By Dr Elodie Camprasse (Deakin University)

Spider crab gathering in Port Phillip Bay. Image credits: Elodie Camprasse

There is a lot we do not know about our precious marine life. In aquatic environments, both freshwater and marine, amazing biodiversity goes unnoticed, particularly in temperate ecosystems. I often wonder why we know so little about the critters in our blue backyards – lack of interest from the public and decision makers? Lack of funding? Constraints imposed by the environment? Probably all of the above.

With a team of researchers at Deakin University, I study an amazing natural phenomenon which unravels every year in shallow parts of Port Phillip Bay and the Great Southern Reef – the gathering of thousands to tens of thousands of Great Spider Crabs (Leptomithrax gaimardii) coming to seek safety in numbers while they shed their shells to grow bigger. This process is called moulting.

Even though this event has been featured in the media worldwide, scientists know very little about the ecology of those spider crabs, their gatherings and their role for other species. Despite the crabs coming together in such big groups, they can be hard to track down. They can march through various areas quickly, as they are looking for a place to settle – they could then be seen by divers or snorkelers, or by people walking on the beach or on piers in an area, but quickly disappear to another location. Even when the crabs are settled into what is called an aggregation, they might move to from the shallows to deeper waters or move away from actual dive sites which are accessible and safe. And if the weather is not suitable for outdoors activities or the water is too rough, the crabs might remain hidden and unreported.

Introducing Spider Crab Cams! In 2022, thanks to funding from the Department of Energy, Environment and Climate Action, our team trialled the deployment of timelapse cameras – our trusty Spider Crab Cams – to monitor the marine environment for us and help us record spider crab activity. The cameras, which snapped images every 5 minutes during daylight hours, were deployed on Bunurong country on the Mornington Peninsula, at known aggregation sites. Though spider crab activity there was very low, citizen scientists reported a spider crab aggregation on Wathaurong country, on the opposite side of Port Phillip Bay on the Bellarine Peninsula. We moved the cameras to the aggregation that was taking place there in June and were able to determine how long the aggregation lasted thanks to the images recorded.

Spider Crab Cams deployed on the Bellarine (left) and the Mornington (right) Peninsulas. Image credits: Michael Anderson (left) & Elodie Camprasse (right) 

Dr Elodie Camprasse and Dr Justin Rizarri deploying a Spider Crab Cam. Image credits: Sam Wines

In total, we obtained more than 66,000 images, and more than 7,000 images had spider crabs in them. The images allow us to determine crab activity, including if the crabs had moulted or not, and how long spider crab remains (potential food for other creatures) were found in the environment. The images also allow us to gather data on the ecological role of the spider crabs and their importance for other species such as predators and scavengers. Even images without spider crabs in them are valuable to document marine life and provide baseline data showing what species are present in the environment at that time of year.

Type of images collected thanks to our Spider Crab Cams

But we could not do this work alone! The Spider Crab Watch program was launched on one of the biggest online platforms for people-powered research, Zooniverse. After an initial phase of beta test to ensure the project would produce suitable results and be enjoyed by citizen scientists without previous experience identifying marine life, we were able to launch and recruit some help to go through the images. We created three series of tasks for citizen scientists to choose from: one to identify spider crabs and their conditions (moulted, unmoulted or dead/remains), one to identify other marine life, and one to characterise human presence and activity (presence of people snorkeling or diving, presence of fishing equipment, etc). We also developed tutorials and a field guide to assist volunteers, particularly those without any prior knowledge of marine species.

The classifications of citizen scientists will be aggregated and compared to gold standard classifications to confirm the accuracy of their work, and start answering questions about spider crabs and their aggregations. In the meantime, the Zooniverse platform has allowed regular interactions with citizen scientists through the “Talk boards” where people are asking questions and are expressing their interest in the project, their curiosity towards the spider crabs and other species. Within 8 months of the launch, more than 3,600 volunteers have helped classified images and our team has received 700+ comments and interactions, helping us increase awareness of spider crabs and of marine species in Australia and beyond.

Curious about the project? Keen to check out the images collected? Why not become a marine scientist for the day and help classify images? Check out the project page.

If you live on the Great Southern Reef and come across spider crabs, you can log your sightings on Spider Crab Watch on iNaturalist.

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