IDENTIFICATION
The twin shells of the brown mussel are dark brown to black and may have a green tinge. In KwaZulu-Natal, mussels form dense beds on wave-exposed rocky shorelines. Mussels attach to the rocks using their hair-like byssus threads (known as the beard).

DISTRIBUTION
In southern Africa brown mussels occur from central Mozambique to False Bayin the Cape but are also found north of Walvis Bay on the west coast. The brown mussel is adapted to live in the lowest zone on rocky shorelines but may extend into the subtidal zone.

FEEDING
As mussels are attached to the rocks they have to rely on delivery of their food by waves and currents. This strategy is called filter feeding. At high tide, mussels open their shells and strain organic particles and plant plankton from the seawater using their gills. Mussels can filter up to 70 litres of seawater a day. As filter feeders, they can accumulate disease organisms and toxins in their flesh. For this reason, harvesters should not collect mussels close to outfall pipes or river mouths and should ensure that they are thoroughly cooked before eating.

REPRODUCTION
When you open mussels, you may notice that there are two colour varieties. Orange mussels are females and males are off-white. Mussels breed in winter and spring, after which they are very thin, having lost up to 60% of their body mass. They practice synchronous spawning with males releasing sperm and females releasing eggs simultaneously. External fertilisation occurs at sea and eggs hatch into larvae that spend approximately two weeks in the ocean currents before settling inshore. Young mussels prefer to settle on adults and harvesters are advised to thin mussel beds being careful not to create large patches of bare rock.

GROWTH
The rate of mussel growth depends on factors such as water temperature, wave exposure and availability of food. In KwaZulu-Natal, mussels do grow fairly rapidly, reaching approximately 55 mm after a year. They can breed at this age.

FISHERY
In KwaZulu-Natal, old mussel middens show that humans have been using mussels for food since at least 300AD. Today the brown mussel is an important resource species harvested by both recreational and subsistence collectors. In KwaZulu-Natal, approximately 11 000 licensed recreational harvesters collectively harvest 200-250 metric tonnes of mussels (Perna perna) per year from 110 km of rocky shore whereas approximately 200 subsistence collectors harvest 12-50 metric tonnes from 3 km of rocky ledge.

MANAGEMENT
At present recreational mussel collectors require a permit to gather 30 mussels per day. The rights of subsistence fishers have also been recognised and management systems (including introduction of permits) are being developed for this sector. To ensure that mussels are harvested sustainably, scientists and managers have developed a zonation plan for KwaZulu-Natal.
This plan incorporates closed areas to serve as reference areas and to provide larvae to seed adjacent exploited areas, closed areas for research and open areas to cater for recreational and subsistence harvesters.

ECOLOGY
As filter feeders mussels play an important role in coastal foodwebs, harvesting a particulate food source that is otherwise unavailable for other groups in the food web. In KwaZulu-Natal, rock lobster, octopus and fish such as Natal stumpnose, pompano, blacktail, and musselcracker, all depend on the brown mussel for food. Dense clumps of mussels constitute a complex three-dimensional habitat and provide homes for many seaweeds and animal species. We need to conserve mussels if we are to conserve the biologically diverse communities they support.

Source: www.kznwildlife.com