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Lobsters

Lobsters

Biology and ecology of lobsters

Lobster Reproduction

Species Of Lobsters

Lobsters And People

Resources

Lobsters are large crustaceans in the order Decapoda, which also includes about 10,000 species of crayfish, crabs, and shrimps. Decapods are characterized by a carapace with fused thoracic segments that form a gill chamber above where the legs join the body. In addition the first three of their eight pairs of thoracic legs are modified into grasping, claw-like structures known as maxillipeds.

Lobsters belong to the family Nephropidae. There are two superfamilies: the true lobsters, Nephropoidea; and the reef lobsters, Enoplometopoidea.

The true lobsters have their three pairs of maxillipeds developed as chelae, or large pincerlike claws used for catching and handling food, and for defense. The first pair of claws is especially large. These animals also have well-developed uropods, a paired appendage that arises from the last segment of the body and forms a major part of the tail fan.

The spiny lobsters, or rock lobsters, belong to the family Palinuridae and are not true lobsters. These animals are not chelate (that is, they do not have large foreclaws), and their third maxilliped resembles a leg.

Biology and ecology of lobsters

Lobsters have a tough outer skeleton, or exoskeleton, made of chitin. Like many crustaceans, lobsters do not have a terminal moltthey continuously grow for their entire life. The largest lobsters can exceed 44 lb (20 kg) in weight, more than half of which is made up of their enormous foreclaws.

Lobsters are found on in intertidal areas living in crevices and caves. They are often found crawling on rocky, muddy or sandy ocean floors where they are most active at night. During the day they typically hide in burrows or cavities in rock piles, which they enter by backing in. Lobsters can crawl in all directions, but when they are foraging they mostly proceed in a forward direction. Smaller lobsters can swim jerkily, by rapidly back-flipping their tail fan.

Lobsters are widely considered scavengers, feeding on dead mollusks, crustaceans and other decaying matter. But recent studies have shown that they may at times prey on live fish or dig for clams. They may even eat kelp or eel grass. Lobsters are also known to be cannibalistic. Lobsters are visual animals, but likely detect of food using their well-developed sense of smell.

Lobster Reproduction

Typical male lobsters will deposit packets of sperm on the underside of the female. The female will later use the sperm to externally fertilize her eggs as they are laid. The female can store the sperm for several months, waiting for the egg-laying season, which typically occurs during July and August. Females breed every two years.

Female lobsters carry their eggs (known as berries) beneath their abdomen, attached to structures called spinnerets. The number of eggs is related to the size of the female, and is typically about 5,000 eggs for a 10 in (25 cm) long female, and 40,000 for a 14 in (36 cm) long animal.

The egg masses are periodically waved on their spinnerets to ensure their access to clean, well-oxygenated water. Female lobsters carry their eggs for 10-11 months. Hatchling lobsters are planktonic and commonly disperse quite widely with water currents. After their fifth molt, when they are about 1 in (2.5 cm) long, the young lobsters settle on the ocean bottom. Lobsters are extremely vulnerable to the vagaries of drift and predation when they are in their planktonic stage, and when they are benthic but small.

Species Of Lobsters

There are at least three genera and 11 species of lobster. The economically important species native to North American waters are briefly described below.

The northern or American lobster (Homarus americanus ) is an abundant and widespread species of the Atlantic coast of North America, ranging as far north as Labrador to as far south as Virginia. This species occurs most abundantly on rocky bottoms, and it ranges over the entire continental shelf, even in some of the deeper waters of the continental slope. Individual animals can reach quite large sizes. Animals caught in relatively deep places on the continental slope have exceeded 3 ft (1 m) in length and 44 lb (20 kg) in weight and are probably more than 100 years old.

The European lobster (Homarus gammarus ) is a closely related species, occurring in temperate waters of western Europe. This species is considerably smaller than the American lobster. The Norwegian lobster or scampi (Nephrops norvegicus ) is an even smaller lobster that ranges from the Norwegian coast to the Adriatic coast in the eastern Mediterranean Sea.

Two species of spiny lobsters are of economic interest in North America. The West Coast spiny lobster (Panulirus interruptus ) occurs on the Pacific coast, and the Caribbean spiny lobster (P. argus ) occurs in the Caribbean Sea, off the Florida coast, and in the Gulf of Mexico. These warm-water species do not have the huge, crushing, and tearing claws of the Homarus true lobsters, but they have a sharp, spiny carapace, and very long antennae.

Lobsters And People

Lobsters are commonly captured as a food for humans, and their fishery is economically important.

KEY TERMS

Continental shelf A relatively shallow, gently sloping, submarine area at the edges of continents and large islands, extending from the shoreline to the continental slope.

Over-harvesting This refers to the capturing of animals faster than they are able to regenerate their populations by breeding, the population declines possibly to the point of extinction in severe cases. Potentially, economically important animal populations can be utilized as a renewable natural resource. However, if they are over-harvested, they are being mined, and managed as if they were a non-renewable resource.

Planktonic Refers to an animal that lives suspended or swimming in the water column. Recently hatched lobsters are planktonic.

American lobsters, caught in the waters off New England, are routinely sold throughout the world and are considered a delicacy. At certain times of the year, for example around the winter holiday season, entire jets may be chartered to send lobsters to France and elsewhere in western Europe.

Lobsters are most commonly caught using traps of various sorts. In general, the traps are baited with a piece of fish, and there are several entrance holes through which hungry lobsters can enter the trap, but cannot exit. Alternatively, lobsters are sometimes caught by scuba divers, or by snorkeling in shallow, warm waters.

Over-harvesting of lobsters is a serious problem and the fishery is managed closely. Management practices monitoring stock sizes, and setting and implementing appropriate catch limits by regulating the number of traps and the sizes of animals that can be taken.

Recent research has also focused on aquaculture techniques for lobster. Lobster ranching would likely involve capturing pregnant females and growing their young offspring in captivity, to be harvested when they reach a marketable size. Lobster farming is more complex, and would involve keeping carefully selected breeding stock, and periodically spawning these mature animals to produce progeny that could be reared under conditions optimized for their growth. Eventually, controlled breeding could lead to the development of breeding stock that was genetically optimized for docility, growth rate, ease of spawning, resistance to disease, and other desirable traits.

Resources

BOOKS

Brusca, Richard C., Gary J. Brusca, and Nancy J. Haver. Invertebrates. Sunderland, MA: Sinauer Associates, Inc., 2003.

OTHER

Gulf of Maine Aquarium. Lobsters. February 23, 1999. < http://www.gma.org/lobsters/ (accessed October 22, 2006).

The Lobster Conservancy. Lobster Biology. 2004. < http://www.lobsters.org/tlcbio/biology.html >(accessed October 25, 2006).

Bill Freedman

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