A severe algal bloom currently sweeping though South Africa’s west coast has so far resulted in the death of an estimated two hundred tons of rock lobsters. The crustaceans wound up stranded in Elands Bay after they moved closer to the shore in an attempt to escape the oxygen-depleted water resulting from the bloom. Yesterday morning saw 80 tons of these spiny crustaceans stranded on the beach, following 70 tons the day before and 30 tons on Monday.

Officials from the South African Department of Agriculture, Forestry and Fisheries managed to rescue about six tons of stranded lobsters, which were removed and released in unaffected areas; however, the majority of the lobsters did not survive and, deemed unfit for human consumption, were dumped at a local municipal site.

So what caused this marine catastrophe? When south-easterly winds churn up tasty nutrients from the ocean floor, tiny microorganisms called phytoplankton or microalgae move in for a feast. This population explosion can turn the ocean surface a red or brown colour giving birth to the term ‘red tide’ – a phrase unpopular with ocean experts as algal blooms sometimes result in a variety of colours.

If a long period of calm weather follows the upwelling, the microorganisms are not dispersed and the algae begin to die and decompose. Bacteria responsible for decomposing the algae deplete the oxygen in the water, forcing marine animals to leave the area or suffocate in the oxygen-exhausted water.

As crashing waves create more oxygen in the water, the lobsters typically head towards the shore but end up stranded once the tide recedes. Weakened by the lack of oxygen, they are unable to make it back into deeper waters and end up dying on the beach.

The mass strandings aren’t the only threat facing South Africa’s lobsters. Commercial exploitation and illegal fishing have resulted in SA’s lobster stocks plunging to a meagre three percent of what they used to be. According to Laura Blamey of UCT’s Marine Research Institute, losing 200 tons of lobster is a serious concern. “For a resource that is so overfished, that’s a lot – especially on the West Coast where catches have dropped,” Blamey told IOL.

Header image: Molonglo Catchment Group