Adaption, Breeding and Cultivation of Seaweeds in the Context of Global Climate Change

Aquaculture of marine macroalgae (i.e. seaweeds) such as the kelp Undaria pinnatifida is expected to contribute to future food and biomass production. Although macroalgal survival, biomass, and morphology are strongly affected by the density of individual plants in natural environments, little is known about the cultivation density (individuals per 1 m of cultivation rope) of macroalgae required to optimize aquaculture production, commercial profit (sales – labor expenses for processing), and quality as food. The present study examined the effect of increasing the cultivation density of U. pinnatifida from 10 to 200 individuals m^-1 on survival rate, biomass production, profit, and morphological features related to quality as food. Survival rate was almost 100% in all treatments, indicating self-thinning did not occur. Biomass production increased with increasing density, suggesting that the maximum density possible is in excess of 200 individuals m^-1. However, although profit rose with increasing density from 10 to 120 individuals m^-1, it did not rise further if density was further increased. Moreover, some morphological features related to quality increased or decreased with increasing density. On balance, these results suggest that 80-120 individuals m^-1 is an appropriate density range to optimize production of this species in terms of both profit and quality as food. However, only 10-30 individuals m^-1 was the density best suited to enhance production of the sporophyll form, which is known to be a nutritious food both for humans and sea urchins.

Laver is the most widely farmed seaweed with the largest culture area in China. The spatio-temporal variations in composition, diversity, and functional properties of bacteria in seawater as well as the environmental variables of seawater in a large-scale laver farm in China were studied. Both the community richness indices and Shannon index in the laver farming area remained at a relatively stable level during laver cultivation. Fifty-nine prokaryotic phyla were detected in all samples, however, only six of these phyla accounted for 98.84% of all sequences. Proteobacteria, Gammaproteobacteria, Rhodobacterales, Rhodobacteraceae, and Octadecabacter were the most predominant bacterial taxa at different levels of classification. The keystone bacterial taxa were Bacteroidetes, Pseudomonadales, Rhodobacterales, Flavobacteriales, Loktanella, and Pseudoruegeria based on network analysis. Members of representative bacterial biomarker taxa in November may be associated with degradation of algal cell wall polysaccharides. A significant increase in metabolic exchange and transformation nutrients occurred in the seawater during the early and late stage of laver cultivation, indicating that the laver reproductive activities (i.e. the formation/release activities of archeospores and zygotospores) probably drove the variation of metabolic functional diversity of bacterial communities. Based on Mantel test and redundancy analysis, we found the hydrographic parameters (e.g. salinity, temperature, DO, pH) as well as the key carbon (e.g. POC, DOC) and nitrogen parameters (e.g. nitrate, DIN, DON, TDN) were crucial environmental variables to shape the bacterial community composition in the surrounding seawater of laver farm. In a word, our results suggested that the microbial community structure and function significantly changed across the different succession stages during laver cultivation. This work provides new insights on the characteristics of bacterial communities in a large-scale laver farming system and solidifies the importance of laver farming in shaping seawater microbiomes.