Effects of temperature, light level, and photoperiod on the physiology of Porphyra umbilicalis Kützing from the Northwest Atlantic, a candidate for aquaculture

Seaweed aquaculture in the Northwest Atlantic has been steadily increasing with five commercial kelp farms already established. Currently, kelp production is limited to winter and spring, and new seaweed crops need to be developed in order to supplement seasonal kelp production. Porphyra umbilicalis is a member of the most economically valuable group of seaweeds known by the Japanese name nori. It is an ideal candidate for aquaculture since it exhibits short production cycles, rapid growth, high nutrient uptake rates, and high pigment and protein content. Further, sexual reproduction appears to be absent in populations in the Northwest Atlantic, which considerably simplifies the production of seed stock. The goal of this study was to determine the conditions that optimize growth, photosynthetic efficiency of photosystem II (F ᵥ/F ₘ), and pigment and protein content of P. umbilicalis. Cultured blades were grown under a matrix of temperatures (10, 15, and 20 °C), light levels (30, 60, 110, and 250 μmol photons m⁻² s⁻¹), and photoperiods (8:16, 12:12, and 16:8 light/dark) in a factorial design for 4 weeks. Growth rates were highest (>9 % day⁻¹) in blades grown between 10 and 15 °C, with light levels ≥110 μmol photons m⁻² s⁻¹ and ≥12 h of light in the day. F ᵥ/F ₘ was significantly affected by photoperiod with this effect dependent on light level; the overall range of F ᵥ/F ₘ values was small. Here, we report detailed information on the growth rate, F ᵥ/F ₘ,, and pigment and protein content of P. umbilicalis grown under 36 treatment combinations. These results provide physiological information on P. umbilicalis from the Northwest Atlantic that will aid in the development of P. umbilicalis aquaculture on a commercial scale.