In New York, the freshwater decapods include thirteen species of crayfish and one species of freshwater shrimp (Table 1: List of NYS Decapods). In addition to these fourteen species, an additional thirteen species of shrimp and crab are frequent inhabitants or rare intruders into the freshwater portion of the Hudson River and in coastal streams on Long Island and in Westchester County. Published accounts of the distribution and abundance of decapods in New York are rare. Crocker (1957) was the last to detail the distribution and status of the crayfishes in the state. Aside from individual accounts dealing with aspects of the natural history of selected species (e.g., Nevin and Townes 1935; Daniels 1998), little has been published on the biology of decapods in New York’s inland waters. Although New York State Conservation Department (NYSCD; 1927-1940) and Crocker (1957) surveyed lakes and streams, only Crocker (1957) compiled the information for publication.
Shrimp, crayfish and crabs are important components in the systems in which they occur. Decapods serve as major processors of detritus in many aquatic systems, are important in the transfer of energy from primary producers to higher-level carnivores, and, in some cases, are higher-level carnivores themselves. Crayfish represent a major component of the diet of the black basses (Micropterus dolomieu and M. salmoides) and mud crabs are important in the diets of sturgeon (Acipenser spp.). Decapods are commercially important as both bait for anglers and some species support a fishery, the catch destined for human consumption. Crayfish are familiar to high school biology students as study specimens. It is the rare stream or lake in New York that lacks decapods. In short, these are well-known, easily-recognized organisms that are ecologically and commercially important.
General information on the life history of crayfishes, shrimps and crabs is widely available in a variety of publications. Holdich and Lowery (1988) review the taxonomy, distribution, growth, reproduction biology, feeding ecology and behavior of crayfishes. A more general account of the ecology and behavior of decapods can be found in Hobbs (1991). Several publications that deal with regional faunas also provide excellent reviews of the ecology, distribution and behavior of decapods (e.g. Squires 1990; Hobbs and Jass 1988; Page 1985).
Decapoda is an order within Crustacea. Williams et al. (1989) list over 1600 species of marine and freshwater decapods in the United States and Canada. New York’s inland waters hold a small percentage of these species. The crayfishes are all in the family Cambaridae; the shrimps found in New York’s inland waters are in four families and the crabs are distributed in six families (Table 1: List of NYS Decapods). Although gross body shape varies within Decapoda, all decapods are animals based on a general plan: they possess a cephalothorax and abdomen and many paired appendages. The name “decapod” refers to the five pairs of walking legs, or pereopods, but each individual also possesses paired antennae, several paired appendages involved in feeding and the swimmerets, or pleopods. The distinguishing characteristic of the order is that, in all decapods, the first three thoracic appendages are modified as maxillipeds. Like all crustaceans, decapods have exoskeletons that require molting with increases in growth.
Not surprisingly, the life history of species in the order is highly variable. In New York’s crayfish, mating generally occurs in fall and eggs are spawned in the spring fertilized by sperm stored by the female over winter in the annularis ventralis, a vesicle on the ventral throrax. Females carry the eggs attached to their pleopods for several weeks to months. These ovigerous females are termed “in berry.” Hatching occurs in spring or early summer in most species and the first several instars remain associated with the mother’s pleopods. In the first growing year, individuals will molt 6 to 10 times and will not become sexually mature until the next growing season or perhaps the following. Females usually molt after the young are shed in late spring or summer. Mature males molt twice each year. They molt in spring and change into form II, or sexually inactive males. By the end of the summer, males have molted a second time and emerge as form I, or in the sexually active form. Shrimps and crabs do not have the seminal vesicle, so the eggs are laid shortly after copulation. In New York species, eggs are attached to the pleopods, although some peneid shrimps release eggs into the water. After hatching, early instars in the crabs are planktonic. The larval stages of these species are first called zoea, which usually are characterized by a long rostral spine. The postlarval stage is termed megalops, which is possesses an unflexed abdomen with all abdominal appendages. After several larval and postlarval molts, crabs settle to the substrate and take on the typical crab appearance.