which shared high densities of Scolecolepides 

 viridis and low densities of Paraonis fu/gens, 

 oligochaetes and Capitella spp. In addition, low 

 abundances of Paraonis fulgens at GN in 1986 

 were more comparable to those collected typically 

 at WP in past years (NUSCO 1987). 



The J" group (Group II) was subdivided into 

 two smaller groups with 1982 and 1984 collections 

 chaining onto these groups at lower similarity. 

 Collections in the first group, which included 

 1987, shared relatively low numbers of Capitella 

 and Scolecolepides viridis and higher numbers of 

 oligochaetes than the second group (1986, 1985 

 and 1983 collections). The separation of 1984 

 and 1982 from other sampling years was due to 

 low oligochaete abundances. 



Discussion 



Intertidal communities sampled during start-up 

 and through the first year of 3-unit operation 

 exhibited spatial patterns in community abun- 

 dance and composition and seasonal fluctuations 

 in abundance that were consistent with those ob- 

 served during the baseline period (NUSCO 1987). 

 Higher infaunal abundances and number of species 

 continued to occur at JC, the most sheltered of 

 our sampling stations. Communities at WP, the 

 most exposed station, generally included lower 

 numbers of individuals and species. A similar 

 pattern of increasing density and number of spe- 

 cies along gradients of decreasing exposure to 

 wind and wave-induced scour have been reported 

 in many studies (Holland and Dean 1977; Withers 

 and Thorpe 1978; Maurer and Aprill 1979; 

 Tourtellotte and Dauer 1983). At the population 

 level, the .IC community continued to be domi- 

 nated by oligochaetes and other surface deposit- 

 feeding forms whose abundance can be enhanced 

 by the presence of algal and eelgrass detritus 

 (Soulsby et al. 1982; Hull 1987). In contrast, mo- 

 bile carnivores and large, burrowing deposit- 

 feeding feeding organisms {Haploscoloplos fragilis, 

 Paraonis fulgens, rhynchocoels, and SlreptosylUs 

 arenae) which are more typical of exposed habitats 

 (Dexter 1969; Maurer and Aprill 1979; 



Tourtellotte and Dauer 1983), were consistent 

 dominants at WP and GN. Spatial distributional 

 patterns and seasonal fluctuations evident in Mill- 

 stone intertidal communities are typical of tem- 

 perate intertidal beaches, where physical factors 

 such as wind and wave-induced beach scour or 

 the resulting habitat characteristics (e.g., sediment 

 size, silt/clay content, sediment stability and po- 

 rosity) strongly influence the structure of 

 macrofaunal communities (Green 1969; Holland 

 and Polgar 1976; Croker 1977). 



Although spatial patterns were consistent be- 

 tween pre-operational and operational periods, 

 there were temporal changes in community abun- 

 dance and species composition evident at all sam- 

 pling stations. Many of these differences appeared 

 to be continuations of trends which were first 

 evident before 3-unit commenced. For instance, 

 increased macrofaunal abundance was observed 

 at JC since 1985, before 3-unit operation started 

 as the result of higher densities of principally 

 oligochaetes. At WP, lower annual community 

 abundance in 1986 continued a trend first evident 

 before 3-unit operation and reflected unusually 

 low numbers of both oligochaetes and 

 polychaetes. At both GN and WP, lower abun- 

 dances during the 1986-87 were observed in 

 oligochaetes, Paraonis fulgens, rhynchocoels and 

 Haploscoloplos fragilis. These reductions were 

 evident in December 1985 and March 1986, before 

 3-unit operation and were evident at our reference 

 station, suggesting that the declines were a re- 

 sponse to large-scale regional events. At .IC, re- 

 ductions in total abundance and species number 

 in December 1985 and March 1986 were also 

 evident, although they were not as extensive as 

 those at GN and WP. There were, however, un- 

 usually low densities of Scolecolepides viridis and 

 Ifediste diversicolor in .lune 1987. Low densities 

 of Scolecolepides viridis were also evident at GN 

 in June 1987, further indicating a possible area- 

 wide decrease, independent of power plant oper- 

 ations. 



During the operational period, several events 

 occurred which might have induced the temporal 

 changes in intertidal community structure and 



84 



