Seaweed biotechnology implications to aquaculture

Seaweeds are valuable resources for economically important phycocolloids such as agar, carrageenan, and alginic acid and are also being used in food, feed, fertilizer, cosmetics, pharmaceutical, nutraceuticals, biofuel, and agro-based applications. Seaweeds are ecosystem engineers that provide space for many marine organisms and structure and maintain the coastal biodiversity of sea. The Food and Agriculture Organization (FAO 2018) report stated that global production of seaweeds annually has been estimated at 32.4 million tons fresh, with a market value of USD 11.7 billion. Almost all of the seaweed biomass production (97.1%) was produced through aquaculture practice, while a tiny fraction was harvested from the wild stocks. The continued and indiscriminate harvesting of seaweeds from its natural beds over a long period has resulted in dwindling of resources in nature and that in turn severely affected the dependent seaweed industries as well. The gap between the demand and supply can be bridged through mariculture practices of seaweeds by cultivating the useful species on commercial scale. Only 10 species are being commercially cultivated, and among these Eucheuma spp. (35%), Laminaria japonica (27%), Gracilaria spp. (13%), Undaria pinnatifida (8%), Kappaphycus alvarezii (6%), and Porphyra spp. (4%) have a major share in global seaweed biomass production (FAO 2018). The repeated vegetative propagation of the same plants has led to a loss of genetic diversity and resulted in slow growth, reduction in phycocolloid yield with poor quality of phycocolloid, and susceptibility to disease. In order to improve quality of seed material, several techniques such as tissue culture/micropropagation, protoplast isolation and fusion, hybridization, gene transfer, grafting, utilizing gene marker, parthenocarpy, chimerism, chemical-induced mutants, and haploid spore are being employed. Tissue culture/micropropagation technique is widely used for the production of a large number of individuals within a short period and also selection of higher yielding strains that could be used as future seedlings for seaweed cultivation. Protoplast fusion and gene transfer method are advanced methods for developing good quality seedlings for commercial production. Among chemical mutagens, N-methyl-N′-nitro-N-nitrosoguanidine was found efficient for developing mutants in seaweeds and spermine, and a polyamine was also used for early maturation of cystocarp and mass release of spores in Gracilaria cornea. Grafting, a simple conventional method, is being employed for intragenic species. In India, somatic hybridization and tissue culture methods are employed for good quality seedling production in K. alvarezii and Gelidiella acerosa for commercial farming, and seedlings developed from tissue culture showed higher biomass yield, growth rate, and agar/carrageenan qualities than normal/wild seedlings.