Most South Australian’s experience with crabs involves eating them or catching them and usually if they are local they are our blue swimmer species.
As divers we do see blue swimmer crabs in Saint Vincent’s Gulf but most crabs we see around jetties and reefs are way more interesting.
We have spider crabs and sand crabs and decorator crabs and hermit crabs and rock crabs and helmet crabs and sponge crabs just to name a few we see regularly.
This Sponge Crab (Austrodromidia octodentata) is one of many species which grow algae and sponge on its shell as a form of camouflage. Very often the entire top surface of one of these guys will be just one big sponge.
This guy obviously has no sponge and looking more closely at the fine brown covering of its shell I wonder if the hair-like structures are an open invitation for a new sponge resident, ie crab carapace for rent.
For now it seems happy about the vacancy as it goes about its benthic business.
Photo: Robert Rath, ‘SpongeBob’, 1/200s f/7.1 ISO100 50mm