American lobster

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American lobster
American lobster (Homarus americanus)

American lobster ( Homarus americanus )

Systematics
Order : Decapods (decapoda)
Subordination : Pleocyemata
Partial order : Large crayfish (Astacidea)
Family : Lobster-like (Nephropidae)
Genre : Lobster ( Homarus )
Type : American lobster
Scientific name
Homarus americanus
Milne Edwards , 1873
Yellow American lobster
Blue American lobster
Ventral view of a female

The American lobster ( Homarus americanus ), also known as the northern lobster or Maine lobster , is a type of decapod crustacean from the lobster-like family (Nephropidae).

features

Size and growth

American lobsters usually reach a length of 10 to 64 centimeters and a weight of 1 to 6 kilograms. Since growth does not culminate but slows down with age and is also dependent on temperature, lobsters can, however, become significantly larger and heavier under favorable conditions. The heaviest American lobster ever caught weighed 20.1 kilograms.

The growth takes place via regular moults . To do this, a lobster lies on its side in its cave, bends into a V-shape, and reduces its extremities by dehydrating. After the old outer shell, the exuvia , has been shed, a lobster is initially unable to move and is therefore defenseless. Within several hours, the lobster swells to its new size and the shell begins to harden. The increase in size per molt is between 10 and 20%.

colour

The coloration of American lobsters ranges from olive-green to green-black hues with mostly black speckles; Completely yellow or blue lobsters can also occur, but like albinotic individuals are extremely rare and are based on gene mutations. The color is essentially influenced by the coloring of the parent animals, the diet and exposure to sunlight, which camouflage colors ( somatolysis ) can cause.

anatomy

As with all decapods, the body of the American lobster consists of the segmented tagmata cephalothorax and abdomen. The former is covered by a carapace that ends in a pointed rostrum at the front . On each side of the rostrum there is a stalked compound eye, which consists of around 14,000 ommatidia . Lobsters have two types of antennae pairs. The longer, whip-like pair is the sense of touch, the shorter is two-part and serves the sense of smell.

The first three of the five pairs of striding legs (pereiopods) on the thorax segments have scissors ( chelae ) formed by Propodus and Dactylus . The foremost pair of scissors is many times larger and stronger. The chela, known as cracking scissors, is larger, while the thorned gripping scissors are narrower.

The movable abdomen consists of six segments and ends with the telson , which together with the uropods forms the fan-like tail.

The first pair of swimming legs ( pleopods ) can be used to distinguish the sexes . These are hardened in males, but soft and pliable in females. In comparison, adult males are slightly larger and have longer claws in proportion to their height than females of the same age.

distribution

The American lobster is native to the North American Atlantic coast. The distribution area extends from the coastal areas of the Canadian province of Labrador around the island of Belle Isle in the north to Cape Hatteras in the US state of North Carolina in the south. However, the species is much rarer south of Delaware than further north, for example in Maine.

Naturalized by humans, this lobster species has been found as a neozoon on the Norwegian, Swedish and Danish Atlantic and North Sea coasts since 1999 .

Natural range of the American lobster on the east coast of North America
Female with eggs on the underside of the abdomen

Reproduction and life cycle

The pairing takes place from summer to autumn. For this purpose, the males create a mating den and thus woo a female. They decide on a partner a few days before the actual mating and send out a pheromone that makes the males less aggressive. Mating usually takes place shortly after the female moults and can last for one to several days. After mating, the male protects the female for some time. The sperm packets ( spermatophores ) can be kept in the semen bag of females for several months to years.

The eggs are fertilized externally and can occur up to 15 months after mating. The females spawn, with the eggs from the oviduct being carried past the semen receptacle. The eggs fertilized in this way are attached to the swimming legs on the underside of the abdomen. Depending on the size and age of the female, the number of eggs can reach up to 60,000. Between 15 and 50% of the eggs do not hatch, caused by disease, parasites or predators and also by fishermen who have to throw egg-bearing females back into the sea. During the incubation, the volume of an egg increases.

After nine to eleven months of incubation, the larvae, which are only a few millimeters in size, hatch. These initially live as plankton just under the sea surface and shed their skin four times within 3 to 12 weeks, depending on the temperature. The fourth moult is a metamorphosis , as both the large chelae and the uropods up to the third moult are missing. The lobsters, now known as post larvae, are around 14 millimeters in size, look for a protected spot on the sea floor and from now on remain benthont . With the change of habitat there is also a change in diet.

Juvenile lobsters rarely leave their cave or shelter; they only become more agile when the carapace is around 25 to 40 millimeters long. American lobsters are sexually mature with a carapace length of around 60 millimeters. The age of sexual maturity is variable, since it depends mainly on the temperature, which determines the molting rate. American lobsters usually reach sexual maturity around four years after hatching. Only about one in 10,000 hatched larvae reaches adolescence .

ecology

habitat

In the sublittoral areas of the coast, the species lives at depths between 0 and 480 meters, but is usually found between 4 and 50 meters. Depths of up to 700 meters also appear to be maximally possible. In doing so, it is always dependent on hiding places such as caves or crevices, which is why the habitats are characterized by rocky or harder mud seabed. The temperature at the mentioned depths can range from 2 ° C to 20 ° C; the salinity is over 25 psu, whereby low salt contents can also be survived for a short time.

American lobsters are predominantly nocturnal loners. Adult animals tend to spend the summer months near the coast at shallower depths because the water is warmer there. In winter they retreat to deeper areas because there is less water turbulence. Apart from this annual migration, lobsters are relatively local or only migrate to a limited extent.

food

American lobsters are omnivorous in their larval stages . In addition to phytoplankton in the form of dinoflagellates , algae or diatoms, they also eat representatives of zooplankton, such as water fleas and copepods . Adult lobsters feed on crabs, shellfish such as clams, e.g. B. the scallop , starfish , sea ​​urchins , nematodes , poly-bristles and snails. The prey can also be eaten as carrion, especially by very young lobsters; Eating algae or other aquatic plants is also very rare. As soon as American lobsters have caught prey, they withdraw with it into their cave and eat it there. Cannibalism rarely appears in American lobsters in nature. On the other hand, cannibalism can certainly occur in overcrowded aquariums or holding basins, where freshly skinned, i.e. still soft and thus defenseless conspecifics can be eaten.

Enemies

American lobsters feed several predators as larvae in plankton. Above all, cod , flounder , bullhead , catfish , Zoarces americanus , American monkfish and dogfish are to be mentioned . For adult lobsters, humans are by far the most important predator.

American lobsters have the ability to autotomy and self- amputate limbs in order to escape in danger or to escape the grip of a predator. Separation from scissors or other extremities can also occur if the lobster does not fully manage to shed the exuvia. Limbs removed in this way are regenerated during the subsequent moult, but initially appear smaller than usual. With further moults, however, they return to their normal size.

When American lobsters are touched, frightened or threatened, they emit acoustic signals in the form of hum. The average frequency of the hum, which lasts up to 1 second, is 183 Hz. The meaning of this signal is unclear.

Pathogens

American lobsters can be infected by a few pathogens or parasites, the two most important of which are arguably gaffkemia and shell disease .

Gaffkaemia caused by the bacterium Aerococcus viridians has been known since 1947. The bacterium is an encapsulated, gram-positive tetracoccus that cannot move freely. The infection occurs through wounds or tiny holes in the shell and very few pathogens can trigger the disease. The hepatopancreas , the heart and then also the hemolymph , where the bacterium multiplies quickly , are primarily affected . Infected lobsters lose weight and become lethargic, and the tail can turn orange to pink. Depending on the temperature, death can occur after just two days. Although this disease has mainly been observed in aquariums and holding facilities, it has also been described in natural habitats. The prevalence of gaffkemia in nature is a few percent, although it must be assumed that this is underestimated because lethargic and emaciated lobsters are far less likely to fall into lobster traps than healthy ones. In addition to hygiene measures and research into the use of antibiotics in lobster tanks, there is a vaccine against gaffkaemia. This is arguably the first vaccine ever developed for marine invertebrates.

A shell disease caused by various bacteria has been known since the 1930s; various Vibrio species have been isolated , including V. vulnificus , V. parahaemolyticus and V. alginolyticus as well as Shewanella spp. and Aeromonas hydrophilia . The bacteria penetrate through pores or the roughened epicuticle into the shell of the carapace, the abdomen and also the legs and initially cause smaller dents or depressions. In the further course, these infested areas can grow into dark spots and the peel can be broken down. Since only the exoskeleton and no internal organs are affected, a lobster can temporarily get rid of this disease by shedding its skin. The prevalence of shell disease therefore depends on the season as well as the sex and age of the lobster. It is higher in May and June in females and old animals. In the far advanced stages of the disease, the infected areas can hinder the moulting to such an extent that the lobster is no longer able to shed the old shell and therefore dies. It is estimated that around 30% of the lobsters on the coast of southern England and Long Island are infected with the bacteria. So far it is not completely clear which combinations of pathogens, environmental factors and the disposition of the lobster trigger the disease; transmission of the disease from lobster to lobster seems impossible.

Systematics

Thomas Say described the American lobster as Astacus marinus based on a specimen caught in Long Branch , New Jersey . Since this name already existed, only Henri Milne Edwards provided a valid first description based on Say's notes in 1837 in the "Histoire naturelle des Crustacés" 2: p. 334. Synonyms of the species are Astacus marinus (Fabricius, 1775) Say, 1817; Astacos americanus Stebbing, 1893 and Homarus mainensis Berrill, 1956.

In addition to the American lobster, the Homarus genus also includes the European lobster ( Homarus gammarus L. 1758). Although the two species can be distinguished by a missing sting on the rostrum of the carapace in the European lobster, a reliable differentiation is only possible by means of a genetic examination.

American and European lobsters can produce hybrids . This already happened in the wild, as a hybrid egg-bearing American lobster female was caught off Norway in 2009. Whether these hybrids in turn are fertile is the subject of research.

use

Lobster traps
Lobster prepared for eating

The American lobster has been fished since 1605. The natives of North America probably used lobsters as fertilizer for their fields or as bait when fishing. During the colonial days, lobster was less of a delicacy than “poverty food” that was served to prison inmates or the poor. This was mostly caught by hand on the coastline. As a food, lobster was initially only available on the east coast of North America. It was only with the canning around 1840 that it spread to regions further away from the coast. The live lobster trade has dominated since around 1875.

A total of 100,000 tons of American lobsters were landed in 2009. In the 1980s the amount was around 40,000 tons and increased to 75,000 tons in the 1990s. Until 2006 the annual catch stagnated at 80,000 tons. Around 36,000 tons of lobsters were landed on the coast of the US state of Maine alone in 2009, which corresponded to a value of almost 240 million dollars. The American lobster is fished mostly with lobster traps , the small dimensions as bycatch in trawl nets of trawlers .

Despite this fishing, the American lobster population is stable and relatively robust. It is therefore listed as Least Concern in the IUCN Red List.

To counteract overfishing , a number of rules must be observed when fishing for lobsters. In addition to the limitation of the issuing of licenses and the fishing season, caught lobsters must not be less than a certain carapace length. In the regions of Canada, this lower limit is between 71 and 84 millimeters. The US state of Maine only allows fishing for lobsters with carapace lengths between 81 and 127 millimeters (3.25 and 5 inches). Females carrying eggs are generally protected and may not be caught or landed.

In Norway, a bounty is paid for every American lobster caught because, as a neozoon, it seems quite capable of displacing the European lobster from its natural range, or the local small populations of the European lobster in the North Sea as a new competitor for the same habitats and endangering food.

literature

  • Bruce Phillips (Ed.): Lobsters: Biology, Management, Aquaculture and Fisheries . Wiley-Blackwell, Oxford, UK; Ames, Iowa 2006, ISBN 1-4051-2657-4 .
  • Lipke B. Holthuis: Marine Lobsters of the World . An Annotated and Illustrated Catalog of Species of Interest to Fisheries Known to Date. Ed .: Food and Agriculture Organization (=  FAO Fisheries Synopsis . Volume 125 ). Rome 1991, ISBN 92-5103027-8 .

Individual evidence

  1. ↑ a b s. Literature: Holthuis, p. 58
  2. ↑ Heaviest Marine Crustacean. Guinness World Records, archived from the original on May 28, 2006 ; accessed on November 19, 2011 (English).
  3. ↑ a b c d e f g h Eleanor Ely: The American Lobster. In: Rhode Island Sea Grant. University of Rhode Island, June 3, 1998, archived from the original June 23, 2012 ; accessed on November 29, 2015 .
  4. ↑ a b c d e f g h i J. Stanley Cobb, Kathleen M. Castro: Homarus Species . In: Bruce Phillips (Ed.): Lobsters: Biology, Management, Aquaculture and Fisheries . Wiley-Blackwell, Oxford, UK; Ames, Iowa 2006, ISBN 1-4051-2657-4 , Chapter 9, pp. 310-339 .
  5. ↑ a b c d e f A Guide to Lobstering in Maine. Maine Department of Marine Resources, 2009, accessed November 21, 2011 .
  6. ↑ Albino Lobster Landed At Captain Joe and Sons 7/23/10. GoodMorningGloucester, July 24, 2010, accessed July 26, 2012 .
  7. ↑ a b c d e f g h i j k Nathalie Paille, Luc Bourassa: American Lobster. St. Lawrence Global Observatory, accessed November 25, 2011 .
  8. ↑ s. Literature: Holthuis, p. 17
  9. ↑ a b c d e f Gro I. van der Meeren, Josianne Støttrup, Mats Ulmestrand, Jan Atle Knutsen: Invasive Alien Species Fact Sheet: Homarus americanus . Ed .: Online Database of the North European and Baltic Network on Invasive Alien Species. NOBANIS. 2006 ( nobanis.org [PDF; 138 kB ]).
  10. ↑ Eric M. Thunberg: Demographic and Economic Trends in the Northeastern United States Lobster (Homarus americanus) Fishery, 1970-2005. (PDF; 510 kB) (No longer available online.) In: Northeast Fisheries Science Center Reference Document 07-17. National Marine Fisheries Service, 2007, archived from the original on October 4, 2011 ; Retrieved November 21, 2011 .
  11. ↑ a b Homarus americanus in the endangered Red List species the IUCN 2011. Posted by: M. Butler, A. Cockcroft, A. MacDiarmid, R. Wahle, 2011. Accessed November 19, 2011th
  12. ↑ a b c d e f Species Fact Sheets Homarus americanus. Food and Agriculture Organization of the United Nations, accessed November 19, 2011 .
  13. ^ Heidi Pye Henninger, Winsor H. Watson III: Mechanisms underlying the production of carapace vibrations and associated waterborne sounds in the American lobster, Homarus americanus . In: J. Exp. Biol. Volume 208 , 2005, pp. 3421–3429 (English, full text ).
  14. ^ A b c d Richard J. Cawthorn: Diseases of American lobsters (Homarus americanus): A review . In: Journal of Invertebrate Pathology . tape 106 , 2011, pp. 71-78 , doi : 10.1016 / j.jip.2010.09.010 .
  15. ↑ a b Jeffrey D. Shields, Fran J. Stephens, Brian Jones: Pathogens, Parasites and other Symbionts . In: Bruce Phillips (Ed.): Lobsters: Biology, Management, Aquaculture and Fisheries . Wiley-Blackwell, Oxford, UK; Ames, Iowa 2006, ISBN 1-4051-2657-4 , Chapter 5, pp. 146-204 .
  16. ↑ Barbara Somers: Lobster Shell Disease. (No longer available online.) In: Rhode Island Sea Grant. University of Rhode Island, 2005, archived from the original on September 20, 2011 ; accessed on November 23, 2011 (English).
  17. ↑ Knut E. Jørstad, PA Prodohl, A.-L. Agnalt, M. Hughes, E. Farestveit, AF Ferguson: Comparison of genetic and morphological methods to detect the presence of American lobsters, Homarus americanus H. Milne Edwards, 1837 (Astacidea: Nephropidae) in Norwegian waters . In: Hydrobiologia . tape 590 , 2007, pp. 103-114 , doi : 10.1007 / s10750-007-0762-y .
  18. ^ Marie Hauge: Unique lobster hybrid. Institute of Marine Research Norway, May 2010, accessed November 21, 2011 .

Web links

Commons : American Lobster  - Collection of images, videos, and audio files