Blue mussels are shallow water organisms, occurring to a maximum of 10 metres depth on shallow sandy bottoms in estuaries, in seagrass beds or on rocky shores, where they form dense beds by attaching to the substrate via a mass of byssal threads. They tend to be most abundant at or near low tide level, where the food supply of phytoplankton (marine plants) is most concentrated.
Mussels are bivalve molluscs. Mussel shells are blue in colour and covered by a black layer, they are fan shaped, angular at one end and rounded at the other. The valves, or shells, can close tightly so that the animal can withstand periods at low tide out of the water. Blue mussels are filter feeders. They pump water through the gills which filter out small particles such as phytoplankton, zooplankton and other organic material. Sediment is discharged while food is retained and passed into the stomach for digestion. The life expectancy for the blue mussel can be up to 15 years, however adverse environmental conditions such as pollution will reduce the size of the mussel and its lifespan. Individuals can grow to 12 centimetres long.
Mussels spawn, by releasing up to 8 million eggs and sperm into the water column, and is triggered by the cooler water temperatures at the onset of winter once the animal reaches approximately 3 centimetres in length (11 months old). Once fertilisation has taken place, a free-swimming larvae is formed and spends a period of time floating in the plankton which is determined by environmental factors such as temperature. Eventually the larvae settle upon suitable substrate with their byssal threads.
Blue mussels were most likely introduced to Australia by ships arriving from Europe, as they are a notorious fouling species. They have economic importance due to their edibility, and are now the only local mussel raised commercially and is commonly served in restaurants. The blue mussel occurs commonly in temperate waters from Geraldton, WA to NSW and around Tasmania. It is also widespread overseas.
Occurrence at the Busselton Jetty:
Blue mussels tend to colonise the upper regions of the piles, from the shoreline to the end of the jetty. They grow close together and form large clusters. When a blue mussel dies the empty shells are often used as a home by False Tasmanian blennies.