Namibian Coast Sulpher Eruptions

Sulphur Eruptions Responsible for Mass Braai-ing along the Coast!

For a few precious evenings in March the whole of Walvis Bay and Swakopmund were steeped in the scent of butter soaked crayfish roasting over an open fire. Coastal residents were happy to oblige the spindly legged crustaceans which seemed to storm the beaches and tide pools en masse, clambering for the opportunity to join our braais, imploring us to roast them up and serve them with chips. Of course, the crayfish were not actually eager to jump into our braai fires, but there were hundreds of thousands of them hiding away in the shallow rock pools and washed up on the beach for a few days. This happens every now and then, usually at this time of year, because of “red tides” and, sometimes, subsequent sulphur eruptions that cause crayfish and other sea life to flee the area. As most other sea creatures are more mobile than the crayfish, they will head further out to sea, or swim north or south along the shore, but the short distance swimmers can often only find refuge toward the shore. Other species do find their way into the rock pools, including fish and sharks. We even saw an octopus, but the most common species found on or near the shore are the crayfish. Other species can actually suffer worse. Oysters and mussels often cannot even make it to the

relative safe havens of the rock oxygen, though, and if they end up pools. near shore they risk being stranded on the beach out of sheer exhausAnja Van Der Plas, oceanographer tion. and senior biologist at Sea Fisheries, explains that because of global As if suffocation was not bad current and tidal patterns, the water enough, it gets worse for our eight off our shores tends to swirl in from legged friends. In a large enough the South. algae bloom, oxygen levels will go all the way down to zero. When Having cooled down off the shores this happens, anaerobic bacteria of Antarctica, the sea water begins (bacteria that use chemicals other to warm up again when it reaches than oxygen for respiration) start us. In summertime, the air is not munching away at the dead algae. only warmer here, but the seas are By this time, the algae has typically calmer. This results in stratified settled on the ocean floor. temperature gradients. In other words, the water on the top of the The bacteria continue doing their ocean is warmed by the sun, and jobs decomposing the algae, and because the sea is not churning that give off hydrogen sulphide as a bywater around as it does in winter, product. This builds and builds, the temperature at the surface stays and eventually erupts to the surface. warm, while the temperatures be- These gases are poisonous to most neath remain cooler. species, and the effects can be devastating. The warm, calm surface water makes for great swimming condi- The damage extends beyond the tions, and it also makes a very cozy fish to the fishing industry. environment for algae. In the right Through the last major sulphur conditions this can cause a major eruption in 2006, oyster and mussel algae bloom. This is what causes a farmers lost as much as 80% of “red tide,” as the thick layer of al- their crop, which takes as long as gae discolours the water giving it a thirteen months to replenish. On reddish or brownish tint. the whole, a sulphur eruption is a very disruptive and damaging As Mrs. Van Der Plas explains, the event, but on the bright side, every real problem begins when these al- couple of years the coast enjoys a gae start to die off. The dead algae kicking crayfish braai. is eaten by aerobic bacteria, who use up all of the oxygen in the area. This is bad news for sea life, who begin to suffocate without the oxygen this water normally supplies. This is the reason behind the crayfish coming to shore. They do not actually flee the sea for higher ground. They do seek out better waters for This Photo, available on the NASA website, shows a massive sulphur eruption along the coast.