World Aquaculture March 2019

WWW.WA S.ORG • WORLD AQUACULTURE • MARCH 2019 35 sunlight intensity treatments. Seaweeds were low in fat, high in carbohydrates (which includes agar and fiber), high in ash, representing minerals, and high in protein. Description of Seaweed Based on visual observations, the color, morphology and fouling of the Gracilaria differed among treatments. Seaweed grown in 100 percent sunlight was orange to red, whereas seaweed grown in 50 percent sunlight was a dark red-brown and, at the lowest light intensity, the seaweed was an even darker red-brown. Seaweed in the two lower light treatments had the most appealing look and would be desirable products for human consumption marketing purposes. Using a dissecting microscope, the morphology of the 100 percent sunlight treatment seaweed showed nubby tips on the thalli and had more branching on the tips compared to seaweeds at the lower light intensities, which had elongated branches (Figs. 8a, b). The greater amount of branching on the tips is typically seen in faster-growing seaweed cultures. By week 5, there was fouling in all the treatments (Fig. 9). To obtain an approximate percentage of fouling, the fouling was removed from seaweed samples for each treatment and replicate (n=2) and weighed. Fouling was greatest at 100 percent sunlight intensity, with fouling at 47 percent of the culture. There was considerably less fouling in the lower light intensity treatments: 18 percent at 50 percent sunlight intensity and 9 percent at 25 percent sunlight intensity. The fouling algae at 100 percent sunlight intensity were the green seaweeds Ulva lactuca, U. intestinalis and two Chaetomorpha spp. There were only two fouling species found in the two lower sunlight intensities: Chaetomorpha sp. and a small amount of U. lactuca . Fouling was minimal at the beginning of the study. The U. lactuca is also grown in the IMTA system and could have easily contaminated the Gracilaria cultures because it is part of the same water system. As the 100 percent sunlight treatment seaweed became more fouled it was difficult to keep the seaweed tumbling with the aeration and the seaweed in some places would become very thick and almost rope-like with fouling. To help reduce fouling in cultures it would be beneficial to have extra tanks for drying and cleaning between weekly harvests. Adding some level of shade will also help reduce fouling and produce a dark red seaweed that would be desirable for the market. Crude Agar Extraction The purpose for conducting crude agar extraction was to understand how much agar could be derived from the seaweed for food purposes. For example, boiling dried Gracilaria in freshwater with cinnamon and nutmeg for 10 min is the beginning of making the thick sea moss drink that is popular in the Caribbean. After boiling, the seaweed is strained from the liquid and sugar and milk is added. The sea moss drink can be served warm or cool. The technique used to determine the native, unmodified agar content of the Gracilaria grown in the three sunlight intensity treatments was a simplified crude agar extraction process described by Gunasekera (1963). Oven-dried seaweed was crushed into small particles by hand and added to freshwater in a 2 percent mixture (19 g seaweed to 800 mL freshwater) and heated to 95-100 C for 4 h. A 2-L beaker with the mixture was placed on a hot plate with stirrer and an aluminum foil cover was placed loosely over the top to reduce evaporation. Small amounts (50-200 mL) of fresh water were periodically added during the extraction to bring the volume back to 800 mL as the water evaporated. The hot solution was poured through a funnel that was positioned over a 1.2-L plastic container that was placed on ice (Fig. 10). A 250-µm Nitex screen was placed inside the funnel to capture solids and allow liquid agar to pass through. A spatula was used to help guide the liquid through the screen and funnel. The liquid in each iced container would form into jelly agar within 20-30 min. Each container with the agar solution was placed in a freezer for 12 hours. Large ice crystals formed in the containers and when defrosted most of the water was drained away, leaving the concentrated agar gel. This moist agar was placed in a drying oven and dried for 72 h at 50-65 C. The agar yield was calculated by dividing the agar DW by the initial DW of the seaweed used in the extraction (19 g). The agar extraction was done on week 5 for each treatment and replicate (n = 2). ( C O N T I N U E D O N P A G E 3 6 ) FIGURES 8 a AND 8 b . Figure 8 a and b. Morphological differences in the Gracilaria tikvahiae grown at three sunlight intensities: a) 100 percent and b) 50 percent and 25 percent (Photo: Megan Davis, FAU HBOI).