Growth and photosynthesis by Gracilariopsis lemaneiformis (Gracilariales, Rhodophyta) in response to different stocking densities along Nan'ao Island coastal waters

Abstract

Gracilariopsis lemaneiformis (Gracilariales, Rhodophyta) is an important economic seaweed in Southern China. Its use as an alternative source of bioenergy, novel source of bioactives and possible carbon sink has been investigated. The common economic driver of these applications is biomass productivity, which requires an understanding of the effects of different cultivation densities (mat density; 4, 8 and 12 g per cluster) for offshore ‘floating raft’ cultivation to maximise productivities. In the present study, the relative growth rate (RGR) and irradiance-saturated maximum photosynthetic rates (Pmax) of thalli of G. lemaneiformis grown at high stocking density were lower than those of the algae grown at low stocking density. In three weather types (cloudy, overcast to clear and sunny conditions), the net photosynthetic rates (Pn) of the thalli grown at high stocking density were lower than those of the thalli cultivated at low density. The canopy Pn and increased algal gross biomass of the low-density algal mat were lower than those of the high-density algal mat. The increased canopy Pn of G. lemaneiformis in the high-density algal mat decreased under cloudy conditions. We suggest that efforts should be devoted to achieving an appropriate stocking density to obtain a relatively high growth rate, photosynthetic productivity and gross biomass accumulation during G. lemaneiformis maricultivation.