Increased Production and Water Remediation by Land-Based Farm-Scale Sequentially Integrated Multi-Trophic Aquaculture Systems—An Example from Southern Taiwan

Carbon capture by macroalgae Sarcodia suae using aquaculture wastewater and solar energy for cooling in subtropical regions

Rapid growth in the aquaculture industry and corresponding increases in nutrient and organic carbon levels in coastal regions can lead to eutrophication and increased greenhouse gas emissions. Macroalgae are the organisms primarily responsible for the capture of CO₂ and removal of nutrients from coastal waters. In the current study, we developed a novel wastewater treatment system in which the red macroalga, Sarcordia suae, is used to capture CO₂ under thermostatic conditions in subtropical regions. In 2020 (without temperature control), the carbon capture rate (CCR) of Sarcordia suae varied considerably with the season: winter/spring (2.1-3.9 g-C m^-2 d^-1) and summer (0.09 g-C m^-2 d^-1). In 2021, solar powered cooling reduced summer seawater temperatures from 31 to 33 °C to 23-25 °C with a corresponding increase in the mean CCR: winter/spring (2-7 g-C m^-2 d^-1) and summer (1.33 g-C m^-2 d^-1). The proposed aquaculture wastewater system proved highly efficient in removing nitrogen (20.7 mg-N g^-1 DW d^-1, DW = dry weight) and phosphorus (4.4 mg-P g^-1 DW d^-1). Furthermore, the high density of Sarcodia (1.10 ± 0.03 g cm^-3) would permit the harvesting and subsequent dumping of Sarcodia in deep off-shore waters. This study demonstrated a low-cost land-based seaweed cultivation system for capturing CO₂ and excess nutrients from aquaculture wastewater year-round under temperature controlled environments in subtropical regions.

The effects of marine farm-scale sequentially integrated multi-trophic aquaculture systems on microbial community composition, prevalence of sulfonamide-resistant bacteria and sulfonamide resistance gene sul1

Aquaculture, one of the most important food production practices worldwide, faces serious challenges of mitigating the detrimental impacts of intensive farming on the environment and increased prevalence of antibiotic resistance. To develop an environment-friendly aquaculture system, a land-based and farm-scale sequentially integrated multi-trophic aquaculture (IMTA) system was established for farming Chanos chanos in southwestern Taiwan. In this system, fishes are cultured in combination with organic extractive shellfish and inorganic extractive seaweed. This study aimed to evaluate the prevalence of sulfonamide-resistant bacteria, microbial community structure, and occurrence of sulfonamide resistance genes in the IMTA and traditional aquaculture systems. Water and sediment samples were collected before raising and after harvesting C. chanos. Our results showed that the occurrence of sulfonamide-resistant phenotypes in the IMTA system was comparable with that in influent seawater, while the traditional system exhibited a high sulfonamide resistance rate. Additionally, the traditional system resulted in a deviation of the bacterial community structure from that of seawater. In the water samples from the IMTA system and influent seawater, Proteobacteria and Bacteroidetes were the two dominant phyla, representing approximately 75% and 15% of the community, respectively. In the traditional system, Actinobacteria, constituting 39% of the community, was the dominant bacterial phylum. Thirty-one sulfonamide-resistant bacterial species were isolated. In conclusion, a sequentially IMTA system showed superior ability to maintain the prevalence of antibiotic resistance and the integrity of the bacterial community structure compared to the traditional farming system, representing a potentially valuable aquaculture system for preserving the sustainability of the marine environment.