<P> The Caribbean is home to about 9% of the world's coral reefs covering about 50,000 km (19,000 sq mi), most of which are located off the Caribbean Islands and the Central American coast . Among them stands out the Belize Barrier Reef with an area of 963 km (372 sq mi) which was declared a World Heritage Site in 1996 . It forms part of the Great Mayan Reef also known as the MBRS and being over 1,000 km (600 mi) in length is the world's second longest . It runs along the Caribbean coasts of Mexico, Belize, Guatemala and Honduras . </P> <P> During the past ten years, unusually warm Caribbean waters have been increasingly threatening Caribbean coral reefs . Coral reefs support some of the most diverse marine habitats in the world, but they are fragile ecosystems . When tropical waters become unusually warm for extended periods of time, microscopic plants called zooxanthellae, which are symbiotic partners living within the coral polyp tissues, die off . These plants provide food for the corals, and give them their color . The result of the death and dispersal of these tiny plants is called coral bleaching, and can lead to the devastation of large areas of reef . Over 42% of corals are completely bleached and 95% are experiencing some type of whitening . Historically the Caribbean is thought to contain 14% of the world's coral reefs . </P> <P> The habitats supported by the reefs are critical to such tourist activities as fishing and diving, and provide an annual economic value to Caribbean nations of US $3.1--4.6 billion . Continued destruction of the reefs could severely damage the region's economy . A Protocol of the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region came in effect in 1986 to protect the various endangered marine life of the Caribbean through forbidding human activities that would advance the continued destruction of such marine life in various areas . Currently this protocol has been ratified by 15 countries . Also, several charitable organisations have been formed to preserve the Caribbean marine life, such as Caribbean Conservation Corporation which seeks to study and protect sea turtles while educating others about them . </P> <P> In connection with the foregoing, the Institute of Marine Sciences and Limnology of the National Autonomous University of Mexico, conducted a regional study, funded by the Department of Technical Cooperation of the International Atomic Energy Agency, in which specialists from 11 Latin American countries (Colombia, Costa Rica, Cuba, Guatemala, Haiti, Honduras, Mexico, Nicaragua, Panama, Dominican Republic, Venezuela plus Jamaica) participated . The findings indicate that heavy metals such as mercury, arsenic, and lead, have been identified in the coastal zone of the Caribbean Sea . Analysis of toxic metals and hydrocarbons is based on the investigation of coastal sediments that have accumulated less than 50 meters deep during the last hundred and fifty years . The project results were presented in Vienna in the forum "Water Matters", and the 2011 General Conference of said multilateral organization . </P>

Is puerto rico in the caribbean sea or the atlantic ocean