Science Centres: Aquatic Biodiversity and Biosecurity

Sea squirts are immobile marine invertebrates. Eudistoma elongatum is a colonial species made up of hundreds of tiny individuals in bag-like bodies attached to the underside of oysters and rack-rails. They extract food from water pumped through a branchial sac in their body cavity.

An invasive sea squirt has been smothering Pacific oyster cultures in Houhora and Parengarenga Harbours in the Far North. According to local oyster farmers, the sea squirt first appeared about two years ago, but seems to have been a growing problem since last October.

NIWA has advised oyster farmers to raise their rack level to above the extreme low water neap (the highest of the neap tides). This is because oysters grow best above that level and the amount of rack structure that the sea squirt can colonise will be minimised. We have provisionally identified the sea squirt as Eudistoma elongatum, possibly originating from eastern Australia.

This work was done for the Houhora Shellfish Farms Association and funded by Technology NZ’s TechNet scheme.