The Hauraki Gulf. Photo: Raewyn Peart
The Hauraki Gulf has been valued at $5 billion a year.
A report from the NZ Institute of Economic Research, commissioned by Auckland Council's Hauraki Gulf Forum, estimated the financial impact of invasive caulerpa seaweed.
Most of that $5 billion price tag comes from recreation, valued at $2.49 billion, and shipping, valued at $1.34 billion.
Economists also estimated the gulf provided $526 million in property value to nearby homes.
But the report stated caulerpa could cause $109 million in damage to fishing activities and $45 million in damage to biodiversity.
"I love our harbour, and I hate wasting money," Auckland Mayor Wayne Brown said in a statement.
"I'm a boatie before I'm mayor, and I have already put a heap of advocacy into cleaning up this invasive weed."
He said the projected financial cost was "extremely frustrating" and more needed to be done to stop the spread.
"The good news is, through Kiwi ingenuity we've found solutions through dredging and the like, but I still believe everyone could be doing more in this space," Brown said. "These costs provide an economic argument for this."
Caulerpa growing on rocks in the Bay of Islands. Photo: Supplied / Rana Rewha
Researchers said caulerpa would also generate ongoing costs for ports and cruises, requiring extra cleaning.
Hauraki Gulf Forum co-chair Nicola MacDonald applauded the government's plan to put $10 million towards research and development for caulerpa removal.
She said caulerpa spread very quickly and crowded fish nurseries, native seaweed and seagrass.
"The invasive exotic caulerpa is the greatest threat facing our marine ecosystem, smothering vital marine habitats, threatening the biodiversity and fisheries of the gulf."
