Estuary health changing

Seagrass beds in Motuweka/Havelock Estuary are declining, indicating the stress the ecosystem is under.

Council’s Principal Coastal Scientist Oliver Wade told last month’s Environment and Planning Committee that estuaries were biodiversity hotspots, providing habitat, nursery grounds and numerous ecosystem services.

“We are losing important habitat,” he said. “Estuaries are the interface between the land and sea and the first place to see the effects of what is happening on land,” he said. Motuweka’s seagrass levels had reduced 95 per cent from 21 hectares in 2014 to one hectare this year.

Healthy seagrass should be “like your lawn” – long, lush and green, Mr Wade said. Instead it was brown and dying.

Motuweka Estuary is a large, 800 hectare estuary surrounded by indigenous forest with the lower catchment mainly exotic forestry and pasture. There are two main freshwater inputs – the Te Hoiere/Pelorus and Kaituna rivers.

At the head of both Te Hoiere and Kaituna are extensive salt marshes with a condition rating of very good, although mud elevated sediments were high throughout.

Meanwhile Nydia Bay’s estuary has been found to be in good to very good condition with the main threat to seagrass being vehicle use.

Council began state of the environment monitoring in the estuary in 2014 and contracted Salt Ecology this year to undertake broadscale mapping of Marlborough estuaries.

For more information go to: www.lawa.org.nz/explore-data/estuaries