Mussels

I don't know of any other place where mussel shells lie as thick a carpet as they do here. as far as the eye can see - millions. If you would try walking through them, you will sink in up to your ankles. and driving through them will have you stuck. According to Jacobus, this was the most difficult and challenging terrain of his hike so far.  So where did it come from and why is it here between the Spoeg river and the Olifants river? Nobody I asked could actually give me a satisfactory answer. Mussels aren't harvested on the West Coast as intensive as on the East Coast. Also, in these cold waters there aren't any predators to speak of which could hunt on this large a scale. Could it be a result of Red Tide?

As any other animal belonging to the class Bivalvia, the mollusks has a pair of large gills used for respiration and filter-feeding.  They use hairs on the gills to pump water into the mantle cavity through an inhalant siphon.  The gills trap tiny particles from the water and move them to the mouth where the edible particles are eaten, while inedible materials such as grains of sand are discarded along with waste water that passes out of  an exhalant siphon at the back of the body.  A bed of mussels can remove all the food from the water above them within an hour.

One big drawback of this effective filter system, is the fact that mussels will gather the toxic organisms associated with Red Tide and store it in their bodies for up to four months.  Although the mussels are not usually harmed, as few as two mussels contaminated with toxic red tide organisms can prove fatal if eaten by humans.

Obviously this can be quite a problem here in the wild part of the West Coast. Annually thousands of visitors flock to this part of the coast for a free holiday. They come to relax and live from the sea. A dangerous situation at best... because you won't see Red Tide, and the locals will probably have forgotten all about the last one, there still can be mussels that are still toxic. Therefor the Marine and Coastal Management branch of the Department of Environmental Affairs and Tourism made available a phone number to call to make sure if mussels are safe to be eaten. Contact the Red Tide Hotline at 021 402 3368.  A recorded message will tell you whether it is safe to collect and eat shellfish.

Three of our country's four mussel species are available on our West Coast in abundance, the ribbed mussel (Aulacomya ater), the black mussel (Choromytilus meridionalis) and the introduced Mediterranean mussel (Mytilius galloprovinciallis).

The Mediterranean mussel is cultivated at Saldanha Bay and preferred above our own mussels because they are bigger and grow faster.  They are grown on ropes which are suspended from wooden frames.  Approximately 2000 tons of cultivated mussels are being produced annually by South African shellfish farmers in Saldanha Bay.  These mussels were imported in the 1970's from Europe and adapted so well to the cold water that they grow and spread at an astonishing speed of 115km per year. They are now found in an area of more than 2000km, going north towards Namibia.  Because they form such dense, multi-layered beds, they dominate the intertidal rocks and supplant our own indigenous species and big limpets (e.g. bearded limpet, Scutellastra argenvillei).  Although it is never a good thing when our indigenous species are supplanted by alien species, this situation resulted in a few interesting and positive changes.

For example smaller intertidal species flourish in dense Mediterranean mussel beds. Furthermore the number of whelk (Nucella cingulate), a predator of mussels, has grown significantly in the areas where these mussels live. The African Black Oystercatcher also adapted its diet to include the invasive Mediterranean mussel. This makes sense because the alien mussel supplanted our own specie, but also, these mussels are bigger and will give more sustenance than our own smaller specie.  As a result it has been reported that these birds' reproductive potential has increased following the mussel establishment.  Which is good news for our threatened Oystercatchers.

The quick spreading of the Mediterranean mussel is not all doom and gloom, but it is important that we learn a valuable lesson from all this. Our indigenous species are precious and worth the effort to protect. Animal and plant species that spread so quickly, are a huge threat to the bio diversity of our country and of the world. We need to monitor these species and vigilantly preserve the unique gifts God has given us.