Scientists farm seaweed in the Solent to test water quality and commercial benefits

Scientists working on restoring areas of the Solent have begun growing seaweed in Langstone Harbour for the first time ever to test its environmental and commercial benefits.

They want to see if sugar kelp (Saccharina latissima) can be successfully farmed inshore, while also improving water quality. The species, commonly used in Japanese cooking or added to food and cosmetics because of its thickening and gelling qualities, is generally grown offshore as it’s easier for suppliers to find space.

But the University of Portsmouth team hopes their study will provide evidence of the environmental benefits in the harbours, as the seaweed removes excess nutrients.

Increased nutrient levels in coastal areas caused by fertilisers, wastewater and sewage discharges, results in the excessive growth of green algae on intertidal mudflats, saltmarshes and seagrass meadows covering thousands of hectares. The process, known as eutrophication, causes ecological, economic and human health issues.

The study is part of the Rapid Reduction of Nutrients in Transitional Waters (RaNTrans) project, which is exploring how nature-based approaches can improve and protect marine ecosystems.

Professor Gordon Watson from the University of Portsmouth and RaNTrans project leader, said: “The overall purpose of culturing the seaweed is to demonstrate how restorative aquaculture can not only be useful commercially, but also has an important role to play in improving our waters.

“So if this works, businesses could farm the kelp and sell the product while simultaneously improving water quality.”

The project team comprises nine partners from across the UK and France testing a variety of methods to improve water quality from culturing oysters to mechanically removing the green algal mat. 

The Solent team will now examine whether the kelp absorbs nutrients and as it grows in dense groupings much like a forest on land, could even provide food and shelter for many species.

As part of the analysis, the team will also look at how much carbon kelp could store. The team believes much of the Solent’s potential to capture greenhouse gases remains untapped.

An estimated 11 million tonnes of CO₂ equivalent is captured each year in UK marine ecosystems and the Solent is one of Europe’s largest blue carbon sites; the term used for coastal marine environments which capture and store carbon.

The University is a founding member of the UK Blue Carbon Forum, formed in 2021 to address the important role of blue carbon in mitigating the current ecological and climate emergency.

Dr Joanne Preston, Reader in Marine Ecology and Evolution based in the Institute of Marine Sciences at the University of Portsmouth, said: “Kelp can capture and store carbon rapidly, so it makes sense to explore ways in which we can utilise these species in our fight against climate change.

“We’re really interested to see how kelp stores carbon, and we will do comparisons of the species and oysters using the data from our earlier deployments.”

By developing the business potential of these sustainably-produced outputs, the team aims to show how these nature-based approaches could also underpin regional job creation.