Mulroy Bay Kelp

The farm that taught us what this actually costs.

Mulroy Bay is a long, sheltered sea inlet on the north Donegal coast, cold and clean enough for sugar kelp and calm enough to work through an Atlantic winter. We began here in 2021 with a few hundred metres of seeded line and a hypothesis. Five seasons later it is the only site in the network where we hold every data point from seeding to soil.

It is also where the original plan came apart. The intention was to dry and pyrolyse the harvest into biochar, lock the carbon and sell the credit. The chemistry worked. The logistics did not. Drying wet seaweed at the volumes required consumed more energy, money and diesel than the resulting carbon was worth, and the credit market was not buying a category it did not recognise.

So the harvest now goes wet, straight from the pier, to dairy and tillage farms within about thirty miles. No drying, no freight, no processing plant. Roughly ninety per cent of the landed weight reaches a field within forty-eight hours of leaving the water. That single change is what makes a metre of rope cost eighteen pounds rather than sixty.

The 2024 season was a hard one, and it is in the report. Sea temperatures at the site averaged 17.5°C against a long-run norm of 12.9°C, which shortened the growing window and cut yield per metre below where it should have been. We still landed 46.8 tonnes off 11,700 metres. A cooler season would have done considerably better.

Positive for people

Three jobs have been created and sustained at the site, which in a rural Donegal parish is not a rounding error. Seasonal harvest work brings in another handful of people at the busiest weeks of May and June, drawn mostly from families already working the bay for shellfish.

The land farmers receive the harvest free. That is the point. The single biggest obstacle to seaweed as a soil amendment is less the science than the fact that few farmers will pay for an input they have not watched work on their own ground. Sponsorship removes the cost of finding out, and the before-and-after soil data is what will eventually build a market that no longer needs sponsors.

Donegal County Council and Atlantic Technological University have both backed the site, and the EU-funded BioDiMoBot programme now runs biohybrid biodiversity sensors here.