Rough weather gets rid of unwanted marine species

Te Whanganui-a-Tara - Rough wet weather may have dampened Wellingtonians' spirits at the beginning of summer, but it also killed unwanted species in the harbour. 

NIWA marine scientists 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.

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 shallow-water locations, such as the solitary sea squirt and the light bulb sea squirt.

Chris Woods, a marine ecologist at NIWA, 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.

“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 to be identified by taxonomic experts, with the results going to Biosecurity New Zealand, who determine what response may be required.”

MPI and regional councils are interested in looking at invasive marine species because they can have traumatic impacts on native flora and fauna, as well as on 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 and Waikare Inlet (Te Moana o Pikopiko-i-Whiti) in the Bay of Islands and Bluff Harbour (Awarua) in Southland.