Life History Notes. Because of the complex life 

 histories of some species, the following discussion 

 clarifies and supplements information presented in the 

 data summary tables. These life history notes identify 

 cases in which the ELMR program has considered 

 alternate life stages, cases in which two or more 

 species are considered as a single unit, and other 

 pertinent life history information. 



For the majority of species considered in this report, 

 growth and development involves a direct progression 

 through several distinct life stages. Accordingly, the 

 ELMR program has compiled information based on 

 five 'lypical" life stages: adult (A), spawning adult (S), 

 juvenile (J), larva (L), and egg (E). Adults were defined 

 as reproductively mature individuals, while juveniles 

 were defined as immature but otherwise similar to 

 adults in appearance. Species with a larval stage 

 typically undergo metamorphosis to the juvenile stage, 

 hence larvae usually differ from juveniles and adults in 

 form and appearance. In addition, most species rely on 

 external fertilization via spawning, by which gametes 

 combine outside the body after being released by 

 males and/or females. 



However, some species depart from this typical life 

 stage scheme in that spawning is replaced by mating 

 (M), i.e. the transfer of gametes internally between 

 male and female. This reproductive mode differs from 

 spawning in that it often involves specialized copula- 

 tory organs (e.g., pelvic claspers in skates) and does 

 not always result in the immediate fertilization of eggs 

 (e.g., spermatophore retention in American lobster and 

 blue crab). Furthermore, two species (Atlantic stingray 

 and cownose ray) are live-bearers and thus distin- 

 guished by a parturition (P) stage, but no egg or larval 

 stage. In addition, egg and/or larval stages are not 

 applicable for certain species because the stage(s) is 

 either absent or better defined by the presence of 

 gravid females. 



Molluscs. Sessile molluscs, such as clams and oys- 

 ters, usually have a patchy rather than a uniform 

 distribution. Therefore, the ELMR framework may 

 identify the salinity zones of colonization, but also may 

 overestimate the areal distribution of these organisms. 

 Specific areas of an estuary may contain acceptable 

 salinity regimes, but suitable bottom habitat for coloni- 

 zation may not exist. Specific habitat requirements and 

 life history characteristics of several mollusc species 

 are provided below. 



• Blue mussel: Not common south of Chesapeake 

 Bay. Occurs in littoral and sublittoral habitat, requires 

 at least some hard substrate for attachment, and may 

 form dense beds. 



• Bay scallop: Often associated with eelgrass beds, 

 sandy substrate, relatively high salinities, and depths < 

 2 m. 



• American oyster: Also known as "eastern oyster" 

 (Turgeon et al. 1 988). Oysters are typically subtidal in 

 Mid-Atlantic estuaries, and they usually attach to firm 

 substrate such as oyster shell. Oyster bars require 

 tidal currents to import food, flush wastes, and prevent 

 sedimentation. 



• Northern quahog: Also known as "hard clam" 

 (Turgeon et al. 1 988, Nelson et al. 1 992). Two species 

 of Mercenaria occur in U.S. coastal waters, but the 

 northern quahog (Mercenaria mercenaria) is by far the 

 predominant species in the Mid-Atlantic region. They 

 are generally found in intertidal and subtidal waters to 

 15 m, and typically in salinities above 20 ppt. Substrate 

 preferences may vary, but they are often more com- 

 mon in sand than in mud. The southern quahog 

 (Mercenaria campechiensis) is not common north of 

 Cape Hatteras, and is generally found in deeper, 

 higher salinity waters. 



• Softshell clam: Substrate preferences may vary, but 

 they are often more common in sand than in mud. Not 

 common south of Chesapeake Bay. 



Crustaceans. Some life history characteristics of ELMR 

 crustacean species are provided below. 



• Brown shrimp: Spawning (S)forthisPenaeid shrimp 

 is considered a singular event involving pairing of 

 males and females, egg fertilization, and egg release. 

 Postlarvae (L) and juveniles (J) are the main life stages 

 utilizing the estuaries. Adults generally move to 

 nearshore spawning grounds, where spawning, egg 

 development, and most of the larval development 

 occur. This species is generally not as abundant in 

 Mid-Atlantic estuaries as it is in the southeast U.S. and 

 Gulf of Mexico. 



• Daggerblade grass shrimp and sevenspine bay 

 shrimp: Soon after pairing with males, female Caridean 

 shrimps fertilize and extrude eggs onto their pleopods 

 where they are held for up to two months until hatching 

 as larvae. Therefore, spawning (S) for these species 

 is defined as the period of egg fertilization and extru- 

 sion. The egg (E) stage is defined as the period when 

 gravid (i.e., "berried") females are generally encoun- 

 tered. Daggerblade grass shrimp (Pa/aemonefespt/fir/o) 

 is closely related to several other species that also 

 occur in Mid-Atlantic estuaries (Anderson 1985, Will- 

 iamsetal. 1988). Riverinegrassshrimp(P.pa/uc/ostys) 

 is a primarily freshwater species that can occur in the 

 upper reaches of estuaries. Marsh grass shrimp (P. 

 vulgaris) and brackish grass shrimp (P. intermedius) 



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