PHYSIOLOGICAL ECOTYPES IN THE MARINE ALGA BOSTRYCHIA-RADICANS (CERAMIALES, RHODOPHYTA) FROM THE EAST-COAST OF THE USA

The comparative ecophysiology of nine culture isolates of the eulittor al red alga Bostrychia radicans (Montagne) Montagne collected at sites from several states along the east coast of the U.S.A. was investigat ed. The growth response in relation to different salinity and light co nditions 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 a nd maxima. The isolates were all adapted to low light levels, i.e. gro wth was already recorded at 2.5 mumol photons . m-2. s-1, and growth r ates peaked between 40 and 60 mumol photons . m-2 . s-1. These low-lig ht requirements were also reflected by the photosynthesis-irradiance c urves: all plants had low light compensation points (2.5 - 9.7 mumol p hotons . m-2 . s-1) and low photon fluence rates for initial saturatio n of photosynthesis (38.1-84.7 mumol photons . m-2 . s-1), indicating that these isolates are ''shade-adapted.'' Isolates from Florida and G eorgia synthesized and accumulated both the osmolytes D-sorbitol and D -dulcitol in increasing salinities, whereas only D-sorbitol was presen t in plants from North Carolina north to Connecticut. D-sorbitol was a lways strongly involved in osmotic acclimation. In various isolates fr om the same location in South Carolina, both polyol patterns were foun d, i.e. D-sorbitol plus D-dulcitol and D-sorbitol only. All data indic ate that B. radicans exhibits a broad ability tolerance and a low-ligh t preference, which explain the successful colonization of this alga o n various intertidal and shaded substrates. The data also clearly indi cate intraspecific differences among the nine isolates, which is inter preted as development of different physiological ecotypes.