Species Description: Eurypanopeus depressus is a mud crab in the family Panopeidae (superfamily: Xanthoidea) that inhabits oyster reefs in temperate, subtropical, and tropical oceans. The depressed mud crab is small with an oval and flattened carapace. The carapace has four lateral teeth on both sides and mottled grayish olive or dark olive brown in color. There are two dark brown chelipeds (claws), one large and one small. Underneath, the legs and body are light colored (Williams 1984).
E. depressus seeks refuge from direct sunlight during low tide as well as from predators hiding in the clusters and valves of Crassostrea virginica and are sometimes found on the mud surface (Grant and McDonald 1979, McDonald 1982, Meyer 1994).
Regional Occurrence: Eurypanopeus depressus inhabits the estuaries along the east coast of North America from Massachusetts to Florida to Texas in the subtidal or intertidal oyster beds (Grant and McDonald 1979, Sulkin et al. 1983, Williams 1984). It is also found in the Dutch West Indies, Uruguay and Bermuda (Williams 1984). The depressed mud crab has been reported from depths ranging from 1 to 27 meters (Williams 1984).
IRL Distribution: Eurypanopeus depressus is common in the oyster reefs in the Indian River Lagoon (Boudreax et al. 2006).
Age, Size, Lifespan: The lengths and weights reported for the depressed mud crab are 1 to 130 mm and 0.5-0.8 g, respectively (Boudreax et al. 2006). Juvenile males reach maturity at 5.1 to 6 mm and females will have their first clutches at 5.5 to 6.4 mm (Williams 1984). Juveniles can reach maturity in the first summer after the eggs can hatch.
Abundance: Intertidal populations of Eurypanopeus depressus can be as dense as 55 individuals per meter squared during the peak summer season (Grant and McDonald 1979). In winter, the population decreases to as low as 6 individuals per meter. In a Florida study, the depressed mud crab was one of the most abundant motile species in Crassostrea virginica beds (Boudreax et al. 2006).
Reproduction: Eurypanopeus depressus has separate sexes. The reproductive season varies depending upon the seawater temperatures in a region (McDonald 1982). In temperate areas from Massachusetts to South Carolina the spawning begins in the spring around March or April and ends in late fall around October or November (McDonald 1982, Williams 1984) while in the subtropical waters of Florida and the tropical waters of the Caribbean, reproduction occurs throughout the year (Williams 1984). E. depressus females carry their eggs under the abdomen.
Embryology: Eurypanopeus depressus larvae have four zoeal stages and one megalopa stage before development to the first crab stage (Costlow and Bookout 1961).
Temperature: The depressed mud crab ceases to reproduce when seawater temperatures drop to 15°C and below (McDonald 1982).
Salinity: The salinity range of Eurypanopeus depressus is reported to be 4.5 to 20.4 ppt (Williams 1984). Under laboratory conditions, individuals have been shown to survive at salinities as low as 0.019 ppt for 28 days however, under these conditions, they experience increased energy expenditure and decreased feeding rates and absorption (Hulathduwa et al. 2007).
Desiccation: Eurypanopeus depressus exhibits low desiccation tolerance and therefore relies heavily upon its habitat for refuge during low tide events. Individuals will die when 30 ppt of the water is lost from its body (Grant and McDonald 1979).
Trophic Mode: Adult Eurypanopeus depressus are omnivores feeding primarily on algae, amphipods, oyster spat, sponges, polychaetes, other crustaceans and detritus (McDonald 1982, Williams 1984). Depressed mud crab larvae are planktotrophic. In the laboratory, larvae are reared on Artemia nauplii and fertilized Arbacia eggs (Costlow and Bookout 1961).
Associated Species: Eurypanopeus depressus are commonly associated with Crassostrea virginica oyster reefs where it often co-occurs with the xanthid crab Panopeus herbestii (Meyer 1994).
Boudreax ML, Stiner JL, and LJ Walters. 2006. Biodiversity of sessile and motile macrofauna on intertidal oyster reefs in Mosquito Lagoon, Florida. Journal of Shellfish Research 25:1079-1089.
Costlow JD and CG Bookout. 1961. The larval development of Eurypanopeus depressus (Smith) under laboratory conditions 1. Crustaceana 2:6-15.
Grant J and J McDonald. 1979. Dessication tolerance of Eurypanopeus depressus (Smith) (Decapoda: Xanthidae) and the exploitation of microhabitat. Estuaries 2:172-177.
ITIS. Integrated Taxonomic Information System. Available online.
McDonald J. 1982. Divergent life history patterns in the co-occurring intertidal crabs Panopeus herbstii and Eurypanopeus depressus (Crustacae: Bracyura: Xanthidae). Marine Ecology Progress Series 8:173-180.
Meyer DL. 1994. Habitat partitioning between the xanthid crabs Panopeus herbstii and Eurypanopeus depressus on intertidal oyster reefs (Crassostrea virginica) in southeastern North Carolina. Estuaries 17:674-679
Sulkin SD, Van Heukelem WF, and P Kelly. 1983. Behavioral basis of depth regulation in hatching and post-larval stages of the mud crab Eurypanopeus depressus. Marine Ecology Progress Series 11:157-164.
Williams AB. 1984. Shrimps, Lobsters, and Crabs of the Atlantic Coast of the Eastern United States, Maine to Florida. Smithsonian Institution Press, Washington, D. C., pp 408-409. 6.