Jonathan Jones’ musings on the red algae which invaded an Australian beach this week:

Ancient oceanic life forms called dinoflagellates have swarmed the waters of Sydney, as seen here at Clovelly beach. The beaches were closed because, although non-toxic, these algae can cause skin irritation. But as this mother and child contemplate the red sea, what images float to mind?

It is hard not to imagine portentous meanings in what is really a natural occurrence. As an uneasy peace was declared in Gaza, as the streets of Egypt shook again, as the fiscal cliff got closer, this gory blossoming of the sea confronted beachgoers with a vivid warning. What new horror is coming? Is it the End?

Photographs: Newspix/Rex Features