1986-87. At EF, oligochaetes were the most abun- 

 dant (71 - 95/core) and consistently dominant 

 taxa during 1986-87. Oligochaetes ranked second 

 at GN and .IC, while the ampelisciid amphipod, 

 Ampelisca abdita ranked second at IN. Aricidea 

 catherinae and Lumbrineris tenuis were dominant 

 in both years at GN and JC. Leplocheirus pinguis 

 appeared among the dominants at all stations ex- 

 cept EF in 1987. 



The IN community, in addition to the top rank- 

 ing Mediotnaslus ambiseta, was dominated by 

 three amphipods, Ampelisca abdita, A. verrilli, 

 and A. vadorum. Leptocheirus pinguis, however, 

 was the most abundant organism (125/core) in 

 1987, but was not abundant in 1986. Other spe- 

 cies present in abundance (> 10/core) at IN in 

 1987 were: the tube building polychaete, Owenia 

 fusiformis the amphipod, Uniciola inorala and 

 the hermit crab, Pagurus longicarpus. 



When compared to 1980-85, there were changes 

 in the dominance structure over 1986-87 relative 

 to 1980-85; most of these were first apparent in 

 1987. A regional change occurred in the abun- 

 dance of arthropods, particularly Leptocheirus 

 pinguis. Abundance of this species, as well as 

 other arthropods {Uniciola irrorata, Ampelisca 

 abdita and A. vadorum), at GN, JC and IN during 

 1987 were well above the 5-year average. A sec- 

 ond area-wide change in dominance occurred in 

 densities of Mediomastus ambiseta. This species 

 had a high BIV ( > 90%) during 1986-87 at all 

 stations compared to the range for 1980-85 

 (60.1-77.6%). 



In 1986-87, 3 taxa at EF, 2 at GN and IN and 

 1 at .IC were among the top ten for the first time. 

 All newly ranked species were generally abundant 

 in only one of the last two years and had low 

 1986-87 BIV's. The number of species included 

 among the dominants in 1980-85, but not during 

 1986-87 were greater, although the majority of 

 these had low BIV's for 1980-85 or were collected 

 in low abundances. Those species with high 5-year 

 BIV's ( > 70%) or high mean abundance 

 ( > 10/core) and not among the top ten in 1986-87 

 were: Tharyx acutiv; and Poly cirrus eximius at 



GN and EF and Aricidea catherinae at IN. 

 Polycirrus eximius was aslo found in lower density 

 at .IC in the last two years, although this species 

 remained among the top ten. Changes in abun- 

 dance of dominant taxa will be described in more 

 detail in the following section. 



Dominant Taxa 



Temporal patterns in abundance of selected 

 subtidal taxa were examined using the same mul- 

 tiple regression analysis procedure used to remove 

 natural sources of variation in abundance and 

 number of species. Taxa selected ranked among 

 the top four numerical dominants (BIV's > 80%) 

 during either the 1980-85 pre-operational period, 

 or the 1986-87 operational period. In some cases, 

 taxa were included to allow comparison at all 

 stations, even though the BIV may not exceed 

 80% (e.g., Aricidea catherinae at EF). Quarterly 

 and annual means plotted in the figures are log- 

 transformed; those described in the text are the 

 exponentials of plotted values. 



Oligochaetes 



These annelids occupy a variety of habitats in 

 the Millstone area, and feed on the fine deposits 

 incorporated into the sediments. Oligochaete den- 

 sities can increase both quickly (Gierc 1975) and 

 markedly (Price and Ilylleberg 1982) as the 

 amount of detritus incorporated in sediments in- 

 creases. Oligochaetes were a dominant taxon at 

 3 of the 4 subtidal stations; at EF this group 

 ranked 1st in both 1986 and 1987; 3rd at GN and 

 2nd at JC in terms of the 2-year BIV. Oligochaetes 

 ranked 7th at IN over 1986-87. 



Throughout the operational period, oligochaete 

 abundance ranged from 35 - 56/core at GN, 23 - 

 123/core at JC, 23 - 127/core at EF and from 1 

 - 6/core at IN (Fig. 12A-D). Oligochaete abun- 

 dance at GN, EF and IN was within the range 

 of previous years while at JC, densities from 

 March 1986 - June 1987 were at their lowest level 

 since June 1981. 



96 



