CAIN: REPRODUCTION AND RECRUITMENT OF RANGIA CUNEATA 



(1973, 1974) reported on the laboratory spawning 

 of Rangia and the combined effects of sahnity and 

 temperature on embryos and larvae. 



The impending action (at the time the work was 

 initiated) of discharge of waste heat into the 

 Rangia community by the Virginia Electric and 

 Power Company's (VEPCO) Nuclear Generating 

 Station at Surry, Va., was a further impetus to the 

 study of the reproductive cycle, especially those 

 factors that initiate gametogenesis and spawning. 



DESCRIPTIONS OF THE STUDY 

 AREA 



The study area in the James River is a transition 

 region between freshwater and salt water. The 

 area has a seasonably variable salinity that ranges 

 between about and 15°/oo, depending on the 

 volume of freshwater input. In the spring, high 

 river flow covers most of this region (except sta- 

 tion A) with freshwater (Figure 1). Occasionally, 

 in late summer and fall the study area may exhibit 

 measurable salinity as far upstream as station C. 

 The mean annual discharge of the James River is 

 approximately 212 mVs (7,500 cfs). 



Figure l.-Location of sampling stations for Rangia cuneata in 

 the James River, Va. (N = nuclear generating station). 



Field and hydraulic model studies of the James 

 River estuary have shown a two-layer density flow 

 pattern, in which the deep, more saline water has a 

 net upstream flow and the surface, fresher water 

 has a net downstream flow. The net sediment 

 transport of the two-layer section averaged over 

 many tidal cycles is upstream (Pritchard 1952). 

 The transition section of the James River is 

 characterized by high natural turbidity and 

 sedimentation from the flocculation of river-borne 

 sediments. 



The distribution of bottom sediment types in 

 the James River estuary has been studied by 

 Nichols (1972). His survey indicates silt-clay subs- 

 trates at stations A, B, C, and D and sand subs- 

 trates at locations As, Bs, Cs, and Ds. 



The distribution of Rangia in the James River 

 was found to be approximately from nautical mile 

 25 to 55 above the river mouth (Figure 2). The 

 downriver extent of its range overlaps the habitat 

 of typical estuarine organisms such as the oyster; 

 at the upriver limit Rangia is associated with 

 completely freshwater forms such as freshwater 

 mussels. In the oligohaline portion of its range it is 

 typically associated with the polychaetes 

 Scolecolepides viridis and Laeonereis culveri; the 

 crustaceans Cyathura polita, Corophium lacustre, 

 a,nd Gammarus sp.; and the bivalves Macoma 

 balthica, Brachidontes recurvus, and Congeria 

 leucophaeta. 



METHODS AND MATERIALS 



The reproductive cycle was investigated by 

 collecting clams at stations A, B, and C (Figure 1). 

 Station A was near the downstream range of the 

 clam. Station B was 18.5 km above station A. Sta- 

 tion C was located (18.5 km above station B) near 

 the mouth of the Chickahominy River in order to 

 include part of the clam's range which seldom 

 experiences salinity changes. All stations were 

 located at approximately the same depth (3-4 m). 

 The clams used in this study were collected from a 

 predominantly silt-clay substrate. Although 

 Tenore et al. (1968) indicated that such sediments 

 were detrimental to Rangia, the clams at the 

 various stations appeared to be thriving over the 

 2-yr study. 



Beginning in February 1970 approximately 20 

 clams, 30-40 mm long, were collected at stations A 

 and B using a modified oyster dredge. Attempts 

 were made to collect clams at these stations every 



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