Interactions between Cultivated Gracilariopsis lemaneiformis and Floating Sargassum horneri under Controlled Laboratory Conditions

Abstract

The golden tide dominated by Sargassum has become a frequently-occurring marine ecological event that may constitute major biotic threats to seaweed aquaculture. In this study, the interaction between cultivated Gracilariopsis lemaneiformis (GL) and floating Sargassum horneri (SH) was investigated by physiological and biochemical measurements under mono-culture and co-culture with different biomass density ratios of 2:1 (2GL:1SH), 1:1 (1GL:1SH), and 1:2 (1GL:2SH). The relative growth rate, net photosynthetic rate, and NO3-N uptake rate of G. lemaneiformis were significantly greater at the biomass density ratio of 2:1 than at mono-culture. However, these physiological parameters and biochemical composition contents (chlorophyll a and soluble protein) of G. lemaneiformis decreased significantly with increasing biomass of S. horneri. Meanwhile, these physiological and biochemical parameters of S. horneri were greater in all co-culture models than at mono-culture. They decreased significantly with decreasing biomass of G. lemaneiformis. These results indicate that the occurrence of floating S. horneri with low biomass can stimulate the growth of G. lemaneiformis, whereas its outbreak may significantly reduce the production and quality of G. lemaneiformis. G. lemaneiformis cultivation may be beneficial to the increased biomass of floating S. horneri.