Wijayathilaka Nayana, Eni Hidayati, Nur Edna Hasreena Ahlun, Jovina Jowinis, and Alessandra Markos
The nocturnal and clustering behavior of black sea urchin (Diadema setosum) are believed to be defense mechanisms for avoiding fish predators. We studied the colony size of Diadema setosum between two reef habitats at Malohom Bay, Pulau Gaya, Sabah. A line transect of 20 m by 5 m along the shore line with two replicates was laid on fore reef and crest, and the number of sea urchin per colony was recorded. The results shows that there is a significant bigger aggregation of Diadema setosum in the fore reef zone than the crest zone. This behavior probably acts as a defense mechanism during sleeping to avoid predators. When they form a colony and stay close to each other, their spikes act like a fortress protecting their delicate parts. Colonization makes it harder for predators to flip them. Aside from predators threat, the bigger size in the fore reef probably because the fore reef provides more space for aggregations.
It is always fun seeing under water living creatures. All the shapes, the colours, the movements,the smell? are fascinating. While snorkeling in Gaya Island carefully counting the sea urchin, I was shocked by the very loud noise heard under water. I could not figure out what was it. I thought Tsunami was going to come in a minute. I thought there might be some electricity spread after the blast. I thought I might be dead at the moment. Then I raised my head out of water and I saw everything was fine. Friends were still there. They heard the blast too. Until now I do not know what was it exactly. I hope it was not a fish bomb. If it was, then other creatures might be dead at that time! 🙁
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