Neotrypaea californiensis (Dana, 1854)
Bay ghost shrimp (English)
Thalassinidean shrimp are among the most common burrowing organisms of marine intertidal and shallow subtidal environments, and may be common in deep-sea habitats as well. These organisms rely on self-constructed burrows for a wide variety of needs including shelter, reproduction, and feeding. Except for a larval phase which may be pelagic, most thalassinidean shrimp spend their entire life within the burrow. (Griffis and Suchanek 1991)
One well known thalassinidean on the Pacific coast of North America is the ghost shrimp Neotrypaea californiensis (formerly known as Callianassa californiensis), which burrows in muddy sand with enough clay and organic matter to make it reasonably cohesive and to provide material for lining its tunnels. This shrimp has a waxy pale pink and orange appearance. The largest individuals may reach 10 cm (excluding appendages). Burrows usually have a number of branches and turnaround chambers, with at least two openings to the surface, providing for some circulation of seawater through the tunnel system. Burrow openings are typically in the middle of little piles of sand or sand mixed with small pebbles. (Kozloff 1993)
This shrimp is abundant in mud flats of bays and estuaries on the west coast of North America. Individuals average from 5 to 8 cm in length and vary from a whitish yellow to orange-red. A striking feature is the possession of an exceedingly large cheliped, or claw, which may be on either the right or left side. This inequality in size of the chelipeds is largely a sexually dimorphic trait, for in the females the difference between left and right is much smaller. (MacGinitie 1934)
These shrimp, which are awkward and relatively helpless outside their burrows, are found most abundantly in tidal regions from zero to one foot in depth, and are restricted to bottoms of mixed sand and mud of a consistency that allows the construction of fairly permanent burrows. Neither very loose sand nor very soft mud will work. Individuals are occupied almost constantly in extending or adding new tunnels to their burrows, which often connect with those of other individuals (such connections, however, are continually being blocked off and tunneled around). The burrows are extensive and are being added to continually because the animals sift sandy mud to extract detritus, which constitute this shrimp's diet. The continual turning over of the soil and the aeration of the subsoil by the burrows of this shrimp are important to the entire community of mud-dwellers, and a variety of other species are commonly found on the bodies and in the burrows of these shrimp. (MacGinitie 1934) These associated animals include pea crabs; the scaleworm Hesperonoe complanata; a small clam, Cryptomya californica, whose siphons open into the burrow instead of to the surface; and the goby Clevelandia ios (although not restricted to Neotrypaea burrows, this small fish is regularly found in their vicinity). (Kozloff 1993) The presence of burrowing Neotrypaea californiensis may increase or decrease populations of other marine soft-sediment species (Posey 1986).
MacGinitie (1934) provides a detailed description of burrowing behavior, as well as a discussion of the functions of the various appendages in offense and defense, walking, digging, feeding, swimming, cleaning, and so on.
Neotrypaea gigas is very similar to N. californiensis, though the claw of the adult male N. gigas is longer and more slender than that of N. californiensis (Brusca and Brusca 1978; see Brunet et al. 2008 and references therein for other characters distinguishing these two species). The Blue Mud Shrimp (Upogebia pugettensis) has a faint bluish color and lacks an oversized claw (Brusca and Brusca 1978). It is much hairier than N. californiensis and usually does not heap up sand around the burrow openings. It may occur in even muddier areas than those where N. californiensis is found, though the two species often occur together. (Kozloff 1993)
Labadie and Palmer (1996) conducted a morphometric analysis of claw size and shape variation in the strikingly heterochelous (i.e. having very different chelae, or claws) ghost shrimp Neotrypaea californiensis. Master claws approached 25% of total body weight in mature males, but rarely exceeded 10% in females. Minor claws were less than 3% of body weight in both sexes. The proportions of right versus left master claws did not differ significantly from 50:50. Males exhibited a greater positive allometry (disprortionate growth of claws) than did females in both master and minor claw size, but master claws differed more than minor claws. Sexual dimorphism was also observed in master, but not minor, claw shape: compared to females, mature male master claws: a) were proportionally higher relative to their length; b) exhibited a deeper propodal notch and consequently a larger gape; c) developed a more slender and more distally hooked dactyl; and d) exhibited more well-developed teeth around the periphery of the claw gape. Evidence suggests that the evolution of these unusual master claws has been significantly influenced by sexual selection.
In males, the major claw is often twice as long as the minor claw; in females, the major claw exceeds the minor claw by less than 50% in length (Carlton 2007).
Neotrypaea californiensis is found in the middle to low intertidal zone from southeastern Alaska to Baja California (Dumbauld et al.1996 and references therein).
Neotrypaea californiensis is found in soft sediment habitats in estuaries and coastal lagoons from southern Alaska to northern Mexico (MacGinitie 1934; Morris et al. 1980, cited in Pernet et al. 2008).
Neotrypaea californiensis is a deposit feeder, ejecting a portion of the material processed in the burrow to produce the surface mounds. (Griffis and Suchanek 1991).
In a study in Willapa Bay, Washington (U.S.A.), ovigerous (egg-bearing) Neotrypaea californiensis were found throughout spring and summer (April to August). Females extruded red eggs in spring that developed and hatched from June to August (evidenced by the presence of empty egg cases on the pleopods, or "swimming legs"). The average density of N. californiensis was 150 to 450 shrimp per square meter (an intermediate density compared to other studies). Females reach sexual maturity at 2 to 3 years of age. The egg-brooding period for these shrimp is 5 to 6 weeks. Females invest about 30 to 40% of their body weight in egg production, producing thousands of eggs each. (Dumbauld et al. 1996 and references therein)
Weitkamp et al. (1992) observed Gray whales (Eschrichtius robustus) in Puget Sound, Washington, U.S.A., creating feeding pits on littoral sand flats dominated by ghost shrimp (Neotrypaea californiensis). The whales removed an extensive biomass of shrimp from the pits. Ghost shrimp standing stock was 2 to 5 times lower inside than outside feeding pits, equivalent to a removal of 3 to 6 kg of shrimp per pit. An estimated 2700 to 3200 feeding pits were present on 19 km of sand flat in 1990, while 19000 feeding pits were documented over the same region in the spring and summer of 1991. Weitkamp et al. estimated that 10 to 12 and 75 tons of shrimp were removed from the pits in 1990 and 1991, respectively. Ghost shrimp represent an energetically valuable prey for gray whales, providing 2 to 15 times higher standing stocks than any other reported prey. (Weitkamp et al. 1992)
Many Neotrypaea californiensis bear symbiotic copepods (Clausidium vancouverense). These small reddish copepods (about 2 mm) can be seen through the translucent portion of the carapace covering the gills (it is unclear whether these they affect host fitness). A related species, Hemicyclops thysanotus, may also be present. In the northern part of their range, Neotrypaea californiensis may be infected by the parasitic bopyrid isopod Ione cornuta, the presence of which is indicated by the carapace bulging in the gill region where it is attached beneath. The fat, asymmetrical female, up to about 2 cm long, is accompanied by a small, slender male. (Kozloff 1993; Pernet et el. 2008) Pernet et al. (2008) discuss the risk of inadvertently introducing this parasite to southern California, where it is apparently not native, via the live bait trade. Pernet et al. found live, brooding I. cornuta at high frequencies (5.8% overall) among ghost shrimp imported from Oregon or Washington and purchased from three southern California bait shops in 2005 to 2007. This is likely higher than in the populations from which these bait shop ghost shrimp were collected, given that their overall estimate of prevalence in northern populations was 1.1% (though the authors note that there is likely among-estuary variation in prevalence that they not detect). Pernet et al. suggest that the higher prevalence of bopyrids in bait shop populations could be due to the preferential harvesting of larger ghost shrimp by bait diggers--as in many host-parasite interactions, larger ghost shrimp are probably more likely to be infected (O’Brien and Van Wyk 1985). The limited data available on the relationship between bopyrid infection and ghost shrimp reproductive status support the hypothesis that I. cornuta prevent successful reproduction in female hosts. (Pernet et al. 2008 and references therein)
Evolution and Systematics
Systematics and Taxonomy
Manning and Felder (1991) published a revision of the American Callianassidae in which they proposed a new genus, Neotrypaea, to which they transferred the shrimp then known as Callianassa californiensis. This change has been widely accepted (e.g., Carlton 2007).
Neotrypaea californiensis is sometimes treated as a pest by commercial oyster farmers in Washington State, U.S.A., who may spray sediments with carbaryl (an organocarbamate pesticide) at low tide to control shrimp populations. The activities of the shrimp increase turbidity and sediment deposition rates and reduce the compaction of intertidal sediments. The chronic disturbance from their burrowing causes oysters and other sessile (stationary) bivalves, especially settling larvae and spat, to either sink into the mud or be smothered and die. (Dumbauld et al. 1996 and references therein) Carbaryl applications kill not only the shrimp but non-target species as well, including economically important ones such as Dungeness Crabs (Cancer magister) and English Sole (Parophrys vetulus). Commercial crabbers and other groups who have economic, recreational, and environmental interests in the estuaries have generally opposed these chemical applications that oyster growers maintain is essential to sustain production levels. This conflict and associated policy issues were reviewed by Feldman et al. (2000).
- Callianassa californiensis Dana, 1854 (synonym)