Life history and photoperiodic responses in Chondrus giganteus forma flabellatus (Gigartinaceae, Rhodophyta) from Japan

The life history and photoperiodic responses of the carrageenophyte Chondrus giganteus forma flabellatus (Rhodophyta) from Japan were investigated in culture. This entity has a Polysiphonia-type life history and the formation of both tetrasporangia and cystocarps is controlled by daylength. A night-break of 1 h in the middle of a 16 h night was effective in inhibiting reproduction, confirming the classical photoperiodic nature of the response. Tetrasporangia formed at daylengths of 12 h or less, whereas cystocarps only developed at daylengths of 10 h or less. The formation of spermatangia required daylengths of 12 h or less, but production was not inhibited by a night-break of 1 h in the middle of a 16 h night.