Grass shrimp, sometimes called hardbacks or popcorn shrimp, are among the most common estuarine inhabitants of South Carolina waters. Their bodies are nearly transparent, except for orange (Palaemonetes vulgaris) or yellow (P. pugio) pigment in the eyestalks. Grass shrimp also have a well-developed rostrum (horn) with teeth along the edges, four spines on the telson (the pointed structure in the middle of the tail fan), and heads that are longer than the rest of the body. Unlike white shrimp (for which they are sometimes mistaken), grass shrimp lack claws on the third pair of walking legs and rarely grow larger than 5 cm (about 2 inches).
Habitat and Biology
Grass shrimp are found in estuarine waters along the Atlantic and Gulf coasts, usually associated with beds of submerged vegetation or oyster shells. Although both can live in a wide range of salinity, P. vulgaris can tolerate somewhat higher salinities than P. pugio; thus, there is some separation of the two species based on preferred habitat.
The grass shrimp spawning season extends from April to September, although this may vary depending on species and geographic location. During mating, which occurs within 7 hours of molting, the male transfers a spermatophore to the female. The eggs are fertilized externally as they are extruded, and the female attaches them to her pleopods, where they remain until hatching 12 to 60 days after they are fertilized. The incubation period varies among species and is shorter in warmer climates. The female molts again a few days after spawning and may produce another brood. Grass shrimp larvae undergo a series of developmental stages (10 zoeae and a postlarva) whose duration depends on water temperature and food availability. Larvae are planktonic and feed on zooplankton, algae, and detritus. However, adults consume a wider variety of foods, including microalgae attached to aquatic plants, small marine worms, and crustaceans. The fecal pellets that are produced by grass shrimp from the unused part of their diet are rich in nutrients and therefore an important component of energy cycling in estuarine ecosystems.
Grass shrimp have no commercial or recreational importance as food for humans, and they have limited value as bait or as food for cultured fish. However, they are an important species from an ecological perspective by serving as a link for energy transfer between trophic levels in the coastal food web. Grass shrimp feed on detritus, algae, and dead plant and animal material. In turn, grass shrimp are consumed in large quantities by commercially important fishes and forage species such as spotted seatrout, red drum, and mummichogs.
Ruppert, E. and R. Fox. 1988. Seashore animals of the southeast. University of South Carolina Press, Columbia, SC.
Williams, A. B. 1984. Shrimps, lobsters and crabs of the Atlantic coast of the eastern United States, Maine to Florida. Smithsonian Institution Press, Washington, DC.