Call for citizen scientists to help aggregation investigation

Despite their global fame, spider crabs and their aggregations are shrouded in mystery. Very little information on their ecology and biology is available. For example, we don't know where the spider crabs come from before the aggregations, what the ecological role of the aggregations is, what triggers them, and why they choose the sites they do – including Rye and Blairgowrie piers. We know the main aggregations take place on the Peninsula in winter, but we also want more information about aggregations that happen at different times of year all around Port Phillip and beyond, and we want to understand the purpose of these aggregations.

A team of researchers at Deakin University is doing surveys to gather data on spider crabs and their aggregations. But using a mix of traditional science and citizen science is crucial because spider crabs and their aggregations can be unpredictable and short-lived; the marine scientists need everyone who lives and plays around the bay to keep an eye out for them and let them know when and where they are seen or not seen. Potentially, the spider crabs and their aggregations can be found anywhere in the bay at any time. The team also welcomes observations from anywhere in Victoria and Australia, as well as past sightings if people have images from previous aggregations to upload.

Anyone can get involved, whether you go boating, sailing, kayaking, stand-up paddleboarding, walking on the beach and on piers, diving, snorkelling and so on. You just need to create an account on iNaturalist and then you can join the fun at www.inaturalist.org/projects/spidercrab-watch

Logging a sighting only takes a few minutes, and video tutorials have been created to guide you through the process. These are available in the Spider Crab Watch ‘about’ section on the iNaturalist project page. The information needed is the date, time, location and what was observed – whether live spider crabs or moults. You’re also encouraged to post if you didn’t see any spider crabs. This is called absence data, and it’s important to tell us where and when spider crabs are absent, particularly as researchers are interested in finding out what triggers the aggregations. Together with presence sightings, this gives us a more complete picture of the habitats spider crabs like and aggregate in.

The team of researchers love sightings with photos, but if you don't have photos you should still submit the details. Obviously you won’t need to post photos

if you don’t see any spider crabs. There are also a few other optional fields you can fill in. People can choose to change their geoprivacy settings for their locations and select either ‘obscure’, which means locations are displayed as a random point in a radius around the site rather than the exact position; or ‘private’, where the locations won't be displayed on a map at all and only project administrators – two researchers at Deakin – will have access to the locations. In these cases, the locations will not be made public during aggregations and will only be used for research.

People interested in taking part in the project can email Dr Elodie Camprasse at elodie.camprasse@deakin.edu.au with any questions. Finally, to get the latest Spider Crab Watch news and results delivered to your inbox, you can sign up at redcap.link/61ovve4j

JOSIE JONES Follow me on Instagram @sharejosie