Land-based seaweed (Gracilaria) cultivation systems may provide products with high quality and biosafety for human consumption, as well as for other high value applications. However, a limitation for this land based system is high management costs. The objective of this study was to determine if the management costs for Gracilaria cultivation can be reduced without a decrease in productivity by using CO 2 injection along with a high stocking density and high photosynthetically active radiation (PAR), and commercially available fertilizers. When Gracilaria tikvahiae was cultivated at a high stocking density and high PAR, coupled with CO 2 enhancement, the productivity was significantly higher than that at a lower stocking density, low light without CO 2 injection. We also found that G. tikvahiae grown in a medium of commercially available fertilizer (Jack's Special, JS) showed a similar growth rate and productivity to that grown in von Stosch's enriched (VSE) seawater, while the cost for JS media is only 2% of the cost for VSE. These results suggest that CO 2 injection and commercial fertilizer may be a potential way to provide sustainability in land-based Gracilaria cultivation systems.Key Words: carbon dioxide; fertilizer; Gracilaria; land based aquaculture; nutrients, sustainability
INTRODUCTIONGracilaria is one of the world's most cultivated seaweeds with over 0.8 million tons of annual production and nearly $160 million annual values (Food and Agriculture Organization of the United Nations 2014). Most of the biomass is used in the phycocolloid industry as the main source of food grade agar (Pereira and Yarish 2008) and as a feed for animals (Qi et al. 2010, Johnson et al. submitted). Gracilaria contributes approximately 66% of the total agar production (Pereira and Yarish 2008). Gracilaria has been cultivated mainly in three different ways, including open water, pond or tank cultures (Hanisak 1987, Abreu et al. 2011. In general, both open water and pond cultures require a nursery (tank culture) system to provide sufficient seedstock through vegetative propagation. One important advantage of tank cultivation is the ease of controlling the culture system (Pereira et al. 2013). This ensures that production meets high quality standards and biosafety for human consumptions, as well as for other high value applications such as cosmeceutical or pharmaceutical products. A limitation for tank culture, however, is high management costs (Hanisak and Ryther 1984, Caines et al. 2014).One way to overcome this challenge is to cultivate seaweed at high stocking densities. However, Lapointe and Ryther (1979) reported that the pH in culture tanks of Gracilaria tikvahiae when grown at a high stocking density increased to ca. 9.0, which resulted in the reduction of yields. Studies on Chondrus crispus revealed that the first inorganic element to be depleted in tank cultures is inorganic carbon, due to rapid absorption of CO 2 /HCO 3 -Received April 10, 2014, Accepted August 26, 2014 *Corresponding Author E-mail: jang.kim@uconn....