If ever there was an image that sums up the magic of diving, it is that of a coral reef. Although coral reefs are the most famous feature of tropical seas, these warm clear waters have much more to offer, such as mangrove swamps, sea-grass beds, and vast tracts of open ocean.
Tropical waters occupy the region within the “20Aï¿½C isotherm”-the irregular hand of water north and south of the equator that seldom drops below 68Aï¿½F (20Aï¿½C). Although undeniably appealing to the diver, they actually present a less attractive environment for marine life. The warm equatorial sun heats the upper layers of the water column, creating a marked temperature difference between the surface water and deeper colder water. Such temperature stratification prevents mixing of the water column, so nutrients are not passed up from deeper water. Marine animals and plants have therefore had to adapt and evolve numerous strategies to cope with the lack of nutrients in the water around them. Perhaps the most remarkable of these is the coral reef. Primary production-the formation of organic compounds from inorganic material is up to 100 times greater in coral reefs than in open tropical waters, and although they cover only 0.2 percent of the ocean environment, they are home to 25 – 30 percent of all fish species.
The reefs of the Indo-Pacific are the richest marine environments on Earth. Their beautiful structure and bright colors, combined with the splendor and variety of animals that inhabit them, make reefs irresistible to divers, and it is no coincidence that many of the world’s best dive sites tire found on coral reefs.
Tropical waters are also home to mangrove swamps and sea grass beds, both arguably as important as coral reefs in the overall health of tropical seas. There are 10 species of mangroves – tropical trees and shrubs that grow in shallow and intertidal coastal waters – and they form flooded forests that act as nurseries for various reef and open-water fish species. The 50 species of sea grass form “meadows’ in shallow waters that are feeding grounds and nurseries for many fish species. The eradication of sea grass beds and mangrove swamps around the world is a real concern, with undeniable impacts on coastal ecology as animal populations are denied crucial areas for tire growth and development of their young.
Reefs Under Threat
Coral reefs worldwide are under intense pressure. The continued development of coastal regions has caused silty water to run into the seas, smothering these delicate systems, and, coupled with the damage caused by destructive fishing methods, it is thought that up to 90 percent of reels have been impacted by humankind. There is also evidence that rising water temperatures are causing a phenomenon known as bleaching, which is fatal to reefs. This occurs when the coral polyps eject the minute algae that sustain them as a response to stress.
Diving a reef can be the highlight of a diver’s life, but we have a very real responsibility when exploring reefs not to harm or disrupt them in any way. A considerate approach is vital if we are to preserve these wonderfully vibrant ecosystems.