Ascophyllum populations have appeared in past 

 reports (NUSCO 1985, 1986, 1987; Ecological 

 Significance of Community Changes at Fox Island 

 - Appendix RSI V in 1987 annual report). Growth 

 and mortality characteristics of local Ascophyllum 

 populations, particularly under 3-unit operating 

 conditions, are discussed below. 



Growth 



Ascophyllum growth was greater at FN (exper- 

 imental station) in the 3-unit operational period 

 (the 1986-87 growing season) than at the control 

 sites, WP and GN (Fig. 11a). Growth was not 

 linear; length data closely fit a Gompertz growth 

 function. This model assumes an upper limit to 

 size (asymptote, a-parameter), which in our study 

 represents the maximum tip length after a growing 

 season. The other model parameters define an 

 inflection point (i.p.), that represents the time of 

 peak growth rate. The Gompertz model has been 

 applied to numerous biological systems (e.g., 

 Ricker 1975; Draper and Smith 1981), as well as 

 lobster and winter flounder growth in this report; 

 it is an excellent descriptor of Ascophyllum tip 

 length vs. time in the present study. Growth at 

 Fox Island was fastest in early spring and peaked 

 2 weeks earlier than at control sites; for the re- 

 mainder of the year growth rate was not signifi- 

 cantly different between experimental and control 

 site plants. The asymptote of the Gompertz 

 growth model corresponded to an average tip 

 length of 98 mm at FN and 86 mm at both WP 

 and GN, but due to the low number of surviving 

 plants and tips, variability was high and the dif- 

 ferences in total growth were not statistically sig- 

 nificant. 



Similar growth responses were seen under pre-op 

 (1979-86) conditions. The Ascophyllum popula- 

 tions at the control sites had similar growth rates 

 and average tip lengths (Fig. 1 lb). Fox Island 

 Ascophyllum plants grew faster and longer (110 

 mm) than plants at either of the control sites 

 (84-89 mm). Longer tips at Fox Island resulted 

 from higher growth rates in spring, with the point 

 of maximum growth reached 2 weeks earlier than 

 at control sites, thus causing the Ascophyllum 



population at Fox Island to have growth that was 

 significantly different (99% probability) from the 

 growth of WP and GN populations. Growth rate 

 during the remainder of the year was similar for 

 all sites. When within-station comparisons are 

 made, growth responses to temperature changes 

 can be better determined. 



Pre-op data at FN exists for only one year, as 

 this station was established in spring 1985. How- 

 ever, to better characterize the response of an 

 Ascophyllum population exposed to elevated water 

 temperatures, we have included data from the 

 original experimental station. Thus, Fox Island 

 pre-op growth data are divided into three periods, 

 representing three thermal regimes: FI pre 

 (1979-84), FL (1984-85), and FN (1985-86). 

 Three-unit operational data for FN are referred 

 to as 3-unit (1986-87). These four groupings for 

 Fox Island Ascophyllum populations are illustrated 

 in Fig. 12a. 



Ascophyllum plants (tips) at Fox Island grew 

 longer than those at WP or GN during all thermal 

 regimes in the pre-op period. At Fox Island, the 

 point of maximum aimual growth was reached 

 earlier in the pre-op period than in the 3-unit 

 operational period, and earliest in the 1984-85 

 thermal regime (May 9, ca. 25 mm in the first 

 month). Warmer than ambient temperatures at 

 FL (2-3 °C warmer under 1-unit, 1-cut conditions 

 in spring 1983; 12-13 °C warmer under 2-unit, 

 2-cut conditions in spring 1984) and at FN (0-2 

 °C warmer under 2-unit, 2-cut conditions in spring 

 1985) enhanced growth because optimal temper- 

 atures for Ascophyllum growth existed for longer 

 periods of time. However, in summer 1984 tem- 

 peratures at FL exceeded 28 °G and Ascophyllum 

 plants died when their physiological limits were 

 exceeded. 



Ascophyllum growth at the new sampling station 

 (FN) in the 3-unit operational period to date 

 (1986-87) was similar to that seen in the single 

 pre-op growing season for which there is growth 

 information (1985-86). Under 2-cut/3-unit oper- 

 ation, these plants were exposed to water temper- 



46 



