Species Description: The coastal mud shrimp, Upogebia affinis, is one of a few species of relatively large, burrowing shrimps found in the IRL. The rostrum, or foremost projection of the carapace, is large, flat and spinous (Ruppert & Fox 1988). Antennae extend about twice as long as the carapace, which is covered on its anterior portion by short, rigid hairs (Williams 1984). The claw-bearing legs, or chelipeds, are stout with hairs below and on the interior, and are ridged exteriorly. The fixed finger of the claw curves upward and is shorter than the movable finger called the dactyl. Both fingers bear small teeth on their inner surfaces, which grow larger closer to the base of the claw. U. affinis is usually gray, blue or yellowish-gray on the dorsal surface, pale blue on the center of the tail fan and the 5th abdominal segment, and light underneath. An oblique blue spot is located on the side of the carapace at the base of the antennae.
Potentially Misidentified Species: The coastal mud shrimp may be confused with ghost shrimps of the genus Callianassa. However, these species are more elongate and delicate than U. affinis, have dramatically unequal claws and a small, smooth rostrum (Ruppert & Fox 1988).
Regional Occurrence: The known range of the coastal mud shrimp extends from Massachusetts to Texas, and throughout the Caribbean south to Brazil (Williams 1984). Populations of U. affinis are found in muddy or silty sediments in estuarine habitats down to a depth of 29 m (Williams 1984). This species builds burrows often consisting of a complex series of tubes and galleries, which may contain one or several individuals of varying age (Frey & Howard 1975; Ruppert & Fox 1988). Mucus secreted from specialized abdominal glands help the shrimp to consolidate the sediments and construct passageways. Shrimp rarely surface again once inside the burrow, and individuals removed from their tubes seem to be unable to rebury themselves.
IRL Distribution: Little information exists on the distribution of U. affinis in the IRL, but shrimp are likely found throughout the lagoon in the sediments of muddy tidal flats. Florida populations have also been located in burrows dug among beds of the seagrass, Halodule wrightii (Williams 1984).
Age, Size, Lifespan: A typically large burrowing shrimp, U. affinis attains lengths up to 10 cm (Kaplan 1988). Mud shrimps are thought to live for up to several years, although this claim is unverified (Williams 1984).
Abundance: Densities of U. affinis in Tampa Bay have been documented at up to 25 individuals per square meter (Bloom et al. 1972), though abundances are generally lower in most locations.
Reproduction & Embryology: The coastal mud shrimp reproduces nearly year round in Florida, but tends to have reproductive seasons that peak in the warmer months for populations at higher latitudes (Williams 1984). Each female can hold about 10,000 fertilized eggs on her first four pairs of pleopods, protecting and aerating them until they hatch. Like most marine invertebrates, the larvae of mud shrimps are planktonic, feeding and developing in the water column before finding a suitable settlement location where metamorphosis to the juvenile shrimp occurs. Larvae of U. affinis pass through 4-5 zoeal stages, measuring from about 0.9 to 4.0 mm in length (e.g. Ngoc-Ho 1981). Although the first post-larval stage of U. affinis has been described (Andryszak 1986), no information exists on mechanisms of initial settlement.
Temperature: The known range of U. affinis throughout warm temperate to tropical climate zones suggests the species prefers and or requires warm waters in order to thrive. Reproduction also appears to be seasonal at higher latitudes, peaking in warmer months (see ‘Reproduction & Embryology’).
Salinity: The coastal mud shrimp is reported to prefer higher estuarine salinities, with a lethal lower limit of 10 ppt (Williams 1984).
Dissolved Oxygen: When dissolved oxygen concentrations decrease inside their burrows, mud shrimp have been known to climb to the surface during low tide in order to draw oxygen-rich water located near the air-water interface over their gills (Hill 1981).
Trophic Mode: Mud shrimps are filter feeders, consuming microscopic plankton and organic material from the water column (Dworschak 1987; Ruppert & Fox 1988). The coastal mud shrimp draws water through its burrow by flapping a series of circular abdominal appendages called pleopods. Next, setae (bristles) on the specialized mouthparts of the shrimp are used to sieve the food particles out of the water column.
Predators: Given that they rarely leave their burrows, mud shrimp predators are likely restricted to benthic-feeding fishes and invertebrates that have the ability to dig or sift through large quantities of sediment. Mud shrimp larvae may be consumed by a variety of fishes and invertebrates.
Parasites: Mud shrimps can be parasitized by the bopyrid isopod, Pseudione upogebiae, which forms a large bulge on one side of the carapace and infests the adjacent branchial chamber (Ruppert & Fox 1988). Other parasites include the isopod Phyllodurus robustus, and the gut-infesting fungus Enteromyces callianassae (Williams 1984).
Associated Species: The commensal clam, Lepton longipes, often lives inside the burrows of the coastal mud shrimp (Ruppert & Fox 1988). This clam species is tiny (about 8 mm) and white, with a prominent foot used to creep through the burrow. Presumably, the relationship between the two species is such that the clam gains protection and food without disturbing the mud shrimp.
The fast moving commensal hesionid worm, Parahesione luteola, is also frequently found inhabiting the burrows of U. affinis (Ruppert & Fox 1988). This species is brown and measures about 1.5 cm in length. Like L. longipes, the worm likely gains food and protection from predators by engaging in such a symbiotic relationship with the mud shrimp.
Other organisms that may cohabitate with U. affinis include: the flatworm, Stylochus ellipticus; the shrimp, Leptalpheus forceps; the copepod, Hemicyclops adhaerens; and the crab, Pinnixa sayana (Williams 1984; Ruppert & Fox 1988).
Aller, RC, Yingst, JY & WJ Ullman. 1983. Comparative biogeochemistry of water in intertidal Onuphis (polychaeta) and Upogebia (crustacea) burrows: temporal patterns and causes. J. Mar. Res. 41: 571-604.
Andryszak, BL. 1986. Upogebia affinis (Say): its postlarval stage described from Louisiana plankton, with a comparison to postlarvae of other species within the genus and notes on its distribution. J. Crust. Biol. 6:214-226
Dworschak, PC. 1987. Feeding behavior of Upogebia pusilla and Callianassa tyrrhena (Crustacea, Decapoda, Thalassinidae). Inv. Pesq. 51: 421-429.
Frey, RW & JD Howard. 1975. Endobenthic adaptations of juvenile thalassidean shrimp. Bull. Geol. Soc. Denmark 24: 283-297. Hill, B. 1981. Respiratory adaptations of three species of Upogebia (Thalassinidea, Crustacea) with special reference to low tide periods. Biol. Bull. 160: 272-279.
Kaplan, EH. 1988. A field guide to southeastern and Caribbean seashores: Cape Hatteras to the Gulf coast, Florida, and the Caribbean. Houghton Mifflin. Boston, MA. USA. 425 pp.
Ngoc-Ho, N. 1981. A taxonomic study of the larvae of four thalassinid species (Decapoda, Thalassinidea) from the Gulf of Mexico. Bull. Br. Mus. Nat. Hist. Zool. 40: 237-273.
Rabalais, NN, Holt, SA & RW Flint. 1981. Mud shrimps (Crustacea, Decapoda, Thalassinidea) of the northwestern Gulf of Mexico. Bull. Mar. Sci. 31: 96-115.
Ruppert, EE & RS Fox. 1988. Seashore Animals of the Southeast: A guide to common shallow-water invertebrates of the southeastern Atlantic coast. Univ. South Carolina Press. Columbia, SC. 429 pp.
Williams, AB. 1984. Shrimps, lobsters, and crabs of the Atlantic coast of the eastern United States, Maine to Florida. Smithsonian Institution Press. Washington, DC. USA. 550 pp.