Invasive Sea Squirt Threatens Tees River Oyster Restoration

On August 4th, 2025, the Tees Rivers Trust, a conservation group, reported the discovery of an invasive leathery sea squirt in one of their oyster pots used to monitor the health of the Tees estuary. The trust had set up the oyster nursery to help restore marine habitats and bring back spawning fish to the river.

Despite this setback, the trust's latest inspection also revealed positive findings. Programme manager Judy Power noted the "amazing growth" of the oysters and the presence of six fish species, including a scorpionfish and butterfish, as well as a tiny baby scallop, a porcelain crab, and various squat lobsters and prawns.

However, the discovery of the leathery sea squirt, known as Styela clava, was a cause for concern. This invasive species poses a threat to oyster and mussel farming by out-competing shellfish for food and space. The trust has reported the finding and promptly disposed of the sea squirt.

Seagrass and oysters were once abundant in the Tees estuary but were lost due to over-exploitation and deteriorating water quality. The trust's efforts aim to restore these vital habitats, which can act as a coastal defense by stabilizing sediment and preventing erosion. In the long term, the trust plans to use stones, gravel, and broken scallop shells to create the right environment for oyster recolonization.