LIFE-HISTORY REGULATION IN THE SUBTIDAL RED ALGA CALLIBLEPHARIS-CILIATA

The life-history strategy of the subtidal red alga Calliblepharis cili ata has been studied in the field and in laboratory culture. Bi-monthl y observations on a C. ciliata population at Roscoff (Brittany, France ) revealed a clear seasonal pattern. In April young plants appeared an d grew through the summer until they became reproductive in autumn. Re lease of tetraspores and carpospores occurred in winter, between Febru ary and April. Responses to temperature and daylength were determined in culture for an isolate from Roscoff. Tetrasporophytes and gametophy tes survived temperatures of c. 5 degrees C up to 25 degrees C, but we re undamaged only at 8-20 degrees C. Blade growth took place at 8-18 d egrees C in long days and at 8-12 degrees C in short days. Tetrasporop hytes 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 respo nses to temperature and photoperiod found in culture accounted well fo r the seasonal pattern in growth and reproduction observed in the fiel d. C. ciliata is a ''season anticipator'': the favourable growing seas on in spring is anticipated by reproduction during the winter period.