November 1983, and has maintained relatively 

 high abundance since. The seasonal periodicity 

 of Polysiphonia noted throughout the area, includ- 

 ing FE prior to the opening of the second quarry 

 cut, has not been seen at FE subsequently. 



Monostroma coverage at MP decreased from 

 spring 1984 through winter 1986, which may have 

 indicated a thermal effect of the 2-umt/2-cut 

 plume since MP is the second closest station to 

 the MNPS discharge. Also, Monostroma abun- 

 dance at WP was atypically low in spring 1987 

 possibly indicating influence of the 3-unit plume. 

 Further monitoring will allow us to determine 

 whether these events represent natural variability 

 or an indication of thermal incursion. 



To summarize, rocky intertidal quantitative data 

 collected during 3-unit operation were within pre- 

 op ranges at most stations. Spatial and temporal 

 abundance patterns of local species have been 

 established and are similar to those observed by 

 other researchers in New England (e.g., Menge 

 1975; Menge 1976; Grant 1977). Seasonality, de- 

 gree of exposure, and competition induced vari- 

 ability in community parameters. The structure 

 of the Fox Island-Exposed community changed 

 after September 1984 when water temperatures 

 exceeded 28 °C, the upper physiological limit of 

 most species present. The FE community had 

 not re-established itself to pre-impact levels by 

 September 1987 (3-unit operation), and it is not 

 expected to under existing thermal fluctuations 

 described in the Temperature section of this report. 



Recolonization Studies 



Natural perturbations to established communi- 

 ties of attached plants and animals result in free 

 space for recolonization, and are an on-going pro- 

 cess in intertidal communities. Factors that de- 

 termine rate of recovery following perturbation 

 include physical or physiological stress, grazing 

 and predation, species competition, and temporal 

 and spatial heterogeneity (Dayton 1975). In ad- 

 dition, life-history stages, degree of exposure, and 

 time of denuding can determine rate of 

 recolonization in intertidal communities. These 



recolonization studies, therefore, simulate natural 

 processes, and allow examination of the factors 

 that influence community recovery. 



Previous studies (e.g., NUSCO 1985) have 

 shown that rates and patterns of recolonization, 

 especially in the first year following denuding, 

 may be characterized by patterns of recovery of 

 two major groups that distinguish local intertidal 

 communities: Balanus balanoides and Fucus 

 vesiculosus. Chondrus crispus, the dominant alga 

 in the low intertidal zone of undisturbed areas, 

 has not recolonized the denuded transects ade- 

 quately ui the first 12 months to warrant inclusion 

 in this report. Preliminary data from the 1986 

 autumn denuding are compared to the 1981 au- 

 tumn denuding; these data will be updated in 

 subsequent reports. Recolonization transects data 

 arc compared to undisturbed transects data for 

 each site to show rate and extent of recovery. 



Rates of community recovery are related to 

 intertidal height, and to the complexity of species 

 assemblages found in each zone. The high 

 intertidal zone consists mostly of barnacles on 

 otherwise bare rock (or occasionally, blue-green 

 algae and ephemerals, which can appear in high 

 intertidal areas within days of denuding) and there- 

 fore appears recovered, or similar in appearance 

 to undisturbed areas, by the end of the first bar- 

 nacle set. On the other hand, the low intertidal 

 zone is dominated by Chondrus and associated 

 epiphytes; as noted earlier, Chondrus recovery on 

 denuded substrata is slow, and it may take at least 

 several years before Zone 3 recolonization 

 quadrats resemble nearby undisturbed areas. 

 Rates of recovery in the mid intertidal zone are 

 intermediate; therefore, this report will emphasize 

 data only from Zone 2. 



Barnacles 



Recolonization of barnacles was observed in 

 spring in all recolonization transects after both 

 autumn denuding experiments. Annual peak bar- 

 nacle abundance, occurring in early summer, was 

 very similar in undisturbed and recolonization 

 transects at the four recolonization sites; peak 



42 



