Potentially Misidentified Species:
At least six other species of Teredo occur in the U.S. south Atlantic,
including T. bartschi, T. fulleri and T. furcifera which
have been recorded from the IRL region of Florida, and T. clappi that
has been found on a ship's keel in Key West (SMS:
http://www.sms.si.edu/irlspec/Tspecies.htm, Carlton and Ruckelshaus 1997). A
number of shipworms from two additional genera, Bankia (B.
carinata, B. fimbriatula) and Lyrodus (L.
bipartitus,L. medilobatus, L. massa) have also been recorded
from Florida. All of these shipworm species are considered either cryptogenic
or introduced (Carlton and Ruckelshaus 1997).
Classification and identification of Teredo species is based on the
shape of the siphonal pallets (see above). The paddle-like shape of these
structures in T. navalis may be useful as a diagnostic key (NIMPIS
II. HABITAT AND DISTRIBUTION
Teredo navalis is believed by several authorities to be native to the
European western Atlantic. It is now,
however, a cosmopolitan species found both in Atlantic and Pacific oceans from
the tropics and subtropics to cool temperate waters of both the northern and
southern hemisphere (Didiulis 2007).
Details of the distribution of Teredo navalis within the IRL region are not
known. The cosmopolitan distribution of the species and its euryhaline nature
(see below), however, suggest it may be well established.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
The largest Teredo navalis individual recorded from the Baltic Sea was 30 cm
in length, and individuals from tropical waters may reach 50 cm (Sordyl et
al.1998). T. navalis digs approximately 1 cm wide burrows up to 0.6-1m
long. (Lane 1959, Turner 1966, NIMPIS, 2002, Rowley 2005, Didiulis 2007, ITIS
T. navalis individuals typically live 1-3 years. (Sordyl et al. 1998).
Modernization of the world fleet away from wodden vessels and improvement in
the chemical treatment of wood pilings and other submerged timbers has greatly
lessened the available manmade substrata available for colonization by
wood-boring marine invertebrates.
Historical abundance of Teredo
navalis in many harbors was so great that this animal was a key factor
limiting the life expectancy of wooden ships. Forbes and Godwin-Austin, in
their book, The Natural History of the European Seas (1859), note that
T. navalis abundance in the Welsh harbor of Sebastopol was once so great
as to cause the destruction of submerged ship timbers in just eight years on
Reproduction in Teredo navalis is sexual and individuals become reproductive
as 6 weeks post-settlement. Spawning is temperature dependant, occurring from
April-September in Barnegat Bay, New Jersey, and slightly later (May-October)
at Woods Hole, Massachusetts, once the water has warmed somewhat. Salinities
of 12 ppt or greater may be required. Male gametes are released to the
water column and subsequently taken in through the incurrent siphons of other
individuals in which fertilization occurs internally within the epibranchial
cavity (Grave 1928, 1942, Coe 1941, Lane 1959, Richards et al. 1984, NIMPIS
2002, Didiulis 2007).
Fecundity in this species is high with individual worms capable of brooding 1-5
million larvae (Grave 1928). Evidence of hermaphroditism has been recorded in
young animals but the sexes appear to be separate as adults (NIMPIS, 2002).
Teredo navalis larvae are brooded within the gills until a velum and a
straight-hinged shell have formed at which time they are released to the water
column. Duration of the planktonic phase appears in debate, with various
authors citing a period ranging from less than 4 days to as much as 2-4 weeks.
While residing in the plankton the larva develop siphons, gills and a prominent
foot (Costello and Henley 1971, NIMPIS 2002, Didiulis 2007).
At settlement, T. navalis individuals undergo a rapid metamorphosis
during which the larval velum is shed and consumed (Lane 1959, Didiulis 2007).
IV. PHYSICAL TOLERANCES
Teredo navalis individuals survive water temperatures as high as 30°C,
although growth may cease above 25°C. Minimum reproductive temperature is
reported as approximately 11-15°C (NIMPIS 2002). The species has recently been
reported from Weser Estuary, northern Germany where winter water temperatures
of 0.7°C were recorded (Tuente et al. 2002).
The NEMESIS database
provides a salinity range of 5-45 ppt for the euryhaline Teredo navalis. A
lethal low salinity limit of 5 ppt has been suggested for larval individuals
(Tuente et al. 2002).
Teredo navalis can survive extended periods of anoxia (up to 6 weeks) by
suspending feeding activities and remaining sealed in burrows, metabolizing
stored glycogen reserves for energy (Richards et al. 1984).
V. COMMUNITY ECOLOGY
Teredo navalis is primarily xylophagous, feeding directly on wood. Some
authors suggest a limited degree of filter feeder on water column plankton as
well, although Mann and Gallager (1985) report experimental results indicating
non-significant growth enhancement in T. navalis when phytoplankton was
provided in addition to wood.
Genus Teredo is unique even among wood-boring bivalves in its ability to
feed solely on wood (Gallager et al. 1981). It does so with the aid of
symbiotic cellulolytic, nitrogen-fixing bacteria contained in specialised
epithelial cells on the gills (Popham and Dikson 1973, Distel et al. 2002).
T. navalis uses its sculpted shell to rasp wood particles that are moved
via cilia to the mouth for ingestion. Water is obtained through the incurrent
siphons and is used for feeding as well as respiration and excretion/egestion
Teredo navalis is likely to occur in association with other shipworm species within submerged timbers.
VI. INVASION INFORMATION
Teredo navalis has been transported by ships for so many centuries that its
historic native distribution cannot be known with certainty. Its center of
endemism is believed to be European, however; there exists substantial evidence supporting the assertion that the species
is correctly considered exotic and introduced on both coasts of the Americas
(Ruiz et al. 2000, NIMPIS 2002).
In 1839, T. navalis was first reported in Massachusetts Bay in the
sheathing of foreign wooden vessels. A century later the species was abundant
in samples taken fromm Nova Scotia to Massachusetts The species was first
collected from Long Island Sound in 1869, again from the timbers of a sailing
vessel. Within several decades the species was collected in abundance in test
boards from all around New York Harbor (Brown 1953).
This shipworm occurred at low densities around Chesapeake Bay as early as 1878.
As recently as the mid 1950s, the species was reported as rare in Chesapeake
Bay (Andrews 1956). Subsequently, T. navalis has been collected from
North Carolina and southward to Florida, Texas, the Bahamas, and Puerto Rico
On the U.S. west coast, introduction of T. navalis into San Francisco Bay in
1913 led to a serious invasion and substantial negative economic impact (Cohen
Potential to Compete With Natives:
Where Teredo navalis co-occurs with native shipworm species, some degree of resource competition is likely.
Possible Economic Consequences of Invasion:
Turner (1966) proposed Teredo navalis as likely the most widespread marine
wood borer in the world. The historic negative economic impacts of T.
navalis invasion may rival those of any other introduced marine species.
It is the species believed responsible for a massive infestation of Dutch dikes
in the 17th century. It was also described by a Dutch commission in 1731 as a "horrible
plague" threatening to destroy the dikes protecting the lowlands of Holland
(Cohen and Carlton 1995, Reise et al. 1999). The damage inflicted by the
shipworms prompted replacement of wooden dikes with stone.
Massive T. navalis infestation was also responsible for the destruction
of an unknown number of wharves, piers, ferry slips and other wooden harbor
structures at a rate of a major structure a week for a period of two years in
San Francisco Bay from 1919-1921. Cohen (2004) notes that in current dollars
this would have equated to between $2 billion and $20 billion in damage.
In general T. navalis has a centuries-long history of causing damage to
sailing vessels, piers, pilings, marinas, and any other submerged wooden
structures. In 1946, shipworms were estimated to cause $55 million/year of
damage to waterfront structures in U.S. (Scheltema and Truitt 1954).
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Page last updated: October 5, 2007