Land-Based Tank Cultivation of Ulva spp. (Chlorophyta) from Charleston, South Carolina: A Pilot Aquaculture Study for Seasonal Biomass Production and Potential Anthropogenic Bioremediation

The lack of an established seaweed aquaculture industry in the Atlantic Southeast reflects the persistent challenges in identifying macroalgal species that can consistently produce year-round under regional environmental conditions. As a result, in this study, locally abundant Charlestonian Ulva spp. were selected as sustainable algal candidates for a pilot investigation, due to their resilience to abiotic (e.g., seasonal changes in temperature and nutrients) and biotic (e.g., predation and epiphytes) factors, thus allowing for practical land-based aquaculture. Ulva spp. were analyzed for their seasonal biomass and potential bioremediation applications using the existing land-based aquaculture infrastructure of the SCDNR in Charleston, South Carolina. The biomass of tank-cultivated Ulva spp. was monitored on a biweekly basis for 16 months and was found to be highest (31.8 kg) in the spring, increasing by 22% in just two weeks as water temperatures rose. A synthetic nutrient fertilizer was incorporated into aquaculture at the latter stages of this study to observe the effects on algal biomass while simulating an anthropogenic event. Interestingly, inorganic supplementation did not induce growth but was absorbed by the algal tissue, significantly lowering the δ15N to <7‰. Additionally, Vibrio spp. bacteria proliferated following the inorganic nutrient spike, while coliform populations decreased. Biochemical composition analyses comparing tank-cultivated and wild in situ Ulva spp. revealed variations in essential trace element (e.g., potassium: tank—19,530; wild—5520 mg/kg) concentrations, yet shared similar trace metal (e.g., arsenic: tank—4.47; wild—4.52 mg/kg) and pesticide (e.g., DEET: tank—0.048; wild—0.040 mg/kg) concentrations. This is the first reported macroalgal aquaculture research in South Carolina and serves as a pilot study for future research or commercialization in the Lowcountry and the greater southeastern coastal communities of the United States.