Geoscience Reference
In-Depth Information
CALANUS FINMARCHICUS
is the most important copepod in the Gulf of Maine, and in winter is found
throughout the Atlantic Ocean, from the Arctic south to Chesapeake Bay. Because of its relatively large
size—more than 3 millimeters (0.1 inches) as an adult—it is the largest contributor to biomass in the zooplank-
ton community in the gulf, even though it may not always be the most abundant species. Its presence is so
dominant on Georges Bank that famed oceanographer Henry Bigelow described the Georges Bank ecosystem
as a “Calanus community.”
The copepod's anatomy reflects its up-and-down lifestyle of vertical migration in the water column. The
body consists of a six-segmented fused head and thorax, which sports a single median eye and the feeding and
swimming appendages, and a smaller, five-segmented abdomen. The cylindrical, rather than spherical, body
shape, and the copepod's elongated antennae, which are held at right angles to its body, are used to slow the
copepod's sinking in the water column. The antennae are covered in tiny hairs (setae), which increase the sur-
face area in contact with the water and therefore further reduce the rate of sinking. The smaller second set of
antennae, with their rotary motion, are the main swimming appendage, along with the thoracic swimming feet.
The first pair of thoracic appendages has been adapted for feeding.
Copepods reproduce sexually. The male grasps the female with its antennae and, using its thoracic append-
ages, transfers a sperm package called a sper-matophore to the female at the genital opening. The fertilized
eggs are shed into the environment and develop through six stages. At each molt the organism undergoes
metamorphosis, adding new appendages or modifying existing ones. During the fifth phase of its life cycle,
Calanus enters a state of diapause, a period of delayed development and reduced metabolism. During this
phase, at the onset of the warmest months of late summer, the copepods migrate to the deepest basins in the
gulf, where they remain through the fall and winter. They undergo their final molt in the spring, emerging as
adults and migrating vertically again to feed on the phytoplankton riches at the surface, and in turn to be fed on
by predators higher in the food web, including fish, seabirds, and whales.
THE COMPLEX LIFE OF A LOBSTER
CONSIDERED BY
most as a culinary delicacy and luxury, lobsters are the most sought-after seafood along the
eastern seaboard. This was not always so, however. In the 18th century, in Massachusetts, it was forbidden to
serve lobster to prisoners and servants more than twice a week, and until the mid-20th century, poor school-
children in Maritime Canada hid the fact that they had to eat lobster sandwiches for lunch. The American lob-
ster is found along the coast between Cape Hatteras and the Strait of Belle Isle between Newfoundland and
Labrador but is especially abundant in the Gulf of Maine, along the Atlantic coast of Nova Scotia, and in the
southern Gulf of St. Lawrence.
As the bearers of a flexible shell, lobsters belong to the class Crustacea and are cousins to crabs, shrimp, and
copepods. They have five pairs of legs, including an exaggerated pair of asymmetrical claws at the front of the
body: the crusher and the pincer, used for defense and food gathering. The smaller legs are covered with hairs,
which function as taste organs, and the compound eyes, consisting of 13,500 light-capturing, image-forming
organs called ommatadia, are mounted on flexible stalks at the front of the body. It is not known whether noc-
turnal lobsters perceive, or need to perceive, color, but they have a highly developed sense of smell, with the
first antennae acting as the “nose.”
Lobsters are bottom-dwelling creatures that generally live in water depths of less than 50 meters (164 feet)
and prefer cobble habitat, where as juveniles they seek shelter from predators in the crevasses among algae-
covered stones. As adults, lobsters have few enemies other than humans, and it is believed they can live fifty
years or more. But first they must survive a series of vulnerable stages in their complex life cycle.
Shortly before she must shed her shell, the female initiates the mating ritual by poking the tips of her claws
into the shelter of the male, with whom she will form a brief pair bond of a week or two. After a few days of
