Ecosystems

The origin of coral reefs

The oldest finds of reefs date back to approximately 500 million year ago. Back then, waters with a mean temperature of 20°C could be found up to a latitude of 40-45 degrees north and south. In the Palaeozoic age (560-290 million years ago), reefs covered a surface of 5 million square kilometres and had an extremely high rate of vertical growth (up to 200 ms per million years). Approximately 360 million years ago, there was a period of approximately 4 million years during which reefs were reduced to 1,000 square kilometres, disappearing nearly everywhere. The causes of this change were the decrease in the earth's temperature and the collision of the ancient super-continent Gondwana with the North-American shield, which caused the sea current to change. From then on, the movements of the earth's crust and the climatic changes continued to affect, alternately, the growth and destruction of reefs. A new sea, the Thetis, formed in the Mesozoic age (approximately 260 million years), extending east to west and joining together the Atlantic, the Mediterranean, the Indian Ocean and the Pacific, and this change led to a new development of the reefs. The Mediterranean, a sea that today has no reefs at all, used to have the largest number of corals, being home to 65 genera versus the approximately 30 genera living in the entire Atlantic today. Around the end of the Tertiary (25 million years ago), the Thetis split up under the pull of the continental drift and today's oceans rose, affecting the distribution of reefs all over the world. Madreporic formations moved towards the Indo-Malay region, after the Mediterranean Thetis had closed up, and India moved closer to Asia. In the Pliocene (11-14 million years ago), the reefs of the western Atlantic also grew apart from the Asian Pacific area because of the appearance of the lands that later on would have become Central America. The two main coral regions that still exist today were born during this era: the Caribbean and the Indo-Pacific.