Diadema (IMAGE) University of Exeter Caption Diadema are rare on Caribbean reefs now but used to be very important bioeroders. Their decline, due to disease, has been one major reason why erosion rates are now much lower. Credit University of Exeter Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.