Influence of temperature and photoperiod on the re-attachment process ofGelidium sesquipedale (Clem.) Born. et Thur. (Gelidiales: Rhodophyta)

Thalli of the economically important rhodophyteGelidium sesquipedale were cultured for 8 weeks under laboratory conditions, and the influence of temperature and photoperiod on the re-attachment process were studied. Four different temperatures (16, 18, 20, 22 °C) and four different photoperiods (6:18, 12:12, 14:10, 16:8) were used and the results obtained in the thalli responses such as apical growth (measured as elongation of principal apex), rhizoidal cluster production and number of necrotic patches were tested.During the re-attachment process, the best results were obtained at temperatures of 16–18 °C, when rhizoidal cluster production was high and necrotic patch development was low (18 °C) or absent (16 °C). Temperatures of 20 and 22 °C favoured high rhizoidal cluster production, but also a high production of necrotic patches that finally led to death. The results suggest that long-day photoperiods (14:10, 16:8) produce a higher number of rhizoidal cluster bands than short-day photoperiods (6:18) at the same temperature.