A collaboration of coast and countryside organisations on The Lizard Peninsula

Common MusselsCommon (or Blue) Mussels are a familiar find on our shores. Look for them attached to rocks in rockpools, and in the zone between high and low tide.
Photo: Amanda Scott

COMMON MUSSEL

Scientific name: Mytilus edulis

Other common names: Blue Mussel

What to look for:

Colouring and appearance: The shell is longer than it is wide and approximately triangular with rounded edges and concentric growth lines. However, the shape and the colour (purple to blue, with occasional brown specimens) do vary.
Size: Usually from 5 to 10 cm, but with some as small as 2 cm and others as large as 20 cm.
Where: Common round the whole British coastline.

Common MusselsThe elongated bivalve shells and dark blue to purple colour of Common (or Blue) Mussels are a familiar sight on British shores. These molluscs live in the intertidal zone (this is the zone above water level at low tide, but underwater at high tide). They attach to rocks or other hard surfaces using byssus threads – strong filaments produced by glands in their feet that anchor them securely. Although they stay in one place for long periods of time, they are semi-sessile, meaning they can move to new locations if necessary. They are filter feeders, straining food particles from the water.

A group of Common Mussels might all look similar to each other, but the species does in fact have separate sexes. To reproduce, males and females release their sperm and eggs into the seawater. For each egg, there can be up to 10,000 sperm. Even so, many eggs do not become fertilized and, of those that do, only a few reach maturity.

It's not uncommon to see Common Mussels in large groups, called aggregations, in which they use their byssus threads to attach to each other. The purpose of this may be to maximise reproductive success or improve protection from predators. Long-term persistent aggregations can form mussel beds of very dense populations.

Common Mussels are, of course, eaten by humans, but are also enjoyed by seabirds, such as Oystercatchers, as well as crabs and starfish. Dog Whelks enjoy feasting on them, too, but the Mussels have a protection against them: they use their byssus threads, which are very sticky, to trap the Whelks and prevent them moving on, meaning they slowly starve.

Did you know…?

…In the Wadden Sea (an intertidal zone in the North Sea, lying along the European coastline from The Netherlands to Denmark), there are mussel beds of millions of individuals covering areas several kilometres in size.

 

Published: February 2021
Author: Amanda Scott
Photo: Amanda Scott

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