EFFECTS OF REDUCED TEMPERATURES 

 ON PREVIOUSLY STRESSED POPULATIONS 

 OF AN INTERTIDAL ALGA 



R. L. VADAS,* M. KESER,t and B. LARSONf 



*Departments of Botany and Plant Pathology and Oceanography and Zoology, 

 and tDepartment of Botany and Plant Pathology, University of Maine, 

 Orono, Maine 



ABSTRACT 



Relocation of a surface thermal discharge through a multiport diffuser and 

 removal of a causevi^ay substantially reduced temperatures in an estuary 

 surrounding a nuclear power plant. Although stressed and moribund during 

 thermal discharge, basal portions of adult thalli of Ascgphyllum nodosum 

 showed considerable resilience to thermal stress and potential competition from 

 other species and survived. Previously stressed populations recovered fully; all 

 measures of vigor being indistinguishable from prestress years. Growth in apical 

 tips was sensitive to small shifts in ambient water temperature, suggesting that 

 Ascophyllum might be a good indicator for thermal and perhaps other stresses in 

 marine ecosystems. Growth data indicate that thermal enhancement occurs in 

 Ascophyllum, artificially from thermal effluent and naturally from increased 

 insolation to newly exposed mud flats. 



Altering physical, chemical, or biological components of ecological 

 systems often provides insight into the structure and role of 

 individual components. Manipulative experiments, for example, are 

 powerful tools in analyzing causal relationships in marine com- 

 munities (Connell, 1961; Paine, 1966; Dayton, 1971). Gradients of 

 stress, whether natural or man-induced, also provide the opportunity 

 for gaining insight into the responses of species to such stresses and 

 potentially to their roles in community organization. 



The Maine Yankee Atomic Power Company (MYAPCO) pro- 

 duced a sequence of varying thermal and physical stresses on rocky 

 intertidal communities in Montsweag Bay, Maine. The sequence 



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