The positives of Wellington’s wet weather: marine pest control


The tempestuous wet weather may have dampened Wellingtonians' spirits at the beginning of summer, but it had at least one positive effect - killing some unwanted species in the harbour. 

Marine scientists from NIWA have been on the hunt for high-risk invasive species as part of their latest biosecurity survey, designed to detect marine animals and plants that come in from overseas. Also known as non-indigenous marine species (NIS), these organisms can have detrimental impacts to Aotearoa New Zealand’s environment and economy.

Thankfully, no signs of any new NIS were found this time. And for already established populations, it seems that the recent heavy rains in the capital reduced salinity in the harbour, causing significant mortalities in some NIS at some shallow-water locations, such as the solitary sea squirt and the light bulb sea squirt.

Chris Woods is a marine ecologist at NIWA and is part of the team who undertakes the surveys. He says the survey threw up some fascinating observations.

“We were most interested to observe the devastating effects of reduced salinities. It seemed to kill off NIS at locations where these invasive organisms can predominate over native organisms, which is good news for our native species.”

He says the surveys are a vital part of the government’s biosecurity response.

“If we have anything that we suspect is new to New Zealand, or have shifted significantly in their known geographic range, we take samples and send them off to be formally identified by taxonomic experts, with the results going to Biosecurity New Zealand, who determine what response may be required. MPI and regional councils are really interested in looking at invasive marine species because they can have traumatic impacts on our native flora and fauna, as well as on our economic activities by affecting things such as vessel maintenance.”

The team use divers, various traps and sampling gear to search under the water and collect anything that appears suspicious. They use a variety of methods designed to sample a range of soft and hard habitat types, such as mud bottoms, rocky shores, and artificial structures including marina pontoons, pilings, moorings, jetties, and commercial vessel berths.

The survey is done bi-annually in the winter and summer. It is part of Biosecurity NZ’s wider marine biosecurity system and covers 12 major ports and marinas, including Wellington, Ōpua Marina/Waikare Inlet (Te Moana o Pikopiko-i-Whiti) in the Bay of Islands and Bluff Harbour (Awarua) in Southland.


NIWA diver Roberta D'Archino inspects pontoons at Seaview Marina. [Photo: Chris Woods, NIWA]
Peter Marriott and Serena Cox prepare to dive at Lambton Harbour. [Photos: Chris Woods, NIWA]
Clavelina lepadiformis at Seaview Marina on the underside of marina pontoons show the impact that reduced salinity can have on marine organisms. [Photos: Chris Woods, NIWA]
Moribund (at the point of death) Ciona robusta. [Photos: Chris Woods, NIWA]