Evaluate the structural morphology and evolutionary stages of coral reef ecosystems: Statement I: Fringing reefs develop directly along the coastline of islands or continents, separated from the shore by a narrow, shallow lagoon. Statement II: Atolls consist of circular or elliptical coral reefs enclosing a central lagoon, typically formed on subsiding volcanic islands where upward coral growth keeps pace with sea-level rise. Which of the following is correct?

💡 Solution & Explanation

Statement I is incorrect because a true fringing reef develops directly adjacent to the shore with little or no intervening lagoon, whereas barrier reefs are separated from the land by a deep, wide lagoon. Statement II is correct because, according to Charles Darwin's subsidence theory, atolls evolve as volcanic islands gradually sink and coral reefs grow upward to maintain position within the photic zone, eventually leaving a central lagoon surrounded by a ring of coral islands.