Findings: Getting stuck in with friends

They might not appear to be the most sociable of creatures, but ecologists have found that limpets have discovered that there is safety in numbers, writes Steve Farrar.

While such behaviour is understood in animal species such as herds of antelope or shoals of fish, it has seldom been seen in anything as simple as a rock-hugging shellfish.

The findings could have important implications for limpet conservation and commercial collection.

Tim Theobalds and Mark Browne, postgraduate researchers at Plymouth University, and Ross Coleman, senior lecturer in ecology and behaviour, drew their conclusions after simulating a bird attack on a group of limpets.

The experiments suggested that by grouping together, the shellfish were warned of a predator's presence and were hence able to tighten their grip on the rock on which they lived.

Mr Theobalds had noted that oystercatcher birds usually attacked a single limpet within a particular group before they flew off to locate another set.

This was curious as a bird could presumably save energy by working its way through the entire cluster.

Mr Theobalds simulated the sharp peck that an oystercatcher delivers to a limpet by rolling a marble down a steel tube aimed at the front of the creature.

Five seconds later he measured the neighbouring limpets' clamping response by attaching a digital spring scale to them and then pulling until they came off the rock. He found that after such an attack, the shellfish were significantly harder to remove.

"The early warning signal received, in the form of vibrations from the attack of a neighbouring limpet, gives them a clue that a predator is in their midst and they must clamp down," Mr Theobalds said.

"Thus, the motivation for grouping behaviour appears to be as valid for the simple limpet as it is for the more complex fish."

The findings were presented to the British Ecological Society's winter meeting at York University yesterday.