Kūtai at Cable Bay – Nine years on

Photo by Peter Miles
ROV Snoopy goes for its maiden ocean swim.

In 2014, the Mussel Reef Restoration Trust deployed approximately 70 tonnes of kūtai across a vast 10.5-hectare area in Cable Bay, near Rotoroa Island. 

Nine years on, recent monitoring surveys reveal some exciting findings about the current state of the mussel beds and their impact on the marine ecosystem.

The last official monitoring survey in 2016 estimated that only 22% of the initially deployed mussels remained on the seabed. However, since then, informal dives occasionally conducted in the area provided encouraging signs of mussel survival. 

To assess the mussel population accurately, Revive Our Gulf commissioned Coast & Catchment to conduct a comprehensive video survey. The video survey revealed that while no dense mussel beds were found, scattered live mussels were observed throughout the deployment area. These mussels were typically seen in small clumps of fewer than 3–4 individuals, indicating a resilient but dispersed population.

The substrates across the deployment area showed considerable variation. The majority of the region consisted of muddy/sandy substrate with scattered shells and diverse epibiota-like sponges. Interestingly, pockets of relatively dense biogenic habitat and scattered mussel shells were identified, indicating remnants of the mussel beds. Live mussels seemed to prefer substrates with moderate to high shell content, leading to slightly higher survivability in such areas.

Examples of live mussels (arrows) observed in the video transects.
Examples of live mussels (arrows) observed in the video transects. Image supplied by Coast & Catchment.

One of the most significant findings was the notable increase in marine life diversity within the deployment area. Various epibiota, particularly sponges, were found to be quite common and the density of epibiota in the deployment area was much higher than what was observed before the mussel deployment, suggesting that the restoration project may have had a positive impact on overall marine biodiversity.

While the video survey did not uncover dense mussel beds, it provided evidence that scattered live mussels are still present in the area. 

This allows us to continue to build our knowledge about site suitability for restoration. By understanding the factors that impact kūtai survival at different sites we can better tailor our restoration efforts to each location’s unique conditions.

Coast & Catchment and Revive Our Gulf team