Mass lobster walkout on West Coast

Algae are simple plants found in the world’s oceans that produce about 70% of the oxygen in the atmosphere, are a food source for small fish and crustaceans and play a vital role in marine ecosystems. But too much of a good thing can have dire consequences.

In certain conditions, microscopic forms of algae called dinoflagellates bloom rapidly as a result of excess nutrients from upwellings in the ocean and gather in dense patches on the ocean’s surface.

These harmful algal blooms (HABs) are colloquially termed “red tides” because of their colour. They produce toxins that can be fatal to marine life and harmful to humans who ingest the contaminated seafood.

This phenomenon often results in another, known locally as crayfish walkouts.

Red tides deplete oxygen due to the overabundance of algae, which can lead to mass walkouts of rock lobsters that try to escape the anoxic conditions.

These mass strandings of West Coast rock lobster are common in South Africa’s late summer and can decimate tons of an already severely diminished resource.

Even small red tides can be a serious threat to the health of marine ecosystems and can have devastating impacts on the fisheries economy.

The department of forestry, fisheries and the environment (DFFE) has activated the West Coast Rock Lobster Contingency Plan and issued a situation red alert for coastal communities on the West Coast of the Western Cape following the development of a HAB.

A statement released by the DFFE estimated the bloom had caused five tons of West Coast rock lobster to walk out in one day, and cautioned that with more walkouts expected in the coming days, all government role players should be ready to rescue live lobsters on short notice.

“There has been a build-up of large red tides in the greater St Helena Bay region over the past few weeks,” said the department.

“These blooms of phytoplankton presently extend 50km to 60km, dominating waters in the vicinity of Elands Bay, Lambert’s Bay and Doring Bay.”

Toxins that may accumulate in the shellfish pose a risk to human health and the department warns the public “not to collect and consume any dead or decayed fish and shellfish washed ashore”.

The toxins are poisonous to humans when ingested but can also cause respiratory problems and skin irritation.

“All recovered live lobster will be rehabilitated and safely returned to sea once the red tide threat has abated,” said the department.

Daily Maverick