Belize Barrier Reef

Coral reefs are built by hard corals.

Baby corals stick to rocks under the sea. As they grow, the reef grows too.

NOAA explains that coral reefs are built by hard, or stony, corals. A reef begins when young coral larvae swimming in the sea attach to rocks or other hard surfaces near the edge of land. As the corals grow and spread, the reef takes one of three main shapes: a fringing reef, a barrier reef or an atoll.

A barrier reef runs along a shore but farther out, with a lagoon of open water between it and the land. NOAA says a coral reef can take up to 10,000 years to form.

NOAA: reefs are built by hard (stony) corals; free-swimming larvae attach to submerged rock or other hard surfaces along the edges of islands or continents, and growing corals produce fringing, barrier or atoll structures. Barrier reefs border shorelines at a distance, separated by a lagoon of open, often deep water. Massive corals grow 0.3-2 cm a year and branching corals up to 10 cm; a reef can take up to 10,000 years to form, and barrier reefs and atolls 100,000 to 30 million years, depending on size.

UNESCO: in Belize, the rise and fall of sea level over the millennia, together with karst topography and clear water, produced patch, fringing, pinnacle and barrier reefs, faros, off-shelf atolls, rare deep-water reefs, the Blue Hole and Rocky Point, where the barrier reef touches the shore.

Sea turtles and manatees find homes here. So do hundreds of kinds of fish.

Seabirds nest on some of the islands, called cayes.

UNESCO lists more than 500 kinds of fish and 65 kinds of stony coral on the reef. Animals that need protection live here too, such as the West Indian manatee, green, hawksbill and loggerhead sea turtles, and the American crocodile.

Red-footed boobies nest on Half Moon Caye. UNESCO also names top hunters on land, in the sea and in the air: jaguars at Bacalar Chico, great hammerhead sharks at the Blue Hole and ospreys at Glover's Reef.

UNESCO records about 247 taxa of marine flora (246 in its criteria text) and 178 terrestrial plants, over 500 fish species, 65 scleractinian corals, 45 hydroids and 350 molluscs, plus many sponges, marine worms and crustaceans. Species of conservation concern include the West Indian manatee (Trichechus manatus), green (Chelonia mydas), hawksbill (Eretmochelys imbricata) and loggerhead (Caretta caretta) turtles and the American crocodile (Crocodylus acutus).

Bird colonies: red-footed booby on Half Moon Caye, brown booby on Man O'War Caye, common noddy on Glover's Reef. Top predators named by UNESCO: jaguars of Bacalar Chico, great hammerheads of the Blue Hole, ospreys of Glover's Reef; endemic species include island lizards, fishes, tunicates and sponges.

Hundreds of islands called cayes sit along the reef.

Some cayes have white sand. Others are green with mangrove trees.

The reef area has about 450 cayes, islands of sand or mangroves. UNESCO describes bright white sand cayes and green mangrove cayes set in blue water.

The reserve covers every step from land to deep ocean: beach forests, wetlands and mangroves, seagrass beds, reefs in the lagoon, the outer barrier reef and atolls. Animals use these places to lay eggs, feed and raise their young.

UNESCO: about 450 sand and mangrove cayes; rare littoral forest on sand cayes is home to endangered plants and animals. The property contains an intact ecosystem gradient from the terrestrial to the deep ocean (littoral, wetland and mangrove ecosystems, seagrass beds with lagoonal reefs, the outer barrier reef platform and oceanic atolls) that supports spawning, nesting, foraging and nursery functions.

UNESCO quotes Charles Darwin as calling it the most remarkable reef in the West Indies.

Always swim with a buddy. Children should wear a life jacket in the sea.

The sun's rays bounce off water. Wear a hat and sunscreen.

The CDC says to always swim with a buddy, choose places with lifeguards when you can, and have children wear life jackets in natural water. Oceans can hide dangerous currents, waves and rocks, and weather can change quickly, so check the forecast first.

The sun's rays also reflect off water and sand. UNESCO says climate change brings risks of coral bleaching, stronger hurricanes and rising seas, and that overharvesting sea life, building on the coast and tourism need careful management.

CDC drowning prevention: swim with a buddy, preferably where lifeguards are present; life jackets for children in and around natural water; natural waters hide currents, waves, rocks and poor visibility; check the forecast, as conditions change fast. CDC sun safety: UV reflects off water and sand; use shade, covering clothing, a brimmed hat and broad-spectrum SPF 15+ sunscreen.

UNESCO: climate change brings risks of coral bleaching, stronger and more frequent hurricanes and sea-level rise; other management challenges are overharvesting of marine resources, coastal development, tourism and industrial development.