OK, "the Middle Stone Age in Southern Africa ", hmmmnn...
According to the anthropologist Carleton S. Coon in his mid-20th Century book and intellectual tour de force, The Origin of Races, southern Africa (the vast region south of the Limpopo River) was inhabited solely by the Capoid people before Europeans arrived. Capoid ethnic people survive today as the Bushmen of the Kalahari.
When was the MSA supposed to have ended for the precolonial Bushmen? How have their tools changed from the tools you found on the beach?
RE: Archaeology at the beach... the MSA