Sea Slugs are sometimes called the butterflies of the sea, but they’re more than just a pretty face! Not only are they adorned in a bewitching spectrum of colours, they’re also excellent indicators of how our environment is changing.

With 20 successful Melbourne Sea Slug Census events to date, our records of sea slug species found in Victorian coastal waters continue to grow.

Collecting photos of sea slugs present at different times during the year helps us to monitor these species and track any changes. But we need your help!

Winter Census 2024

Get out and about this winter to rock and ramble along the coast and search for slugs. The slugs themselves are not that fond of overheating in the sun, so whether you’re snorkelling, diving or walking the intertidal “think like a slug” and search the cooler shady spots for these cryptic critters.

Head to the ocean and search for sea slugs anywhere on the Victorian coast between Friday 28 June and Sunday 7 July and submit your images to iNaturalist!

Each of your observations increases knowledge on these short-lived and unusual molluscs. The images you send in will help us unravel the mysteries of these critters and detect changes in sea slug populations.

iNaturalist is a great community of experts and enthusiasts that can help you hone your identification skills and learn more about all kinds of wonderful wildlife. If you’re not already on the platform, you can head here for a guide and videos to help you sign up and start uploading your valuable images!

About iNaturalist and how to upload photos

Please note: the guide has been created for our Marine Life of Victoria project, but the steps for joining iNaturalist still apply. Your sea slug images will automatically be added to the Census if they meet the criteria (a sea slug taken anywhere along the Victorian coast during Census times).

Autumn census 2024

Visit the autumn census project page

The most recent Melbourne Sea Slug Census was in autumn 2024. You can check out what was found on iNaturalist project page.

Remember, you don’t need an iNaturalist account to check them out- although we strongly encourage you to join in on the fun! Having our data on iNaturalist allows the project founders to compare data from Censuses held around the country, as well as providing open access to the images that are being submitted.


In Partnership with the Melbourne Sea Slug Census:



The Sea Slug Census is supported by the Victorian Government.


Caption: Tambja verconis, one of the more commonly spotted sea slugs in Victorian waters 📷 Kade Mills

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

Sea slugs are actually 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!)

Caption: Your sea slugs shots can become valuable data. If you take a photo of a sea slug during a Census, upload it to iNaturalist to contribute to the Sea Slug Census project.

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 and upload it to iNaturalist. Your photo will be identified by the iNaturalist community and verified by experts. These observations help inform scientists when and where we see 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!

If you are heading to the coast, 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.

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

Heavy rain can impact water quality on our coasts, especially after flooding. 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 EPA Beach Report.

If you’re 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 any COVIDSafe restrictions . More information can be accessed at the Victorian government coronavirus page and Parks Victoria. Take care and stay safe while enjoying our wonderful wild places.

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.

Caption: A photo of Ceratosoma brevicaudatum showing all the features that help with identification 📷 Jack Breedon


Uploading to iNaturalist:

Sharing your observations with the iNaturalist community is easy!

First of all, you’ll need to sign up to iNaturalist- check out this guide if you’re unsure where to start. Next, find the project you’re interested in and click on the green button in the top right of the page. Note: you don’t have to join any projects to upload your images, but doing so will keep you in the loop with any project updates.

Drag and drop your images to upload them. You can add multiple photos per observation by stacking them on top of one another. For each observation, iNaturalist will make ID suggestions. You can either stick with the suggested ID or enter your own. If you’re unsure, just go with what you’re confident of – e.g. Mollusca, or even Animalia- it’s a start, and someone will be able to help narrow it down.

Add the location and date data. If you took all your observations at the same place on the same day, you can select all observations and enter that info on the left. Or, you can add this info under each observation.

Lastly, you can choose to add your observations to relevant projects you’re a member of. Note that any images that meet the date, location and species criteria for our Sea Slug Census projects will be automatically added to that project. But, you can also make sure they feature in projects like Marine Life of Victoria Project and Victorian Nudibranch.

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 2022

Our first Census with the iNaturalist format, March saw 79 different species of slugs identified from 323 observations. Photos were submitted from Warrnambool in the west right around to Mallacoota in the far east of the state.

The ReefWatch team, along with VNPA’s NatureWatch and Youth teams, also journeyed to East Gippsland in March for citizen science, sun, saltwater and of course sea slugs. We were joined by an amazing crew of curious locals and passionate nudi nerds, lead by local legend Holly Baird. We had a very warm welcome at Marlo Pub for some science-in-the-pub style chats on the Thursday night, followed by rockpool rambles and snorkels over the weekend. Big thanks to everyone who turned up to one or more of the events and tried their luck hunting for sea slugs at beautiful Salmon Rocks, Cape Conran.

While the iNaturalist community is a great resource for identifying species and sharing knowledge, we’re very lucky to still have Bob Burn at the ready to help out with any unusual finds. Bob was pleased to see this submission from nudi nerd Nick Shaw – Burnaia helicochorda. Some of you might recognise this beautiful aeolid from Bob’s own Museum Victoria Field Guide!  Another great find Nick, and a first for our Melbourne Sea Slug Census records.

The fact that we’re still seeing new entries to our database after 13 local Censuses just goes to show how many sea slug species call Victorian waters home- and how much their occurrence can vary in space and time. Running Censuses frequently throughout the year and across many years will help us understand more about the ecology of these mysterious molluscs and we thank everyone who has contributed their slug shots to this citizen science project.

Caption: Burnaia helicochorda was one of the more interesting slugs to turn up during the March Melbourne Sea Slug Census 📷 Nick Shaw (source: iNaturalist CC-BY-NC)

Expanding the Census

Our feature creature for 2022 is Hypselodoris bennetti– a colourful chromodorid found from Southern Queensland right around into central Victoria, most commonly spotted in the east of the state. We wanted to highlight one of the species that you might not find in Port Phillip or Westernport bays. While we’re known officially as the “Melbourne” local organisers of the Sea Slug Census program, we’re encouraging people from all over Victoria to take part and help us learn more about when and where we find sea slugs right along our coastline.

Caption: Hypselodoris bennetti– one of the colourful chromodorids that can be found in sponge gardens and rocky reefs on the east coast of Victoria 📷 Holly Baird

March/April 2024

Check out iNaturalist to view the March/April census sightings.

March/April Sea Slug Census results


January 2024

Check out iNaturalist to view the January census sightings.

January Sea Slug Census results


October/November 2023

Check out iNaturalist to view the October/November census sightings.

October/November Sea Slug Census results


August 2023

Check out iNaturalist to view the August census sightings.

August Sea Slug Census results


April 2023

Check out iNaturalist to view the April census sightings.

April Sea Slug Census results


January 2023

Have a look at all of the January sightings on iNaturalist.

January Sea Slug Census results


October 2022

You can check out everything that was seen during the October census on iNaturalist.

October Sea Slug Census results


July 2022

All the photos and stats from the July census can be viewed on iNaturalist!

July Sea Slug Census results


March 2022

In March this year we moved to iNaturalist to collect our Sea Slug Census data. You can see where sea slugs were observed, who found the most species, and what those slugs look like all at our March Census project page.

Check out the March Sea Slug Census Results


January 2022

Our first Census for 2022 saw the ReefWatch team join Otway Ocean Care at Marengo reef for some sea slug searches. Around the state, over 80 people joined in the Census fun. In all, 17 individuals or groups recorded 70 species of sea slug from over 300 photos, another fantastic effort.

Download report for January 2022


October 2021

With stay-at-home orders lifted, many people returned to the coastal places they loved just in time for our October Census. 18 individuals or groups submitted over 450 photos between them! In all, we recorded 92 species of sea slug.

Download report for October 2021


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 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

Kade Mills, ReefWatch Coordinator