Common names for freshwater glass shrimp include grass shrimp, popcorn shrimp, glass pawns, hardbacks and jumpers. Several diagnostic features distinguish the caridean shrimps, to which the genus Palaemonetes belongs, from the penaeidean shrimps. In the caridean forms, the pleura of the second abdominal somite overlap those of the first, and the third walking legs lack claws or chelae. Palaemonidae may be from members of the families Alpheidae, Processidae, and Hippolytidae by having the second walking leg with an unjointed carpus (the segment just proximal to the chela). Glass shrimp are transparent to yellowish brown. Few exceed 50 mm in total length. Males can be separated from females by the presence of the appendix masculina attached to the appendix interna on the endopod of the second pair of pleopods. Also, the endopod of the first pleopod is larger in males than in females of the same age.
Life Cycle: The spawning season of grass shrimp extends from February through October but may vary with species and geographical location. An exception is P. paludosus, which spawns all year in southern Florida. In the prespawning female, the ripening ovaries are discernable as greenish or grayish brown masses of tissue dorsal and posterior to the stomach, and additional setae develop on the ventral surface of the abdomen and thorax. The female\'s molting condition and subsequent mating and spawning were described for P. vulgaris by Burkenroad (1947). He reported that after molting, the female is receptive to the male but that apparently the male recognizes her condition only if physical contact is made with her exoskeleton.
The eggs hatch 12 to 60 days after fertilization, depending on species and geographical location. In warmer climates, the incubation period is usually shorter. Osmotic swelling of the inner membrane, struggling by the larva (protozoea), and ventilatory movements by the female assist in freeing the larva from the egg membrane (Davis 1965). The female molts again within a few days after spawning and may produce an additional brood, depending on the species or time of spawning. Depending on the species and environmental conditions, there may be from 3 to 11 morphologically distinct stages during larval development. Transition from one stage to the next occurs during molting.
Habitat, Food Source(s), Damage: Grass shrimp eat a wide variety of aquatic foods. Depending on the availability of a particular food they may be detritivores, primary consumers, or secondary consumers. Larvae are planktonic and feed upon zooplankton, algae, and detritus. Grass shrimp also are predators of meiofauna and small infaunal polychaetes, oligochaetes,nematodes, epiphytic fauna, and even motile prey such as mysids.
In estuaries, numerous fish species and other aquatic carnivores, some of which are valuable sport and commercial fishes, eat large quantities of grass shrimp. Grass shrimp are also eaten by forage fishes such as Fundulus spp., which in turn are preyed upon by larger fishes. As prey, grass shrimp play an important role in the transfer of energy from the producer and decomposer levels to higher consumer levels. Grass shrimp frequently inhabit water near underwater structures and are particularly attracted to dense stands of underwater macrophytes. These stands not only support an abundance and diversity of food for shrimp, but also provide a refuge from predators. Grass shrimp are more prone to predation when displaced from preferred substrata such as macrophytes and oyster shells
References and Resources: Chicago Wilderness Magazine; http://chicagowildernessmag.org/issues/ spring2001/glassshrimp.html; Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Gulf of Mexico): Grass Shrimp. http://www.nwrc.usgs.gov/wdb/pub/0091.pdf; U.S. Fish and Wildlife Service. 1983-19 . Species profiles: life histories and environmental requirements of coastal fishes and invertebrates. U.S. Fish Wildl. Serv. Biol. Rep. 82(11). U.S. Army Corps of Engineers, TR EL-82-4; Anderson, G. 1985. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (Gulf of Mexico) -- grass shrimp. U.S. Fish Wildl. Serv. Biol. Rep. 82(11.35) U.S. Army Corps of Engineers, TR EL-82-4. 19 pp.