Colourful sea slugs may be the favourites of photographers looking for a great social media post, but this weekend the creatures are being snapped for science.

Volunteer 'citizen scientists' are joining university experts for a Sea Slug Census at Coffs Harbour on the New South Wales Mid North Coast.

The project is not only expected to uncover new species — it may help discover more about climate change.

Director of the Southern Cross University (SCU) National Marine Science Centre, Professor Steve Smith, said sea slugs — also known as nudibranchs — were good indicators of the health of the ocean.

"One of the things about sea slugs is that they have very rapid life cycles, so most of them will live for much less than a year," he said.

"The other thing is that they have very specific feeding requirements so if there's a change in the environment, we're likely to see that reflected in changes to the structure of these sea slug assemblages very quickly."

Volunteers spend several days diving or scouring rock pools looking for the colourful nudibranchs. ( Supplied: Southern Cross University )

Census covers Australia and Indonesia

The Sea Slug Census program started almost six years ago at Port Stephens and has now expanded into 40 censuses in 10 locations along the Australian east coast.

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These are coordinated by SCU marine scientists, with the first international event held in Indonesia in November 2018.

At each location volunteers spend several days either diving or scouring rockpools to photograph any sea slug finds, before sending their images to scientists for verification.

Since the census began, more than 1,200 participants have photographed around 450 nudibranch species, including some previously unknown to science.

"They have also helped to map changing distribution patterns for many species — most likely related to climate change," Dr Smith said.

"We recently published a paper that indicated 37 species which have been found for the first time way, way south of the previously-known distribution.

"What we're getting and what's predicted under all climate change models is that we get a strengthening of the East Australian Current," he said.

"[That] pushes down the east coast bringing warm tropical water and carrying those little larvae, not just of sea slugs, but of all different species."

This species of sea slug looks like a flamenco dancer's skirts and has been named a 'Spanish dancer'. ( Supplied: Southern Cross University )

The census also aims to document the diversity and distribution of the sea slugs.

"There's a massive range in diversity," Dr Smith said.

"We've got things that look like they've got fingers growing off their backs [and] we've got huge things called 'Spanish dancers' that do literally look like a flamenco dress flapping around in the water.

"Then we've got these minute tiny things which, when you actually get them under a microscope or under a lens, have amazing patterns and diversity which you'd never pick."

Citizen scientists vital to census

The project can only be run with the help of the volunteers who spend hours in the ocean and on beaches seeking out the sea slugs.

Nicola Fraser will be one of those taking part in the census this weekend in Coffs Harbour.

Marine research volunteer Nicola Fraser will be searching for the sea slugs this weekend. ( Supplied: Ian Shaw )

As president of the volunteer-run Solitary Islands Underwater Research Group (SIURG), Ms Fraser has taken part in previous studies and counts and enjoys the challenge.

"I hadn't even heard of the term 'citizen science', but I really get a buzz out of it," she said.

"I'm not just out there diving and playing around, so to speak; I'm actually collecting data that's useful.

"You don't need any special training. All people have to do is find sea slugs and take photos of them."