Ōhiwa mussels in rapid decline

By Wena Harawira

In the Bay of Plenty, a marine ecologist is warning of a rapid decline in mussel numbers in the Ohiwa harbour.

According to a survey by Dr Kura Paul-Burke, sea stars and pollutants into the harbour are destroying traditional mussel beds and without them, the bio-diversity of the harbour is under threat.

In 2009 Ngāti Awa kaumātua showed Dr Paul-Burke the location of their mussel beds on the western side of Ōhiwa, which contained about 112 million mussels.

“In 2016, there’s an estimated 480,000 mussels present. So it’s declined from 112 million to under 500,000,” said Dr Paul-Burke.

A major problem has been an explosion in the sea star population which has preyed on mussels and other shellfish.

“We mapped them at an estimated 4 hectares of sea stars within the original mussel bed boundaries. Behind them was complete devastation, just dead mussel debris everywhere,” she said.

The beds have also been affected by the build-up of sedimentation and pollutants in the water. Mussels are a key part of a healthy bio-diversity, creating reefs and filtering water. But Dr Burke-Paul says she needed to use a torch and wipe away silt smothering shellfish.

“The layers and layers of silt are significant,” she said.

Dr Paul-Burke has made a number of recommendations as part of the Ōhiwa Harbour Strategy that focuses on the sustainable management of the harbour and its resources. She hopes this will help restore mussel the population.