Developing systems for the commercial culture of Ulva species in the UK

Abstract

The green seaweed, Ulva, is highly valued in terms of animal feed, food and biofuel, as well in the delivery of crucial remediation services including wastewater treatment and CO2 removal. Accordingly, Ulva cultivation has gained significant research interest worldwide. Notwithstanding these research efforts, Ulva cultivation is still in its infancy and knowledge to underpin such developments remains limited. A common challenge in Ulva cultivation is the fluctuating productivity with time due to vegetative fragmentation and/or periodic reproduction. In this study, three methods were employed to address this challenge. Firstly, culture conditions were optimised to establish a balance between growth and reproduction. Secondly, a refined culture method was developed, which more than tripled growth of Ulva over an 18-day cultivation as compared to a standard method. Thirdly, a sterile strain was obtained by mutating a wild strain with ultraviolet radiation. This new strain grew five times faster over an 18-day cultivation and absorbed nitrate and phosphate 40.0% and 30.9% quicker compared to the wild strain respectively. The chemical composition of the sterile strain showed a lipid content of more than double that of the wild strain, while the protein content was 26.3% lower than the wild strain. Several tissue preservation techniques were developed to enable settlement and growth trials to be conducted on demand. The merits or otherwise of the preservation techniques were determined for gametes, germlings and thalli. In addition to cultivation-related techniques, the co-effects of climate change factors (global warming and ocean acidification) and eutrophication on Ulva cultivation were investigated. These three variables interacted in a complex pattern to differentially affect life history stages, as well as altering the chemical composition and functional properties of Ulva. These findings make tangible contributions to the ability to successfully and commercially cultivate Ulva in terms of culture conditions, tissue preservation and the development of mutant strains. Further, by placing Ulva culture in a climate change context, this work provides valuable insight into the limits to resilience of Ulva to a changing climate. This will inform the future development of the Ulva culture industry over the coming decades.