Following the build-up of harmful algal blooms - called red tides - on the West Coast over the past few weeks, the Department of Environment, Forestry and Fisheries (DEFF) has issued a Situation Yellow alert under the West Coast Rock Lobster Contingency Plan and placed all government role-players on standby.

The recent red tides have resulted in several marine species, including rock lobsters, octopus, white mussels and some fish species, washing up on the beach,

"In terms of the contingency plan, the DEFF is the lead department supported by other organs of State including the West Coast district municipality, the Cederberg municipality, the South African Police Services, the South African National Defence Force and Western Cape provincial administration.

"These role-players are currently preparing for a Situation Red because beaching has taken place and there is a possibility that there may be beaching in excess of 10 t at a single or multiple localities in the area," the DEFF states.

Weather conditions are not favourable as a north-westerly wind is currently blowing and keeping the algal bloom concentrated in the bay. As is often the case in summer and late summer, there has been a build-up of large red tides in the greater St Helena Bay region over the past few weeks.

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

The blooms are dominated by a group of phytoplankton known as dinoflagellates and their inshore accumulation, particularly during periods of calm, often leads to their decay and the subsequent development of low oxygen conditions, which cause marine mortalities.

Such mortalities were observed on the beaches of Elands Bay earlier on January 17 and, with the prediction of light westerly winds over the next few days, the risk of further mortalities is high, states the department.

"However, notwithstanding the red tides, West Coast rock lobster catches are still good and this indicates that oxygen levels are still high. The new moon spring tide occurred two days ago, thus limiting the possibility of a mass stranding within the next 10 days," the DEFF says.

RED TIDES
Red tides are a natural phenomenon in coastal waters and are caused by a dense accumulation of microscopic algae. Some of the algal species are harmful because they contain toxins, which are poisonous to humans. Poisoning may either take place through the consumption of seafood that is contaminated by toxic algae, or 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 significant environmental and social 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.

Red tides are particularly common in the productive West Coast upwelling regions, such as the Benguela, California, Humboldt, Canary and Somali upwelling systems.