Seagrass power: how nature is healing a polluted lagoon

In Portugal's Ria de Aveiro lagoon, the once-thriving Largo do Laranjo was a vibrant underwater meadow carpeted in Zostera noltei seagrass. But decades of industrial pollution left mercury and arsenic into the waters, poisoning the sediments and wiping out the underwater greenery. The toxins lingered, buried but not gone, until an EU-funded project proved that nature could heal itself.

With EU support, researcher and biologist João Pedro Coelho and his team set out to restore the lost seagrass meadows. Through the ReMoliço project, they demonstrated that seagrass doesn't just grow back - it locks away contaminated sediments, reduces erosion and brings ecosystems back to life.

A persistent problem, a natural solution

By the 1990s, stricter regulations had improved water quality in the lagoon. However, the damage ran deeper. Trapped contaminants in the sediments continued to resurface with every tide, poisoning wildlife and disrupting the ecosystem.

The solution? Bring back the seagrass. These underwater plants act like natural water filters, trapping pollutants and stabilising the seabed with their roots. As João Pedro Coelho explains: "The system began restoring itself naturally."

From experimentation to restoration

The project began in 2019 with nine months of laboratory trials to test how well seagrass could survive in contaminated conditions. The team tested different transplantation methods, eventually settling on 20×30 cm sediment blocks - large enough to protect the plants' delicate roots. They planted the blocks directly into the degraded estuary.

With funding from the European Maritime and Fisheries Fund (EMFF), the team built tidal simulation tanks, hired specialised and refined their transplantation method.

The results were faster than expected.

Fast environmental recovery

The changes were visible within months

• Contamination levels dropped
• Erosion decreased
• Biodiversity began to recover
  

While the team noted that different ecosystem functions recover at varied paces - with chemical stabilisation and sediment retention occurring much faster than the full return of biodiversity - the overall improvement is undeniable. The area, once avoided due to contamination risks, is now gradually becoming safer for activities such as fishing, birdwatching and recreation.

From local success to European model

ReMoliço's approach is now scaling up with follow-up projects such as RemediGrass and LIFE SeagrassRIAwild, which expanded restoration efforts to 300 m² in 2025.

Community engagement has also grown, with volunteers actively participating in transplantation activities (six events organised in 2024), as well as living lab sessions involving NGOs, authorities, students and local stakeholders.

With EU funding, what began as an experiment is now a replicable model for restoring contaminated coastal areas across Europe.

More information

ReMoliço project

RemediGrass

LIFE SeagrassRIAwild