An extremely rare species of sea slug or ‘gravel maggot’ has been discovered on a remote beach in South Westland.

Named Smeagol, after Gollum from Lord of the Rings, the nationally critical species was discovered at the Hautai Marine Reserve by a group of University of Canterbury scientists and marine rangers, who used a new technology called eDNA.

Smeagol, an extremely rare sea slug. Photo: Wildwind, iNaturalist

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. 

Neale said the gravel maggot lives up to 30cm down under the gravel beach surface which makes it very hard to find and study, but the eDNA method is one way to do that.

The species had previously only been known to exist in New Zealand on a small coastal beach in Wellington and in Kaikoura.

"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,” said Neale.

“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.” 

“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 surrounding oceans.”  

“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.”