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Abstract

The comparative ecophysiology of nine culture isolates of the eulittoral red alga Bostrychia radicans (Montagne) Montagne collected at sites from several states along the east coast of the U.S.A. was investigated. The growth response in relation to different salinity and light conditions as well as photosynthesis-irradiance curves were studied. In addition, the effect of salt treatment on the content of the isomeric polyols D-sorbitol and D-dulcitol was also studied. All isolates grew between salinities of 5.3 and 70 ppt but with quite different optima and maxima. The isolates were all adapted to low light levels, i.e. growth was already recorded at 2.5 mumol photons . m-2. s-1, and growth rates peaked between 40 and 60 mumol photons . m-2 . s-1. These low-light requirements were also reflected by the photosynthesis-irradiance curves: all plants had low light compensation points (2.5 - 9.7 mumol photons . m-2 . s-1) and low photon fluence rates for initial saturation of photosynthesis (38.1-84.7 mumol photons . m-2 . s-1), indicating that these isolates are ''shade-adapted.'' Isolates from Florida and Georgia synthesized and accumulated both the osmolytes D-sorbitol and D-dulcitol in increasing salinities, whereas only D-sorbitol was present in plants from North Carolina north to Connecticut. D-sorbitol was always strongly involved in osmotic acclimation. In various isolates from the same location in South Carolina, both polyol patterns were found, i.e. D-sorbitol plus D-dulcitol and D-sorbitol only. All data indicate that B. radicans exhibits a broad ability tolerance and a low-light preference, which explain the successful colonization of this alga on various intertidal and shaded substrates. The data also clearly indicate intraspecific differences among the nine isolates, which is interpreted as development of different physiological ecotypes.