Potentially Misidentified Species:
Alpheus heterochaelis is the largest and likely the most abundant of at
least 11 Alpheus species documented from the Indian River Lagoon. The other
known IRL snapping shrimp are: Alpheus armillatus, A. bouvieri,
A. cristulifrons, A. floridanus, A. formosus, A.
normanni, A. nuttingi, A. paracinitus, A. thomasi, and
II. HABITAT AND DISTRIBUTION
Alpheus heterochaelis is native to the western Atlantic Ocean, occurring
from North Carolina and Bermuda to Brazil and the West Indies (Kaplan 1988).
Alpheus heterochaelis occurs in suitable habitats throughout the IRL system.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Adult Alpheus heterochaelis may reach a length of between 3.0 and 5.5 cm
(Kaplan 1988), but individuals encountered are often considerably smaller,
e.g., 6-20 mm carapace length (Nolan and Salmon 1970).
Despite their tendency to be heard and not seen, field sampling studies
indicate that Alpheus heterochaelis is generally among the numerical
dominant decapods within its preferred habitats. Lift net surveys conducted in
intertidal oyster reefs of Mosquito Lagoon by Boudreaux et al. (2006), for
example, revealed A. heterochaelis to be the most abundant motile
species, with more than 2,400 individuals collected over a single sampling
Working in Beaufort, NC, Nolan and Salmon (1970) noted a seasonality to A.
heterochaelis abundance in which population densities were highest in early
summer but became scarce after the end of July.
Like most other alpheid shrimp, Alpheus heterochaelis individuals are
most often encountered as mated pairs and social monogamy appears to be a
widespread phenomenon. A study by Rahman et al. (2003) suggests that mate
guarding by the male appears to be the key factor leading to social monogamy in
A. heterochaelis, i.e., rather than shared territoriality or biparental
care of young. The authors indicate that the female molt cycle is highly
cryptic and that females are only receptive for a few hours immediately after
molting. Mate guarding through male-female pairing is therefore advantageous
to the male because it maximizes mating opportunities and also to the female
because it minimizes the need to search for a mate during the vulnerable
soft-bodied receptive phase.
Nolan and Salmon (1970) indicate that A. heterochaelis collected in
their study were most often (~65% of animals collected) captured as
male-femalel pairs and that such pairs could be found at all times during the
study (April-August). Individuals in the majority of pairs collected from the
field differed by 2 mm or less in carapace length, with a non-significant trend
for females to be slightly larger than males.
Male-female interactions under laboratory conditions begin similar to same sex
agonistic interactions (see below). In a nontrivial number of instances,
however, aggressive face-off and antennulation between a male and female gave
way to mutual aquiescence and pair formation, typically in under an hour.
Nolan and Salmon (1970) noted that the mechanisms underlying sexual
discrimination had yet to be elucidated, but predicted that chemical cues
played a role. In earlier experiments conducted by Hazlett and Winn (1962),
exposure to extract from crushed shrimp of the opposite sex elicited a less
aggressive response than did extracts from individuals of the same sex.
Knowlton (1973) notes in his description of early development of Alpheus
heterochaelis from North Carolina that total brood gestation time from
laying to hatching was approximately 28 days at 25 ¼C.
This species is unusual in that it exhibits an abbreviated larval life cycle
consisting of just three larval stages. At 22-25 ¼C, the first instar lasts
only 1-2 hours, the second instar for approximately 28 hours, and the entire
larval period lasts just 4-5 days (Knowlton 1973).
All A. heterochaelis larval stages are non-feeding, and developing
animals appear to rely entirely on large yolk and oil reserves for nutrition
during this period. Feeding commences at the onset of the postlarval stage
once the mouthparts are fully developed (Gross and Knowlton, 1991).
With the first postlarval stage, the young animals begin to resemble adults in
most aspects. Notably, however, the cheliped asymmetry typical of the family
does not arise until some time later (Knowlton 1973).
IV. PHYSICAL TOLERANCES
The northern distribution limit for Alpheus heterochaelis has been
reported to be in the vicinity of Cape Hatteras, NC (Nolan and Salmon 1970),
and this limit is likely dictated by thermal tolerance. Winter low
temperatures average around 4.4-6.6°C, but historic low temperatures of less
than -14°C have been recorded.
Alpheus heterochaelis appears to have a salinity tolerance sufficient to
allow it to persist in shallow subtropical estuarine habitats susceptible to
wide seasonal fluctuations. Matheson et al. (1999) collected individuals from
Florida Bay mud banks experiencing salinities that ranged from mesohaline (12.8
ppt) to hyperhaline (49 ppt).
V. COMMUNITY ECOLOGY
The concussive force of the snapping shrimp claw snap is sufficient to stun and
even kill small prey at close distance. In light of recent findings that
cavitation bubbles are the true source of the concussive pop, the potency of
the claw snap attack is now better understood. Cavitation is the phenomenon of
formation and subsequent implosion of cavities or bubbles in a flowing liquid
in a region where the pressure of the liquid falls below its vapor pressure.
Cavitation bubbles formed by the action of boat propellers implode with such
force as to be capable of damaging the propeller. Small prey located within a
few millimeters of the tip of the snapping claw are exposed to similar
destructive forces that are short-lived but considerable (Versluis et al 2000).
Worms, small shrimp, crabs and other crustaceans, and even small fish such as
pearlfish and gobies may be stunned or killed by the concussive claw snaps of
Alpheus heterochaelis (Hazlett, 1962, Herberholz and Schmitz 1998).
Nolan and Salmon (1970) report the observation of grazing in
laboratory-maintained A. heterochaelis, Òpicking algae off a shell and
passing it to the mouth parts,Ó but how representative this is of natural
behavior is unknown.
Nolan and Salmon (1970) speculate that some interspecific competition for
shelter may occur in areas where multiple species of snapping shrimp co-occur,
but also note that microenvironmental preference differences among species may
moderate such interactions.
Most competitive interactions in this species are likely agonistic
intraspecific interactions, including competition for refuge areas and mates.
When two shrimp of the same sex interact in an experimental laboratory setting,
one shrimp will become dominant over the other. This occurs after an initial
face-off period followed by mutual contact between the second antennae of the
opposing animals and aggressive posturing and claw snapping (Herberholz and
Schmitz 1998, Nolan and Salmon 1970).
Studies by Herberholz and Schmitz (1998) have greatly increased understanding
of how aggressive signals (e.g., claw snaps) are sensed by conspecifics.
Mechanoreceptive setae on the snapper claw allow individuals to detect the
rapid water jet produced by the claw snap of a conspecific facing it in close
proximity. Agonistic intraspecific encounters of this sort may convey a
warning to other snapping shrimp that a shelter or territory is occupied
Male A. heterochaelis are more aggressive than females in their
agonistic intraspecific snapping behavior, both in terms of snap frequency and
the water velocities produced. Herberholz and Schmitz (1998) suggest that
shrimp receiving water jet signals should be able to discern the sex of their
opponent. Visual, chemical, and tactile cues may also be important in sex
recognition in A. heterochaelis. Distant chemoreception, for example,
plays a role in sex recognition in the cogener Alpheus edwardsii.
Hughes (1996a, b) experimentally confirmed a visual component to size
assessment in A. heterochaelis intraspecific interactions, and also
demonstrated that chemical cues could mediate the response of individuals to
In intraspecific encounters, the snap does not injure the opponent because the
interaction distance (9 mm on average) is sufficient to avoid implosion danger
(Versluis et al 2000). This non-lethal aggression may represent an instance of
stereotyped fighting, in which aggressive motivation is conveyed without
damaging physical contact occurring. Stereotyped fighting has been suggested
for a number of decapod species, including mantis shrimp, hermit crabs, fiddler
crabs, and others (Dingle and Caldwell 1969, Hazlett 1966, Crane 1966, Nolan
and Salmon 1970).
Alpheus heterochaelis is a suitable prey item for several fish species.
work performed by the Virginia Institute of Marine Science's Chesapeake Bay
Trophic Interaction Laboratory Services group for example, has revealed that
A. heterochaelis is a component of the diet of the ecologically and
recreationally important weakfish (Cynoscion regalis). For the most
part, however, the importance of A. heterochaelis relative to that of
other dietary items has not been examined in detail.
Sillman et al (2003) describe a commensal association between Alpheus
heterochaelis and the black-clawed mud crab (Panopeus herbstii), a
benthic, burrow-building east coast mud crab. The authors report that 11% of
occupied P. herbstii burrows they examined also housed snapping shrimp
which were unable to construct burrows of their own. Mud crabs did not prey on
the snapping shrimp although they regularly consume similarly sized
crustaceans. The authors conclude that this association may allow A.
heterochaelis to expand its intertidal habitat range. Note that this
observed inability of A. heterochaelis to construct burrows on its own
is at odds with earlier observations by Nolan and Salmon (1970) who reported
the species was able to manipulate and excavate in certain substrata to
construct their own shelters or improve existing rudimentary refuge.
In the IRL and elsewhere, Alpheus heterochaelis and other members of the
genus are often parasitized by the bopyrid isopod Probopyria alphei
(Rupert and Fox 1988).
Alpheus heterochaelis is a benthic species inhabiting a variety of
shallow marine habitats and typically residing within some manner of physical
protective structure. It is common on reefs and oyster beds, in and around
seagrass beds, and in salt marshes and mudflats. Nolan and Salmon (1970) note
that A. heterochaelis lived in and among clumps of oyster shells,
presumably burrowing into the mud underneath (but see above). Heck and Orth
(1980) report that otter trawls from vegetated (Zostera marina) habitats
contained A. heterochaelis, although the number of animals collected in
this study was very small.
Early field surveys recording Alpheus spp. snapping levels noted a
night-time increase in shrimp noise, suggesting elevated activity (Knudsen et
al. 1948, Knowlton and Moulton 1963). Another historic study revealed a
crepuscular rhythm in which snapping shrimp sound production peaked shortly
after sunset and again shortly before sunrise (Johnson et al. 1947).
Laboratory investigations by Nolan and Salmon (1970) revealed that A.
heterochaelis spent the greater part of its time during the day under or
partly under cover, and increased the amount of activity away from shelter at
night. Field surveys by these authors also confirmed an increase in sound
production at night as well as discernable crepuscular peaks.
Population-wide snapping activity declines during the day, but does not
disappear. This is likely reflective of the multiple roles of snapping
behavior, i.e., to subdue prey, to defend territory, and to facilitate
intraspecific agonistic interactions.
VI. SPECIAL STATUS
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J. Masterson, Smithsonian Marine Station
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