With nine 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 Ninth Melbourne Sea Slug Census was held between Friday 2 and Monday 5 July. While restrictions and some less-than-ideal weather meant that fewer people were out and about during that time, we still received over 150 photos and some great finds. Results and report can be found below.

The next Melbourne Sea Slug Census is scheduled for the 22 – 25 October. If restrictions on outdoor activities change in response to the evolving situation in Victoria we may have to postpone or cancel- we’ll post updates here and on the ReefWatch facebook page.

If you are heading to the coast during this time, please remember to follow all advice from health and environmental authorities around social distancing, access to sites and water quality, and make sure you’re complying with current COVIDSafe restrictions. 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 places.

You can download the guide to taking and submitting photos to the Census here.

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!

Thank you all for your continued support of this project and understanding during these challenging times. The next Sea Slug Census will be held between the 22-25 October 2021. These dates will be subject to current restrictions on outdoor activities. If you are heading to the coast during this time, please remember to follow all advice from health and environmental authorities around social distancing, access to sites and water quality in your area, and make sure you’re complying with current COVIDSafe restrictions. Take care and stay safe while enjoying our wonderful wild spaces.

Download guidelines for the October 2021 Census

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.

July 2021

After postponing the Winter Census due to lockdown, we were just able to squeeze a rescheduled event in to a period of Covid-free time before heading back into stay-at-home orders. As such, there were some delays in getting your wonderful photographs identified by the experts. But the report is now ready for viewing!

Download report for July 2021

We thank everyone who contributed to the July Census while continuing to follow health advice and keep their communities safe. The weather during this time was not ideal, and between rough conditions and ongoing restrictions fewer people were out and about. Despite all this, 8 teams or individuals managed to photograph 57 species of sea slug between them!

We’re continuing to see more photographers find multiple species and get 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 and honourable mentions for the categories of Best and Most Interesting photos!


Best Photo: Holly Baird, Goniobranchus tasmaniensis

Holly’s Goniobranchus tasmaniensis from Beware Reef is such a clear and stunning photo of this species, and this large-spotted colour form is different to most individuals seen throughout the rest of the state – however, it is considered the “normal” form for NSW populations.
Bob Burn also notes that this photo clearly shows ‘the diagnostic red ring around each rhinophoral sheath and gill cavity”. Plus, you have to love the colourful shrimp posing for a pic in the background. Congratulations Holly!

Peter Fuller’s Ercolania boodleae was an honourable mention. Steve Smith of the Sea Slug Census program noted the great perspective and depth-of -field in this portrait of a common though diminutive local species. Thanks for your lovely contributions Peter.

Caption: Holly Baird’s vibrant Goniobranchus tasmaniensis was judged Best Photo for July 2021 by Bob Burn

Caption: Peter Fuller’s Ercolania boodleae received an honourable mention from our judges for Best Photo




Most Interesting Photo: Nick Shaw, Eubranchus sp. RB3

This tiny Eubranchus is described as ‘A small white species with a red patch on the head and black spots on the cerata’ and is known only from the rockpools of Point Londsale. Bob Burn notes that very few specimens have ever been recorded. Great find Nick.

Caption: Nick Shaw encountered a very small and rarely seen Eubranchus that has only ever been spotted in and among the tide pools at Point Lonsdale. A great find.

Steve Smith nominated an additional two images for honourable mentions in this category, noting that both show interesting biological/ecological features or behaviour in the sluggy subjects. The first is Holly Baird with a feeding pair of Polycera capensis, and the second went to  Ian Scholey’s Aeolidiella drusilla with egg mass. Well done Holly and Ian!

Caption: Ian Scholey’s photo of Aeolidiella drusilla shows the slug next to what appears to be a freshly laid, delicate egg ribbon
Caption: Holly Baird’s image of a pair of Polycera capensis feeding on a blue bryozoan. This species is an introduced slug, originally described from South Africa, and appears to be establishing a population in Victoria.


Most Slugs Spotted: Nick Shaw

Nick Shaw is the reigning champion for our Winter Census events, this time finding 37 species- which is more than the total number of species spotted the last time we held a Winter Census in 2019! Great effort Nick.

Everyone who contributed photos found multiple species, and 3 out of 8 teams 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.


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).

The next Sea Slug Census will be our October Census – usually a bumper time for sea slugs! If you are out and about anywhere along the Victorian coast between 22-25 October be sure to send in your slug shots.

July 2021

Special thanks to the 8 teams or individuals who braved the chilly waters in between lockdowns to submit photos of 57 different sea slug species, from Port Phillip Bay to far east Gippsland. Capturing data from different times of the year, including during winter, helps us gain a better understanding of our southern sea slugs and their occurrence in space and time.

Download full report for July 2021

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