With seven successful Melbourne Sea Slug Census events to date, our records of sea slug species found in Victorian coastal waters are continuing to grow. Collecting photos of sea slugs present at different times throughout the year will enable us to monitor these species and track any changes, but we’ll need your help!

The Eighth Melbourne Sea Slug Census was held between Friday 5 and Monday 8 March. March proved to be a popular time for the Sea Slug Census project, with 6 separate Census events held across the country and one in Vanuatu! Results and report can be found below.


With stay-at-home orders still in place for the Melbourne region for at least another week, and the travel restrictions in place for the long weekend, we made the difficult decision to postpone the Sea Slug Census planned for 11-14 June.

While not everyone who contributes to the Census is affected by these restrictions, we hope those in the regions understand that this decision allows for a more representative snapshot of our slug species right around the Victorian coast. A postponed Census means that everyone who wants to contribute can do so whilst abiding by the rules and guidelines that are keeping us safe.

The new dates for our winter Sea Slug Census will be 2-5 July 2021. You can download the guide with updated dates and deadlines here.

If you were able to explore your local coastline over the long weekend and did manage to photograph some sea slugs, your observations can still be useful. You could submit your findings to our Marine Life of Victoria project on iNaturalist, or send them directly to [email protected].

If you are heading to the coast during this time, please remember to follow all advice from health and environmental authorities around current Covid-19 restrictions, access to sites and water quality. More information about current restrictions can be accessed at the Victorian government coronavirus page and Parks Victoria. Take care and stay safe while enjoying our wonderful wild spaces.


In Partnership with the Melbourne Sea Slug Census:-

The Sea Slug Census is supported by the Victorian Government.

Caption: Tambja verconis, a nudibranch commonly spotted in Port Phillip Bay. Photo Liz Harper

What is a sea slug and how will you know if you’ve found one?

Sea slugs are actually snails i.e. they are sea snails (marine gastropod molluscs) that have seemingly lost their shells. Also known as nudibranchs, they are found in most marine habitats, occurring in shallow rock pools and in the deep sea. Knowing when you find one can be easy when they are the size of a football, or extremely difficult when they are smaller than the nail on your pinkie finger. Generally, if it is in saltwater and it moves like a slug it is most likely a ‘sea slug’. If you are unsure, take a photo and we will let you know.

Sea Slugs are one of the most popular and most photographed groups of marine invertebrates, with ~400 species known in Victoria. They are excellent indicators of environmental change because they have rapid life-cycles (less than 12 months), very specific food requirements, and respond to changing oceanographic conditions.

Yet there is very little basic knowledge on their diversity, distribution and ecology. To learn more about them we teamed up with Southern Cross University to have Victoria’s first Sea Slug Census in Port Phillip Bay, Westernport Bay and surrounds. The information gathered during Sea Slug Censuses will help marine scientists to update knowledge about the diversity and distribution of this spectacular group of molluscs.

To learn more about sea slugs in Victoria, check out these links:

A Museum Victoria field guide – Nudibranchs and related molluscs

Port Phillip Bay Taxonomic Toolkit

Australian Geographic – Nudibranchs: indicators of climate change

Facebook group for nudi-nerds and info on SSC events around the country (and world!)

Contributing to this project is simple! All you need to do is take a photo of any sea slug you see if you’re out and about on the coast during Census times. Your photo will be identified by experts to confirm when and where we are seeing different species of sea slug in Victorian waters. All data from the Melbourne Sea Slug Census goes towards the Sea Slug Census project, a community based initiative to document the biodiversity of our oceans through collaboration between divers and scientists. See the Sea Slug Census facebook group for details on other Census activities being held all around Australia- and even further abroad!


With travel restrictions in place over the long weekend we made the difficult decision to postpone the Sea Slug Census planned for 11-14 June.

Thank you all for your continued support of this project and understanding during this challenging times. The new dates for our winter Sea Slug Census will be 2-5 July 2021. 

Download UPDATED guidelines for the July 2021 Census

If you are heading to the coast, please remember to follow all advice from health and environmental authorities around current Covid-19 restrictions (including social distancing), access to sites and water quality. More information about current restrictions can be accessed at the Victorian government coronavirus page and Parks Victoria. Take care and stay safe while enjoying our wonderful wild spaces.

Photographing sea slugs for identification:

To help our experts with their identification, try to get a clear shot of the slug’s body from the side and/or include as many creature features (rhinophores, gills/cerata, oral tentacles) as possible. As always when out and about in nature, be mindful of limiting your impact on your subject and their surrounds.

A note on water quality if you’re out exploring our coast:

Heavy rain can impact water quality on our coasts, especially after fires and periods of smoke haze. In general the EPA recommends avoiding swimming near stormwater or river outlets 24–48 hours after heavy rain. Within Port Phillip Bay, you can check your local beach conditions at the Yarra and Bay Beach Report- https://yarraandbay.vic.gov.au/

In the lead up to the Winter 2021 Melbourne Sea Slug Census we heard from Professor Steve Smith, the founder of the nationwide Census project, on how our slug shots are helping better understand nudibranch biodiversity and where to next.

We were also treated to a series of tips, tricks and stunning photos from a panel of passionate sea slug spotters. These are the kinds of nudi nerds that cast their keen eyes over reefs, piers and rockpools every time there’s a Census so if you’ve ever wanted to know how, when and where to find sea slugs watch the videos below! We hope these talks inspire you to keep a look out for sea slugs on your next coastal adventure.


The Sea Slug Census: a citizen science program to document sea slug biodiversity and distribution

Professor Steve Smith of the Sea Slug Census project gives us an overview of the sea slug groups, why he was interested in using citizen science to study them, how the project has grown and what he’s learned from 66 Sea Slug Census surveys and counting! He also lets us know what happens to the data (your beautiful sea slug images) and plans for the future with this fantastic project that ReefWatch is delighted to be a part of.

Tips from a Seasoned Sea Slug Sleuth

Ian from the Victorian Sub-Aqua Group shares his 5 major tips for spotting sea slugs. Ian has been recording sea slugs at his favourite site, Blairgowrie, since 2017 and is up to over 120 species in the area alone! So it’s well worth listening to what he has to say about the way that you move, as well as what to look out for, if you want to observe these fascinating creatures on your next dive.


Snorkeling for Sea Slugs

Nick, another Census legend, gives us a different perspective on searching for sea slugs by taking us to the rockpools and sheltered bays that he regularly snorkels. He encourages you to think like a slug, talks about the best times and conditions to find sea slugs in shallow waters and near the surface, and shows us that persistence pays off.

Sea Slugs of East Gippsland

Holly from East Gippsland shares with us the colourful critters that can be found at places like Beware Reef, Mallacoota and Gabo Island. We learn that the slugs of eastern Victoria are a little different than the ones we find along the central bays areas and west coast and certainly worth seeing for yourselves!


Nocturnal nudibranchs and searching the seafloor

Rebecca is the Melbourne Sea Slug Census project’s reigning champion for finding slugs, spotting the most species in 6 out of 8 Censuses to date (and a PB of 60 species over one Census weekend). As part of her tips for locating sea slugs she talks about how many nudibranchs come out to play at night, looking for places that provide refuge for slugs to gather and using evidence of slug activity to hone in on a slug before you actually see it.

March 2021

It was a triumphant return to the project after a challenging year, and we thank everyone who contributed to the March Census while continuing to follow health advice and keep their communities safe. This March, 7 different locations hosted Census events and the challenge was set to see who could find the most species and greatest diversity of sea slugs.

The Victorian cohort managed to photograph 98 species of slug- the most species ever recorded during a Melbourne Census and considerably higher than what we found this time last year. More and more photographers are finding multiple species and getting their eye in for the small cryptic and unusual species. We were especially excited to see quite a lot of non-nudibranch sea slugs including some beautiful sacoglossans (sap-sucking sea slugs), headshield slugs, bubble shells, and side-gill slugs being photographed as this will bolster our records on Victoria’s sea slug diversity. Well done everyone.

With both the quantity and quality of images coming through it is getting quite difficult for our experts to select just a few winning entries for the categories of Best and Most Interesting photos. As per the report, we continue to award a single winner and honourable mention for both categories but read on for more highlights from this impressive haul of slug shots.


Best Photo: Jeremy Bishop, Okenia sp. RB2

Jeremy’s Okenia sp. RB2 caught the eye of the judges due to the beautiful details on display and the stark contrast between this pale dorid and the background that helps to showcase its features. There are several known yet unnamed, tiny Okenia in Victoria, but this was the first time that sp. RB2 has been spotted during a Census (it was also sighted by one other photographer this time). Well done, Jeremy.

Ian Scholey’s Tritonia sp. RB3 was an honourable mention, selected again for the impressive detail captured. This slug’s delicate velar tentacles (mouthparts) and branchial processes along its back are in great focus and again is a very well framed shot. Thanks Ian for another fantastic submission.

Caption: Jeremy Bishop’s delicate Okenia sp. RB2 was judged Best Photo for March 2021 by Bob Burn

Caption: Ian Scholey’s Tritonia sp. RB3 received an honourable mention from our judges for Best Photo

Most Interesting Photo: Rebecca Lloyd, Janolus sp. RB5

Rebecca Lloyd was awarded both the winning photo and honourable mention for two shots that contain extra biological information on her subjects. The winning photo of a rarely spotted Janolus sp. RB5 shows the slug nestled in among its bryozoan food source, while the judges were also impressed with her photo of two Doto pita on a hydroid food source with a curling egg ribbon in the upper left of the image.

There are many species of sea slug for which we don’t know much about their reproductive and feeding habits so photos like these can be of great value- well done Rebecca.

Caption: Rebecca Lloyd’s photo of Janolus sp. RB5 on its food source was judged Most Interesting photo by project founder Steve Smith
Caption: Steve Smith also gave an honourable mention to Rebecca’s pair of Doto pita, seen here with both their food and their twisting egg ribbon


Ultimate Nudi Hunter: Rebecca Lloyd

Rebecca maintains her title as the Ultimate Nudi Hunter for Melbourne, topping the list for March with 38 species. Nick Shaw was close behind with 35 species. A fantastic effort as always!

Nearly everyone who contributed photos found multiple species, and there were 11 teams or individuals who found at least 10 different species apiece.  It is also exciting to see more and more people are sending in photos of lesser known (and less sighted) slugs, some of which are only a few millimetres long and often well-hidden on their food source.

We hope that the reports you can download below, as well as the information here, can help hone everyone’s ID skills and where to start looking if you want to find more sea slugs the next time you’re out and about.


Most Photogenic Slug: Ceratosoma brevicaudatum

We don’t normally hand out awards to the slugs themselves, but we felt it was worth celebrating this species, officially the most sighted slug during Census times (with 142 individuals photographed since April 2018!).

It’s not hard to see why- not only is this beautiful slug one of the first that divers and snorkelers will notice, its relatively large size and striking patterns make it a wonderful subject to photograph. Here is a sample of some lovely C. brevicaudatum slug shots submitted to the March 2021 Census.

Celebrating our Sacoglossans

Our feature creature for 2021, Roburnella wilsoni, isn’t a nudibranch – it is actually a species of sap-sucking sea slug, or sacoglossan.

Caption: Roburnella wilsoni- the “feature creature” of the Melbourne Sea Slug Census for 2021. Photo credit: Nick Shaw

Sacoglossans feed by slicing open the cell walls of green and red algae using their knife-like radula (think a spikey tongue covered in tiny little teeth) and sucking out the contents- including the photosynthetic organelles (plastids) that convert solar energy into food. While many sacoglossans simply digest all of the cell contents, some species can preserve the fully functioning plastids in their own bodies and survive on the products of photosynthesis for months on end. That is why sacoglossans are often referred to as “solar-powered” slugs!

Because they are algae-eaters, most sacoglossans are green, red or brown in colour, and some have evolved leaf-like cerata that mimic their food source. They are often quite small, many only a centimetre or two in length. So, they can be a little tricky to spot (especially compared to their often brightly coloured nudibranch cousins). However, this fascinating group of slugs deserves our attention! You can find sacoglossans in intertidal and subtidal habitats, although because of their algal diet they are usually not found in very deep, low-light environments. Victoria has a rich diversity of sacoglossans, from typically slug-like Elysia species seen crawling around in shallow tide pools, to the unusual bivalved gastropods in the Juliidae family, to the Sacoproteus species that look like a strand of caulerpa (sea grapes).

Below are some of the sacoglossans recorded in March. If you’re patient, you might find one on your next adventure!

The next Sea Slug Census will be a Winter Wonderland edition – if you are out and about anywhere along the Victorian coast between 11-14 June be sure to send in your slug shots!

March 2021

36 teams submitted a total of 492 photos to the March 2021 Census, and in all, 98 species were recorded. This is the most ever recorded for a Melbourne Census and included good representation of the major sea slug groups. There were quite a few first-time sightings to add to our records, and our database on Victoria’s sea slugs continues to grow. Many thanks to all the teams and individuals that contributed to this fantastic Census.

Download full report for March 2021

March 2020

250 photos were submitted to the Census for March, and with everything going on we had to rely on snail mail to get them through to our expert Bob Burn for identification and judging. We ended up recording 61 species of sea slug! And we’re still adding species to our project records each new Census. Well done everyone.

Download full report for March 2020

January 2020

Smoke from the recent bushfires had severely impacted much of the Victorian coast this weekend, but around 100 intrepid nudi hunters made the best of conditions and submitted over 200 photos to the Census. We still recorded 72 species of sea slugs! And the quality of photos made Bob Burn’s judging of the competition a tricky task. Thanks to everyone who submitted to our first true summer edition of the Census.

Download full report for January 2020

October 2019

What can we say other than we were blown away by the number of nudis spotted this time! 88 species to be exact, some new additions to our records and a few entries that left our experts pleasantly surprised. October certainly seems like a busy time for both our nudis and the keen citizen scientists who search for them!

Download full report for October 2019

June 2019

Our winter wonderland edition of the Melbourne Sea Slug Census saw many people brave the cold water, but only 6 groups of nudi hunters managed to photograph slugs during that time. Still, 29 species of slug were sighted, with some really beautiful submissions and new species to add to the Melbourne census records. A commendable effort for a very chilly weekend!

Download full report for June 2019

March 2019 

Melbourne Sea Slug Census III was held over the 15-18 March. Many groups reported seeing far less slugs than expected, but all in all, over 100 nudi hunters that were out and about across the weekend recorded 48 individual species between them. Well done everyone!

Download full report for March 2019

October 2018 

The second Melbourne Sea Slug Census took place on the 12-15 October. Over four days, enthusiastic teams and individuals managed to find an incredible 75 species of sea slugs! It was a fantastic effort and the overall quality of images submitted impressed everyone involved in sorting and identification. Some of the species photographed during this Census have rarely been seen in Victoria, even by our leading experts!

Download full report for October 2018

April 2018

The first Melbourne Sea Slug Census was held on the on the weekend of 21-22 April. Thank you to the over 150 people who photographed different sea slugs (nudibranchs) in Port Phillip Bay, Western Port Bay and surrounds and submitted them to ReefWatch. Together, we found a total of 53 species of nudibranch!

Download full report for April 2018

We’re very pleased to share with you all the stunning entries we received in our Southern Sea Slugs Photo Competition (July 2020). These talented photographers certainly met the brief by showcasing how wonderful and diverse our temperate species really are.

It might come as no surprise that the competition was dominated by those beautiful dorid and aeolid nudibranchs, but we did have one colourful headshield slug representing the non-nudi species!

Photos were judged by Dr Julian Finn of Museums Victoria. Julian is a researcher and museum curator focusing on marine invertebrates. He is also a talented photographer and cameraman, and his images are featured in many field guides as well as Museum Victoria’s Marine Life Exhibition. You can check out some of his work, both in marine science and visual storytelling, here.

Winning Photo

PT Hirschfield, Two Verconia verconis

The award for winning photo goes to PT Hirschfield, for this incredible shot of two Verconia verconis crawling over their food sponge. In his judging Julian noted:

This image features a pair of chromodorid nudibranchs Noumea [Verconia] verconis, that imitate the colour and shape of the sponge they feed on.  

A highlight of this image is the framing, with the forward-facing individual in the foreground and the rear-facing individual in the background. This framing produces a superb image that is both pleasing to the eye and extremely informative. By providing two perspectives of the same species, the viewer can gain a greater understanding of the morphology of this intriguing animal and fully appreciate its beauty.”

Congratulations PT, fantastic work!


Runners Up

Nick Shaw, Phyllodesmium macphersonae

A striking shot of this fascinating aeolid. Julian had this to say about Nick’s photo:

This image features an aeolid nudibranch Phyllodesmium macphersonae with deep blue, yellow-tipped cerata, each containing a duct of the digestive tract. 

The orientation of the subject in the frame makes this image a standout. With the nudibranch facing the lens, and with sufficient depth of field, the key features (i.e. the oral appendages, smooth rhinophores and anterior cerata) are all in focus. The rear of the animal blurs smoothly, giving the image depth. An impressive image.”

Astute readers may also recognise this one from way back in the very first Melbourne Sea Slug Census report from April 2018! Well done Nick.


Liz Harper, Ceratosoma brevicaudatum

This beauty was captured in fine detail here in Liz’s shot- you can clearly see even the minute eggs coiling around inside the egg ribbon that the slug is laying down. Julian notes:

This image features the chromodorid nudibranch Ceratosoma brevicaudatum, reportedly Victoria’s most common nudibranch and, on account of its large size, often the first nudibranch observed by new divers and snorkelers. 

Unlike most images of this species, this image includes both the animal and a coil of freshly laid eggs. The framing and exposure of this image draws the viewers eye from the nudibranch to the eggs. The orientation of the nudibranch in the image results in all of the key structures (i.e. rhinophores, gills and branchial appendages) being in focus. This makes for a very pleasing, informative and natural-looking image.

Well done Liz for an exceptional entry!


Please enjoy the full gallery of competition entries:

Nicole Mertens, ReefWatch Project Officer