ECOTYPIC VARIATION IN CYSTOCLONIUM-PURPUREUM (RHODOPHYTA) SYNCHRONIZES LIFE-HISTORY EVENTS IN DIFFERENT REGIONS

Temperature and daylength responses were determined in culture for iso lates of the red alga Cystoclonium purpureum (Hudson) Batters from Nov a Scotia (NS, Canada), Helgoland (HE, Germany), and Roscoff (RO, Franc e). Most isolates survived temperatures of -1.5 degrees/-2 degrees to 23 degrees C, whereas 25 degrees C was lethal. Only the RO-gametophyte s died at 23 degrees C. Optimal growth conditions were 10 degrees-20 d egrees C in both long and short days for the NS isolates and 8 degrees -15 degrees C and 8 degrees-18 degrees C at daylengths of >12 h for th e RO and HE isolates, respectively. Tetrasporophytes and gametophytes of the NS isolate reproduced at 10 degrees-20 degrees C in long and sh ort days within 5 months. At lower temperatures reproduction was limit ed or slow. The European isolates formed tetrasporangia at 10 degrees- 20 degrees C (HE) or 5 degrees-18 degrees C (RO), spermatangia at 5 de grees-15 degrees C (HE) or 5 degrees-20 degrees C (RO), and carpospore s at 5 degrees-15 degrees C (HE) or 10 degrees-15 degrees C (RO). Shor t days either blocked or delayed reproduction of the European isolates . The phenology of C. purpureum was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. In early spring, growth was rapid and plants started to form reproductive structures. In summ er, tetra- and carpospores were shed followed by degeneration of the u pright axes while branched holdfast persisted. New upright axes and ju venile plants were formed in autumn, but these remained small during t he winter months. Published data indicate that the seasonal pattern at Nova Scotia is similar, although the onset of growth and reproduction is delayed until the end of spring. These observations correspond wel l with the results of the experiments. The life history of C. purpureu m is regulated by temperature and daylength. In the eastern Atlantic, the limiting effect of short days confines growth and reproduction to spring and summer. In the western Atlantic, low winter temperatures al one bring about the same seasonal pattern. After plants have reproduce d, uprights degenerate in spite of continuing favorable conditions.