64 MARCH 2023 • WORLD AQUACULTURE • WWW.WAS.ORG Dulse Production Trials After system construction, two trials were run; neither using any fertilizer inputs. The average starting dulse weight was 60 g per panel (Trial 1) and 65 g per panel (Trial 2). Trial 1 ran for one week, and Trial 2 ran for three weeks. During both trials, water flow rates were maintained at 189 L/ hr, and temperature recorded hourly via a HOBO® temperature data logger (Onset, Bourne, MA) placed in the tank, and was maintained between 12 and 15 C with an average of 13.5 C. Dulse weight was measured at the beginning and end of each trial, with an additional weight check at the end of week two in Trial 2. Once the trial period ended, an analysis of growth was conducted. Weights were determined by packing dulse into corresponding mesh bags and spinning them in an industrial salad spinner for 30 seconds. Then the dulse was placed on a tared balance and the weight recorded. Rapid growth of dulse occurred within the pilot aeroponics system. The final weight was 149 g (Trial 1) and 236 g (Trial 2) (Fig. 2). Dulse growth was 12.7 g/d (Trial 1) and 8.1 g/d (Trial 2). Total dulse yield was 94 g/m2-d (Trial 1) and 60 g/m2-d (Trial 2). Specific growth rate (SGR; ln (final weight – initial weight)/number of trial days)) was 15 percent/d (Trial 1) and 11 percent/d (Trial 2). SGR in tumble culture tanks can reach 15 percent/d under ambient summer light conditions (Demetropoulos and Langdon 2004). A similar panel experiment in tanks had an SGR of 10-14 percent/d (Evans et al. 2021). Bottom panels produced more dulse biomass than top panels (Fig. 3), most likely due to dulse on the bottom panel receiving extra water from the misters at the top of the system. As the need for food production grows, so does the need to find new cultivation methods for marine organisms. Macroalgae are now receiving more focus for aquacultural development in the United States as there has been an increased demand for environmentally responsible and sustainably grown protein (Kim et al. 2019). With a composition of 20 percent protein along with a nutritionally complete amino acid profile (Mouritsen et al. 2013), dulse (Palmaria spp.) is poised to become a more common food source for both people and farmed animals. Pacific dulse (Palmaria mollis) is primarily grown in tumble culture, a method that uses tanks of seawater with aeration to suspend and circulate the dulse (Evans et al. 2021). By following vertical terrestrial farming techniques (Despommier and Ellingsen 2008), an aeroponics system was recently developed as a way to grow dulse using seawater misters, eliminating the need for large tanks of water. The Pilot Dulse Aeroponics System A pilot dulse aeroponics system (Fig. 1) was constructed using a 200-L Kalwall tank (Kalwall Corporation, Manchester, NH), four 1-m PVC pipes fitted with eight 7.6 L/hr misters (Dig Corporation, San Diego, CA), and a 10-µm filter (PRM Filtration, Butner, NC). Dulse was placed on vertical mesh panels inside the tank, between the misters. The panel structure was divided into two square 37 cm × 37 cm sections. On each of these sections, five dulse plantlets were oriented to obtain optimal seawater spray and light. An external LED light array (ScynceLED, Mesa, AZ) provided 26.0 mol photons/m2-d and ran continuously during each trial. Is Aeroponics the Future of Pacific Dulse Cultivation? Stephanie King, Ford Evans, Hillary Egna and Chris Langdon FIGURE 1. Schematic drawing of the dulse aeroponics system. FIGURE 2. Dulse weights for top and bottom panels during both trials, with a fitted growth curve.
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