Growth and reproductive responses of the conchocelis phase of Pyropia hollenbergii (Bangiales, Rhodophyta) to light and temperature

Abstract

Effects of light and temperature on conchocelis growth of Pyropia hollenbergii were evaluated with the hypothesis that conchocelis phase is most adapted to environmental extremes as compared to the gametophyte phase. Growth rates were measured weekly over a 3-month experimental period. Our results have shown that the best growth rate was 6.4 to 7.5 % area day⁻¹ at 25 °C, at photon fluence rates between 50 and 150 μmol photons m⁻² s⁻¹ and at a photoperiod of 15:9 h L: D. The upper temperature tolerance limit of Py. hollenbergii was at 33 °C at a photon fluence rate between 10 and 50 μmol photons m⁻² s⁻¹ and photoperiods of 9:15 and 12:12 h L:D. At a temperature of 5 °C, growth was inhibited (<0.5 % area day⁻¹), but no mortality was observed. Archeospores were detected at 5–35 °C. Maximum archeospore production was observed at 5–10 °C, 50–150 μmol photons m⁻² s⁻¹, and at 9:15 h L:D. The highest number of conchosporangia was detected at 15–20 °C, 100–150 μmol photons m⁻² s⁻¹, and at 15:9 h L:D. The conchocelis phase of Py. hollenbergii is the critical perennating phase and is adapted to survive the highest temperatures in its habitat in the Gulf of California. The monospore and conchosporangium production is controlled by the combination of the temperatures and photon fluence rates.