water mark. The two most conspicuous plants
along the rocky shore are types of brown algae, knotted wrack and bladder wrack, which cover the rocks like
