Photosynthesis and growth rates of Laurencia brongniartii J. Agardh (Rhodophyta, Ceramiales) in preparation for cultivation

Abstract

Laurencia brongniartii is usually found at depths below 4 m, but can be found in shallow subtidal areas in crevices and on the walls of a coral reef in Amami Oshima Island, Kagoshima Prefecture, Japan, where irradiances were significantly lower than those at similar depths in open water. In preparation for the possible cultivation of this species for its antibiotic compounds, the effects of temperature and irradiance on photosynthesis and growth were measured. Photosynthesis and growth rates of L. brongniartii explants were highest at 26 and 28 °C, which closely corresponded to temperatures found during August to late December when it was most abundant. The estimated maximum photosynthesis rate (P _max) was 4.41 μmol photon m⁻² s⁻¹ at 26 °C and 4.07 μmol photon m⁻² s⁻¹ at 28 °C. Saturating irradiance occurred at 95 μmol photon m⁻² s⁻¹ at 26 °C and 65 μmol photon m⁻² s⁻¹ at 28 °C. In contrast, growth experiments at 41.7 μmol photon m⁻² s⁻¹ caused bleaching of explants and the maximum growth rate observed during the study was 3.02 ± 0.75% day⁻¹ at 28 °C and 25 μmol photon m⁻² s⁻¹. The difference in the saturating irradiance for photosynthesis and the irradiance that caused bleaching in growth experiments suggests that long-term exposure to high irradiance was detrimental and should be addressed before the initiation of large scale cultivation.