by
Jenny Edwards
A Mulberry Whelk may not look like a fierce predator to you but from the viewpoint of a tubeworm, barnacle or oyster that is exactly what it is. It is also known as the Oyster Borer for obvious reasons as you will see.
Mulberry whelks (Morula marginalba) are small shells, usually to about 20mm long, often seen huddled together in crevices at mid tide levels of estuaries and rocky shores. If the shore is still wet and sheltered from large waves they can be found on their prey. On rocky ocean shores smaller ones are more common on tube worms while the larger ones seem to prefer Pink Surf Barnacles. In estuaries they are frequently seen where oysters are numerous. The whelk’s shell has rows of rounded black lumps which do make it look a bit like a mulberry.
All predatory whelks have a long siphon used to sense chemicals in the water, a bit like an underwater nose. Their shells have a groove at the front which protects the siphon.
When feeding the whelk crawls onto the barnacle, tubeworm or shellfish and drills a hole in the calcium carbonate covering of its prey. In the case of barnacles, whelks usually attack the doors that open to allow the animal to feed. The whelk releases an acid from a gland in the front part of its foot. This softens the calcium carbonate which is then licked away by the rasp-like tongue (radula) of the whelk. When a hole has been made in the prey the whelk inserts its tube-like mouthpart into the victim and, with its radula, tears off and eats the soft tissues.
This all happens at a snail’s pace, which is appropriate since whelks are snails. It takes 30-40 minutes for each application of the acid then about a minute of rasping before the process is repeated. The whelk takes about 8 hours to penetrate a shell 2mm thick and can take up to 4 days to get into a larger barnacle.
The Mulberry Whelk releases its eggs and sperm into the sea from spring to autumn when microscopic planktonic algae (phytoplankton) are most available. The larvae feed on the phytoplankton and go through several changes in body shape before the few survivors settle in suitable intertidal habitats.