Investigation into the novel application & utilisation of algae to aid in developing sustainable Irish freshwater aquaculture

Abstract

Aims and Rationale: Aquaculture is the fastest growing food producing industry in the world producing >50% of the world’s seafood. Food Wise 2025, an initiative set by the Irish government to develop the Irish Agri-Food industry, predicted that aquaculture production has the potential to increase to 81,700 tonnes per annum by 2023. However, several issues have hampered the growth of freshwater aquaculture including licensing issues, environmental concerns and spatial limitations. With the destruction of the surrounding marine environments becoming a real threat, land-based aquaculture and freshwater aquaculture is predicted to become a more common practice across Ireland; however, increasing issues with uncertainties associated with global warming and climate variances will also play a significant factor in the future sustainable intensification of this industry. Although research is still significantly lacking, interest in algae as natural means of supporting and enabling development of aquaculture is increasing for water quality and waste mitigation. This timely and novel study investigate the role of algae in conventional pond-based aquaculture systems and is the first to report on the transitioning to a fully recirculated aquaculture process using the peatlands. Thus, the overarching aim of this timely study is to investigate algae as a means to assist in addressing current and future issues within the Irish freshwater aquaculture industry with a global orientation. Methodology and Findings: A novel ecotoxicological toolbox, representative of Irish freshwaters, was developed to help address aquaculture licensing issues and inform the aforementioned environmental concerns. Native algae and daphnid species were compared to standardised species where this toolbox was first piloted using a traditional flow-through aquaculture system between April 2018 and October 2018. The toolbox consisted of measuring conventional physicochemical parameters currently used to assess water quality along with using two ISO standardised bioassay (Pseudokirchneriella subcapitata algal bioassay and Daphnia crustacean bioassay); thereafter, the toolbox was applied to monitoring freshwater aquaculture between March 2019 and August 2019. Findings revealed that reliance upon physicochemical analysis alone would only provide a snap shot in time of the water quality. Supplementation with algal, from perspective of real-time ecotoxicological toolkit, enables a broader determination of overall aquaculture effluent and recirculated water quality that includes capacity for potential use as novel early warning intervention for the industry. This study constitutes the first to investigate development of integrated multi-trophic aquaculture system (IMTA) on the peatlands as a next-generation approach to sustainable production of farmed fish along with mitigating against environmental discharge of effluent to receiving waters in the Irish Midlands. However, as this was an entirely novel IMTA concept built in protected areas of the peatlands that are conserved ecologically and for their biodiversity, this important research evaluated the efficacy of this novel process using both conventional physiochemical parameter monitoring in tandem with using this ecotoxicological toolbox of algal communities that was first applied between May 2019 and August 2019. Research findings revealed that using algae as one of its primary means of wastewater assimilation, was unlikely to cause adverse effects on the surrounding peatland. Physicochemical parameters provided a baseline of conditions best suited for algal growth. Algae and cyanobacteria communities were enumerated using microscopy and real-time flow cytometry, and were identified using microscopy and Illumina DNA sequencing. Characterisation found a vast variety of algal species present in the system with 1864 species across 210 genus identified. The majority of species present were considered beneficial or neutral; whereas, some algal/cyanobacteria species were considered as potentially hazardous where their appearance coincided with fish mortalities in the IMTA process. Fluctuations in physicochemical parameters due to increased rainfall attributed to two successive storms also coincided in fluctuations in algal numbers in this IMTA process and with increases in fish mortalities. During such instances of low nitrate (algae’s preferred nutrient source), vi low levels of algae were also observed. Findings revealed that this environmental flux provided an opportunity for cyanobacteria (whose preferred nutrient source is ammonium) to outcompete beneficial algae for its nitrogen nutrient source; increased cyanobacteria levels resulted in increased fish mortalities. Use of the toolkit, along with characterising and monitoring the physicochemical parameters, enabled real-time monitoring of the IMTA that included substantial variances in the system caused by uncertainty with climate (storms); thus, highlighting the potential utility of this toolbox for supporting predicting, modelling and management decision marking. This timely study also showed that despite advances to remove end-of-time solutions for treating effluent, and smart use of algae/bacteria for recirculation of waste water – climate variance can significantly impact upon nextgeneration sustainable approaches for freshwater aquaculture. This uncertainty due to climate change was not considered at the outset of the project, nor was the simultaneous occurrence of a COVID-19 pandemic that affected ability to take samples on site to support a battling industry, and for trouble shooting; yet this was achieved. This timely project also addressed pressing unprecedented challenges for the freshwater aquaculture industry during periods affected by global warming or climate change. During May 2018, Ireland experienced its highest ever recorded temperature (>30oC) with absence of rainfall for 16 weeks leading to drought. During this time, the algal bioassay component of this novel ecotoxicological toolbox was shown to be capable of monitoring environmental flux and can be potentially used as an early warning indicator for climate variance for the aquaculture industry. During February 2020, Ireland experienced two extratropical cyclone storms less than a week apart, increasing rainfall levels from a monthly average of 70.3mm to 197.5mm. This erratic weather was the main cause of algae and physicochemical fluctuations that subsequently led to aforementioned instances of fish mortalities within the novel peatland IMTA system. This highlighted the need for developing real-time monitoring tools that respond to rapid variances in the environment, which is a limiting factor in the gap associated with conventional physicochemical methods that are traditionally used by the industry. Conclusions and Implications: The application and utilisation of algae has demonstrated a range of potential benefits and implications for the Irish freshwater aquaculture industry. This research has led to the potential development of a sustainable water quality control tool for fish farms, which will support and enable real-time monitoring catering for holistic environmental situations. Findings from this novel research will potentially support future proofing of the industry by providing smart tools for informing development of the industry that is pivoting towards the use of IMTA processes. The information generated and openly shared will assist in harmonising traditional and novel processing applications within the industry. This is particularly timely, as the Irish EPA are currently investigation the regulation of wastewater in aquaculture. This study also highlights potential solutions for complex challenges, including use of specific beneficial algal to offset disturbances to balanced aquaculture processes. It is envisaged that data generated through this novel project will inform future digitalisation for intensification of the industry. The findings of this project are strongly aligned with the refreshed national priority for research areas, including food, health and wellbeing.