Pagurus longicarpus, the long-armed hermit crab, is a small western
Atlantic hermit crab. It belongs to the genus Pagurus, all members of which
have unequal chelipeds (claws) in which the right is substantially larger than
the left. In the case of P. longicarpus, the oversized claw is long and
slender and approximately cylindrical in shape. Body color is highly variable,
ranging from beige to off-white to greenish-grey to brown (Voss 1983, Rupert
and Fox 1988).
Like all hermits, P. longicarpus protects its soft, assymetrical abdomen
by tucking it into and tightly curling it around the columella of the shell
from a dead gastropod (Barnes 1987).
Potentially Misidentified Species
Pagurus longicarpus is one of at least 16 hermit crab species reported
from the Indian River Lagoon, at least 6 of which belong to the genus
Pagurus. The most abundant large IRL hermits, the striped hermit
(Clibanarius vittatus) and the giant hermit (Petrochirus
diogenes) are easily discernable from various species of Pagurus by
their size. P. longicarpus can usually be distinguished from
co-occurring congeners by the cylindrical shape of its enlarged cheliped (as
compared to the flattened claw of P. pollicaris, for example).
HABITAT AND DISTRIBUTION
Pagurus longicarpus is a wide-ranging temperate species that can be
found along the Atlantic coast from Nova Scotia south through Hutchinson
Island, FL, and again along the Gulf coast from the Shark River in southwest
Florida west to Galvaston, TX (Fotheringham 1976, Camp et al. 1977). The
geographically disjointed distribution and discernable morphological
differences between the Atlantic and Gulf populations suggests P.
longicarpus may have been subject to past vicariance events whereby
geographic or ecological barriers subdivided the ancestral population. Genetic
analysis by Young et al. (2001) supports this hypothesis; mitochondrial DNA
sequence data suggests the two populations diverged around 0.6 million years
Pagurus longicarpus likely occurs throughout the IRL system, although
the southern end of the estuary roughly coincides with the southern end of the
range of the Atlantic population.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Pagurus longicarpus is a small hermit crab, with adult individuals
attaining a length of around 2.5 cm or less (Rupert and Fox 1988).
Williams (1984) reports that Pagurus longicarpus is one of the most
common shallow-water decapods along the US east coast and Gulf of Mexico.
As is typical of decapod crustaceans, reproduction in Pagurus
longicarpus is sexual, internal fertilization is employed, and the sexes
are separate. Individuals must partially emerge from the protection of their
gastropod shells and press their ventral surfaces together to allow copulation
(Barnes 1987). Females extrude eggs into their shells, gather them via the
pleopods, and then brood them in a manner similar to other crabs.
Wilber (1989) found a number of relationships between female P.
longicarpus egg production and shell characteristics such as size and
condition. Of particular interest, the author noted that medium-large and
large females inhabiting seagrass beds who occupied severely damaged or fouled
shells were only half as likely to be reproductive as females occupying shells
of better quality. Reduced incidence of reproductive females in poor quality
shells may be the result of poor nutrition due to the fact that relatively less
protected individuals may spend more time buried than individuals occupying
intact shells and, therefore, less time foraging. Wilbur (1989) also notes
that seagrass-resident female crabs occupying moon snail (Polinices
duplicatus) shells or shells larger than their predicted shell size
exhibited enhanced clutch sizes compared to other individuals.
Based on the presence of large numbers (75%) of ovigerous female P.
longicarpus during a three-month study near Alligator Harbor, Franklin
County, FL, suggests that females typically produce more than one clutch per
reproductive season (Wilber 1989).
Roberts (1970b) indicates that brooding of eggs in P. longicarpus lasts
only a few weeks. Roberts (1970a) identified and described four distinct
planktonic zoeal larval stages and one megalops stage for P.
longicarpus. This is a smaller number of planktonic stages than occurs for
many decapods. The author suggested that except under suboptimal conditions,
there is no planktonic prezoeal stage.
Roberts (1971) described some behavioral aspects of the megalops. At first,
the megalops is an active swimming stage, but swimming activity declines with
time. If individuals encounter suitable shells, they enter the shells and
swimming activity ceases. If no suitable shell is found, swimming activity
nevertheless becomes very infrequent after two days. The author found no
evidence indicating that the species is capable of delaying metamorphosis until
a suitable shell is located.
Fotheringham and Bagnall (1976) collected larval P. longicarpus from the
water column in Christmas Bay, TX, from September through May, suggesting a
long reproductive season for the species in the southern portion of its range.
Pagurus longicarpus occurs as far north as Nova Scotia, indicating the
species tolerates a wide range of temperatures. Examining the effects of
extreme high temperatures, Fraenkel (1960) reports that 40°C. is 100% lethal but
that individuals exposed to 36°C. for one hour survived as long as they were
given 24 hours to recover at room temperature. Vernberg (1967) indicates that
individuals acclimated to higher temperatures survived experimental temperature
increases of the same magnitude (i.e., acclimation temperature + 5, 10, or
15°C.) longer than individuals acclimated to lower temperatures.
As an inhabitant of littoral estuarine habitats, Pagurus longicarpus is regularly exposed to measurable seasonal and tidal salinity fluctuations,
Roberts (1971b) reports a salinity range of 18-35.5 ppt as optimal for larval
development through the megalopal stage. Biggs and McDermott (1973) suggest a
slightly broader optimal range of 15-36 ppt for adult P. longicarpus
collected from southern New Jersey.
Pagurus longicarpus is capable of regenerating lost limbs, Weis (1982)
noted rapid limb regeneration and molting after autotomy of 1-4 appendages in
Pagurus longicarpus is an omnivorous, generalist scavenger capable of
consuming edible material from the surfaces of sand grains and also able to
consume larger pieces of detrital plant and animal material (Roberts 1968,
Caine 1975). In both cases, one (typically the smaller of the pair) or both of
the chelipeds pick up particles and transfer them to the mouth. When feeding
on enriched sand, the edible component is removed from grains by brushing
activity of the setae-covered third maxilipeds. When larger detrital particles
are consumed, considerably more complex mouthpart interactions are involved in
the process of tearing off and ingesting small food fragments (Roberts 1968).
Benthic diatoms form much of the diet, and small infauna (e.g., polychaetes)
are often inadvertently consumed as well (Roberts 1968, Caine 1975). Many of
the food items normally consumed are of comparatively low nutritional quality
and so must be consumed in large quantities (Wilbur 1989).
Laboratory experiments by Whitman et al. (2001) demonstrate that P.
longicarpus is also capable of facultative suspension feeding, but the
authors concede that further study is required to evaluate the importance of
this strategy in the wild. In addition to brine shrimp nauplii,
laboratory-maintained P. longicarpus were capable of feeding on a
variety of more ecologically relevant planktonic prey including first zoeal
stages of Dyspanopeus sayi, Carcinus meanus, and Palaemonetes
vulgaris, as well as newly hatched veligers of the gastropod Crepidula
Laboratory studies reveal that P. longicarpus may resort to cannibalism
if insufficient dietary resources are provided (Allee and Douglas 1945).
Planktonic larval P. longicarpus are likely to be opportunistic
foragers. In the laboratory, they have been shown to be capable of consuming a
variety of microalgal species, several types of microcrustaceans, and
polychaete larvae (Roberts 1974). These dietary items were not equally capable
of sustaining larval crabs through all larval stages.
Competition among hermit crabs for dietary resources may occur despite the
generalist foraging habits of Pagurus longicarpus and co-occurring
Interspecific and intraspecific competition among hermit crabs for a
potentially limiting supply of gastropod shells is also believed to be
typically severe. Vance (1972) noted that species-specific shell preference
may allow the coexistence of similar species through resource partitioning.
Allee and Douglas (1945) demonstrated that P. longicarpus lacking shells
typically attack shell-bearing conspecifics without regard for the size of the
competitor. They note, however, that attacks were only successful if the
housed individual was smaller than the attacker.
Experiments by Wilber (1990) on P. longicarpus from Wakulla Beach, FL,
indicated that behavioral shell selection exhibited a compromise between shell
species and relative size and that animals avoided relatively large shells more
than relatively small shells. This suggests that a larger-than-optimal shell
has more negative attributes than an undersized shell.
Field studies conducted by Rittschoff et al. (1992) demonstrated that several
hermit crabs, including P. longicarpus, exhibit behavioral responses to
chemicals originating from crushed conspecifics. Looking further at the hermit
crab Clibanarius vittatus, these authors report that behavioral
responses are dependent on crab size, type of shell inhabited, and shell size
and fit. Chemical cues originating from dead conspecifics typically elicited
aggression/shell investigation responses in crabs occupying relatively small
shells and alarm responses by crabs in relatively large shells. This suggests
that the need to acquire limited high-value shell resources is sufficiently
strong to preempt behavioral defense against predation even in the face of
potentially imminent predation threat.
Tricarico and Gherardi (2007) conducted experiments to assess the factors that
motivate P. longicarpus to switch shells. Offering test animals a
choice of shells of varying quality, the study suggests motivation to acquire
new shells was entirely dictated by the value and quality of the shell the
animals currently inhabited rather than by the shell it is offered. Other
studies (e.g., Pechenil and Lewis 2000, see below), however, suggest that
selection may at times be based on the quality of the shell being offered.
Gherardi et al. (2005) examined the role of odor in individual recognition by
P. longicarpus and discovered that individual crabs are capable of
discriminating between larger conspecifics inhabiting high-quality shells and
smaller conspecifics inhabiting low-quality shells, provided the crabs are
familiar with one another. The authors conclude that crabs appear capable of
associating odor information from other individuals with memories of past
Tunberg et al. (1994) lists a number of predators of hermit crabs, including
fish, gastropods, crabs, and octopods. Many such species, although not all,
can extract hermit crabs from their protective shells without inflicting any
shell damage (Bertness 1981). Laboratory studies of blue crab (Callinectes
sapidus) predation on the seagrass-associated Pagurus maclaughlinae
reveal an alternate strategy, in which blue crabs secured the shell of a prey
hermit with one cheliped and progressively crushed the outer lip of the shell
(rolling it as it does so) until the hermit could no longer retract into the
spire of the shell (Tunberg et al. 1994).
P. longicarpus reportedly will not feed if it is not safely occupying a
shell, suggesting that perceived vulnerability to predation is sufficient to
alter crab behavior. Allee and Douglis (1945) report that isolated shell-less
P. longicarpus maintained in the lab die sooner than shelled animals,
due in part to the fact that exposed animals cease eating.
A study by Kuhlmann (1992) on the predation of Pagurus longicarpus
showed that predation rate was independent of shell species, shell size, and
shell damage. Experiments by Heck and Wilson (1987) employing tethered
predatory decapods in seagrass beds similarly revealed a lack of correlation
between hermit crab predation rate and the thickness or ornamentation of their
gastropod shell homes. Other studies, however, suggest P. longicarpus
shell selection behavior may be mediated by predator presence. Rotjan et al
(2004), for example, demonstrate that the prsence of chemical cues from the
predatory green crab Carcinus meanus alters P. longicarpus shell
choice behavior in favor of intact shells.
The polychaetes Lepidonotus sublevis and Dipolydora
(=Polydora) commensalis may take up residence in the lumen of the
shell and may feed on developing crab embryos (Fotheringham 1976, McDermott
1999). The turbellarian Stylochus zebra can also be found in P.
longicarpus shells (Lytwyn 1979).
A number of colonial epifaunal hydroids are known to occur on the shells of
Pagurus longicarpus and other pagurid hermit crabs, although the
literature indicates that preference for hydroid-colonized versus -uncolonized
shells varies among and within crab species. Brooks and Mariscal (1985), for
example, report that north Florida Gulf coast P. longicarpus initially
selected for hydroid-colonized (Hydractinia echinata, Podocoryne
selena) shells but subsequently switched to bare shells even when predators
were present. Although emphasis has been placed on the potential benefits of
crab-hydroid symbiosis (e.g., protection for crabs to predators), Weissberger
(1995) demonstrated that shell colonization by the hydroid Hydractinia
symbiolongicarpus offered New England P. longicarpus no protection
from predation by the American lobster Homarus americanus. Moreover,
Damiani (2003) reports that female P. longicarpus occupying shells
colonized by H. symbiolongicarpus experience reproductive costs
including depressed ovigery, smaller clutch size, and increased frequency of
Wilber and Herrnkind (1994) report that the predatory crown conch (Melongena
corona) can be important as a source of new shells for co-occurring P.
longicarpus populations. Working at Wakulla Beach on the northern Gulf
coast of Florida, these authors reported average rates of new shell
(Littorina irrorata) acquisition ranging from 4 to more than 23 new
shells per day in P. longicarpus subpopulations surveyed within 40 meter
squared salt marsh plots. The number of newly acquired shells by the crabs
varied directly with M. corona, supporting the contention that predation
events constituted a major source of shells.
Tricario and Ghererdi (2006) indicate that simulated gastropod predation
attracted P. longicarpus, and concluded that nondestructive gastropod
predator density ultimately regulates the supply of high-quality shells for
this hermit crab.
Studies conducted by Pechenil and Lewis (2000), however, indicate that not all
shells made available by co-occurring predators are equally valued by crabs.
They showed that shells that have been drilled by natacid gastropods are
avoided by P. longicarpus, even as shells with other forms of damage
were deemed suitable by crabs. The authors suggested that strong behavioral
avoidance of drilled shells may indicate such shells would expose resident
crabs to increased predation, osmotic stress, and eviction by competing
Pagurus longicarpus occurs in a variety of estuarine and coastal
habitats from the intertidal to as deep as 45 m (Gosner 1979). Heck and
Spitzer (undated), describing the fauna of the northern Gulf of Mexico, listed
seagrass meadows, mud and sand bottoms, and beach surf zones as likely inshore
habitats in which to encounter this species. The species is also a common
inhabitant of oyster reef habitats.
Pagurus longicarpus is active primarily during daylight hours.
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