this site also exhibited symptoms of nitrogen limitation. In 

 contrast, Ammen Laminaria at the 30 m site exhibited a 

 considerable increase in cellular nitrate (Fig. 15) , and retained 

 a relatively small pool of mannitol (Fig. 13) , suggesting that 

 light rather than nitrogen was the limiting factor at this site. 

 The inability of coastal L. digitata to utilize the inorganic 

 nitrogen available at the Ammen site (Fig. 15) suggests that these 

 plants were severely energy limited. 



Overall, the data in this paper support the idea that the 

 Ammen Laminaria population is genetically different from the 

 coastal population of L. digitata which it closely resembles. The 

 Ammen population seems well adapted to life in a low irradiance 

 environment. However, caution is necessary when interpreting 

 these results for two reasons: First, the plants used were mature 

 sporophytes and it is possible that the observed responses 

 reflected their exposure to previous growth conditions rather than 

 responses to conditions during the transplant experiments. 

 Second, although reciprocal transplants were used to study the 

 response to light, it is clear that other environmental factors 

 (especially nitrogen availability) influenced the results. 

 Because of this, the differences in the photosynthetic physiology 

 of the two groups of plants have been investigated in more detail 

 under controlled laboratory conditions. These results will be 

 presented elsewhere. 



ACKNOWLEDGEMENTS 



Ships and submersibles were provided by the National 

 Oceanographic and Atmospheric Administration's National Undersea 

 Research Program through the University of Connecticut at Avery 

 Point. Technical and scuba assistance were funded in part by an 

 NSF grant (OCE-8600262) to Robert S. Steneck. Eguipment for 

 photosynthetic measurements was purchased through an NSF grant 

 (OCE-8700763) to Ian R. Davison. Janet E. Kuebler was supported 

 by a research assistantship from the Center for Marine Studies at 

 the University of Maine. The authors would like to express their 

 sincere gratitude to Ms. C. Pfister for her invaluable assistance 

 throughout this project. 



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