Optimizing cultivation and shipping environments for an edible green alga, Caulerpa chemnitzia var. laetevirens (Bryopsidales) from Japan: Effects of temperature, irradiance, desiccation and salinity on photochemical efficiency

Abstract

The effects of four stressors, temperature, irradiance, desiccation and salinity, on the photochemical efficiency (ΔF/) of an edible green alga, Caulerpa chemnitzia var. laetevirens from Kagoshima, Japan, were determined for optimizing cultivation and shipping environments using a pulse amplitude modulation-chlorophyll fluorometer. The ΔF/ remained stable at 24–34°C during the 3-day temperature exposures ranging from 8 to 36°C; however, it dropped at higher and lower temperatures. During continuous exposure for 6 h to irradiance levels of 400 (low) and 1000 (high) μmol photons m⁻² s⁻¹ at 16, 24 and 32°C, the decrease in ΔF/ was pronounced at high irradiance. Moreover, ΔF/ also dropped at 16°C even under low irradiance, suggesting the occurrence of low temperature–light stress. Desiccation experiments under 50% humidity and up to 5 h of aerial exposure at 24°C and dim light (20 μmol photons m⁻² s⁻¹) indicated that ΔF/ was well tolerated within 1 h of desiccation; however, it dropped quickly as the desiccation period prolonged, suggesting that, if more than 20% of the interior water was lost, ΔF/ dropped progressively. However, during a similar experiment up to 14 days of aerial exposure under saturated humidity (99%) and dim light (12:12 h light/dark photocycle), as the interior water of the frond was maintained because of the saturated humidity, ΔF/ appeared to be well maintained for up to 5 days. Similar to desiccation, this alga exhibited stenohaline characteristics (30–40 psu) under the salinity gradient of 0–80 psu for up to 7 days of culture at 24°C and under dim light (12:12 h light/dark). In conclusion, this alga can be cultivated by modifying the techniques used for cultivating Japanese Caulerpa lentillifera and adjusting its environment accordingly. To ensure appropriate shipping conditions, it is essential to maintain saturated humidity in a plastic container at room temperature.