American lobster

The American lobster is a species of lobster found on the Atlantic coast of North America, chiefly from Labrador to New Jersey. It is also known as Atlantic lobster, Canadian lobster, true lobster, northern lobster, Canadian Reds, or Maine lobster. It can reach a body length of, and a mass of over, making it not only the heaviest crustacean in the world, but also the heaviest of all living arthropod species. Its closest relative is the European lobster Homarus gammarus, which can be distinguished by its coloration and the lack of spines on the underside of the rostrum. American lobsters are usually bluish green to brown with red spines, but several color variations have been observed.

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. It has been introduced to Norway and potentially Iceland.

Description

Homarus americanus commonly reaches long and weighs in weight, but has been known to weigh as much as, 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 long and weighs. The longest American lobsters have a body long. According to Guinness World Records, the heaviest crustacean ever recorded was an American lobster caught off Nova Scotia, Canada, weighing.
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 several 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.
Head

The antennae measure about long and split into Y-shaped structures with pointed tips. Each tip exhibits a dense zone of hair tufts staggered in a zigzag arrangement. These hairs are covered with multiple nerve cells that can detect odors. Larger, thicker hairs found along the edges control the flow of water, containing odor molecules, to the inner sensory hairs. The shorter antennules provide a further sense of smell. By having a pair of olfactory organs, a lobster can locate the direction a smell comes from, much the same way humans can hear the direction a sound comes from. In addition to sensing smells, the antennules can judge water speed to improve direction finding.
Lobsters have two urinary bladders, located on either side of the head. Lobsters use scents to communicate what and where they are, and those scents are in the urine. They project long plumes of urine in front of them, and do so when they detect a rival or a potential mate in the area.

Thorax

The first pair of pereiopods is armed with a large, asymmetric pair of claws. The larger one is the "crusher", and has rounded nodules used for crushing prey; the other is the "cutter" or "gripper", which has sharp inner edges and is used for holding or tearing the prey. Whether the crusher claw is on the left side or right side of its body determines whether a lobster is left or right "handed".

Coloration

The normal coloration of Homarus americanus is bluish green to brown with red spines due to a mixture of yellow, blue, and red pigments that occur naturally in the shell. On rare occasions these colors are distorted due to genetic mutations or conditions creating a spectacle for those who catch them. In 2012 it was reported that there has been an increase in these "rare" catches due to unclear reasons. Social media influence making reporting and sharing more accessible to a drop in predator populations have been suggested as possible reasons. The lobsters mentioned below thus usually receive media coverage due to their rarity and eye appeal.

Color	Image	Rarity	Description
Blue		1 in 2 million	Some lobsters become blue as a result of a genetic mutation that causes the lobster to produce an excessive amount of a particular protein. The protein and a red carotenoid molecule known as astaxanthin combine to form a blue complex known as crustacyanin, giving the lobster its blue color. While an estimated 1 in 2 million lobsters are blue, they may not be as rare as they are portrayed given how many lobsters are caught in a given year. David Spiegelhalter from the University of Cambridge pointed out that a rough analysis shows that 200 million lobsters are caught in the North Atlantic every year. He stated that if the odds are correct then it would mean 100 of them would be blue. Spiegelhalter concluded that the catches are not all that surprising, and that these lobsters probably turn up most years. In any case, when blue lobsters are caught they are either released back into the sea or placed in local aquariums.
Red		1 in 10 million	Red lobster coloration is the typical result of cooking, which is caused by the chemical astaxanthin reacting with boiling water. The estimated odds of catching a live red lobster are 1 in 10 million. Director Bob Bayer from the Lobster Institute at the University of Maine stated in 2016 that "the genetics of red lobsters are not as well understood" when compared to blue lobsters.
Yellow or orange		1 in 30 million	Yellow lobsters are the result of an unspecified rare genetic mutation, while orange lobsters are caused by a lack of proteins which help to bond the different pigments. Most orange lobsters are described as "calico", with a mixture of orange and black colors present. Yellow and orange lobsters are typically placed into aquariums, as predators can easily spot them if they are released back into the wild. The odds of catching a yellow lobster stand at 1 in 30 million.
Split		1 in 50 million	Several lobsters have been caught that show a different color on the left and right side of the body. According to a researcher at the University of Rhode Island, this split colorization is the result of a genetic condition which causes both sides of the lobster to develop independently. Split-colored lobsters often show sexual characteristics of both sexes, with exceptions. The chance of finding a split-colored lobster is estimated at 1 in 50 million.
Iridescent or white		1 in 100 million	It is estimated that 1 in 100 million lobsters are albino, entirely lacking in colored pigments. "White" lobsters that still have trace colors present in the shell are similarly rare; these are not categorized as albino but rather as leucistic. Neither of these genetic conditions are unique to lobsters.

Life cycle

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 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 long, and swims with its pleopods. At this stage, the lobster's claws are still relatively small so they rely primarily on tail-flip escapes if threatened.
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 long, and after six years it may weigh. 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. If threatened, adult lobsters will generally choose to fight unless they have lost their claws.