Algae and corals in coral reefs produce organic material. The island is surrounded by coral reefs. These islands have a collection of coral reefs. They inhabit the deep slopes of coral reefs. Coastal communities near coral reefs rely heavily on them. Barracudas reside near the top of the water and near coral reefs and sea grasses. Explosions are particularly harmful to coral reefs. They tend to school around coasts and islands with coral reefs. Carnivores are the most diverse of feeding types among coral reef fishes. These are found in coral reef gastric cavities. Puerto Rico is home to over 5,000 square kilometers of shallow coral reef ecosystems. Each is a national park surrounded by coral reefs. It consists of three lagoons separated by arms of coral reefs. The hologenome theory originated in studies on coral reefs. It is one of the four coral reef regions in India.