440 VADAS, KESER, AND LARSON 



Regional and local temperature variability complicates these 

 patterns, however. Annual mean water temperatures in Maine in 

 1976 were the highest recorded since the 1950s (Welch, 1977). 

 Additionally, the removal of the causeway increased the depth of 

 high tides by 0.06 m and lowered that of low tides by 0.27 m (Maine 

 Yankee Atomic Power Company, 1975). This change increased 

 significantly the amount of mud flat exposed during low tide and 

 affected water temperatures in Montsweag Bay (Dean and Officer, 

 1977). 



Percent Cover 



The surface area covered by Ascophyllum, the dominant species, 

 varied within normal limits (Vadas, 1972) at the four sites. 

 Variability was lowest at Hodgson Island (control) and highest at 

 Foxbird Island (previously stressed site). Generally, variability rarely 

 exceeded ±6% between years at any site, and most values were not 

 significant (P > 0.05). Coverage in the upper intertidal, zone 1, at 

 Foxbird Island, except for 1975, was significantly below prestress 

 periods, however. Conversely, plants in the mid- to low-intertidal, 

 zone 2, recovered gradually but completely; differences between 

 1977 and the first stressed year (1973) were not significant 

 (P> 0.05). 



The cover of Fucus was highly variable at all sites. Significant 

 differences among years occurred periodically at all sites. This was 

 caused primarily by the relatively short life span (3 to 5 years) of 

 Fucus, by ice damage, and by rapid recolonization patterns rather 

 than by predictable environmental influences. At Foxbird Island the 

 thermal discharge destroyed most adult Fucus populations. Normally 

 sporelings of Ascophyllum do not readily colonize areas denuded 

 naturally or artificially (Keser and Vadas, unpublished), but both 

 Ascophyllum and Fucus reestablished in large numbers in 1975 after 

 relocation of the effluent. Fucus reestablished at a slow rate in zone 

 2 but since 1976 has been significantly higher (P < 0.05) than during 

 the stressed years. This increase in Fucus was caused in part by the 

 availability of bare substrate that previously was occupied by 

 Ascophyllum and Fucus. 



To permit comparisons with earlier studies (Vadas, Keser, and 

 Rusanowski, 1976), we listed the combined and transformed 

 percentages of both species in Table 1. The actual area covered by 

 these two species increased significantly (P < 0.05), by approxi- 

 mately 29% between 1974 and 1977. 



