Loss of seagrass

The Waitematā harbour was once host to enormous seagrass  (Zostera) beds which played a crucial role in providing habitat for juvenile fish. However the extensive harbour works, including port development and reclamations, had considerably reduced the seagrass beds by the 1930s. Then the remaining areas were virtually wiped out during the 1940s by an outbreak of fungal slime.

Waitemata harbour bridge
Port and waterfront development in the Waitematā harbour has contributed to the loss of extensive seagrass beds in the area.

The Tāmaki Strait was also an area with hosted seagrass beds. The steam trawler Doto, chartered by the government to do exploratory trawling in the Hauraki Gulf during 1901, found a net they hauled up after trawling along the Tāmaki Strait full of ‘grass and weeds’, indicating the extensive seagrass beds in the area.

Tamaki Strait looking from Waitawa Regeional Park
There is evidence that in 1901 there were extensive seagrass beds in the Tāmaki Strait, shown here from Waitawa Regional Park.

A major cause of seagrass loss is sediment from land development washing into the sea. When the health of a harbour or estuary deteriorates, seagrass is one of the first things to be lost. And with the seagrass beds goes part of the ability of the marine system to produce fish.

“If the sub tidal seagrass is lost, then juvenile fish production goes with it. It has a cascade effect.”

One of the few places with remaining seagrass beds in the Gulf is Huruhi Harbour at Great Mercury Island.

Huruhi Harbour, Great Mercury Island
One of the few places sub tidal seagrass beds can now be seen in the Hauraki Gulf is at Great Mercury Island.

 

 

 

 

 

 

 

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