The clean-up crew

A group of researchers is investigating whether sea cucumbers can help to minimise the environmental impacts of fish farming. They recently completed a feasibility study to assess how well the creatures perform under laboratory conditions, and hope that their positive results will allow them to undertake further research.

The feasibility study was undertaken by Blue Remediation, a company set up by four PhD students from the University of Strathclyde and Heriot-Watt University. Their research was assisted by the UK Seafood Innovation Fund, with support from the Sustainable Aquaculture Innovation Centre (SAIC).

Blue Remediation’s founders – friends Melinda Choua, Ana Rodriguez, Soizic Garnier and Marta Ponti – hit upon the idea of using sea cucumbers to process salmon aquaculture waste in the autumn of 2019.

“We initially thought about a much wider project, using sea cucumbers as part of an integrated multi-trophic aquaculture (IMTA) project, then applied for a place on a mentoring programme led by Women in Scottish Aquaculture (WiSA) in January 2020. This helped us to narrow down and formulate our project idea,” explained Ponti.

The project aimed to be a starting point for reconciling fish production and environmental conservation. Bioremediation, the process of using living organisms to remove pollutants and toxins, is already commonly used in agriculture, particularly in Asia and China, to restore polluted soil. However, it is new to aquaculture in Europe.

Wrasse and lumpfish are already in use as cleaner fish, helping to keep down sea lice numbers, and sea urchins have been trialled in the past to graze in salmon cages. Sea cucumbers, which are from the same family as sea urchins and are naturally found in Scottish waters, could help deal with deposits of uneaten food and fish faeces on the seabed.

There are more than 1,250 known species of sea cucumbers, which are basically a digestive tract with a hole at either end, housed in an oblong body that resembles a fat cucumber. Found on the seabed worldwide, they range widely in size from size from around two centimetres to nearly two metres.

These creatures move around by constantly changing the water pressure in the rows of feet that run the length of the bodies, making them expand and contract. As they move, sea cucumbers ingest the seafloor, breaking it down into small fragments internally, then excrete it back out again. In doing so, they play an important environmental role by removing excess organic matter from the sediment.

The goal of Blue Remediation’s study was to ascertain whether it would be feasible to offer farmers a sustainable alternative to reduce their seabed impact, which is a factor that currently limits fish production. The foursome reasoned that using a natural method to improve the condition of the seabed would allow salmon farmers to increase the allowable amount of  fish biomass in their cages.

Melinda Choua explained that WISA had been a huge accelerator in helping the team to get the project off the ground, and invaluable in introducing them to Mowi, which became their industrial partner, supplying sediment from their Loch Leven site. Salmon faeces were provided by the University of Stirling’s Institute of Aquaculture, so that the researchers could mimic the natural ecosystem.

“WISA also provided us with a mentor, Michael Mason, who put us in touch with all the different organisations dealing with Scottish aquaculture… Michael was also invaluable in helping us to understand how to put together a business in Scotland,” she said.

To answer their initial questions, the researchers designed the study to look at a number of variables, such as absorption efficiency and benthic waste accumulation, in order to find the optimum conditions and number of sea cucumbers that producers could deploy beneath their cages. Eighteen Scottish sea cucumbers were fed on a variety of diets, and their appreciation of salmon faeces was clear.

“The study was carried out by researchers at SAMS, led by Dr Georgina Robinson, but due to Covid-19 restrictions, we were not able to see it first hand, which was a disappointment. However, alongside the extensive regulatory frameworks that are in place for Scottish salmon farming, we believe we have identified a possible natural solution that could absorb some of the waste that is inevitably produced by fish and the process of feeding them,” said Ponti.

As part of the project, the researchers built a computer model that integrates with existing and NewDEPOMOD computer models, developed by SAMS, which predict the impact of fish farm discharges on the seabed.

Excited by their findings, Blue Remediation is seeking funding to undertake a larger trial, which will refine their computer model, determine the impact of introducing and integrating different species, look at the potential for breeding sea cucumbers in captivity, investigate potential impacts on wild cucumbers, and determine parameters for monitoring their health and wellbeing and controlling disease.

“Using sea cucumbers in Scottish waters has great potential, but there are still a number of questions that we need to find the answers to, including what to do with them when their useful life is over. Sea cucumbers are considered a delicacy in Asia and can fetch up to $3,000 per kilo, so there may be added value in mainstream sea cucumber cultivation, going hand in hand with the environmental benefits. There is also potential for using them in pharmaceutical applications,” said Rodriguez.

One tricky area is working out how to contain the sea cucumbers on the seabed under salmon cages, since as Ponti points out: “They are great escape artists!”

”It may all sound easy, but there would need to be many trials before it reached maximum efficiency and could be used as an industrial application. However, we are very excited by the potential we have seen so far,” she said.

Heather Jones, CEO of SAIC, believes there are exciting opportunities to build sustainable aquaculture systems in Scotland.

“With research projects exploring cost-effective, data-led methods, such as using sea cucumbers, we could transform the sector’s approach to waste management. Integrated multi-trophic aquaculture is still in its infancy in Scotland, but could be a valuable, sustainable, circular method of ensuring resources don’t go to waste,” she said.

Find out more about the UK Seafood Innovation Fund at seafoodinnovation.fund