Aspects of the reproductive phenology ofSaccorhiza dermatodea(Phaeophyta, Laminariales) in Newfoundland

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Abstract
The phenology of Saccorhiza dermatodea is described from the island of Newfoundland, Canada, and the possible roles of daylength and temperature in controlling the annual cycle are examined. New sporophytes first appear in late March or early April and continue to appear until late May or early June; there is, however, considerable year-to-year and local variation in the timing of the first appearance of the new sporelings. The reproductive maturation of the sporophytes is rapid, commencing at the end of September. Within 2 weeks of the first appearance of sorus tissue, 100% of the population is fertile. Fertile sporophytes may persist until July of the following year. Viable zoospores were obtained from the beginning of the fertile period until April of the following year. The annual cycle is correlated with seasonal temperature and daylength fluctuations. The new generation of sporophytes appears when water temperature is at its winter low, nutrients are maximal and daylength and light intensity are increasing. Germlings may be produced by gametophytes derived from spores released in the spring by sporophytes of the previous year, although it is more likely that the species overwinters either as gametophytes or as microscopic sporophytes whose development remains arrested until suitable growth conditions occur. The onset of sporophyte reproduction coincides with the reduction in daylength following the fall equinox; it is apparently not, however, coincident with a major change in water temperature.