by Jenny Edwards
"Thousands die of dehydration on our beaches!" This would be a world headline if it applied to people but luckily for us it doesn’t. Goose barnacles have been the ones to suffer lately.
There are many species of goose barnacles but the most common ones to land on our shores are the short-necked (Lepas anserifera), and the long-necked (Lepas anatifera).
The short-necked goose barnacle, found in tropical waters and all around Australia, is smaller and has a shorter stalk. Its shell valves are finely ridged and edged with orange.
The long-necked goose barnacle, found around the world, is larger with a mobile stalk up to 20cm long, that is purple-brown in adults but almost colourless in young animals. Its shell valves are smooth and white with brownish tints.
The common names are completely misleading. The “neck” is actually a movable attachment which anchors the crustacean to something that floats. This is often driftwood.
Goose barnacles have nothing to do with geese, but medieval Europeans once thought them to be an intermediate stage in the development of migratory geese, since eggs and goslings were never seen. They were believed to grow to a certain size then drop off into the sea and develop into adult geese. The barnacles’ feathery feet that are used to catch prey from the plankton probably helped get the myth started.
Barnacles are hermaphroditic; each individual is both male and female. Its long penis can reach a nearby barnacle which acts as the female. Fertilised eggs are released into the ocean and the first larval stage is similar to that of prawns.
After several stages in the plankton the larva attaches itself using cement organs in its small antennae, and develops five white shell valves to cover most of its body. The valves open to allow the animal to feed.
They grow very rapidly. The long-necked goose barnacle can grow from tiny settled larva to 30 mm shell length in 17 days and is then mature and ready to release eggs.
Barnacles are not loved by owners of boats and ships. Barnacle growth on the hull can slow a vessel by 30-40%. However, they are prized by others. In some parts of the world goose barnacles are considered a sea food delicacy.