Distribution of Microalgae Supplemental Feed in a Land-Based Integrated Multi-Trophic Aquaculture System

With the current decline in world fisheries it is necessary to develop more sustainable methods of marine resource production. An Integrated Multi-Trophic Aquaculture (IMTA) system is one such method. In an IMT A system the waste nutrients of fed species are used to culture other species, thus increasing the efficiency of feed use. A land-based IMTA (LB-IMTA) system was utilized in the cunent study in which one of the waste nutrient utilizing species was oysters. Oysters in this system were determined to be not getting an adequate amount of waste nutrient feed necessary for normal growth. Therefore, oysters would need supplemental microalgae to grow normally, however the addition ofmicroalgae to the LB-IMTA might have detrimental effects, e.g., spreading throughout the system and changing the balance of nutrient flow or blooming throughout the system. Therefore, a study was designed to determine the fate of microalgae added to an LB-IMTA under a worst case scenario. With no oysters in the LB-IMTA system (total volume 61,740 L), 30 L ofmicroalgae (average density= 6.3x106 cells/mL) were added into the oyster tanks. Microalgae cells were tracked over time by sampling at distinct sites throughout the LB-IMTA system. Microalgae concentrations (i.e., #/mL) in the samples were determined with the aid of a Flocam®. Three microalgae species were individually tested: Dunaliella tertiolecta, Chaetoceros gracilis, and Isochrysis galbana Caribbean strain. Overall, the data indicated that all three micro algae species spread to almost all parts of the system after only 15 minutes, but nearly all of the microalgae was gone after 3 hrs; avg. = 8 cells/mL, which was 0.26% of the average theoretical homogenous concentration (3061 cells/mL). The primary removal of microalgae was most likely by the bead filters, which remove fine particles. The filtration components of the HBOI LB-IMTA were able to remove the excess microalgae and should limit any potentially detrimental effects caused by an overabundance of microalgae.