World Aquaculture March 2019

32 MARCH 2019 • WORLD AQUACULTURE • WWW.WA S.ORG organic matter (urchins, shellfish) and hence the biological and chemical processes in the system are complementary (Wills et al. 2012, Laramore et al. 2018) (Fig. 1). These types of IMTA systems are extremely flexible (Chopin 2006, Wills et al. 2012) and are receiving more attention because nutrients are recycled to grow multiple species (Lockwood 2018). The goal of this study was to explore how Gracilaria tikvahiae grown in the HBOI IMTA outdoor tank system could produce seaweed for human consumption. The seaweed was cultured at three levels of sunlight to determine the light intensity that would produce seaweed with a desirable morphology, growth rate and nutritional profile. Study Design The 6-wk study (June 14 — July 26, 2018) was conducted in the outdoor component of the HBOI IMTA system (Fig. 2). There were three natural sunlight intensity treatments (100, 50 and 25 percent), each with two replicates. Tanks in the 100 percent treatment were exposed to full sunlight, tanks in the 50 percent treatment were covered with 50 percent shade cloth and tanks in the the 25 percent sunlight were covered with 75 percent shade cloth. Shade cloth was attached to ¾” PVC pipe frames with zip ties (Fig. 3). Seaweed tanks were rectangular fiberglass troughs (3.1 m × 0.66 m × 0.33 m; L × W × H) (Fig. 4). Water entered the tank at one end through a 1” PVC pipe with a flow rate of 2.5 - 2.7 L/min. Water returned to the IMTA system through a 2” PVC standpipe with a mesh cover that was located at the opposite end of the tank. Tanks were filled with 573 L of water, leaving a 5-cm freeboard. The turnover rate for each tank was 6-7 times per day. An air blower provided aeration and turbulence to the seaweed cultures through four ¾” PVC pipe airlines that extended the length of the tank bottoms and were drilled with small holes. The Gracilaria tikvahiae used in the study was sourced Overview The farming of aquatic plants, overwhelmingly comprised of seaweeds, has been growing rapidly throughout the world and is now done in 50 countries (FAO 2018). Cultivated seaweed production has increased by nearly 50 percent over the last ten years and the global demand for seaweed has surpassed current supply. In 2016, the global seaweed market was valued at US$ 11.7 billion for approximately 30 million t of live weight volume. Of this production, 97 percent of seaweed was farmed. Seaweeds are a commodity used in the food industry and for animal feed, fertilizers, pharmaceuticals and cosmetics. The red seaweed Gracilaria spp. represents 14 percent (4.2 million t live weight) of global total seaweed production (FAO 2018). The popularity of Gracilaria is due to its contribution to the global agar market, especially from Indonesia and China, which are the largest producers (Porse and Rudolph 2017). In 2015, the world agar market was valued at US$ 246 million (US$ 17/kg) for 14,500 t of agar sales and is estimated to continue growing at 2 percent per year (Porse and Rudolph 2017). Agar is widely used in the food industry, for pharmaceuticals and cosmetics, and in chemical and scientific research. Gracilaria , also known as ogo, ogonori and sea moss, is gaining popularity in the USA as a food item. It is consumed as a salad vegetable, as an addition to poke dishes in Hawaii and Asian countries, used to make a beverage called sea moss or Irish moss in the Caribbean (Smith et al. 1984), used as an accent to seafood, other culinary dishes, cocktail beverages in California and can be boiled and added to kanten deserts and jellies as a thickening agent. Gracilaria tikvahiae , is found in the semi-tropics to tropics (Littler et al. 2008) and has been farmed since the 1970s at Florida Atlantic University —Harbor Branch Oceanographic Institute (HBOI), Fort Pierce, Florida (Hanisak and Ryther 1984, Hanisak 1987). For the past six years, G. tikvahiae and the green alga Ulva lactuca (sea lettuce) have been incorporated into the HBOI land-based Integrated Multi-Trophic Aquaculture (IMTA) system. In the HBOI IMTA system, aquaculture of fed organisms (finfish and shrimp) is combined with the culture of organisms that extract dissolved inorganic nutrients (seaweeds) or particulate Growing Red Seaweed for Human Consumption in an Integrated Multi-Trophic Aquaculture System Tyler C. Bianchine, Megan Davis, Paul S. Wills and M. Dennis Hanisak FIGURE 1. Diagram of the IMTA system components at HBOI (Figure: Paul Wills, FAU HBOI).