Coral reefs are biotic structures composed of living organisms, primarily made up of corals. These corals are marine invertebrates that belong to the class Anthozoa and play a crucial role in building the reef itself. The corals secrete calcium carbonate, forming a hard skeleton that structures the coral reef over time.
Moreover, coral reefs are ecosystems that host a diverse array of marine life, including fish, invertebrates, and other organisms. The interactions among these various species contribute to the reef’s complex biological community. Therefore, since coral reefs are formed by and are home to living organisms, they are classified as biotic.