DISCUSSION 



Temporal changes in exposure panel communities are closely associated with seasonal water temper- 

 atures and the suites of fouling and wood-boring life stages which are available for settling. In Nov-May, 

 the coldest exposure period, panel communities were dominated by cold and temperate water species: 

 Balanus crenatus, Mytilus edulis and Laminaria saccharina. In May-Nov, the warmest exposure period, 

 these dominant species shifted to the warmer water assemblages of Cryptosula pallasiana, B. eburneus, B. 

 improvisus, Limnoria spp., Cfielura terebrans and Teredo navalis. These seasonal trends in recruitment for 

 fouling and wood-boring species have been well documented in other studies (Nair and Saraswathy 1971; 

 Osman 1977, 1978; Sutherland and Karlson 1977; Ibrahim 1981). 



The fouling community at EF was different from those at ambient water sites; large primary covers 

 on EF panels were related to accelerated growth in response to elevated temperatures. Cory and Nauman 

 (1969) found that dry weight production of fouling species was on the average 2.8 times greater in the 

 power plant effluent at Chalk Point, Maryland than in its intake waters. Young and Frame (1976) reported 

 that the optimum temperature for growth of Balanus spp. was approached more closely during the winter 

 in the Oyster Creek power plant's discharge canal than in the intake canal where growth rate was reduced 

 by cold water. 



Conversely, effluent temperatures during the wjirmest months of the year had negative effects. Set- 

 tlement and survival of some species were adversely affected by effluent temperatures, since seasonal 

 temperatures exceeded the upper tolerance levels for some of their life stages. Similar exclusion of temperate- 

 boreal species from the Millstone Quarry has been discussed in the Rocky Intertidal section of this report. 

 Laminaria saccharina, a temperate-boreal brown alga, has never been collected on panels at EF, yet was 

 a consistent dominant at ambient water sites in Nov-May. Adult stages of Mytilus edulis have an upper 

 thermal tolerance of 26-27 °C (Gonzalez and Yevich 1976; Johnson et al. 1983) and the effluent temperatures 

 exceeded 26°C from June to September. I^arge populations of mussels were observed in the Millstone 

 Quarry during several May collection periods, but totally disappeared during June and July. In addtion, 

 remains of dead barnacles and bryozoans were generally 2.5 times greater at EF than at other sites. This 

 abiotic cover peaked on EF panels during the warmest exposure period of the year (May-Nov). 



2.1 



