/ 13 February 2023

Harmful algal bloom causes five tonnes of West Coast rock lobster to crawl out of the ocean

Rock Lobster
An estimated five tonnes of rock lobster have crawled to the shores of the West Coast after algal blooms, also known as red tides, developed in the past few weeks.

An estimated five tonnes of rock lobster have crawled to the shores of the West Coast after algal blooms, also known as red tides, developed in the past few weeks.

The department of forestry, fisheries and the environment has activated the West Coast rock lobster contingency plan, issuing a Situation Red Alert which places all government people in the sector at the ready.

Albi Modise, the department’s spokesperson, said its officials, local municipalities, law enforcement and local residents are working together to assist in rescuing live lobsters and with clean-up operations. 

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

Blooms extend for 60km

There has been a build-up of large algal blooms in the greater St Helena Bay region, which extend 50km to 60km, in the vicinity of Elands Bay, Lambert’s Bay and Doring Bay. Red tide, which often occurs in summer, is dominated by a group of phytoplankton known as dinoflagellates

Their inshore accumulation, particularly during periods of no wind, leads to their decay and the subsequent development of low-oxygen conditions. These cause marine mortalities, as was observed on the beaches of Elands Bay this week. 

“With the prediction of light westerly winds over the next few days, the risk of further mortalities is high,” Modise said.

“Some of these dinoflagellates are also capable of producing toxins that may accumulate in shellfish and may pose a risk to human health. For this reason, members of the public are warned not to collect and consume any dead or decayed fish and shellfish washed ashore as a result of the red tide as this could pose a serious health hazard.”

Common phenomenon

Red tides are particularly common in West Coast regions, such as the Benguela, California, Humboldt, Canary and Somali upwelling systems. They have periodically led to rock lobster strandings in the Benguela upwelling region off the West Coast. 

The best-known examples are the strandings of hundreds of tonnes of rock lobsters in Elands Bay in 1997 and 2000. In 2014, an extensive and long-lasting red tide took place for the first time along the South Coast, extending from Knysna to beyond Gqebera and causing wide-scale mortalities of fish. Last year, an estimated 500 tonnes of rock lobster walked out on the West Coast.

Maryke Musson, an executive manager of the South African Association for Marine Biological Research, said red tides occur on the West Coast because of the “beautiful rich nutrient water coming from the deep ocean during upwelling”. 

There is “nothing new and nothing freaky” about them, she added.

“Globally, the expectation is that it might happen more frequently, and with a higher severity, purely because of global warming. These little dinoflagellates like it when the water is slightly warmer as well — it offers them a better environment to multiply like crazy.” 

Economic hit

Modise said poisoning can take place through the consumption of seafood that is contaminated by toxic algae, by toxic aerosols or water-bound compounds that cause respiratory and skin irritation. 

“Other red tides cause harm through the depletion of oxygen (anoxia), which affects all marine creatures and can lead to mass mortalities of the entire marine communities or mass walkouts of rock lobsters that try to escape the anoxic conditions. 

“Red tide occurrences can therefore have major environmental, as well as societal, implications, with knock-on effects on coastal economies. Fisheries and aquaculture industries suffer from the episodic mortalities of stocks caused by red tides, while poor water quality and foul smells associated with these occurrences affect coastal tourism.”

Musson said rock lobster was an important economic species already under threat because they are slow-growing and the stock assessment indicates that they’re already heavily depleted and are under severe pressure from fishing.

The fishery is one of the few livelihoods “authentic” to the West Coast, she said. 

“I feel very sorry for the fishing communities who are already in a challenging situation and then they have to deal with these walkouts as well. But it’s so lovely to see the fishermen working hard to get the lobster back in because they know that if they don’t, they are not going to have a livelihood because there won’t be any rock lobster to fish.”