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Species Name: 
Alpheus heterochaelis Say, 1818

Common Name(s):
Bigclaw Snapping Shrimp

Synonymy:
Alpheus lutarius (de Saussure, 1857)
Crangon heterochaelis (Hay and Shore, 1918)
Halopsyche lutaria (De Saussure, 1857)

Species Description:
Alpheus heterochaelis, the bigclaw snapping shrimp, belongs to the snapping shrimp or pistol shrimp family (Alpheidae), whose members possess a single, large chela (claw) that has been modified such that it is capable of producing a distinct snapping or popping sound. The acoustic claw snap of Alpheus heterochaelis is important as a means of stuning/killing prey, in defense, and as part of a theat display in agonistic intraspecific encounters as well (Herberholz and Schmitz 1998)

Individuals are typically dark translucent green with orange and blue tipped uropods. The rostrum is small and the carapace edge is smooth and spineless and large snapping claw is strongly notched on both the upper and lower margins at the base of the fingers. The snapping claw can be either the left or right claw, and it attains a length nearly half that of the body. The opposite paired claw remains an unmodified pincer. The snapping claws of male A. heterochaelis are larger and broader than those of females of equal size (Nolan and Salmon 1970, Herberholz and Schmitz 1998).

A. heterochaelis is the largest and most colorful of the snapping shrimps of the southeastern United States (Rupert and Fox 1988).

Sound-production in Alpheus heterochaelis had long been believed to be the result of either rapid closure of the oversized pistol claw or of the separation of two smooth disk areas at the base of each of the fingers of the large claw. The true basis for snapping shrimp sound production was described in 2000 by Versluis et al. The authors explain that the very rapid claw closure emits a high-velocity (25m/s) jet of water whose speed exceeds cavitation conditions to create a small (expanding from miscroscopic to around 3.5mm at maximum size), extremely short-lived cavitation bubble. High-speed imaging revealed that the characteristic popping sound was actually produced by the rapid (<300 µs after formation), violent collapse of the cavitation bubble.

Lohse et al. (2001) studied this phenomenon further and found that as the snapping claw cavition bubble collapses a very short, intense flash of light is emitted. The authors conclude from this observation that the collapsing bubbles experiences extremely high internal pressures and temperatures exceeding 5,000°C.

Curiously, auditory organs have not been identified in A. heterochaelis and may be absent. Mechanoreception and chemosensory reception may therefore be the most important means for individuals to analyze signals from conspecifics (Herberholz and Schmitz 1998). This subject is taken up in more detail below.

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 A. viridari.

II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
Alpheus heterochaelis is native to the western Atlantic Ocean, occurring from North Carolina and Bermuda to Brazil and the West Indies (Kaplan 1988).

IRL Distribution:
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).

Abundance:
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 season.

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.

Reproduction:
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.

Embryology:
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).