in local barnacle and predatory snails abundances 

 was the coverage and periodicity observed at FE 

 since September 1984. These changes were related 

 to the opening of the second quarry cut, and 

 attributed to elevated water temperatures 

 (NUSCO 1985, 1986, 1987). 



Mussels 



Mussels (mostly Mytilus edulis) were present at 

 aU rocky shore sampling sites during the 3-unit 

 operational period, usually occupying < 5% of 

 the available space (Fig. 6). Mussels typically 

 occurred as clumps of adults in rock crevices 

 where they could persist for long periods (in ex- 

 cess of 20 years, Bayne 1976) or as juveniles that 

 settled among barnacles in mid-summer, but were 

 eliminated by late summer by Urosalpinx and 

 Thais. One exception to this generality occurred 

 at Seaside Sheltered in July 1986, when 8% of 

 the low intertidal (Zone 3) was covered by a mass 

 of adult mussels that washed into one transect of 

 the study area, presumably after being dislodged 

 from a nearby population. These mussels did 

 not firmly attach themselves and were washed 

 away by the next sampling period. Similar events 

 occurred at SS and SB in 1982 (NUSCO 1983); 

 however, these mussels persisted for as long as 

 two years. 



Mussels have not been a dominant component 

 of local rocky shore communities; in the pre-op 

 period, mussel cover exceeded 10% only at Bay 

 Point and Giants Neck. Other researchers in 

 New England have reported that Mytilus is supe- 

 rior to Balanus as a competitor for available space 

 (e.g., Menge 1976; Grant 1977; Lubchencho and 

 Menge 1978), and as a result dominates intertidal 

 areas. We have also noted the competitive dom- 

 inance of mussels in exclusion cage studies (e.g., 

 NUSCO 1985, 1987). A common fmding of these 

 studies was that mussels could exclude barnacles 

 only when predation pressure was reduced, by 

 physical conditions (e.g., wave shock) or experi- 

 mental manipulation; these conditions are not 

 representative of the Millstone area. 



An atypical pattern of mussel abundance was 

 noted at Fox Island-Exposed (Fig. 6). In both 

 summers of the 3-unit operational period to date, 

 mussels settled densely among barnacles in the 

 mid and low intertidal zones. These mussels grew 

 rapidly and increased coverage to ca. 30%, 

 outcompeting barnacles as they did so. However, 

 the mussels were almost totally eliminated by au- 

 tumn. Both the initial rapid growth and subse- 

 quent high mortality were attributed to elevated 

 water temperature. Incursion of warm water pro- 

 duced optimum growth conditions in early sum- 

 mer; however, maximum temperature for adult 

 survival is reported to be ca. 27°C (Read and 

 Cumming 1967; Bayne 1976; Gonzalez and 

 Yevich 1976). This temperature occurred in the 

 quarry (Schneider 1981; Johnson et al. 1983) and 

 at FE under 3-unit operating conditions. 



FuctJS 



The perennial brown alga, Fucus vesiculosus, is 

 found throughout intertidal communities locally, 

 but is especially abundant in the mid intertidal 

 zone (Fig. 7). Growth conditions are optimal in 

 Zone 3, but Fucus is usually outcompeted by 

 Chondrus (cf. Lubchenco 1980). Station- 

 to-station variability exists in Fucus abundance, 

 related to degree of exposure. Consistently low 

 Fucus abundance was typical of BP (Zone 2, 

 0-3% in the pre-op and 3-unit operational peri- 

 ods), an exposed sampling site prone to physical 

 stress caused by storm activity and ice damage. 

 The other stations, however, were more moder- 

 ately exposed, and reflected conditions suitable 

 for Fucus growth (Topinka et al. 1981; Keser and 

 Larson 1984). Overall, average Fucus canopy in 

 Zone 2 was about 32%, excluding BP data. 



Temporal variability is also evident in local 

 Fucus populations. Fucus occupies new substrata 

 following settlement of zygotes in spring (Knight 

 and Parke 1950; Keser and Larson 1984), and 

 growth of germlings which achieve peak abun- 

 dance in late summer. Typically, Fucus settles 

 between barnacles and utilizes the spatial escape 

 until it is large enough to be unpalatable to graz- 

 ing snails (Keser 1978; Geiselman and McCoimell 



Rocky Intertidal Studies 



29 



