Short term effects of irradiance on the growth of Pterocladiella capillacea (Gelidiales, Rhodophyta)

  • Rita F. Patarra 1cE3c - Centre for Ecology, Evolution and Environmental Changes/ Azorean Biodiversity Group and University of Azores, Faculty of Sciences and Technology, Department of Biology, 9501-801 Ponta Delgada, Azores


Pterocladiella capillacea has been economically exploited for agar extraction in the Azores for many years. Harvesting dropped to a full stop in the early 1990s due to a population collapse, but restarted in 2013. Since then it has been intensively harvested and overexploitation must be prevented, with both sustainable harvesting and effective cultivation practices. This study represents the first attempt to determine optimal conditions for P. capillacea production in the Azores, and evaluates its vegetative growth in two experiments using von Stosch’s medium designed to test entire thallus and tips portions response to different irradiances (30, 70 and 150 μmol photons m-2 s-1). The best relative growth rate (RGR) was recorded at 150 μmol photons m−2 s−1 for the entire thalli and tips after two-weeks and three-weeks, respectively, indicating that an acclimation period is necessary to assure the growth of this alga under experimental conditions. Higher RGR was obtained at higher irradiance (3.98 ± 2.10% fm day-1), but overall, growth rates were low or negative. Epiphytes were a serious problem towards the end of the entire thallus experiments, where Feldmannia irregularis proliferate at all irradiances. Future cultivation approaches complemented with other relevant environmental factors (e.g. pH, photoperiod, salinity), are recommended.