长棘海胆聚集突显珊瑚礁生态系统平衡

aggregation of black longspine sea urchins (Diadema setosum) rests on a sandy seabed in the Andaman Sea, Thailand. These echinoids display extended venomous spines used for defence and spacing within the group. Their presence reflects grazing pressure on algal growth, an important ecological function that helps maintain balance between algae and coral reef substrates in shallow tropical waters.