LATITUDINAL TRENDS IN THE GROWTH AND REPRODUCTIVE SEASONALITY OF DELESSERIA-SANGUINEA, MEMBRANOPTERA-ALATA, AND PHYCODRYS-RUBENS (RHODOPHYTA)

The seasonality of Delesseria sanguinea, Membranoptera alata, and Phyc odrys rubens (Rhodophyta) was studied at Helgoland (North Sea, Germany ) and Roscoff (Brittany, France). Plants were collected at bimonthly i ntervals, and growth and reproduction were monitored. Growth of blades was observed mainly in spring, although small blades were found on pl ants of M. alata and P. rubens all year round. In summer, plants start ed to degenerate and in autumn they became fertile. The reproductive s eason of D. sanguinea lasted from October to February/April at both lo cations, whereas reproductive plants of M. alata and P. rubens were fo und until April at Helgoland and until June and August, respectively, in Roscoff. Lower winter temperatures at Helgoland than at Roscoff may have caused these differences in the duration of the reproductive sea son. Using published data, the seasonal patterns at Helgoland and Rosc off were compared to those found at other locations (e.g. Barents Sea; Maine, USA; Isle of Man, UK) and local temperature/daylength conditio ns. Blade growth was synchronized across all populations and occurred in spring when temperatures were usually still suboptimal for growth. Maximum reproduction was generally found in the colder half of the yea r but started earlier in autumn in the Barents Sea. Adaptive strategie s in the seasonal control of growth and reproduction are discussed. Ad equate timing of the history events (e.g. appearance of juveniles in s pring) appears more important than maximal growth and reproduction of adults during the season with the most favorable temperatures.