An extremely rare species of sea slug or ‘gravel maggot’ has been detected for the first time on a remote beach in South
In late January, a team of three scientists from the University of Canterbury (UoC) Marine Ecology Research Group and
two Māhaki ki Taiao rangers travelled to Hautai Marine Reserve, 85km south of Haast. Hautai holds the title of New
Zealand’s most remote mainland marine reserve.
The trip was a great success, despite COVID and some wild weather complicating trip planning.
“We saw a large storm system approaching and managed to squeeze this work into a tight weather window, and get
helicoptered out shortly before it hit,” says UoC researcher Shawn Gerrity.
This trip is part of the Department of Conservation’s marine monitoring work. It was repeating monitoring work last done
in 2017 to see if any changes have occurred.
Aside from repeating the previous monitoring this team also employed a new and growing technology for detecting the
presence of species: eDNA.
eDNA works by passing a litre of seawater through a very fine filter. DNA fragments are left in the water by plants and
animals that have been in the area recently. These fragments collected in the filter are sent to Wilderlab in Wellington
to be analysed. About 500 different species were detected from the eDNA samples from Hautai Marine Reserve, ranging from
bacteria to dolphins.
“We were incredibly shocked and delighted that the results came back confirming the presence of Smeagol within the sample that was taken” says Don Neale, Marine Ranger for the West Coast.
The gravel maggot’s scientific name, Smeagol, comes from the mysterious pale-skinned character in The Lord of the Rings. “The gravel maggot has a similar lifestyle,
living up to 30cm down under the gravel beach surface. That makes it very hard to find and study, but the eDNA method is
one way to do that.”
“It has previously only been found in two places – a small beach on the south coast of Wellington, which was thought to
be its only home, until it was discovered that a genetically-distinct population also exists in Kaikōura.
It’s not yet known whether this new population at Hautai Marine Reserve is its own species or related to one of the two
known populations, which are 750km and 950km away, respectively.”
“To figure this out would be a pretty major undertaking,” says Don. “We would need to go back in to Hautai and spend
some time digging carefully around gravel or under boulders to see if we can find any live gravel maggots there.”
This may not be likely any time soon, considering access to the study area requires a helicopter or a two-day walk from
the nearest road end. But Don hopes there will be an opportunity to do some searching the next time monitoring is done
around the Hautai Marine Reserve.
Little is known about the Smeagol sea slug or its ecological role. “Although they’re very small and inconspicuous, coastal animals like Smeagol likely have some role to play in recycling nutrients from beachcast kelp back into the thriving ecosystems of the
“Their name, ecology, and threat status all give Smeagol a bit of an iconic status” says researcher Don. “And it goes to show how much more there is to learn about our marine
environments, with dozens of new species discovered in New Zealand every year.”