Lobatus gigas, originally known as Strombus gigas, commonly known as the queen conch, is a species of large edible sea snail, a marine gastropod mollusc in the family of true conches, the Strombidae. This species is one of the largest molluscs native to the Caribbean sea, and tropical northwestern Atlantic, from Bermuda to Brazil, reaching up to 35.2 centimetres (13.9 in) in shell length. L. gigas is closely related to the goliath conch, Lobatus goliath, a species endemic to Brazil, as well as the rooster conch, Lobatus gallus.
International trade in the Caribbean 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 endangered in the Caribbean as a whole, but is commercially threatened in numerous areas, largely due to extreme overfishing.
Lobatus gigas is native to the tropical Western Atlantic coasts of North and Central America in the greater Caribbean tropical zone. Although the species undoubtedly occurs in other places, this species has been recorded within the scientific literature as occurring, in:Aruba, (Netherlands Antilles); Barbados; the Bahamas; Belize; Bermuda; North and northeastern regions of Brazil (though this is contested); 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, with the Florida Keys and 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 lives at depths from 0.3–18 m. to 25–35 m. Its depth range is limited by the distribution of seagrass and algae cover. In heavily exploited areas, the queen conch is more abundant in the deepest range. The queen conch lives in seagrass meadows and on sandy substrate, usually in association with turtle grass (species of the genus Thalassia, specifically Thalassia testudinum and also Syringodium sp.) and manatee grass (Cymodocea sp.). Juveniles inhabit shallow, inshore seagrass meadows, while adults favor deeper algal plains and seagrass meadows. The critical nursery habitats for juvenile individuals are defined by a series of characteristics, including tidal circulation and macroalgal production, which together enable high rates of recruitment and survival. L. gigas is typically found in distinct aggregates that may contain several thousand individuals.
Strombid gastropods were widely accepted as carnivores by several authors in the 19th century, a concept that persisted until the first half of the 20th century. This erroneous idea originated in the writings of Jean-Baptiste Lamarck, who classified strombids with other supposedly carnivorous snails. This idea was subsequently repeated by other authors, but had not been supported by observation. Subsequent studies have refuted the concept, proving beyond doubt that strombid gastropods are herbivorous animals. In common with other Strombidae, Lobatus gigas is a specialized herbivore, that feeds on macroalgae (including red algae, such as species of Gracilaria and Hypnea), seagrass and unicellular algae, intermittently also feeding on algal detritus. The green macroalgae Batophora oerstedii is one of its preferred foods.