Growth responses of Pterocladiella capillacea (Rhodophyta) in laboratory and outdoor cultivation

The growth and photosynthetic responses of Pterocladiella capillacea to NH₄, PO₄, CO₂-enrichment, pH, irradiance and temperature were evaluated for winter or summer plants cultivated under laboratory and outdoor settings. In the laboratory, using a gradient table, optimal growth temperature and irradiance for winter plants occurred at 10-20°C and 100 μmol photon m^-2 s^-1, averaging 24.3% per week. The optimal growth conditions found for summer plants were 10-20°C and 20 μmol photon m^-2 s^-1, averaging 29.0% per week. In a pH-stat cultivation system photosynthetic rates and growth rates were largely unaffected by pH in the range 6.5-8.5, however, they both decreased significantly above 8.5. In outdoor settings, using 40 L tanks, P. capillacea was more responsive to the frequency the algae were fed with NH ₄ and PO₄ rather than the relative concentrations of these nutrients. The average growth rates during winter were 28.3% and 12.5% per week when NH₄ and PO₄ were included once and twice a week for 24-h periods, respectively, while summer plants grew 15.0% and 25.3% per week at these nutrient regimes. Algae grown in seawater (containing 13.8 ± 1.8 μM CO₂) or CO₂-enriched seawater (averaging 33.7 ± 13.2 μM CO₂) had similar growth rates or even reduced productivity under CO₂-enrichment during winter. Concentrations of chlorophyll a were in average significantly higher in winter as compared to summer especially when nutrients were included twice a week. Phycoerythrin levels were also higher for plants fed with nutrients twice a week particularly during summer time. Although agar yields were limited and not seasonally dependent, this study shows high growth capacity for P. capillacea as compared to previous investigations. Future mariculture prospective using current tank cultivation techniques for this species will likely depend on market demands for high quality agar.