| Lobatus gigas | |
|---|---|
| A live subadult individual of Lobatus gigas, in situ surrounded by turtle grass | |
| A dorsal view of an adult individual of L. gigas from Chenu, 1844 | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| clade: | Caenogastropoda |
| clade: | Hypsogastropoda |
| clade: | Littorinimorpha |
| Family: | Strombidae |
| Genus: | Lobatus |
| Species: | L. gigas |
| Binomial name | |
| Lobatus gigas (Linnaeus, 1758) |
|
| Synonyms[7] | |
|
Strombus gigas Linnaeus, 1758[1] |
|
Lobatus gigas, commonly known as the queen conch, is a species of large edible sea snail, a marine gastropod mollusk in the family of true conchs, the Strombidae. This species is one of the largest mollusks native to the Tropical Northwestern Atlantic, from Bermuda to Brazil, reaching up to 35.2 cm (13.9 in) in shell length.
The queen conch is herbivorous and lives in seagrass beds, although the exact habitat varies during the different stages of its development. The adult animal has a very large, solid and heavy shell, with knob-like spines on the shoulder, a flared thick outer lip and a characteristic pink-colored aperture (opening). The flared lip is completely absent in younger specimens. The external anatomy of the soft parts of L. gigas is similar to that of other snails in the same family: it has a long snout, two eyestalks with well-developed eyes and additional sensory tentacles, a strong foot and a corneous sickle-shaped operculum.
The shell and soft parts of living Lobatus gigas serve as a home to several different kinds of commensal animals, including slipper snails, porcelain crabs and cardinal fish. Its parasites include coccidians. The queen conch is hunted and eaten by several species of large predatory sea snails, and also by starfish, crustaceans and vertebrates (fish, sea turtles and humans). The meat of this sea snail is consumed by humans in a wide variety of dishes. The shell is sold as a souvenir and used as a decorative object. Historically, Native Americans and indigenous Caribbean peoples used parts of the shell to create various tools.
International trade in queen conch is regulated under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) agreement, in which it is listed as Strombus gigas. This species is not yet truly endangered in the Caribbean as a whole, but it is commercially threatened in numerous areas, largely due to extreme overfishing; the meat is an important food source for humans. The CITES regulations are designed to monitor and control the commercial export of the meat of this species as well as the shells (often sold to be used as decorative objects). Both of these trades were previously so prevalent that they represented serious threats to the survival of the species. However, the CITES Convention does not monitor or regulate any domestic use.
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The queen conch was originally described from a shell in 1758 by the Swedish naturalist and taxonomist Carl Linnaeus in his ground-breaking book Systema Naturae.[1] Linnaeus named the species Strombus gigas, and that remained the accepted name for over two hundred years. Linnaeus did not mention a specific locality for this species in his description, giving only "America" as the type locality.[9] The specific name is the Ancient Greek word gigas (γίγας), which means "giant", referring to the large size of this snail compared with almost all other gastropod mollusks. Strombus lucifer, which was considered to be a synonym much later, was also described by Linnaeus in Systema Naturae.[1]
In the first half of the 20th century, the type material for the species was thought to have been lost; in other words, the shell on which Linnaeus based his original description and which would very likely have been in his own collection, was apparently missing, and without type material to formally define the species, this created a problem for taxonomists. To remedy this, in 1941 a neotype of this species was designated by the American malacologists William J. Clench and R. Tucker Abbott. In this case, the neotype was not an actual shell or whole specimen, but a figure from a book that was published in the 17th century, 23 years before Linnaeus was even born, the 1684 Recreatio mentis, et occuli by the Italian scholar Filippo Buonanni. This was the first book published that was solely about seashells.[9][10][11][12] In 1953 however, the Swedish malacologist Nils Hjalmar Odhner searched the Linnaean Collection at Uppsala University and discovered the original shell upon which Linnaeus had based his description, thereby invalidating Clench and Abbott's neotype designation.[13]
The family Strombidae has recently undergone an extensive taxonomic revision, and a few subgenera, including Eustrombus, were elevated to genus level by some authors.[14][15][16] Petuch (2004)[17] and Petuch and Roberts (2007)[18] recombined this species as Eustrombus gigas, and Landau et al. (2008) recombined it as Lobatus gigas.[16]
As well as the English names "queen conch" and "pink conch", common names for this species in the languages spoken where it occurs include caracol rosa and caracol rosado in Mexico, caracol de pala, cobo, botuto and guarura in Venezuela, caracol reina and lambí in the Dominican Republic.[19][20][21][22][23]
The adult shell of this species is usually 15–31 cm (6–12 in) in length,[24][25] and the maximum reported size is 35.2 cm (13.9 in).[7][12][26] The shell is very solid and heavy, with 9 to 11 whorls and a widely flaring and thickened outer lip.[12] In the shells of adult snails, a structure called the stromboid notch is present on the edge of the lip. Although this notch is not as well developed in this species as it is in many other species in the same family,[12] the shell feature is nonetheless visible in an adult dextral (normal right-handed) specimen, as a secondary anterior indentation in the lip of the shell, to the right of the siphonal canal, assuming the shell is viewed ventrally. In life, the animal's left eyestalk protrudes through this notch.[12][27][28][29]
The spire (a protruding part of the shell which includes all of the whorls with the exception of the largest and final whorl, known as the body whorl) is usually higher (more elongated) in this species than it is in the shells of other strombid snails, such as the closely related and even larger goliath conch, Lobatus goliath, a species endemic to Brazil.[12] In Lobatus gigas, the glossy finish or glaze around the aperture of the adult shell is colored primarily in shades of pink. This pink glaze is usually pale, and may show a cream, peach or yellow coloration, but it can also sometimes be tinged with a deep magenta, shading almost to red. The periostracum, a layer of protein (conchiolin) which is the outermost part of the shell surface, is thin and a pale brown or tan color in this species.[25][27][28]
The overall shell morphology of L. gigas is not solely determined by the animal's genes; environmental conditions such as geographic location, food supply, temperature and depth, and biological interactions such as exposure to predation, can greatly affect it.[30][31] Juvenile conchs develop heavier shells when exposed to predators compared to those that are not exposed to predators. Conchs also develop wider and thicker shells with fewer but longer spines when they are living in deeper water.[31]
The shells of very small juvenile queen conchs are strikingly different in appearance from those of the adults. Noticeable is the complete absence of a flared outer lip; juvenile shells have a simple sharp lip, which gives the shell a conical or biconic outline. In Florida, juvenile queen conchs are known as "rollers", because wave action very easily rolls their shells, whereas it is nearly impossible to roll the shell of an adult specimen, due to its weight and asymmetrical profile. Subadult shells have a flared lip which is however very thin; the flared outer lip of an adult shell constantly increases in thickness with age, until death.[32][33][34]
Index Testarum Conchyliorum (published in 1742 by the Italian physician and malacologist Niccolò Gualtieri) contains three illustrations showing the morphology of adult queen conch shells from different perspectives. The knobbed spire and the flaring outer lip, with its somewhat wing-like contour expanding out from the last whorl, is a striking feature of these images. The shells are shown as if balancing on the edge of the lip and/or the apex; this was presumably done for artistic reasons as these shells cannot be balanced like this.
Considered as one of the most prized and sumptuous shell publications of the 19th century, a series of books titled Illustrations conchyliologiques ou description et figures de toutes les coquilles connues, vivantes et fossiles (published by the French naturalist Jean-Charles Chenu from 1842 to 1853), contains several illustrations of both adult and juvenile L. gigas shells, and one uncolored drawing depicting some of the animal's soft parts.[35] Almost forty years later, a colored illustration from the Manual of Conchology (published in 1885 by the American malacologist George Washington Tryon) shows a dorsal view of a small juvenile shell with its typical brown and white patterning.[34]
Many details about the anatomy of Lobatus gigas were not well known until 1965, when the zoologist Colin Little published a general study on the subject.[36] More recently, in 2005, the Brazilian malacologist Luiz R. L. Simone gave a detailed anatomical description of the species.[15]
Lobatus gigas has a long extensible snout with two eyestalks (also known as ommatophores) that originate from its base. The tip of each eyestalk contains a large, well-developed lens eye, with a black pupil and a yellow iris[12] (if amputated, the eyes can be completely regenerated),[37] and a small slightly posterior sensory tentacle.[24] Inside the mouth of the animal is a radula (a tough ribbon covered in rows of microscopic teeth) of the taenioglossan type.[36]
Both the snout and the eyestalks show dark spotting in the exposed areas. The mantle is darkly colored in the anterior region, fading to light gray at the posterior end, while the mantle collar is commonly orange, and the siphon is also orange or yellow.[36]
When the soft parts of the animal are removed from the shell, several organs are distinguishable externally, including the kidney, the nephiridial gland, the pericardium, the genital glands, stomach, style sac, and the digestive gland.[36] In adult males, the penis is also visible.
Lobatus gigas has a large and powerful foot, which has brown spots and markings towards the edge, but is white nearer to the visceral hump (the part of the animal that stays inside, protected by the shell, and which accommodates a number of internal organs). The base of the anterior end of the foot has a distinct groove, which contains the opening of the pedal gland. Attached to the posterior end of the foot for about one third of its length is the dark brown, corneous, sickle-shaped operculum, which is reinforced by a distinct central rib. The base of the posterior two-thirds of the animal's foot is rounded; only the anterior third of the foot is applied to the substrate during locomotion.[15][36]
The columella, the central pillar within the shell, serves as the attachment point for the white collumellar muscle. Contraction of this large strong muscle allows all of the soft parts of the animal to withdraw into the shell in response to undesirable stimuli.[36]
Lobatus gigas is native to the tropical Western Atlantic coasts of North and Central America.[28] It lives in the greater Caribbean tropical zone.[28]
Although the species undoubtedly occurs in more individual places than are listed here, the countries, regions, and islands where this species has been recorded within the scientific literature as occurring are, in alphabetical order:[7][38][39]
Aruba, of the Netherlands Antilles; Barbados; all of the islands and cays of the Bahamas; Belize; Bermuda; North and northeastern regions of Brazil (though this is contested by some authors);[12] Old Providence Island in Colombia; Costa Rica; the Dominican Republic; Panama; Swan Islands in Honduras; Jamaica; Martinique; Alacran Reef, Campeche, Cayos Arcas and Quintana Roo, in Mexico; Puerto Rico; Saint Barthélemy; Mustique and Grenada in the Grenadines; Pinar del Río, North Havana Province, North Matanzas, Villa Clara, Cienfuegos, Holguín, Santiago de Cuba and Guantánamo, in the Turks and Caicos Islands and Cuba; South Carolina, Florida, including East Florida, West Florida, the Florida Keys and the Flower Garden Banks National Marine Sanctuary, in the United States; Carabobo, Falcon, Gulf of Venezuela, Los Roques archipelago, Los Testigos Islands and Sucre in Venezuela; St. Croix in the Virgin Islands.
Lobatus gigas has an unusual means of locomotion, which was described in 1922 by the American zoologist George Howard Parker (1864–1955).[40][41] The animal first fixes the posterior end of the foot by thrusting the point of the sickle-shaped operculum into the substrate, then it extends the foot in a forward direction, lifting and throwing the shell forward in a so-called leaping motion. This way of moving is considered to resemble that of pole vaulting,[42] making L. gigas a good climber even of vertical concrete surfaces.[43] This odd leaping form of locomotion may also help prevent predators from following the snail's chemical traces, which would otherwise be a continuous trail on the substrate.[44]
Lobatus gigas lives at depths from 0.3 m to 18 m[28] or to 25 m.[26] It lives in seagrass meadows and on sandy substrate,[45] usually in association with turtle grass (species of the genus Thalassia, namely Thalassia testudinum[32] and also Syringodium sp.)[30] and manatee grass (Cymodocea sp.).[46] Juvenile individuals are found in shallow, inshore seagrass meadows, which are different from the deeper algal plains and seagrass meadows where adult individuals live.[28][47]
The critical nursery habitats for juvenile individuals are defined by a series of combined factors, both habitat characteristics (such as tidal circulation) and ecological processes (such as macroalgal production), which together provide high rates of both recruitment and survival.[48] Lobatus gigas is typically found in distinct aggregates, which may contain several thousand individuals.[31]
Lobatus gigas is gonochoristic, which means each individual snail is either distinctly male or distinctly female.[29] Females are usually larger than males in natural populations, with both sexes existing in similar proportion.[45] After internal fertilization,[31] the females lay eggs in gelatinous strings, which can be as long as 75 feet (or about 23 m).[28] These are layered on patches of bare sand or seagrass. The sticky surface of these long egg strings allows them to coil and agglutinate, mixing with the surrounding sand to form compact egg masses, the shape of which is defined by the anterior portion of the outer lip of the female's shell while they are layered.[31][49] Each one of the egg masses may have been fertilized by multiple males.[49] The number of eggs per egg mass may vary greatly depending on environmental conditions, such as food limitation and temperature.[31][49] Commonly, females produce an average of 8–9 egg masses per season,[29][50] each containing 180,000–460,000 eggs,[28] but numbers can be as high as 750,000 eggs per egg mass depending upon the conditions.[31] Lobatus gigas females may spawn multiple times during the reproductive season,[28] which lasts from March to October, with activity peaks occurring from July to September.[29]
After hatching, the emerging two-lobed veliger (a larval form common to various marine and fresh-water gastropod and bivalve mollusks)[51] spend several days developing in the plankton, feeding primarily on phytoplankton. Metamorphosis occurs in about 16–40 days from the hatching,[31] when the fully grown protoconch (embryonic shell) is about 1.2 mm high.[45] After the metamorphosis, Lobatus gigas individuals spend the rest of their lives in the benthic zone (on or in the sediment surface), usually remaining buried during their first year of life.[52]
The queen conch is known to reach sexual maturity at approximately 3 to 4 years of age, reaching a shell length of nearly 180 mm and weighing up to 5 pounds.[28][29] Individuals may usually live up to 7 years, though in deeper waters their lifespan may reach 20–30 years[28][31][45] and maximum lifetime estimates reach 40 years.[53] It is believed that the mortality rate tends to be lower in matured conchs due to their thickened shell, but it could be substantially higher for juveniles. Estimates have demonstrated that the mortality rate of L. gigas decreases as the animal size increases, and can also vary due to habitat, season and other factors.[52]
Strombid gastropods were widely accepted as carnivores by several authors in the 19th century, a conception that persisted until the first half of the 20th century. This erroneous idea probably originated in the writings of Jean-Baptiste Lamarck, who classified strombids alongside other supposedly carnivorous snails, and this idea was subsequently repeated by other authors. The claims of these authors, however, were not supported by any in situ observations.[54] Lobatus gigas is now known to be a specialized herbivore,[25] as is the case in other Strombidae,[14][54] feeding on macroalgae (including red algae, such as species of Gracilaria and Hypnea),[34] seagrass[46] and unicellular algae, intermittently also feeding on algal detritus.[54][55] The green macroalga Batophora oerstedii is one of its preferred foods.[28]
A few different animals may establish a commensal interaction with L. gigas, which means both the organisms maintain a relationship where one individual benefits (the commensal) but the other obtains no advantage (in this case, the queen conch). Some commensals of this species are also mollusks, mainly slipper shells (Crepidula spp.).[30] The porcelain crab, Porcellana sayana, is also known to be a commensal,[30] and a small cardinal fish, known as the conch fish (Astrapogon stellatus),[30] sometimes lives in the mantle of the conch for protection, bringing L. gigas no apparent benefit.[28] L. gigas is very often parasitized by protists of the phylum Apicomplexa,[56][57] which are common parasites of mollusks. Those coccidian[56] parasites, which are spore-forming, single-celled microorganisms, initially establish themselves in large vacuolated cells of the hosts digestive gland, where they reproduce freely.[56][57] The infestation may proceed to the secretory cells of the same organ, and the entire life cycle of the parasite will likely occur within the same host and tissue.[56]
L. gigas is a prey species for several carnivorous gastropod mollusks, including the apple murex Phyllonotus pomum, the horse conch Pleuroploca gigantea, the lamp shell Turbinella angulata, the moon snails Natica spp. and Polinices spp., the muricid snail Murex margaritensis, the trumpet triton Charonia variegata and the tulip snail Fasciolaria tulipa.[12][24][58] A variety of crustaceans are also known predators of conchs, such as the blue crab Callinectes sapidus, the box crab Calappa gallus, the giant hermit crab Petrochirus diogenes, the spiny lobster Panulirus argus and several other species.[24][58] The queen conch is also prey to echinoderms, such as the cushion star, Oreaster reticulatus, and vertebrates, including fish (such as the permit Trachinotus falcatus[59] and the porcupine fish Diodon hystrix), loggerhead sea turtles (Caretta caretta) and humans.[24][58]
Conch meat has been eaten by humans for centuries, and has traditionally been an important part of the diet in many islands in the West Indies. It is consumed raw, marinated, minced or chopped in a wide variety of dishes, such as salads, chowder, fritters, soups, stew, pâtés and other local recipes.[24][42][46][60] In the Spanish-speaking regions, for example in the Dominican Republic, Lobatus gigas meat is known as lambí. Although the queen conch meat is used mainly for human consumption, it is also sometimes employed as fishing bait (usually the foot is utilized for such purpose).[46][53] L. gigas is among the most important fishery resources in the Caribbean: its harvest value was US$30 million in 1992,[31] increasing to $60 million in 2003.[61] The total annual harvest of meat of L. gigas ranged from 6,519,711 kg to 7,369,314 kg between 1993 and 1998, and later its production declined to 3,131,599 kg in 2001.[61] Data about imports of queen conch meat into the United States shows a total of 1,832,000 kg in 1998, as compared to 387,000 kg in 2009, a drastic reduction of nearly 80%, twelve years later.[62]
Queen conch shells were used by Native Americans and Caribbean Indians in a wide variety of ways. The South Florida Indians (such as the Tequesta), the Carib, the Arawak and Taíno used conch shells to fabricate tools (such as knives, axe heads and chisels), jewelry, cookware and also used them as blowing horns.[24][63] Aztecs used the shell as part of jewelry mosaics like the double-headed serpent.[64] Brought by explorers, queen conch shells quickly became a popular asset in early modern Europe. In the late 17th century they were widely used as decoration over fireplace mantels and English gardens, among other places.[42] In contemporary times, queen conch shells are mainly utilized in handicraft. Shells are made into cameos, bracelets and lamps,[46][65] but have also been traditionally used as doorstops or decorations by families of seafaring men.[65] The shell of the queen conch has been, and continues to be, popular as a decorative object, though its export is now regulated and restricted by the CITES agreement.[24]
Very rarely (about 1 in 10,000 conchs),[24] a conch pearl may be found within the mantle of the animal.[24][33] Though they occur in a range of colors corresponding to the colors of the interior of the shell, the pink conch pearls are considered to be the most desirable.[66] These pearls are considered semi-precious,[12] a popular tourist curio,[46] and the most attractive among them have been used to create necklaces and earrings. A conch pearl is a non-nacreous pearl (formerly referred to by some sources as a 'calcareous concretion' – see the pearl article), which differs from most pearls sold as gemstones.[66]
Within the conch fisheries, one of the threats to sustainability stems from the fact that there is almost as much meat in large juveniles as there is in adults, but only adult conchs can reproduce and thus build up a population.[60] In many places where adult conchs have become rare due to overfishing, larger juveniles and subadult animals are taken by the fishermen before the snails have had a chance to mate and lay eggs.[60][67]
On a number of islands, subadult conchs form the vast majority of the harvest.[68] The abundance of Lobatus gigas is declining throughout the species' range as a result of overfishing and poaching, and populations of the species in Honduras, Haiti and the Dominican Republic, in particular, are currently being exploited at rates that may be unsustainable.[53] In fact, trade from many Caribbean countries is known or suspected to be unsustainable, and illegal harvest, including fishing of the species in foreign waters and subsequent illegal international trade, is a common and widespread problem in the region.[53] The Caribbean "International Queen Conch Initiative" is an attempt at a fisheries management scheme for this species.[39]
The queen conch fishery is usually managed under the regulations of individual nations. In the United States all taking of queen conch is prohibited in Florida and in adjacent Federal waters. No international regional fishery management organization exists in the whole Caribbean area, but in places such as Puerto Rico and the Virgin Islands, queen conch is regulated under the auspices of the Caribbean Fishery Management Council (CFMC).[53] In 1990, the Parties to the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region (Cartagena Convention) included queen conch in Annex II of its Protocol Concerning Specially Protected Areas and Wildlife (SPAW Protocol) as a species that may be used on a rational and sustainable basis and that requires protective measures. Because of this recognition, in 1992 the United States proposed queen conch for listing in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES); this proposal was adopted, and queen conch became the first large-scale fisheries product to be regulated by CITES.[53]
Although this species has been mentioned in CITES since 1985[31] and has been listed in Appendix II[69] since 1992,[70] it is only since 1995 that CITES has been reviewing the biological and trade status of the queen conch (Note: this species is known by the name Strombus gigas in CITES) under its "Significant Trade Review" process. Significant Trade Reviews are undertaken when there is concern about levels of trade in an Appendix II species. Based on the 2003 review,[61] CITES recommended that all countries prohibit the importation of queen conch from Honduras, Haiti and the Dominican Republic, according to Standing Committee Recommendations.[71] Queen conch meat continues to be available from many other Caribbean countries, including Jamaica and the Turks and Caicos Islands (British West Indies), which have well-managed queen conch fisheries.[53]
This article incorporates public domain text (a public domain work of the United States Government) from the reference.[53]