Vegetative propagation and lateral proliferation 

 from surviving holdfasts replace lost plant material 

 (Printz 1956; Baardseth 1970a; Keser et al. 1981), 

 and these replacement processes maintain the 

 A scophy Hum populations at consistent levels. The 

 effects of thermal stress were seen only at FL, 

 less than one month after the opening of the 

 second quarry cut in August 1983 and in the 

 following summer. Before the second quarry cut 

 was opened, Ascophyllum mortality was not as- 

 sociated with proximity to the discharge, but 

 rather to the increased physical stress associated 

 with a higher degree of exposure. 



Ascophyllum is not expected to recolonize at 

 FL, even though conditions may be lethal only 

 for a short time in summer. The critical phase 

 for Ascophyllum appears to be the establishment 

 and growth of germlings on the substrate (Rueness 

 1973), and these stages are more susceptible to 

 environmental impact than are adults (Bird and 

 McLachlan 1974). Since repopulation involves 

 long-term survival of individuals, even short-term 

 exposure to lethal water temperatures in summer 

 will prevent Ascophyllum recovery. The substra- 

 tum previously occupied by Ascophyllum at FL 

 will continue to be dominated by ephemeral algae, 

 notably Codium fragile. The localized scale of 

 this impact (150 m) must be emphasized. Sam- 

 pling of control populations will continue to pro- 

 vide information to the rocky intertidal monitoring 

 program, as to whether thermal effects may be 

 seen over a larger area (FS, MP, WP), and as to 

 whether trends seen to date will continue during 

 extended 3-unit operation. 



Summary 



1. Exposure of local rocky shores to the full 

 power 3-unit plume varies with tidal stage as 

 well as distance from the discharges. On an 

 ebbing tide the plume was deflected to the 

 east, across Fox Island, and elevated water 

 temperatures at FL and FE (75 m and 100 

 m east of the discharges, respectively) for 

 9- 1 1 hours per tidal cycle. During maximum 

 tidal flooding, temperatures were close to 



ambient levels for 1-2 hours, as the plume 

 was deflected to the west and the heated wa- 

 ter was displaced. About 250 m west of the 

 discharges, at MP, water temperatures were 

 4 °C above ambient at high tide and 2-3 °C 

 above ambient during low slack water as the 

 plume spread laterally. Consistent full power, 

 fuU cooling water operation has not existed 

 during periods of maximum ambient water 

 temperature; it is during these conditions that 

 intertidal communities at nearby stations may 

 be affected by the 3-unit thermal plume. 



2. Overall, 128 benthic algal species have been 

 identified in the 3-unit operational period. 

 Relative species proportions in the first 12 

 months of the 3-unit operational period were 

 virtually identical (45:26:29) to those of the 

 pre-operational summary. Spatial and tem- 

 poral patterns of occurrence were evident in 

 the local intertidal qualitative collections. 

 Community changes at FE (i.e., a decrease 

 in species numbers, shift in divisional pro- 

 portions, loss of perennial species, and in- 

 creased abundance and persistence of oppor- 

 tunistic species) were attributed to elevated 

 water temperatures resulting from opening 

 the second quarry cut, not from Unit 3 start- 

 up. Most of these community changes have 

 persisted during 3-unit operation, as water 

 temperatures approaching 28 °C have oc- 

 curred at FE in summer. 



3. Local communities, and the factors respon- 

 sible for structuring them, have remained rel- 

 atively stable since Unit 3 began operation 

 and were similar to communities under pre- 

 operational conditions. Seasonality, degree 

 of exposure, and competition induced vari- 

 ability in community parameters. 



4. Recolonization experiments were undertaken 

 to isolate factors that influence the structure 

 of rocky intertidal communities. Locally, 

 recolonization was influenced by time of year 

 in which denuding occurred and it was related 

 to degree of exposure and intertidal height. 

 After the 1986 autumn denuding, barnacles 



Rocky Intertidal Studies 



51 



