Bioremediation of ozone-produced oxidants in marine RAS using Ulva ohnoi

Author(s): Sabine Weidlich, Clara Priemer, Tania Aires, Martin Brenner, Wolfram Weckwerth, Aschwin Engelen, Andreas Kunzmann
Abstract: Maintaining good water quality is essential to the success of recirculating aquaculture systems (RAS). Among water treatment tools, ozone (O₃) has garnered interest from aquafarmers worldwide due to its various beneficial effects. Beyond its germicidal properties, ozone improves solid removal, oxidises toxic nitrogen compounds, and degrades a broad spectrum of biogenic and artificial molecules. However, the ozonation of seawater produces by-products (‘ozone-produced oxidants’ (OPO)), which can pose significant risks to animal health. In this experiment, we evaluated the capacity of the seaweed Ulva ohnoi to bioremediate OPO in an Integrated Multi-Trophic Aquaculture (IMTA)–RAS setup cultivating gilthead seabream (Sparus aurata). Effluent water was ozonated and then passed through a cultivation unit containing U. ohnoi. OPO concentrations in the water were measured before and after the seaweed unit, and the reduction in OPO was compared to control systems without U. ohnoi. Additionally, we assessed the effects of OPO on growth, metabolic composition, photosynthetic efficiency, and associated microbiomes of U. ohnoi by comparing seaweed exposed to ozonated water with controls grown without ozonation. The results showed that Ulva-containing systems achieved an 11% higher reduction in OPO than controls. However, OPO induced oxidative stress in U. ohnoi, leading to reduced growth, altered morphology, and elevated levels of chlorophyll, phenolic compounds, soluble sugars, and selected amino acids. The microbiome associated with U. ohnoi shifted, with a reduction in complex carbohydrate-metabolising bacteria. This study demonstrates that U. ohnoi can reduce OPO concentrations in marine RAS, but with impacts on the chemical composition, morphology, and microbiome of the seaweed.
Organisation(s): Department of Microbiology and Ecosystem Science, Functional and Evolutionary Ecology, Department of Pharmaceutical Sciences
External organisation(s): Leibniz Centre for Tropical Marine Research, University of Algarve
Journal: Journal of Applied Phycology
ISSN: 0921-8971
DOI: https://doi.org/10.1007/s10811-026-03850-8
Publication date: 04-2026
Peer reviewed: Yes
Austrian Fields of Science 2012: 106022 Microbiology, 106021 Marine biology
Keywords
ASJC Scopus subject areas: Aquatic Science, Plant Science
Sustainable Development Goals: SDG 14 - Life Below Water
Portal url: https://ucrisportal.univie.ac.at/en/publications/d03088f2-cfc5-46d4-900f-e2a908ad06e4