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Homarus
Homarus
Homarus
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Homarus
Temporal range: Albian–Recent
Homarus gammarus
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Family: Nephropidae
Genus: Homarus
Weber, 1795
Type species
Astacus marinus
Fabricius, 1775
Extant species

H. americanus – American lobster
H. gammarus – European lobster

Homarus is a genus of lobsters, which include the common and commercially significant species Homarus americanus (the American lobster) and Homarus gammarus (the European lobster).[1] The Cape lobster, which was formerly in this genus as H. capensis, was moved in 1995 to the new genus Homarinus.[2]

Description

[edit]

Homarus is one of three extant genera of clawed lobsters to show dimorphism between claws – a specialisation into a crushing claw and a cutting claw. The other similar genera are Nephrops, which is much more slender, and has grooves along the claws and the abdomen, and Homarinus, the Cape lobster from South Africa, which is even smaller, and has hairy claws.[3]

While analyses of morphology suggest a close relationship between Homarinus and Homarus, molecular analyses using mitochondrial DNA reveal that they are not sister taxa.[4] Both genera lack ornamentation such as spines and carinae, but are thought to have reached that state independently, through convergent evolution.[4] The closest living relative of Homarus is Nephrops norvegicus, while the closest relatives of Homarinus are Thymops and Thymopides.[4]

Species

[edit]

Eight extinct species are known from the fossil record,[5] which stretches back to the Cretaceous,[6] but only two species survive. These two species, the American lobster and the European lobster, are very similar and may have speciated as recently as the Pleistocene, during climatic fluctuations.[6] The best characters for distinguishing them are the geographic distribution, with the American lobster in the western Atlantic and the European lobster in the eastern Atlantic, and by the presence of one or more teeth on the underside of the rostrum in H. americanus but not in H. gammarus.[7]

Image Scientific name Common name Description Distribution
Homarus gammarus Linnaeus, 1758 European lobster or common lobster may grow to a length of 60 cm (24 in) and a mass of 6 kilograms (13 lb), and bears a conspicuous pair of claws.[8] In life, the lobsters are most of the time blue, only becoming "lobster red" on cooking.[9] Homarus gammarus is a highly esteemed food, and is widely caught using lobster pots,[8] Mostly around the British Isles.[10]
Homarus americanus H. Milne-Edwards, 1837 Atlantic lobster, Canadian lobster, true lobster, northern lobster, Canadian Reds, or Maine lobster. commonly ranges from 20–60 cm (8–24 in) in length and 0.5–4.1 kg (1.1–9.0 lb) in weight, but have been known to reach lengths of 64 cm (25 in)[11] and weigh as much as 20 kg (44 lb) or more, making this the heaviest marine crustacean in the world.[12] An average adult is about 23 cm (9 in) long and weighs 700–900 g (25–32 oz).[11] Atlantic coast of North America, from Labrador in the north to Cape Hatteras, North Carolina in the south


Fossil species

[edit]
Fossil of Hoploparia bearpawensis; the relationships between Homarus and Hoploparia remain unclear.

The boundaries between Homarus and the extinct genus Hoploparia are unclear, and some species, such as Hoploparia benedeni have been transferred between the two genera. Eight species have been assigned to Homarus from the fossil record.[13] They are:[14][Note 1][16]

Distribution

[edit]

The two extant species of Homarus are both found in the North Atlantic Ocean. H. americanus is found from Labrador to North Carolina in the western North Atlantic,[17][18] while H. gammarus is found from Arctic Norway to Morocco, including the British Isles and the Mediterranean Sea.[8][17]

Life cycle

[edit]
Zoea larva of H. gammarus

Mating in Homarus is complex and is accompanied by a number of courtship behaviours.[17] Males build mating shelters or burrows, and larger males can attract more females, producing a polygynous mating system.[17] A few days before moulting, a female will choose a mate, and will remain in his shelter until the moult. The male will then insert a spermatophore into the female's seminal vesicle, where it may be stored for several years.[17] The eggs of Homarus species are laid in the autumn, being fertilised externally as they exit, and are carried by the female on her pleopods.[17]

The eggs generally hatch in the spring as a pre-larva, which rapidly develops into the first larval phase.[17] This is followed by three zoeal phases, the total duration of which can vary from two weeks to two months, depending on the temperature.[17] At the following moult, the young animal becomes a post-larva, with a gross form resembling the adult lobster.[17] Although it can swim, using its pleopods, the post-larva soon settles to the bottom and lives as a juvenile for 3–5 years.[17]

As adults, Homarus species moult increasingly infrequently. The size at sexual maturity varies with temperature; it is around 70 mm (2.8 in) for female H. americanus in southern New England, but 100 mm (3.9 in) around the Bay of Fundy.[17] In H. gammarus, the size at sexual maturity is less well defined, but is in the range 80–140 mm (3.1–5.5 in).[17]

Notes

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References

[edit]
[edit]
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Homarus

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Homarus is a of marine clawed lobsters belonging to the family Nephropidae within the order Decapoda, encompassing two extant species: the (H. americanus) and the European lobster (H. gammarus). These crustaceans are distinguished by their elongated bodies covered in a chitinous , ten jointed legs including unequal chelipeds (one crushing and one cutting ), and a smooth lacking prominent ridges or spinules. The was established by Weber in 1795, with the Cancer gammarus Linnaeus, 1758, now recognized as H. gammarus. Taxonomically, Homarus species are part of the superfamily Nephropoidea and are characterized by smooth abdominal somites without grooves separating tergites from pleura, and the absence of a median spine on the male first abdominal sternite. Biologically, they exhibit in claw size and function, with males typically larger, and they undergo a complex life cycle involving planktonic larval stages before settling as juveniles on the seafloor. These lobsters are benthic dwellers, primarily scavenging or preying on small organisms, and can grow to lengths exceeding 60 cm, with lifespans potentially over 100 years in some individuals. The distribution of Homarus is confined to the Atlantic Ocean: H. americanus inhabits coastal waters from to in the northwest Atlantic, while H. gammarus ranges from to in the northeast Atlantic and . Ecologically, they play key roles in marine food webs as both predators and prey, but populations face threats from , , and habitat alteration. Economically, the genus supports major fisheries, with H. americanus alone contributing billions annually to North American markets and H. gammarus being a staple in .

Taxonomy

Etymology and history

The genus name Homarus derives from the Latin homarus, referring to a kind of or , a term that entered scientific through influences from humarr via homard. The taxonomic of Homarus begins with the description of the European lobster as Cancer gammarus by Carl Linnaeus in the 10th edition of Systema Naturae (1758), marking the starting point for binomial in zoology and placing it within the broad genus Cancer for crustaceans. In 1775, Johan Christian Fabricius provided a revised description under the name Astacus marinus in Systema Entomologiae, elevating the taxonomic detail by assigning it to the genus Astacus for freshwater crayfishes and marine lobsters, reflecting early efforts to distinguish clawed decapods. This revision highlighted emerging debates on generic boundaries, as Fabricius's work emphasized morphological traits like chelae structure, influencing subsequent classifications. The genus Homarus was formally established by Friedrich Heinrich Weber in 1795 in Nomenclator entomologicus, with Astacus marinus Fabricius, 1775 (a junior synonym of Linnaeus's Cancer gammarus) designated as the , solidifying its separation from broader groupings. Throughout the , taxonomic revisions addressed species delineation and geographic variants, including Henri Milne Edwards's 1837 description of the as Homarus americanus in Histoire Naturelle des Crustacés, which sparked debates on whether it represented a distinct species or of H. gammarus based on color, rostral , and distribution. Additional contention arose over the , initially described as Cancer (Astacus) capensis by Johann Friedrich Wilhelm Herbst in 1792 and later placed in Homarus as H. capensis, which led to its reclassification into the separate genus Homarinus in 1995 due to morphological differences like reduced chelae size. A key milestone came with the establishment of the family Nephropidae by James Dwight Dana in 1852 in Crustaceologia, which encompassed Homarus and related clawed lobsters, providing a familial framework based on carapace grooves and abdominal somites to resolve prior uncertainties in higher classification. These 19th-century developments, including synonymies and familial placements, laid the groundwork for modern taxonomy, emphasizing Linnaean foundations while incorporating empirical observations from global collections.

Classification and phylogeny

Homarus belongs to the phylum Arthropoda, subphylum Crustacea, class , order Decapoda, suborder , infraorder , superfamily Nephropoidea, and family Nephropidae. This placement reflects its position among the true clawed lobsters, characterized by a robust body form adapted to marine benthic environments. The genus is one of several within Nephropidae, which comprises approximately 57 extant species across 21 genera, including , , and Nephropsis. Phylogenetically, the superfamily Nephropoidea, including Homarus, forms the to Enoplometopoidea within the infraorder , a relationship supported by analyses of morphological characters and molecular data from nuclear genes such as 18S rRNA, 28S rRNA, and H3, as well as mitochondrial genes including 16S rRNA and COI. These studies resolve as monophyletic, with Nephropoidea diverging from Enoplometopoidea during the Triassic-Jurassic transition, highlighting the ancient origins of clawed lobster lineages. Evidence from 18S rRNA sequences and further indicates that Nephropidae, encompassing Homarus, diverged from other astacidean lobsters approximately 140 million years ago during the . Within Nephropidae, Homarus is distinguished by key morphological synapomorphies, including chelate (clawed) pereiopods on the first three thoracic segments and features such as a prominent rostrum armed with dorsal and ventral spines, a complete branchiocardiac groove extending from the posterior margin to the antennal region, and a postcervical groove that reaches the dorsal midline but does not extend fully to the hepatic area. These traits differentiate Homarus from related genera like , which exhibits a more elongate body and reduced rostral dentition, underscoring the genus's specialized adaptations within the family.

Description

Physical characteristics

Homarus species exhibit a distinctive elongated body plan typical of clawed lobsters in the family Nephropidae. The is covered by a robust, calcified that extends forward into a short, spiny rostrum, providing protection for the head and thoracic segments. The first pair of pereopods bear large, asymmetrical chelae (claws), with one typically adapted for crushing and the other for cutting; the remaining pereopods function as walking legs, with smaller chelae on the second and third pairs. The is muscular and segmented into six pleonites, terminating in a fan-like formed by the and paired uropods, which aid in . Coloration in live specimens is generally to bluish-black on the dorsal surface, fading to lighter tones ventrally, owing to pigments bound to proteins in the ; upon cooking, heat denatures these proteins, releasing unbound and resulting in the characteristic red hue. Adult Homarus lobsters typically reach lengths of up to 60 cm from rostrum tip to , though exceptional individuals can exceed this, with maximum recorded weights around 20 kg for males. Growth occurs through molting, with size varying by age, nutrition, and environmental factors. is evident in mature individuals: males develop disproportionately larger chelae relative to body size, enhancing their competitive and foraging capabilities, while females exhibit broader abdomens to accommodate egg brooding. Species within the genus show subtle morphological variations, particularly in coloration. , the American lobster, displays a more mottled pattern with greenish-black spots over a bluish-green to olive-brown base, accented by orange highlights on the claws and joints. In contrast, , the European lobster, tends toward a more uniform bluish-black dorsum with white or yellowish spots and a paler ventral surface, though both species share the overall body form and can exhibit rare color anomalies due to genetic mutations.

Anatomy and physiology

The nervous system of Homarus species is decentralized, featuring a dorsal anterior (supraesophageal ganglion) located between the eyestalks, connected via circumesophageal connectives to a subesophageal , and a paired ventral nerve cord extending through the and with segmental ganglia from thoracomere 4 to abdominal segment 6. This structure allows for coordinated sensory-motor integration typical of decapod crustaceans. Vision is mediated by compound eyes borne on movable stalks, which provide wide-angle detection of light and motion through thousands of ommatidia. Balance and acceleration are detected by statocysts housed in the basal segment of the antennules, where sensory hairs respond to the movement of statoliths (often grains) to generate neural signals transmitted directly to the via afferent axons. The circulatory system is open, with a dorsal, triangular heart situated in the posterior cephalothorax within the pericardial sinus, pumping hemolymph containing hemocyanin into seven arteries, including the paired antennal, antennular, and hepatic arteries, and the unpaired dorsal abdominal artery, with hemolymph returning via open sinuses. Respiratory functions occur in the branchial chambers, where approximately 20 pairs of filamentous gills (including podobranchs, arthrobranchs, and pleurobranchs) extract oxygen from seawater, facilitated by the rhythmic pumping action of the gill bailer (scaphognathite) on the second maxilla to maintain water flow. The digestive system comprises a foregut with cardiac and pyloric chambers, where a gastric mill equipped with ossicles grinds food particles, followed by a midgut featuring a hepatopancreas (digestive gland) that secretes enzymes for hydrolysis and absorbs nutrients, and a hindgut leading to the rectum for waste expulsion. Molting physiology centers on ecdysis, the shedding of the old exoskeleton during premolt, during which calcium is reabsorbed from the cuticle and stored as gastroliths in the cardiac stomach to support rapid postmolt mineralization. Post-ecdysis, the new cuticle is calcified primarily using environmental calcium taken up actively through the gills, involving Ca²⁺-ATPase and Na⁺/Ca²⁺ exchangers to maintain homeostasis despite low hemolymph calcium levels immediately after molting.

Species

Extant species

The genus Homarus comprises two extant species, both of which are large marine decapods prized for their ecological and economic roles. Homarus americanus, commonly known as the , is native to the western , ranging from , , to , with the highest abundances along the northeastern U.S. coast from to . This species exhibits deeper transverse grooves on its , particularly the cervical groove, which contributes to its more rugged exoskeletal texture compared to its congener. H. americanus holds significant commercial importance, supporting a major that landed 112.6 million pounds valued at $617 million in 2024, primarily through trap fisheries in the U.S. and . Homarus gammarus, the European lobster, inhabits the eastern from to , extending into the . It features a smoother with fewer pronounced ridges and a lighter overall coloration, typically blue-black dorsally with yellowish ventral surfaces and coalescing spots. Like its American counterpart, H. gammarus supports valuable fisheries across , though on a smaller scale than H. americanus. Genetic analyses, including allozyme surveys of 28 loci, reveal close relatedness between the species, with only 3.7% fixed allelic differences and a of 0.052, indicating divergence around 1–2 million years ago during the middle Pleistocene. Despite this similarity, the species maintain distinct populations, and hybridization has been documented in areas of , such as escaped H. americanus in European waters, with hybrids identifiable via SNP markers but often morphologically indistinguishable.

Fossil species

The fossil record of the genus Homarus is limited, comprising six valid extinct species documented from deposits spanning the to the late . A comprehensive 2017 appraisal recognized these six taxa as valid, including a new species, H. hungaricus, described from the Upper of , emphasizing their morphological affinity to extant species while noting diagnostic differences such as granulation and cheliped proportions. The following table summarizes the known fossil species, their temporal ranges, and key localities:
SpeciesGeological AgeKey LocalitiesMorphological Notes
H. benedeni (Albian, ~110 Ma) (e.g., )Basal form with generalized nephropid chelipeds; type species for early records.
H. klebsiLimited material; shows subtle pleonal spine variations.
H. lehmanni (Rupelian, ~34–28 Ma) (e.g., )Known from incomplete carapaces; exhibits finer tuberculation than later forms.
H. morrisiRobust chelipeds; represents peak Paleogene diversity in .
H. percyi (Rupelian, ~34–28 Ma)Similar to H. morrisi but with distinct cutter claw .
H. hungaricusLate (Chattian, ~28–23 Ma) (Mány Formation)Partial specimens showing ornate and asymmetrical claws; differs from extant species in pleonal groove depth.
These fossils provide key evolutionary insights into the genus, with the earliest appearances in the stage of the (~110 million years ago), represented by H. benedeni, marking the initial diversification of Homarus within Nephropidae. A notable stratigraphic gap occurs through the , despite abundant nephropid fossils from that interval, suggesting either unrecognized survival or regional extirpation followed by recolonization. Oligocene species, concentrated in European epicontinental seas, display progressive refinements in claw morphology, with evidence of increasing asymmetry and robustness compared to forms, indicative of adaptations to varying predatory pressures. Phylogenetic analyses place these extinct taxa as stem-group relatives to the two living species, sharing core traits like the spiny and elongate rostrum. Extinction patterns among Homarus align with a broader decline in nephropid diversity during the Paleogene-Neogene transition (~23 Ma onward), where species vanish from the record amid cooling climates and reduced shallow marine habitats in . This shift coincides with the radiation of modern faunas, leaving only the extant lineages to persist into the present.

Distribution and habitat

Geographic range

The genus Homarus comprises two extant species with distinct transatlantic distributions in the Northern Hemisphere. Homarus americanus, the American lobster, is endemic to the western North Atlantic Ocean, ranging continuously along the coastal shelf from the Labrador coast of Canada southward to Cape Hatteras, North Carolina, USA. Due to climate change and warming waters, populations have exhibited northward range shifts, with abundances decreasing in southern areas like southern New England and increasing in northern regions such as the Gulf of Maine and Canadian waters as of 2025. This species is most abundant in nearshore waters from Maine to New Jersey, with populations extending offshore to depths of up to 700 meters from Maine to North Carolina. Higher densities occur in the northern portions of its range, particularly in the Gulf of Maine and along the Scotian Shelf. Homarus gammarus, the European lobster, occupies the northeastern and western , with a range extending from (north of the ) southward to and the archipelago. Its distribution includes rocky coastal areas around the , , and into the Adriatic and western Black Seas, though populations exhibit genetic fragmentation indicative of limited contemporary connectivity, potentially exacerbated by historical . Unlike H. americanus, H. gammarus does not naturally overlap with its congener, though rare hybridization events have been documented in European waters from escaped or released H. americanus imports. Both species rely on planktonic larval stages for dispersal, enabling connectivity across their ranges via ocean currents, with modeled larval transport distances reaching up to several hundred kilometers in H. americanus populations of the Gulf of Maine and similar scales inferred for H. gammarus in the North Sea. Efforts to introduce H. americanus to European waters, including releases in the during the 19th and 20th centuries, have failed to establish self-sustaining populations, with no verified naturalized groups persisting today.

Habitat preferences

Homarus inhabit benthic environments characterized by hard substrates that provide shelter from predators and environmental stresses. Preferred substrates include rocky or cobble bottoms, where individuals can utilize crevices, boulders, and algal cover for refuge, while soft mud or sandy areas are generally avoided due to insufficient structural complexity. Adults typically occupy depths ranging from 4 to 50 meters, though larger individuals may venture deeper, up to 150 meters in some cases, particularly for . These lobsters require cold-temperate waters with temperatures between 5 and 20°C for optimal physiological function, as higher temperatures can induce stress and reduce survival rates. levels of 25 to 35 parts per thousand are essential, supporting their osmoconforming , while low ensures clear water conditions that maintain suitability. Habitat preferences differ slightly between species, with Homarus americanus exhibiting a broader tolerance, allowing it to inhabit more variable coastal environments along the western Atlantic, compared to , which favors stable, cooler coastal reefs in the eastern Atlantic.

Biology

Life cycle

The life cycle of Homarus , the American lobster (H. americanus) and European lobster (H. gammarus), encompasses distinct developmental stages from egg to adulthood, characterized by a planktonic larval phase followed by a benthic lifestyle. Eggs, measuring approximately 1-2 mm in , are fertilized internally and carried by the female beneath her (pleopods) for 9-12 months until , with varying from 5,000 eggs in smaller females to over 100,000 in larger ones (e.g., length >140 mm). Upon hatching, larvae enter a planktonic phase consisting of three zoeal stages (I-III), followed by a postlarval stage (IV), during which they undergo molting and feed on while drifting in surface waters. For H. americanus, this period lasts 4-6 weeks (typically 25-35 days, up to 100 days in cold water at ~10°C), while for H. gammarus it is shorter, approximately 3 weeks; warmer temperatures accelerate development and shorten duration, though excessively high temperatures (above 24-25°C) can reduce survival rates. After the final larval molt, post-larvae (stage IV) settle to the , transitioning to a demersal existence by seeking structured habitats such as rocky substrates or eelgrass beds for shelter. Juveniles remain benthic, undergoing frequent molts—often multiple times in the first year—to support rapid growth, with length increasing by 10-17% per molt. Molting frequency declines with age, shifting to annual or biennial cycles in later stages, and growth increments average 10-15% annually in length under optimal conditions. is typically reached after 5-8 years for both , depending on environmental factors like , which influences metabolic rates and overall development pace. Adults continue to grow through periodic molting, achieving lifespans of 50-100 years in the wild for H. americanus and up to 70+ years for H. gammarus, though averages are lower (around 30-50 years) due to predation and environmental stressors. Cooler s generally slow growth and extend intermolt intervals, while optimal ranges (around 16°C) promote faster progression through all phases.

Reproduction and development

Reproduction in Homarus species, including H. americanus and H. gammarus, is characterized by internal fertilization and involves distinct mating behaviors tied to the female's molt cycle. Mating typically occurs seasonally during late spring and summer, when water temperatures rise, prompting premolt females to seek out dominant males in sheltered dens. The male guards the female before and after her molt, protecting her from predators and rival males during her vulnerable soft-shell phase, which can last several days. Shortly after the female molts (within 24-48 hours), the male deposits a spermatophore—containing sperm—into her seminal receptacle using his first pair of pleopods; this process lasts about 60 seconds and results in a portion of the spermatophore hardening into a plug to prevent sperm displacement. The stored sperm remains viable for up to two years, allowing delayed fertilization. Approximately 9-12 months after , the female extrudes fertilized eggs through her oviducts, attaching them to the setae on her swimmerets beneath the , where she broods them externally until ; varies with female size, ranging from about 5,000 eggs in smaller individuals (e.g., 83 mm length) to over 100,000 in larger ones (e.g., 140 mm or more), reflecting an adaptive strategy to maximize reproductive output in variable marine environments. However, egg survival is low due to factors like predation, fungal infections, and physical loss during brooding; overall, only 0.1-1% of eggs typically survive to the settlement stage, underscoring the high mortality inherent in their life history. Embryonic development within the brooded eggs is lecithotrophic, relying solely on yolk reserves for nutrition without external feeding, a process that lasts 9-12 months and is influenced by temperature and oxygen availability. Upon hatching, primarily in summer, the eggs release free-swimming, planktotrophic larvae that actively feed on plankton to fuel their growth through three zoeal stages (I-III) and a postlarval stage (IV). For H. americanus, these stages last 4-6 weeks; for H. gammarus, approximately 3 weeks. The postlarval stage (IV) transitions to a benthic lifestyle upon settlement on suitable substrates. This biphasic development enhances dispersal potential while balancing energetic demands in coastal ecosystems.

Ecology and interactions

Behavior and diet

Homarus species exhibit nocturnal behavior, emerging from shelters primarily at night to hunt and scavenge as opportunistic omnivores. Their diet consists mainly of benthic such as mollusks (including bivalves and gastropods), crustaceans like rock crabs, echinoderms, polychaete worms, and occasional small fish or , with an ontogenetic shift toward larger, harder-shelled prey like crabs in adults. Specialized s play a key role in feeding: the larger crusher is used to break open hard-shelled prey at weak points like hinges, while the smaller cutter tears flesh from softer tissues or detaches appendages. In social contexts, adult Homarus display territoriality, particularly around shelters and foraging areas, with interactions often resolved through agonistic displays such as meral spreading and claw waving to signal dominance without frequent physical combat. Larger individuals typically prevail in encounters, which are infrequent (about 0.2 per observation hour), promoting stable hierarchies and reducing energy expenditure on fights. Lobsters show strong shelter fidelity, occupying the same crevice for weeks, though premolt individuals may migrate short distances to new shelters to avoid predation vulnerability during ecdysis. Sensory capabilities are dominated by chemoreception, with antennules serving as primary organs for detecting food odors from afar through responses to , sugars, and other compounds in low concentrations (down to 10^{-7} M). This allows precise orientation toward prey plumes in turbulent water, complemented by diurnal hiding in rocky crevices—a aligned with their preferred structured habitats.

Predators and threats

Homarus species face a range of natural predators, particularly during vulnerable juvenile stages. Juvenile lobsters are preyed upon by various fish, including Atlantic cod (Gadus morhua), shorthorn sculpin (Myoxocephalus scorpius), and striped bass (Morone saxatilis), as well as wrasses such as Labrus bergylta and Labrus mixtus in European waters. Seabirds like eiders and seals, including harbor seals, also consume early-stage juveniles, contributing to high post-settlement mortality rates. Among adults, cannibalism is a significant threat, with larger individuals preying on smaller conspecifics, especially in dense populations or under stress. Abiotic threats further endanger Homarus populations through environmental stressors and diseases. Epizootic shell disease (ESD), caused by chitinolytic , leads to shell , pitting, and melanization, primarily affecting H. americanus in southern waters and reducing affected individuals' survival and reproductive success. Impoundment shell disease (ISD), distinct from ESD and caused by bacterial , affects lobsters held in facilities, leading to lesions and is influenced by and , with recent studies as of 2025 linking it to altered shell microbiomes. Similar shell diseases occur in H. gammarus, potentially posing an emerging threat due to differences in cuticular structure compared to H. americanus. The 2025 benchmark stock assessment for H. americanus indicates ongoing challenges, with southern stocks showing declines attributed to -driven factors, while northern stocks remain more stable. Microplastic represents an additional emerging threat, with fibers ingested by larvae reducing survival and respiration rates, and detected in edible muscle tissue of commercially caught H. americanus in as of November 2025. exacerbates these risks by decreasing larval growth and development, particularly when combined with warming. Hypoxia, often resulting from decomposition following harmful algal blooms, causes mass mortalities by depleting dissolved oxygen levels, as observed in where low-oxygen events led to die-offs. stress exacerbates these issues, with prolonged exposure to warmer waters impairing respiratory and immune functions, increasing disease susceptibility. Species-specific vulnerabilities highlight differential responses to climate-driven changes. H. gammarus exhibits greater sensitivity to warming waters than H. americanus, with larvae showing lower thermal tolerance at early developmental stages and populations shifting distribution due to rising temperatures. In contrast, H. americanus demonstrates higher tolerance to elevated temperatures, particularly in postlarval stages, though ongoing ocean warming still poses risks across both species.

Human significance

Fisheries and aquaculture

The genus Homarus supports significant commercial fisheries, primarily targeting H. americanus in the Northwest Atlantic and H. gammarus in the Northeast Atlantic, with lobsters captured using baited traps or pots deployed on the seafloor. These traps consist of rigid wire or wooden frames with funnel-shaped entrances that allow lobsters to enter but hinder escape, often connected in trawls to multiple buoys for hauling. In 2023, total landings of H. americanus exceeded 100,000 metric tons, with approximately 55,000 metric tons from the and the remainder predominantly from , particularly in regions like the and ; however, 2024 landings declined to approximately 85,000 metric tons overall due to reduced catches in both countries. For H. gammarus, annual landings are substantially lower, averaging around 5,000 metric tons across , with key fishing areas in the (including ) and . Aquaculture of Homarus species remains limited commercially due to challenges such as high rates of among juveniles, slow growth rates requiring 2–3 years to market size, and difficulties in larval rearing, which have constrained large-scale production. Efforts focus on production of juveniles for enhancement or grow-out, with techniques including compartmentalization to reduce aggression and specialized feeds to improve survival. In the United States, recirculating systems (RAS) in have been developed for H. americanus larval and juvenile culture, utilizing controlled and waste heat from industrial sources to enhance efficiency. Similarly, in , RAS-based farming trials for H. gammarus employ single-cage designs to minimize density-dependent mortality, though overall output remains experimental and supplements rather than replaces wild catches. The Homarus fishery generates an economic value exceeding $1 billion USD annually in ex-vessel landings, primarily driven by H. americanus exports to markets in and , supporting thousands of jobs in harvesting, processing, and distribution. Management includes regulations on minimum carapace lengths to protect immature individuals, such as 83 mm for H. americanus in U.S. and Canadian waters, ensuring only reproductively mature lobsters are harvested. In 2025, the Atlantic States Marine Fisheries Commission (ASMFC) repealed proposed increases to this minimum gauge size (Addendum XXXII), maintaining current limits amid industry concerns.

Conservation and management

The genus Homarus includes two primary species of commercial importance: the American lobster (H. americanus) and the European lobster (H. gammarus). According to the International Union for Conservation of Nature (IUCN) Red List, H. americanus is classified as Least Concern globally, reflecting its wide distribution and relatively stable populations in the western North Atlantic, though regional declines have been noted due to environmental pressures. Similarly, H. gammarus holds a Least Concern status, based on its extensive range across the eastern North Atlantic and Mediterranean, despite localized vulnerabilities in areas like Norway where it is considered vulnerable under national assessments. Key threats to both species include climate change, which drives warming waters and shifts in distribution, and habitat loss from coastal development and pollution, exacerbating population stresses in core habitats. Conservation efforts for Homarus species emphasize regulatory measures to maintain sustainable populations amid ongoing fishing pressures. , the Atlantic States Marine Fisheries Commission (ASMFC) and NOAA Fisheries implement quota systems, trap limits, and size restrictions across seven lobster conservation management areas, with recent adjustments in the including seasonal closures to protect brood stock during peak vulnerability periods. Marine protected areas (MPAs), such as the year-round Western Gulf of Maine Groundfish Closure and targeted lobster reserves, prohibit or limit fishing to allow population recovery and enhance larval recruitment. A cornerstone practice is v-notching, where egg-bearing females are marked with a V-shaped cut in their tail flipper before release; this identifies them for protection in future captures, with studies showing it can increase spawning stock biomass by 33-632% under high compliance scenarios. For H. gammarus, European management relies on national quotas and minimum landing sizes enforced by bodies like the , alongside small-scale MPAs in regions such as and that have boosted local densities and by restricting access. Emerging challenges from pose risks to Homarus shell formation, as reduced seawater pH impairs in larvae and juveniles, leading to thinner exoskeletons and higher mortality rates; experiments indicate up to a 30% decline in larval development under projected CO₂ levels. Restoration initiatives, including hatchery-reared larval reseeding, aim to counter these threats; for instance, collaborative projects in have released over 40,000 H. americanus larvae into coastal waters such as Upper to bolster , while similar efforts for H. gammarus in the UK and use ocean-based nurseries to improve survival post-release. These strategies, integrated with monitoring, seek to enhance resilience against cumulative environmental and anthropogenic impacts.

References

  1. http://www.marinespecies.org/aphia.php?p=taxdetails&id=106862
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