11.5m clams beach in Plett

ENVIRONMENTALISTS believe that the estimated 11.5 million clams washed up in Robberg Beach, in Plettenberg Bay, may be as a result of a combination of strong easterly swells and winds.

Nature Valley Trust (NVT) Program director Mark Brown said the cause was not yet known but they suspected climate change.

“Realistically, we believe it is a combination of strong easterly swells and winds that lead to a large disturbance in the sandbanks where these clams live. These events also lead to sudden water temperature drops at times, which affects marine life, too,” he said.

“There is always a chance that red tide could be a contributing factor, but we have had wash-ups of this nature without red tide being present.”

Brown said the turbulent water movement may prevent the clams from being able to burrow back and thus become subject to waves and consequently wash up on to the beach.

He said clams (Mactra glabrata) were smooth trough shells that occupied the surf zone, burrowing under sand in shallow water.

He urged people not to be confused with white mussels (genus Donax), which live under sand on the beach zone.

“I would definitely not encourage people to eat them, especially now, they are totally off by now. But even when fresh, it is better to… treat all washed-up shellfish as suspect,” he said.

The NVT marine team has undertaken a survey and data collection in an attempt to quantify the biomass of the wash-up.

According to a studies led by SANParks’s researcher Kyle Smith – with assistance from Dr Gwenith Penry, who is a post-doctoral researcher at Nelson Mandela University working for the Nature’s Valley Trust (NVT) marine team – the calculations of the recent wash-up extended to 5 875m² with the average number of clams in the deepest section more than a metre deep at 35 300m³.

“The most plausible reason is that strong easterly swells and winds cause a large disturbance in the sandbanks in which these clams usually reside.

“What we don’t know is why there are so many clams in the area, and why these strong winds are now causing them to wash up,” the team said.