this species was probably enhanced by the higher 

 sih/clay content, given its affinity for inhabiting 

 silty areas that have been recently disturbed (e.g., 

 Boesch 1982; Sanders et al. 1972). Abundances 

 of other species, including Aric.idea catherinae and 

 Polycirrus eximius, significantly declined following 

 siltation of JC. As mentioned previously, these 

 organisiHs are deposit-feeders and thus their de- 

 cline was probably not food-related. However, 

 since they feed near the sediment surface they 

 might be subject to burial. In addition, high 

 sediment load can cause direct mortality in resident 

 populations (Turk and Risk 1981). Changes in 

 sediment parameters similar to those evident after 

 start-up of Millstone Unit 3 have been observed 

 at other power stations (Dean and Ewart 1978; 

 Saenger et al. 1980) 



The IN area also exhibited changes in sediments 

 and infaunal communities during the operational 

 period. Silt/clay values during 1987 were generally 

 lower than those in recent years, but similar to 

 values obtained prior to 1984 (NUSCO 1987). 

 The infaunal community in 1987 exhibited signif- 

 icant increases in the abundances of the 

 amphipods, Ampelisca spp., Leptocheinis pinguis 

 and Uniciola irrorata. These organisms were 

 among the dominants at IN prior to the construc- 

 tion activities and are the 'background' compo- 

 nents of the Nucula-Nepthys community found in 

 Niantic Bay, the area adjacent to the IN station 

 (NUSCO 1980). 



Prior to Unit 3 construction activities, IN was 

 characterized as a dynamic area subjected to 

 strong tidal currents, and the infaunal communities 

 were dominated by suspension-feeding arthropods 

 (NUSCO 1984). Since then, construction impacts 

 (see NUSCO 1987 for summary) have been evi- 

 denced by increased silt/clay content and reduc- 

 tions in infaunal abundance and number of species 

 and the increased dominance of opportunistic 

 deposit-feeding polychaetes such as Polydora ligni, 

 Capilella spp. and Mediomastus amhiseta, which 

 become abundant following stress (Grassle and 

 Grassle 1974; McCall 1977; Swartz et al. 1980; 

 Flint and Younk 1983; Nichols 1985). A reduction 

 in silt/clay content in 1987 may have been a re- 



sponse to increased currents produced by start-up 

 and continuous operation of Unit 3 circulating 

 water pumps. The return to an amphipod- 

 dominated community at IN is believed indicative 

 of recovery from plant-related impacts which oc- 

 curred in previous years. 



Power plant-related impacts during the first year 

 of 3-unit operation appeared most related to 

 scouring (at EF and IN) and to the transport and 

 deposition of this sediment Into .IC. Infaunal 

 habitats immediately beneath the Unit 3 cut have 

 been eliminated due to scouring by the 3-unit 

 discharge; however, given the limited size of the 

 area, loss of this habitat would not significantly 

 alter ecosystem functioning in the greater Mill- 

 stone area. At JC, the deposition of sediments 

 apparently from the discharge area would be ex- 

 pected as a temporary change. Once all available 

 sediment is scoured from the EF area, no addi- 

 tional siltation of JC should occur. Infaunal 

 changes related to this siltation should also be 

 temporary and cause no detectable changes in the 

 ecology of the Millstone area. If however, the 

 sedimentary changes are the result of some plant- 

 induced change in the sedimentation patterns in 

 JC or the infaunal shifts were a response to tem- 

 perature, then more widespread and ecologically 

 significant changes in local infaunal communities 

 might occur. These possible impacts can not be 

 addressed until a more comprehensive operational 

 database is established. 



Conclusions 



Subtidal infaunal communities exhibited 

 changes in abundance, number of species and 

 population abundances following start-up of MiU- 

 stone Unit 3. Infaunal changes appeared most 

 related to shifts in sedimentary characteristics at- 

 tributed to scouring in the Unit 3 intake and 

 discharge areas and to transport of these sediments 

 to adjacent subtidal areas. Changes which might 

 have been mediated by increased water tempera- 

 ture could not be identified separately from power 

 plant-induced sediment changes. 



112 



