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Knobbed whelk, Busycon carica. Photograph JaxShells.

Species Name: Busycon carica Gmelin, 1791
Common Name: Knobbed Whelk
Synonymy: Fusus lamellosus Emmons, E., 1858
  1. TAXONOMY

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Animalia Mollusca Gastropoda Neogatropoda Melongenidae Busycon

    Species Description

    Busycon caricais a member of the family Melongenidae and one of roughly fourteen known species of the subfamily Bucyconinae. Members of the genus Busycon are the largest marine gastropods along the eastern coast of the United States (Ram 1977). Juvenile whelks have small beads on their shells, while adult whelk shells are thick with spines on the shoulder. Knobbed whelk shells are right-handed and have a long siphonal canal. The outer shell is grayish white to tan and may have some dark brown streaks. The brown streaks are more prominent in juvenile shells. The inner shell ranges in colors from pale yellow to orange and even dark red.

  2. HABITAT AND DISTRIBUTION

    Regional Occurrence

    Busycon caricaoccur on the coast of the Atlantic from Cape Cod, Massachusetts to Cape Canaveral, Florida. Knobbed whelks are mainly found in estuaries, bays and shallow shelf waters (Magalhaes 1948). They occur at depths of 1 to 50 meters.

    IRL Distribution

    The knobbed whelk occurs in the Indian River Lagoon, but is not common.

  3. LIFE HISTORY AND POPULATION BIOLOGY

    Age, Size, Lifespan

    Knobbed whelks reach maturity in about three to five years. Whelks are considered to be protandric hermaphrodites initially functioning as males and changing into females as they age (Castagna and Kraeuter 1994, Anderson 2005). Adult females are generally larger than adult males of the same age. Adult whelks may be as long as 30.5 cm (Magalhaes 1948).

    Abundance

    Busycon caricais a common species of the shallow shelf ecosystem and estuaries especially in South Carolina and Georgia. The density of the knobbed whelk in Beaufort, North Carolina was estimated to be 1 individual per 79 2 during non-reproductive seasons (Magalhaes 1948).

    Migration

    Busycon spp. migrate from deep to shallow waters in times of reproduction and low food supply (Magalhaes 1948).

    Locomotion

    Knobbed whelks glide along or just beneath the sand on the ocean floor (Magalhaes 1948).

    Reproduction

    Male and female Busycon caricamate by coupling. The reproductive season for the knobbed whelk in Beaufort, North Carolina is reported to begin in March and lasts through September (Magalhaes 1948). In South Carolina, B. carica reproduces during the fall and spring (Anderson 2005). After fertilization occurs the female lays a string of eggs in deep water and anchors the string to the sand by one end. The capsules of B. carica are wide with two smooth surfaces resembling book covers (Magalhaes 1948, Ram 1977). These strings of eggs consist of up to 40 pouches, with each pouch containing up to 100 fertilized eggs. Field studies have shown that egg strings are laid in the fall on tidal and intertidal flats and over winter to hatch in the spring (Castagna and Kraeuter 1994).

    Embryology

    The fertilized eggs of the knobbed whelk develop slowly and hatch in approximately 3 to 13 months (Anderson 2005). The larva emerge as juveniles and measure approximately 4 mm in length. Under laboratory conditions, the shells of the hatchling were observed to grow 1.5 mm in 22 days (Magalhaes 1948).

  4. PHYSICAL TOLERANCES

    Temperature

    There are no specific studies addressing the temperature tolerance of Busycon carica.

    Salinity

    There are no specific studies addressing the salinity tolerance of Busycon carica.

  5. COMMUNITY ECOLOGY

    Trophic Mode

    Busycon caricais a carnivorous gastropod that feeds on bivalves. They use the lip of their shell to break off and force open the valves of their prey by holding it with its foot. Slow chipping continues until there is an opening that allows the whelk to lodge its shell between the bivalves's valves and then enter its foot to begin feeding. The feeding process generally results in damage to the whelks shell which causes limited growth in adults since a lot of energy is used to repair their shell. Some bay men from estuaries along the New Jersey and New York coasts suggest that B. carica cause severe predation of oysters (Carriker 1951).

    Associated Species

    The deal shells of Busycons are host to several species of Crepidula and oyster spats and often inhabited by hermit crabs (Magalhaes 1948).

  6. ADDITIONAL INFORMATION

    Fishery

    Knobbed whelks are mainly used for their meat. The whelk trawl fishery off the South Carolina coast became an important fishery during 1977 and the spring of 1978 during periodic closure of the shrimp season (Anderson et al. 1985). In Delaware, the whelk dredge landings were 18.5 million tons of meat from 1994-2000 and increased to 241.6 million tons from 2001-2004 (Bruce 2006). Members in this genus are also sold in the tourist trade as ornamentals (Magalhaes 1948).

  7. REFERENCES

    Anderson WD. 2005 Busycon carica. Comprehensive Wildlife Conservation Strategy; SC Department of Natural Resources. Available online as a pdf file.

    Anderson WD, Eversole AG, Anderson BA and KB Van Sant. 1985. A biological evaluation of the knobbed whelk fishery in South Carolina. National Marine Fisheries Service Publication. 2-392-R 76 pp.

    Bruce DG. 2006. The whelk dredge fishery of Delaware. Journal of Shellfish Research 25:1-13.

    Carriker MR. 1951. Observations on the penetration of tightly closing bivalves by Busycon and other predators. Ecology. 32(1):73-83.

    Castagna M and JN Kraeuter. 1994. Age, growth rate, sexual dimorphism and fecundity of knobbed whelk Busycon carica(Gmelin,1791) in a western Mid-Atlantic lagoon system, Virginia. Journal of Shellfish Research. 2(2): 581-585.

    The Georgia Shell Club Whelk Page.

    Hardy's Internet Guide to Marine Gastropods. Available online.

    Magalhaes H. 1948. An ecological study of the genus Busycon at Beaufort, North Carolina. Ecological Monographs. 18(3): 377-409.

    Ram JL. 1977. Hormonal control of reproduction in Busycon: Laying of egg capsules caused by nervous system extracts. Marine Biological Laboratory. Biol. Bull., 152: 221-232.

Report by: Melany P. Puglisi, Smithsonian Marine Station
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Page last updated: October 1, 2008

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