Tagelus plebeius
Stout razor clam

Species Description

The stout razor clam is a marine/estuarine bivalve of the Family Solecurtidae. This species attains a maximum shell length of about 10cm and has a quadrate, elongated shell generally tan-colored. Their inhalant siphons, which can extend to a length of about 12cm, are separate and equipped with rudimentary tentacles at the openings, used to either protect burrow openings or facilitate feeding. They lack a waste canal and have large ctenidia relative to their labial palps. The foot is thick and flexible allowing movement within its mucous-lined burrow which can extend to nearly a meter into the sediment. Its maximum age is given as 14 years, determined from distinctive annuli, although some have characterized this species as having a short life-span, on the order of two years or so.
(Abrahão et al. 2010; Arruda et al. 2003; Holland and Dean 1977(a); Holland and Dean 1977(b).)

Geographic Range

Tagelus plebeius populations range from Massachusetts to Argentina, occupying habitats including sandy beaches, intertidal flats, and subtidal zones down to 10m or so. This clam tolerates a wide range of water temperatures and salinities, tropics to temperate and marine to estuarine.

Current status, Chesapeake Bay.

The stout razor clam is found throughout the Chesapeake Bay. In Maryland waters, this species inhabits sandy sediments from Tangier Sound to the Upper Bay in depths ranging from about 1 m (or less) to at least 7 m..
(Abrahão et al. 2010; Gutierrez and Iribarne 1999; Homer et al. 2011).

Life History

Spawning/Larval Development. Stout razor clams are dioecious and are not sexually dimorphic. T. plebeius exhibits two general spawning "strategies": complete gonadal clearance and progressive spawning. Salinity appears to have only a minor role in spawning activity, while water temperature may dictate which spawning "strategy" is employed. Larval development is rapid, with complete pelagic development occurring at a size smaller than any other bivalve veliger.

Juveniles/Adults. After setting, the small clams can attain a shell length of 50mm within 7-12 months, dependent on water temperature and physical habitat. There is some evidence that sexual maturity occurs early in life, perhaps at shell lengths of 35mm or so. The stout razor clam builds a permanent, mucous-lined burrow, extending some 0.5 to 0.9 m into the sediment. According to some accounts, their siphons extend only to the burrow opening. As their siphons can extend to 10-15 cm, while feeding T. plebeius are located in the upper portion of their burrow.
(Abrahão et al. 2010; Arruda et al. 2003; Chanley and Castagna 1971; Cledon et al. 2004).

Habitat Requirements

The stout razor clam primarily inhabits sandy sediments with little or no substrate overburden. They may also be found in stable mud and soft clay environments, again with little or no overburden.

Within their geographic range, this species inhabits beaches, tidal flats, and subtidal waters to depths of at least 10 m. They are tolerant of a wide range of water temperatures and salinities as implied by their extensive geographic range.

Current status, Chesapeake Bay.

During a recently completed 10-year study, the stout razor clam was found throughout the Maryland portion of the Chesapeake Bay. Their distribution included all of the major Bay tributaries and embayments from the Patapsco River to Tangier Sound and the Potomac River. Stout razor clams were collected from all water depths accessible to the sampling gear, 1.2-4 m. The primary limitation on their distribution was related to sediment/substrate. About 90% of all T. plebeius collected were from areas with no substrate overburden and nearly 75% from hard sediments, primarily sand.
(Abrahão et al. 2010; Allen 1954; Arruda et al. 2003; Holland and Dean 1977(a); Holland and Dean 1977(b); Fraser 1967; Homer et al. 2011).

Ecological Role

As with most aspects of stout razor clams, there are varying accounts of what type of feeder it is. Most accounts classify this bivalve as a suspension feeder, based in part on a few laboratory studies and in part on anatomical properties and behavior. Others have listed this species as a deposit-feeder. From the few studies available in the literature, it appears that T. plebeius may have the ability to employ both feeding modes, dependent on hydrodynamic processes and sediment overburden. Areas with sufficient currents generally don't allow the accumulation of organic material thereby limiting food availability for a deposit feeding organism. In low current situations, however, such material is deposited on the surface of the sediment and the quantity of suspended material is limited. In addition, the presence of sediment overburden may limit the ability of deposit-feeders to acquire food by interfering with the mechanics of their siphons. Given these circumstances, their anatomical features and their wide geographic range and settlement in a variety of ecotypes, it appears that stout razor clams are a highly adaptable species regarding feeding mode.

What is consistent in the literature is that, where found, the stout razor clam is a prominent feature of the benthic community often listed as the dominant bivalve species either in terms of biomass or numbers or both. Where intertidal populations of stout razor clams exist, the American oystercatcher has been listed as its primary predator. Other species that have been cited as preying upon stout razor clams include the whistling swan, sea ducks, several species of elasmobranchs, blue crabs, stone crabs, dog whelks, and several Sciaenidae species.

Holocene deposits of razor clam shells have been cited as crucial habitat in the SW Atlantic region for numerous benthic infaunal species. These deposits provide predator refuge and thereby greatly influence the abundance and diversity of the benthic community.

Current status, Chesapeake Bay.

Prior to 2001, little information is available regarding most aspects of stout razor clam Chesapeake Bay populations. Although a number of studies listed this species as very abundant, these efforts were of both limited geographic and seasonal extent. A major problem in determining the abundance, absolute and relative, of most aquatic communities is related to sampling gear. More specifically, studies focusing on stout razor clams and those investigating benthic invertebrate communities have used sampling gears that are highly size-biased. The use of various types of bottom grabs generally restricts adequately sampling larger individuals, while gear like the hydraulic escalator dredge truncates the actual population size structure by "filtering" smaller individuals. In a recent study, the latter gear was used in a wide geographic range in Maryland's Chesapeake Bay that included numerous habitat types in depths ranging from about 1.3 to 4 m. This study found stout razor clams to be very abundant, until late 2003 when disease ravaged their population, although clams less than about 30 mm were inadequately sampled. As their ecological role, sediment aeration, water filtration, particulate matter recycling, and as a prey species, is tied to their abundance, it can only be assumed that, prior to the disease outbreak, T. plebeius populations were of great importance in the Bay's ecosystem, particularly after the collapse of the softshell clam population.
(Abrahão et al. 2010; Arruda et al. 2003; Fraser 1967; Gutierrez and Iribarne 1999; Holland and Dean 1977(a); Holland and Dean 1977(b); Homer et al. 2011.)

Diseases/Parasites

Tagelus plebeius populations have rarely been examined for histopathological conditions. The most serious disease reported for this species is disseminated neoplasia (DN). Other diseases and conditions known to inflict stout razor clams include procaryote or rickettsial infections, bacterial infections, acidophilic granuloma unknown (AGX) type lesions, and granules and concretions located in the kidney.

Several organisms have been reported to parasitize T. plebeius, the most serious being Perkinsus chesapeaki. Other parasites found in stout razor clams include ciliates, trematodes, nematodes, and tapeworms.

Current status, Chesapeake Bay.

In the Chesapeake Bay region, a Perkinsus sp. infection in stout razor clams was reported in 1954. Unlike Perkinus chesapeaki in Mya arenaria populations, however, there are no records of investigations into T. plebeius disease/parasite conditions until 2000 when Chesapeake Bay stout razor clams were found to be heavily infected with P. chesapeaki. From 2000 through 2009, annual mean P. chesapeaki prevalences in razor clams ranged from 13-100%, with means greater than 50% occurring in 9 of the 10 years. Unlike softshell clams, which exhibited a reduction of infection levels during periods of low water temperature, high prevalences of P. chesapeaki infections in T. plebeius persisted through such periods. It has been suggested that stout razor clams may provide a stable reservoir for this parasite, carrying large populations of P. chesapeaki through low water temperature periods thereby accelerating M. arenaria post-spring infections.

The first reported case of DN disease in Chesapeake Bay T. plebeius populations occurred in 2001. By 2004, sample analyses indicated that SN disease had become epidemic in stout razor clams throughout the Bay, with prevalences on the order of 60-80%. It is not clear if DN disease existed in razor clam populations prior to 2001, as this species has rarely been examined. However, those in the industry have stated that the mass mortalities reported in late 2003, had not been observed in the past.

It is not possible to evaluate which condition, P. chesapeaki infections or DN disease poses the more critical long-term threat to Chesapeake Bay T. plebeius populations. Suffice to say, that both currently are active in Bay stout razor clam populations and that both severely affect survival rates of this species.
(Andrews 1954; Dungan et al. 2002; Holland and Dean 1977(b); Homer et al. 2011; Vazquez et al. 2006)

Chesapeake Bay Population Current Status

The history of the stout razor clam as a commercial species in the Chesapeake Bay is not well documented. Until very recently, landing data were not collected and the only information regarding commerce comes from those in the industry and some fishery independent data from surveys initiated in 2001. Prior to the mass mortality event of 2003-2004, industry reports of 8-10 bushels per hour were in line with survey estimates. After 2004, harvest rates reportedly dropped to 3-5 bph, a range consistent with independent surveys. Since 2004, production has periodically upticked, to an estimated 4-6 bph, but the trend over the last nine years has been consistent; a steady decline in the abundance of stout razor clams. During the last 3 years, harvest rates have declined to 2-3 bph to about 1 bph. These rates conform with fishery independent data collected over that time period.

Literature Cited

Abrahão, J.R., R. S. Cardoso, L.Q. Yokoyama, and A.C.Z. Amaral. 2010. Population biology and secondary production of the stout razor clam Tagelus plebeius (Bivalvia, Solecurtidae) on a sandflat in southeastern Brazil. Zool. 27(1): 54-64.

Allen, J. F. 1954. The influence of bottom sediments on the distribution of five species of bivalves in the Little Annemessex River, Chesapeake Bay. Nautilus 68(2): 56-65.

Andrews, J.D. 1954. Notes on fungus parasites of bivalve molluscs in Chesapeake Bay. Proc Natl Shellfish Assoc 45:157–163.

Arruda, E.P., O. Domaneschi, and A.C.Z. Amaral. 2003. Mollusc feeding guilds on sand beaches in São Paulo state, Brazil. Mar. Biol. 143: 691-701.

Chanley, P. and M. Castagna. 1971. Larval development of the stout razor clam, Tagelus plebeius Solander (Solecurtidae: Bivalvia). Ches. Sci. 12 (3): 167-172.

Cledón M., A.C. Peralta, J Gutierrez, P.E. Penchaszadeh. 2004. Reproductive cycle of Tagelus plebeius in the Mar Chiquita Lagoon, Argentina. J. Shellfish Res. Vol. 23 443-446.

Dungan, C.F., R.M. Hamilton, K.L. Hudson, C.B. McCollough and K.S. Reece. 2002. Two epizootic diseases in Chesapeake Bay commercial clams Mya arenaria and Tagelus plebeius. Dis. Aquat. Org. 50:67-78.

Fraser, T.H. 1967. Contributions to the biology of Tagelus plebeius (Tellinacea: Pelecypoda) in Biscayne Bay, Florida. Bull. Mar. Sci. 17: 111-132.

Gutierrez, J. and O. Iribarne. 1999. Role of Holocene beds of the stout razor clam Tagelus plebeius in structuring present benthic communities. Mar. Biol. Progr. Ser. 185: 213-228.

Holland, A.F. and J.M. Dean. 1977a. The biology of the stout razor clam Tagelus plebeius: I. Animal-sediment relationships, feeding mechanism, and community biology. Ches. Sci. 18 (1): 58-66.

Holland, A.F. and J.M. Dean.1977b. The biology of the stout razor clam Tagelus plebeius: II. Some aspects of the population dynamics. Ches. Sci. 18 (2): 188-196.

Homer, M., C.F. Dungan, and M. Tarnowski. 2011. Assessment of Chesapeake Bay Commercial Softshell Clams, Mya arenaria and Tagelus plebeius, with emphasis on abundance and disease status. Completion Rep. to NOAA Ches. Bay Fish. Sci. Prog., NA07NMF4570326.

Lomovasky, B.J., J.L. Gutierrez, and O.O. Iribarne. 2005. Identifying repaired shell damage and abnormal calcification in the stout razor clam Tagelus plebeius as a tool to investigate its ecological interactions. J. Sea Res. 54: 163-175.

Vazquez, N.N., C. Ituarte, G.T. Navone, and F. Cremonte. 2006. Parasites of the stout razor clam Tagelus plebeius from the Southwestern Atlantic Ocean. J. Shell. Res. 25: 877-886.