How sea urchins save the coral reef

In the 1970s, approximately half of all the rock around the Caribbean was covered with coral, whereas now only between 2 and 3% remains around the island of Saba. One of the problems is the lack of natural grazers that eat algae. Dr. Tom Wijers obtained his PhD with his research on the Diadema antillarum, a sea urchin that he successfully bred in a lab for the first time. His team released two hundred sea urchins into the sea and saw within a day that half of them had been eaten by fish. Was it expensive fish food or is it promising? And how many sea urchins are needed to make a real impact? Wijers explains in the broadcast on NPO 1 (link below).