Life-history regulation in the subtidal red alga Calliblepharis ciliata

The life-history strategy of the subtidal red alga Calliblepharis ciliata has been studied in the field and in laboratory culture. Bi-monthly observations on a C. ciliata population at Roscoff (Brittany, France) revealed a clear seasonal pattern. In April young plants appeared and grew through the summer until they became reproductive in autumn. Release of tetraspores and carpospores occurred in winter, between February and April. Responses to temperature and daylength were determined in culture for an isolate from Roscoff. Tetrasporophytes and gametophytes survived temperatures of c. 5 degrees C up to 25 degrees C, but were undamaged only at 8-20 degrees C. Blade growth took place at 8-18 degrees C in long days and at 8-12 degrees C in short days. Tetrasporophytes reproduced at 8-12 degrees C at daylengths of 8 and 10 h but not 12 h or more. No reproduction was observed in gametophytes. The responses to temperature and photoperiod found in culture accounted well for the seasonal pattern in growth and reproduction observed in the field. C. ciliata is a ''season anticipator'': the favourable growing season in spring is anticipated by reproduction during the winter period.