The Barnacle Window

A coral barnacle of the genus Cantellius.
Image: Gary Cranitch.


23 May 2010
Specimens of barnacles collected during the CReefs Ningaloo expedition by Andrew Hosie of the Western Australian Museum may provide insight into the symbiotic relationship between certain species of barnacles and sponges.
Andrew is the first researcher ever to visit Ningaloo Reef solely to document the diversity of barnacle fauna. He is particularly interested in sponge barnacles.
"It's unknown whether the barnacle burrows into the sponge, or the sponge grows around the barnacle, but effectively by the barnacle's adult stage, it is buried by the sponge with just a small hole uncovered through which the barnacle can feed on plankton," Andrew says.
Most barnacles grow a shell wall made up of a series of overlapping plates, but the shell of certain sponge barnacles leave a membrane-covered window between the animal and the sponge. Andrew hopes to collect specimens from Ningaloo Reef that will enable him to better understand the relationship between barnacle and sponge, and the purpose of the window in the barnacle shell.
"It could be as simple as conserving energy: the barnacle is protected by the covering of sponge so it may not need to build a strong shell. It could enable chemical communication: perhaps the barnacle is convincing the sponge's immune system not to attack. It is possible that the barnacle is deriving nutrients from the sponge, although in some parasitic barnacles that derive nutrients from the host rather than from plankton, the feeding apparatus atrophies, but is not the case with these species," Andrew explains.
Andrew will examine specimens under scanning and transmission electron microscopes to learn more about the window function.
Andrew says that identifying differences between barnacle species, and expanding the taxonomy of marine life more generally is essential for us to understand, and hopefully to protect, the natural world.
He draws on an analogy made by Dr Ashley Rowden of the New Zealand National Institute of Water and Atmospheric Research.
To paraphrase Dr Rowden: "Think of the world as a car. If you are just driving your car to the market on Sundays, you probably don't need to know exactly what all the parts do. You might understand the steering wheel and the gearbox and the tyres; we can think of these as the species that are common, understood and useful to humans.
"But if you are driving your car in the Paris-to-Dakar Rally, you want to have at least some idea of the function of every piston, nut and valve on that car; and we can think of these parts as the species we do not yet know about.
"Until very recently we have understood our world as if we were Sunday drivers, but driving it as hard as if we were in the Paris-to-Dakar Rally.
"The least we can do is learn how it works," he says.