Field and culture studies of the life history of Porphyra dioica (Bangiales, Rhodophyta) from Portugal

Aspects of the life history of Porphyra dioica collected in Porto, Portugal, were investigated under laboratory and field conditions. This is one of the most common Porphyra species on the north coast of Portugal and can be found throughout the year. Field studies showed higher percentage cover, from 23% to 66%, from February to May in 2001 and 2002, compared to other times of the year. The effects of temperature, photon flux density (PFD) and photoperiod on growth and reproduction were tested. Zygotospores germinated fastest at 15°C and a PFD of 25 μmol photons m−2 s−1. Growth rate of the conchocelis was more affected by temperature than by photoperiod. In the three photoperiods tested, growth rate was maximal at 15°C, under 25–75 μmol photons m−2 s−1. Conchosporangium formation was greatest at 15°C, 25–75 μmol photons m−2 S−1 light and short-day, 8: 16 h light–dark conditions. In all conditions tested, conchosporangium formation was almost nonexistent in free-floating conditions. Optimal conditions for conchosporangium maturation (15°C, 8: 16 h light–dark and 5–25 μmol photons m−2 s−1) also promoted spore release after 18 weeks. Aeration appeared to be crucial for normal blade development. No archeospores were observed. Preliminary findings of the conditions for growth of the gametophyte stage are also discussed.