American lobster

Appearance

''Homarus americanus'' commonly reaches 8–24 inches long and weighs 1–9 pounds in weight, but has been known to weigh as much as 44 lb, making this the heaviest crustacean in the world. Together with ''Sagmariasus verreauxi'', it is also the longest decapod crustacean in the world; an average adult is about 9 in long and weighs 1.5 to 2 lb. The longest American lobsters have a body 64 cm long.

The closest relative of ''H. americanus'' is the European lobster, ''Homarus gammarus''. The two species are very similar, and can be crossed artificially, although hybrids are unlikely to occur in the wild since their ranges do not overlap. The two species can be distinguished by a number of characteristics:
⤷ The rostrum of ''H. americanus'' bears one or more spines on the underside, which are lacking in ''H. gammarus''.
⤷ The spines on the claws of ''H. americanus'' are red or red-tipped, while those of ''H. gammarus'' are white or white-tipped.
⤷ The underside of the claw of ''H. americanus'' is orange or red, while that of ''H. gammarus'' is creamy white or very pale red.

Naming

It is also known as true lobster, northern lobster, or Maine lobster.

Distribution

''Homarus americanus'' is distributed along the Atlantic coast of North America, from Labrador in the north to Cape Hatteras, North Carolina in the south. South of New Jersey, the species is uncommon, and landings in Delaware, Maryland, Virginia and North Carolina usually make up less than 0.1% of all landings. A fossil claw assigned to ''Homarus americanus'' was found at Nantucket, dating from the Pleistocene. In 2013, an American Lobster was caught at the Farallon Islands off the coast of California.

Behavior

Mating only takes place shortly after the female has molted, and her exoskeleton is still soft. The female releases a pheromone which causes the males to become less aggressive and to begin courtship, which involves a courtship dance with claws closed. Eventually, the male inserts spermatophores into the female's seminal receptacle using his first pleopods; the female may store the sperm for up to 15 months.

The female releases eggs through her oviducts, and they pass the seminal receptacle and are fertilized by the stored sperm. They are then attached to the female's pleopods using an adhesive, where they are cared for until they are ready to hatch. The female cleans the eggs regularly, and fans them with water to keep them oxygenated. The large telolecithal eggs may resemble the segments of a raspberry, and a female carrying eggs is said to be "in berry". Since this period lasts 10–11 months, berried females can be found at any time of year. In the waters off New England, the eggs are typically laid in July or August, and hatch the following May or June. The developing embryo passes through several molts within the egg, before hatching as a metanauplius larva. When the eggs hatch, the female releases them by waving her tail in the water, setting batches of larvae free.

The metanauplius of ''H. americanus'' is 1⁄3 in long, transparent, with large eyes and a long spine projecting from its head. It quickly molts, and the next three stages are similar, but larger. These molts take 10–20 days, during which the planktonic larvae are vulnerable to predation; only 1 in 1,000 is thought to survive to the juvenile stage. To reach the fourth stage – the post-larva – the larva undergoes metamorphosis, and subsequently shows a much greater resemblance to the adult lobster, is around 1⁄2 in long, and swims with its pleopods.

After the next molt, the lobster sinks to the ocean floor, and adopts a benthic lifestyle. It molts more and more infrequently, from an initial rate of ten times per year to once every few years. After one year, it is around 1–1.5 in long, and after six years, it may weigh 1 pound . By the time it reaches the minimum landing size, an individual may have molted 25–27 times, and thereafter each molt may signal a 40%–50% increase in weight, and a 14% increase in carapace length.

Habitat

The American lobster thrives in cold, shallow waters where there are many rocks and other places to hide from predators. It typically lives at a depth of 4–50 m, but can be found up to 480 m below the surface. Excretory calcinosis in American lobsters in Long Island Sound was described in 2002. The disease causes mineralized calculi to form in the antennal glands and gills. These cause a loss of surface area around the gills, and the lobster eventually asphyxiates. Several reasons have been proposed for the cause of a recent outbreak of the disease. The most generally attributed factor is an increased duration of warmer temperatures in the bottom of the Long Island Sound.

Food

The natural diet of ''H. americanus'' is relatively consistent across different habitats. It is dominated by mollusks, echinoderms and polychaetes, although a wide range of other prey items may be eaten, including other crustaceans, brittle stars and cnidarians.