EFFECTS OF REDUCED TEMPERATURES 435 



included, chronologically, a surface thermal discharge into a shallow 

 cove, the removal of a causeway, and the installation of a diffuser 

 discharge. 



The stresses produced by the thermal discharge and, to some 

 extent, the causeway removal were documented previously (Vadas, 

 Keser, and Rusanowski, 1976). Briefly, the effects of the thermal 

 discharge were confined to the vicinity of the discharge channel. 

 There the dominant intertidal algae, Ascophyllum nodosum (L.) Le 

 Jol. and Fucus vesiculosus L., were affected adversely. The cover of 

 Fucus decreased with the onset of the thermal effluent and was never 

 reestablished. The growth and survivorship of Ascophyllum increased 

 initially but subsequently declined. Increased plant and apical tip 

 mortality and the absence of new grovvd:h contributed to the gradual 

 but incomplete demise of Ascophyllum populations in the discharge 

 channel. The relocation of the discharge and power-plant shutdowns 

 during the initial two summers of operation ameliorated the total 

 impact and inevitable destruction of these populations. Although 

 significant declines occurred in percent cover, biomass, grov^h, and 

 survived of Ascophyllum, basal sections of many plants survived. This 

 paper is concerned with the recovery of previously stressed plants 

 and the effects of the present diffuser discharge on these algae. 



STUDY SITES AND METHODS 



Since detailed information was presented previously (Vadas, 

 Keser, and Rusanowski, 1976), only aspects unique to this study or 

 necessary for interpretation are included here and with the results. 

 The MYAPCO diffuser consists of two 152-m-long fiber-glass pipes 

 with 42 ports, each 43 cm in diameter. The multiport diffuser is 

 located on the southwest side of Foxbird Island (Fig. 1) at a depth of 

 13.4 m below mean low water (MLW). Six sites were monitored in 

 Montsweag Bay, three of which are experimental sites (Bailey Point, 

 Young Point, and Foxbird Island). These sites are near the diffuser 

 (potentially stressed) and are discussed here. Three sites served as 

 regional controls, but only one of these, Hodgson Island, is 

 considered here. Hydrographic samples were taken monthly at each 

 site during high tide at depths of 0.15 and 3.0 m with a 

 salinometer^thermometer. Light extinction coefficients were deter- 

 mined with a Secchi disk. Incident solar radiation was measured with 

 a pyrheliometer at MYAPCO. 



Algal coverage was determined seasonally (spring, summer, and 

 fall) in three permanent, randomly established, vertical-belt transects 

 per site. Data were analyzed by tidal zones. Percentages were 



