Zooplankton of the Atlantic and Gulf Coasts: A Guide to Their Identification and Ecology

Mysids: Opossum Shrimps

MYSIDS Opossum Shrimps Mysids are small, shrimplike crustaceans that, like the amphipods, isopods, and cumaceans , brood their young in a ventral brood pouch. Most of the nearly 1,000 described mysids are coastal and estuarine species . Accessed August 20, 2011. Price, W. W. 1982. Key to the shallow water Mysidacea of the Texas coast with notes on their ecology . Hydrobiologia 93:9–21. Stuck, K. C., Perry, H. M., Heard, R. W. 1979. An annotated key to the Mysidacea of the north central Gulf of Mexico. Gulf Research Reports 6:225–238. Tattersall, W. M. 1951. A review of the Mysidacea of the United States National Museum. US National Museum Bulletin 201:1–292. Whittmann, K. J. 2009. Revalidation of Chlamydopleon aculeatum Ortmann, 1893, and its consequences for the taxonomy of Gastrosaccinae (Crustacea: Mysida: Mysidae) endemic to coastal waters of America. Zootaxa 2115:21–33. SUGGESTED READINGS Fulton, R. S., III. 1983. Interactive effects of temperature and predation on an estuarine zooplankton community. Journal of Experimental Marine Biology and Ecology 72:67–81. Johnson, W. S., Stephens, M., Watling, L. 2000. Reproduction and development of marine peracaridans . Advances in Marine Biology 39:107–260. Mauchline, J. 1980. The biology of mysids and euphausids. Pt. 1, The biology of mysids. Advances in Marine Biology 18:1–369. Wittmann, K. J. 1984. Ecophysiology of marsupial development and reproduction in Mysidacea (Crustacea). Oceanography and Marine Biology: An Annual Review 22:393–428. This page intentionally left blank 188 IDENTIFICATION AND BIOLOGY OF COMMON ZOOPLANKTON Neomysis americana Occurrence. Neomysis is often referred to as the most abundant shallow-water mysid from Cape Cod to northern Florida; peak abundance occurs in the Middle Atlantic states, where it inhabits almost all major waterways. It occurs from the upper ends of estuaries (almost freshwater) to 36 psu in the ocean but appears most abundant in the deeper portions of brackish and high-salinity estuaries. Although generally present all year, peak numbers occur in the summer from the Chesapeake Bay north. In the southern part of its distribution, mysids can be most abundant in estuaries during winter and spring. Biology and Ecology. Neomysis is a strong swimmer capable of directed movements even in strong tidal systems. Recent studies have found that most individuals remain near the bottom during day and night; however, at night, there is a tendency for the population distribution to expand vertically. The extent of the partial vertical redistribution varies according to stage of tide, depth, light penetration, and season. Neomysis has a tendency to aggregate and may occur in large shoals with densities of hundreds to thousands per cubic meter. Reproduction occurs in all but the coldest months, with large overwintering adults reproducing and dying off in the spring, giving rise to a first summer generation of mysids composed of smaller mature individuals. Females typically produce 10–40 young, depending on adult size. Juvenile Neomysis are more commonly encountered than adults in collections high in the water column. Neomysis may be the most important source of food for many young estuarine fishes, including weakfish, summer flounder, striped bass, and American shad. References. Herman 1963; Hulburt 1957a; Sato and Jumars 2008; Williams et al. 1974; Winkler et al. 2007; Zagursky and Feller 1985. Mysis stenolepis and M. mixta Occurrence. Mysis stenolepis occurs from Massachusetts to New Jersey, where it occupies intertidal and shallow subtidal areas, including seagrass beds. Mysis mixta is a less common open-ocean relative that occurs as far south as New York. Biology and Ecology. Unlike most cold-water crustaceans, both species reproduce during the winter. Large females may brood and release more than 150 young mysids in early spring before dying. Some older publications (1902–15) place these species in the genus Michtheimysis. A comparison of the predation and feeding ecology of co-occurring Mysis stenolepis and Neomysis americana showed that the diets of these omnivorous species showed a flexibility in foraging behavior that minimized direct competition for prey. References. Amaratunga and Corey 1975, 1979; Richoux et al. 2004; Winkler et al. 2007. MYSIDS 189 to 30 mm, to 25 mm Neomysis americana Mysis stenolepis • carapace without distinct rostrum (1) • antennal scale long; about 10 times longer than wide (2) • statocyst large and prominent (3) • telson: - terminal margin has two pairs of spines with the outer pair much longer than the central pair (4) - 35-40 lateral spines on each side arranged in clusters of short and long ones...