Overview

Comprehensive Description

The heavy shell of the southern quahog, Mercenaria campechiensis, is ovate trigonal and inflated with valves of equal size (Andrews 1994). Several concentric growth lines are present on the gray to whitish exterior. Three cardinal teeth (the middle one split) on each valve help to hold the shell together at the hinge. In empty shells, the interior color is often porcelaneous white with purple marks occurring rarely. Two muscle scars are present on the interior surface, both attached to the pallial line.
  • Abbott, RT & PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and the West Indies, 4th Edition. Houghton Mifflin. New York, NY. USA. 350 pp.
  • Andrews, J. 1994. A Field Guide to Shells of the Florida Coast. Gulf Publishing. Houston, TX. USA. 182 pp.
  • Arnold, WS, Bert, TM, Marelli, DC, Cruz-Lopez, H & PA Gill. 1996. Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats. Mar. Biol. 125: 129-139.
  • Busby, D. 1986. An overview of the Indian River Clamming Industry and the Indian River Lagoon. Florida Sea Grant Extension Program. Technical Paper No. 44. Project IR-85-7. 45 pp.
  • Dillon, Jr., RT. 1992. Minimal hybridization between populations of the hard clams, Mercenaria mercenaria and Mercenaria campechiensis, co-occurring in South Carolina. Bull. Mar. Sci. 50: 411-416.
  • Stewart, VN. 1981. Sea-stats: a summary of information and statistics on Florida's marine organisms and the marine environment. No. 7: Clams. Florida Department of Natural Resources. 11 pp.
  • Surge, D & KJ Walker. 2006. Geochemical variation in microstructural shell layers of the southern quahog (Mercenaria campechiensis): implications for reconstructing seasonality. Palaeoecol. 237: 182-190.
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Source: Indian River Lagoon Species Inventory

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Distribution

occurs (regularly, as a native taxon) in multiple nations

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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The range of the southern quahog extends from Chesapeake Bay to Florida, Texas and the Yucatán Peninsula to Cuba (Andrews 1994). Populations are normally found from intertidal sand flats to offshore depths of up to 120 feet (Abbott & Morris 1995). The clam uses its muscular foot to burrow into the sediment, where it is camouflaged from potential predators.Indian River Lagoon (India River Lagoon) Distribution: The range of the southern quahog extends south to the St. Lucie Inlet (Stewart 1981), although most populations are probably located in the northern India River Lagoon.
  • Abbott, RT & PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and the West Indies, 4th Edition. Houghton Mifflin. New York, NY. USA. 350 pp.
  • Andrews, J. 1994. A Field Guide to Shells of the Florida Coast. Gulf Publishing. Houston, TX. USA. 182 pp.
  • Arnold, WS, Bert, TM, Marelli, DC, Cruz-Lopez, H & PA Gill. 1996. Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats. Mar. Biol. 125: 129-139.
  • Busby, D. 1986. An overview of the Indian River Clamming Industry and the Indian River Lagoon. Florida Sea Grant Extension Program. Technical Paper No. 44. Project IR-85-7. 45 pp.
  • Dillon, Jr., RT. 1992. Minimal hybridization between populations of the hard clams, Mercenaria mercenaria and Mercenaria campechiensis, co-occurring in South Carolina. Bull. Mar. Sci. 50: 411-416.
  • Stewart, VN. 1981. Sea-stats: a summary of information and statistics on Florida's marine organisms and the marine environment. No. 7: Clams. Florida Department of Natural Resources. 11 pp.
  • Surge, D & KJ Walker. 2006. Geochemical variation in microstructural shell layers of the southern quahog (Mercenaria campechiensis): implications for reconstructing seasonality. Palaeoecol. 237: 182-190.
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Source: Indian River Lagoon Species Inventory

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Physical Description

Morphology

The overall shape is ovate, with a rounded anterior margin and a lightly pointed posterior margin. The valves are the same size and shape (equivalve), and there is no gape when they are closed. The valves are ornamented with growth lines and comarginal ribs. As the animal grows, the ribs become denser and finer. The lunule is impressed and heart-shaped, and it extends approximately half of the anterior dorsal margin. The umbo points anteriorly and projects dorsally. The escutcheon is impressed and covers the posterior dorsal margin; its width is approximately 1/4th of its length.

The exterior color is white or light tan, but other details vary. Some shells have a light brown zig-zag pattern. The escutcheon may be a dark brown. There may be comarginal dark lines. The interior color is white. There is sometimes purple coloration along the interior margin.

The ligament is exterior and extends half of the posterior dorsal margin. The nymph supports the ligament and has a rugose texture. There are three cardinal teeth on each valve. On the left valve, the central tooth is bifid, the anterior can be slightly bifid, and posterior teeth are not bifid. The posterior tooth has merged with the nymph. On the right valve, the central and posterior teeth are bifid and the anterior tooth is not. There are no lateral teeth. There are crenulations on the interior shell margin. The anterior and posterior adductor muscle scars are similar in size and shape. The pallial sinus is tapering and shallow.

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Size

The southern quahog is approximately 7 to 15 cm (Andrews 1994), although some individuals have been documented at over 17 cm in length (Stewart 1981). Lifespan varies with environmental conditions and other factors, but the maximum documented age for the southern quahog is around 22 years old (Stewart 1981). Most growth occurs in the first 2-3 years of life.Reproduction &
  • Abbott, RT & PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and the West Indies, 4th Edition. Houghton Mifflin. New York, NY. USA. 350 pp.
  • Andrews, J. 1994. A Field Guide to Shells of the Florida Coast. Gulf Publishing. Houston, TX. USA. 182 pp.
  • Arnold, WS, Bert, TM, Marelli, DC, Cruz-Lopez, H & PA Gill. 1996. Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats. Mar. Biol. 125: 129-139.
  • Busby, D. 1986. An overview of the Indian River Clamming Industry and the Indian River Lagoon. Florida Sea Grant Extension Program. Technical Paper No. 44. Project IR-85-7. 45 pp.
  • Dillon, Jr., RT. 1992. Minimal hybridization between populations of the hard clams, Mercenaria mercenaria and Mercenaria campechiensis, co-occurring in South Carolina. Bull. Mar. Sci. 50: 411-416.
  • Stewart, VN. 1981. Sea-stats: a summary of information and statistics on Florida's marine organisms and the marine environment. No. 7: Clams. Florida Department of Natural Resources. 11 pp.
  • Surge, D & KJ Walker. 2006. Geochemical variation in microstructural shell layers of the southern quahog (Mercenaria campechiensis): implications for reconstructing seasonality. Palaeoecol. 237: 182-190.
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Source: Indian River Lagoon Species Inventory

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Type Information

Syntype for Venus campechiensis quadrata Dall, 1902
Catalog Number: USNM 6989
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Dry
Locality: Florida, United States, North Atlantic Ocean
  • Syntype: Proc. U.S. Natl. Mus. 26(1312): 377.
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Holotype for Venus apodema Dall, 1902
Catalog Number: USNM 6243
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Dry
Collector(s): A. Schott
Locality: Humboldt Bay, Gulf of Panama, North Pacific Ocean
  • Holotype: Proc. U.S. Natl. Mus. 26(1312)_: 396, 406, pl. 15, fig. 8.
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Holotype for Mercenaria kennicottii Dall, 1871
Catalog Number: USNM 75017
Collection: Smithsonian Institution, National Museum of Natural History, Department of Invertebrate Zoology
Preparation: Dry
Collector(s): J. Swan
Locality: Washington, Neeah Bay, North Pacific Ocean
  • Holotype: Am J Concology. 7(2): 147,pl.16,fig.1.
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Look Alikes

Similar to Mercenaria mercenaria. Mercenaria campechiensis can be distinguished by the ribs, which become more dense and fine as the animal grows; whereas, Mercenaria mercenaria is distinguishable by a central smooth region on the valves, with stronger ribs anteriorly and posteriorly.

Similar to Pitar morrhuanus. Mercenaria campechiensis is distinguishable by its lack of lateral teeth and its posterior tooth (4b) on the left valve, which is fused with the nymph.

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The southern quahog may be confused with its commercially important relative, the northern quahog, M. mercenaria. However, M. campechiensis is heavier and more inflated, and lacks the smooth central area on the outside of the shell that is characteristic of M. mercenaria (Dillon, Jr. 1992; Abbott & Morris 1995).
  • Abbott, RT & PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and the West Indies, 4th Edition. Houghton Mifflin. New York, NY. USA. 350 pp.
  • Andrews, J. 1994. A Field Guide to Shells of the Florida Coast. Gulf Publishing. Houston, TX. USA. 182 pp.
  • Arnold, WS, Bert, TM, Marelli, DC, Cruz-Lopez, H & PA Gill. 1996. Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats. Mar. Biol. 125: 129-139.
  • Busby, D. 1986. An overview of the Indian River Clamming Industry and the Indian River Lagoon. Florida Sea Grant Extension Program. Technical Paper No. 44. Project IR-85-7. 45 pp.
  • Dillon, Jr., RT. 1992. Minimal hybridization between populations of the hard clams, Mercenaria mercenaria and Mercenaria campechiensis, co-occurring in South Carolina. Bull. Mar. Sci. 50: 411-416.
  • Stewart, VN. 1981. Sea-stats: a summary of information and statistics on Florida's marine organisms and the marine environment. No. 7: Clams. Florida Department of Natural Resources. 11 pp.
  • Surge, D & KJ Walker. 2006. Geochemical variation in microstructural shell layers of the southern quahog (Mercenaria campechiensis): implications for reconstructing seasonality. Palaeoecol. 237: 182-190.
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Source: Indian River Lagoon Species Inventory

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Ecology

Habitat

Depth range based on 26 specimens in 3 taxa.
Water temperature and chemistry ranges based on 4 samples.

Environmental ranges
  Depth range (m): 0.5 - 60
  Temperature range (°C): 24.086 - 24.233
  Nitrate (umol/L): 1.798 - 2.736
  Salinity (PPS): 32.616 - 36.149
  Oxygen (ml/l): 4.476 - 5.045
  Phosphate (umol/l): 0.169 - 0.439
  Silicate (umol/l): 2.001 - 3.304

Graphical representation

Depth range (m): 0.5 - 60

Temperature range (°C): 24.086 - 24.233

Nitrate (umol/L): 1.798 - 2.736

Salinity (PPS): 32.616 - 36.149

Oxygen (ml/l): 4.476 - 5.045

Phosphate (umol/l): 0.169 - 0.439

Silicate (umol/l): 2.001 - 3.304
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Trophic Strategy

The southern quahog is a filter feeder, sieving microscopic plankton (mainly diatoms and other microalgae) from the water column. When buried in the sand, the clam extends two siphons above the surface of the sediment. The incurrent siphon imports food and dissolved oxygen from the surrounding water column, while the excurrent siphon expels waste (e.g. Stewart 1981).Predators: Little information is available detailing the predators of M. campechiensis, but the clam is likely preyed upon by a variety of fishes and crustaceans.
  • Abbott, RT & PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and the West Indies, 4th Edition. Houghton Mifflin. New York, NY. USA. 350 pp.
  • Andrews, J. 1994. A Field Guide to Shells of the Florida Coast. Gulf Publishing. Houston, TX. USA. 182 pp.
  • Arnold, WS, Bert, TM, Marelli, DC, Cruz-Lopez, H & PA Gill. 1996. Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats. Mar. Biol. 125: 129-139.
  • Busby, D. 1986. An overview of the Indian River Clamming Industry and the Indian River Lagoon. Florida Sea Grant Extension Program. Technical Paper No. 44. Project IR-85-7. 45 pp.
  • Dillon, Jr., RT. 1992. Minimal hybridization between populations of the hard clams, Mercenaria mercenaria and Mercenaria campechiensis, co-occurring in South Carolina. Bull. Mar. Sci. 50: 411-416.
  • Stewart, VN. 1981. Sea-stats: a summary of information and statistics on Florida's marine organisms and the marine environment. No. 7: Clams. Florida Department of Natural Resources. 11 pp.
  • Surge, D & KJ Walker. 2006. Geochemical variation in microstructural shell layers of the southern quahog (Mercenaria campechiensis): implications for reconstructing seasonality. Palaeoecol. 237: 182-190.
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Source: Indian River Lagoon Species Inventory

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Associations

Although there are no obligate associations documented between the southern quahog and other species, M. campechiensis is commonly found alongside organisms from the various coastal marine habitats in which it resides. For more extensive information on these ecosystems and their associated species found in and around the IRL, please visit Habitats of the IRL.
  • Abbott, RT & PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and the West Indies, 4th Edition. Houghton Mifflin. New York, NY. USA. 350 pp.
  • Andrews, J. 1994. A Field Guide to Shells of the Florida Coast. Gulf Publishing. Houston, TX. USA. 182 pp.
  • Arnold, WS, Bert, TM, Marelli, DC, Cruz-Lopez, H & PA Gill. 1996. Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats. Mar. Biol. 125: 129-139.
  • Busby, D. 1986. An overview of the Indian River Clamming Industry and the Indian River Lagoon. Florida Sea Grant Extension Program. Technical Paper No. 44. Project IR-85-7. 45 pp.
  • Dillon, Jr., RT. 1992. Minimal hybridization between populations of the hard clams, Mercenaria mercenaria and Mercenaria campechiensis, co-occurring in South Carolina. Bull. Mar. Sci. 50: 411-416.
  • Stewart, VN. 1981. Sea-stats: a summary of information and statistics on Florida's marine organisms and the marine environment. No. 7: Clams. Florida Department of Natural Resources. 11 pp.
  • Surge, D & KJ Walker. 2006. Geochemical variation in microstructural shell layers of the southern quahog (Mercenaria campechiensis): implications for reconstructing seasonality. Palaeoecol. 237: 182-190.
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Source: Indian River Lagoon Species Inventory

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Life History and Behavior

Growth

The southern quahog is a protandrous hermaphrodite, with about 98% of individuals beginning life as males and changing to females as they grow older (Stewart 1981). Like most mollusks, M. camphechiensis reproduces via external fertilization, releasing gametes into the water column. Spawning events generally occur in warmer months during neap tides (Stewart 1981). After fertilization, larvae pass through three main planktonic stages before developing into settled, juvenile clams. The first of these is the trochophore stage, which is formed 12 to 14 hours following fertilization. At this stage, larvae are cylindrical and ringed with a row of tiny, beating hairs called cilia. After approximately one day, larvae enter the veliger stage, growing lobes or paddles that resemble butterfly wings. During this stage, the shell and internal organs form. After 6-10 days, larvae develop a foot, are considered competent to settle, and are termed pediveligers. Where their ranges and spawning times overlap, southern and northern quahogs may hybridize with each other to produce the subspecies, M. mercenaria texana (Dillon, Jr. 1992; Abbott & Morris 1995).
  • Abbott, RT & PA Morris. 1995. Shells of the Atlantic and Gulf Coasts and the West Indies, 4th Edition. Houghton Mifflin. New York, NY. USA. 350 pp.
  • Andrews, J. 1994. A Field Guide to Shells of the Florida Coast. Gulf Publishing. Houston, TX. USA. 182 pp.
  • Arnold, WS, Bert, TM, Marelli, DC, Cruz-Lopez, H & PA Gill. 1996. Genotype-specific growth of hard clams (genus Mercenaria) in a hybrid zone: variation among habitats. Mar. Biol. 125: 129-139.
  • Busby, D. 1986. An overview of the Indian River Clamming Industry and the Indian River Lagoon. Florida Sea Grant Extension Program. Technical Paper No. 44. Project IR-85-7. 45 pp.
  • Dillon, Jr., RT. 1992. Minimal hybridization between populations of the hard clams, Mercenaria mercenaria and Mercenaria campechiensis, co-occurring in South Carolina. Bull. Mar. Sci. 50: 411-416.
  • Stewart, VN. 1981. Sea-stats: a summary of information and statistics on Florida's marine organisms and the marine environment. No. 7: Clams. Florida Department of Natural Resources. 11 pp.
  • Surge, D & KJ Walker. 2006. Geochemical variation in microstructural shell layers of the southern quahog (Mercenaria campechiensis): implications for reconstructing seasonality. Palaeoecol. 237: 182-190.
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Source: Indian River Lagoon Species Inventory

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: NNR - Unranked

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NatureServe Conservation Status

Rounded Global Status Rank: GNR - Not Yet Ranked

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