Sea spurge is a Mediterranean pest plant that has made its way to New Zealand and is a threat to our coastal sand dunes. Photo / Supplied
Sea spurge is a Mediterranean pest plant that has made its way to New Zealand and is a threat to our coastal sand dunes. Photo / Supplied
A Mediterranean pest plant with the ability to have a huge and negative impact on sand dunes has made its way from Australia to western coastal areas of New Zealand.
Last week, staff from Horizons Regional Council, Department of Conservation, Horowhenua District Council and the Ministry of Primary Industries headedout to Waikawa Beach to check out this plant invader, known as sea spurge.
It outcompetes native plants by spreading densely but also grows vertically with sand dunes, rather than horizontally like other common dune plants, therefore changing the natural patterns of sand movement.
According to Dr Fiona Thomson, DoC Nelson technical adviser on threats, "... this pest plant is incredibly invasive and [if not eradicated] can dominate and transform coastal environments".
This "unwanted organism" can survive in the sea for up to six years and has made five known incursions along New Zealand's west coast – the first in 2012, then in 2018 and 2019, with two discoveries in 2020.
One of the major issues is the dispersal distance of the sea spurge once it's established on our sand dunes.
HRC environmental programme co-ordinator Craig Davey showing just how quickly sea spurge can spread and establish itself. Photo / Supplied
Last year a survey was conducted at Scotts Beach, Kahurangi National Park and Karekare Beach, Auckland, to measure the distance and bearing of a number of sea spurge plants from one identified as a reproductive adult plant.
"Before [we started] this work, we checked the literature, which said the majority of seeds go less than 2m. We also used a predictive model, using plant traits, which said the maximum dispersal distance would be 4.9m," Thomson said.
The survey recorded a spatial distance of the juvenile plants in relation to the "parent" and it was found that 99 per cent of the seeds were actually dispersed up to 9m away, with some being distributed up to 16m.
This information helped DoC and local biosecurity teams establish the area from which sand/soil needed to be taken to make sure most of the sea spurge seeds are removed.
DoC staff took off the top 30cm of sand around the adult plant as a case study to establish if seed bank removal could be a tool for eradicating sea spurge.
So, what makes this pest plant so bad? If sea spurge continues to grow on sand dunes, over time it will cause some to become totally inaccessible.
The eradication of sea spurge cannot happen without the assistance of local coastal communities, said Craig Davey, environmental programme co-ordinator for Horizons Regional Council.
"We need people to phone the MPI hotline [0800 809 966] if they see these plants ... because our staff can only cover so much of the coastal areas," Davey said.
People who see this plant must NOT remove it themselves as the sap is toxic to humans and animals which means DoC use full PPE when they remove it to avoid any adverse reactions.
According to DoC and HRC, sea spurge has the ability to have a widespread negative impact on our sand dunes if we don't work at stopping it.
