Short description of Homarus americanus, American Lobster

A clawed lobster similar to native European lobsters, but larger (up to 50cm length and weighing 20kg), with dark blue/green to green/brown body colour, red tint on claws and body, and green tint on walking legs. The presence of one or more small spines on the ventral margin of the rostrum is generally a reliable characteristic used to distinguish the American lobster from the European lobster, although this is very occasionally seen on European lobsters. 

Impact summary: Homarus americanus, American Lobster

Competition with native lobsters and other large crustaceans of environmental and commercial importance. Interbreeding with native lobsters potentially affecting alterations in the populations genetics, behaviour, morphology and breeding capacity. Importation of diseases which could pose a serious threat to GB populations and fisheries.

Habitat summary: Homarus americanus, American Lobster

Inshore and offshore populations are found in the native range, inhabiting mud, bedrock, clay, cobble, eelgrass beds, peat reefs and occasionally sandy depressions.

Overview table

Environment	Marine
Species status	Non-Native
Native range	Labrador, New Brunswick, Newfoundland, Nova Scotia, Québec, Far East United States
Functional type	Predator
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	The Solent
Date of first record	1988

Origin

East coasts of North America and Canada.

First Record

First morphologically identified in GB in 1988.

Pathway and Method

Development of transatlantic jet aircraft allowed live American lobsters to be transported into Europe. Subsequently the species appeared in several northern European countries, presumed attributable to accidental or deliberate release from the catering industry given the presence of rubber-banded claws and lack of biofouling. Cruise liners jettisoning unused catering stock over board has also been implicated, as have individuals releasing specimens into the wild for ethical and religious reasons. 

Species Status

It does not appear that theAmerican lobster has become established in GB waters, although numbers are likely to be highly under-reported. It is often the case, however, that there is a substantial time-lag between initial introduction and the establishment of a species, as was seen with the Chinese Mitten crab, another large decapod, that subsequently experienced a population explosion.

Dispersal Mechanisms

Captured individuals have been found bearing eggs, although no juveniles have been found in the wild. The long distance migratory behaviour of this species could enable escapees to travel long distances, one individual having been caught 30 miles away from a holding facility which it is thought to have escaped from.

Reproduction

Mating occurs immediately post moult when the female is still soft bodied. The fertilised eggs are kept in enclosed egg envelopes and attached to the pleopods of the abdomen where the female ‘gardens’ them. Embryos go through the naupliar stage within the egg, hatching in the summer months and immediately moulting into the first of a series of consecutive planktonic larval stages, each punctuated by a moult. The last of these moults, at around 2 weeks of age, results in metamorphosis into a recognisable American lobster and it subsequently begins to inhabit the benthic environment, but still only averages 12.6mm total body length at this point. The post-larval lobsters go through dramatic developments to both internal and external features which are coordinated with behavioural and locomotion changes. Growth is only achieved by moulting, and timing  of sexual maturity varies enormously depending on sea water temperatures.

Known Predators/Herbivores

Larvae and post larvae are vulnerable to pelagic and demersal fish species, and to some extent sea birds such as terns and herring gulls that feed on the young larvae when they aggregate near the sea surface. Settled post larvae are vulnerable to benthic fish, crabs and prawns, particularly on substrate lacking rocky crevices. Adults are vulnerable during and after a moult when their bodies are soft.

Resistant Stages

None known

Habitat Occupied in GB

Potentially this species can occupy inshore and offshore locations, inhabiting bedrock, mud, clay, cobble, eelgrass beds, peat reefs and sandy depressions in its native range.

Common in its native range of eastern America and Canada. A small number of individuals have been caught in Iceland (1960, but not confirmed genetically), Norway (1999 onwards), Denmark (2006 onwards) and Sweden (2008 onwards), and sporadically in the English Channel since 1988. One individual has been  caught and recorded in Scotland, and 2 in the southeast. Established populations have not to date been found in any of these areas, although this potentially could change quite rapidly.

Environmental Impact

American lobsters are larger, more aggressive, more fecund and inhabit a broader range of habitats than the European lobsters, and so could outcompete the native population. Competition for resources is a threat not only to native lobsters but to other environmentally and economically important species such as brown crabs.

Hybridisation with European lobsters has been reported in wild populations. In the laboratory, hybrids produced infertile males but fertile females when backcrossed with European lobsters, suggesting a potential for genetic alteration within wild population if the 2 species interbreed.  

The blood disease gaffkemia is endemic in wild American lobsters and causes heavy mortality in commercial enterprises of this species, but a rapid 100% mortality in the European lobster within a few days of exposure. The pathogen can live and multiply outside the lobster in the slime on transportation boxes and tanks, although there is currently no evidence that the disease is present in European lobster populations. Epizootic Shell Disease poses another serious threat, having previously resulted in the closure of parts of North American fisheries.

Health and Social Impact

None known.

Economic Impact

All notes in environmental impacts (see above) are pertinent to economical impacts, as a threat to native wild lobster populations is a direct threat to valuable GB fisheries.

Identification

Stebbing P, Johnson P, Delahunty A, Clark PF, McCollin T, Hale C & Clark S (2012). Reports of American lobsters, Homarus americanus (H. Milne Edwards, 1837), in British waters. BioInvasions Records Volume 1, Issue 1: 17–23

Biology, ecology, spread, vectors

(see Stebbing et al, above)

Factor JR (ed) (1995) Biology of the lobster Homarus americanus. Academic Press. ISBN 0-12-247570-4.

Management and impact

(see Stebbing et al, above)

General

 van der Meeren G, Støttrup J, Ulmestrand M, Øresland V, Knutsen JA & Agnalt AL (2010). NOBANIS – Invasive Alien Species Fact Sheet – Homarus americanus. – From: Online Database of the European Network on Invasive Alien Species - NOBANIS www.nobanis.org, Date of access 822013.

van der Meeren G, Ekeli KO, Jørstad KE &  Tveite S (2001)  Americans on the wrong side – the lobster Homarus americanus captured in Norwegian waters. ICES CM 2000U:20