A Flourishing Reef Immerse yourself in the Gardens of the Queen. Home to silky sharks, myriad fish, and the critically endangered elkhorn coral, the reef teems with life and vibrancy.

This story appears in the November 2016 issue of National Geographic magazine.

Fifteen years had elapsed since we last explored the Gardens of the Queen. In the necklace of keys, mangrove islets, and reefs about 50 miles off Cuba, we had discovered a marine wilderness that astonished us with its vibrant life.

We returned to Cuba anxious about what we would see in the wake of time and climate change in this national park now covering about 850 square miles. On our first dive we descended into a large stand of elkhorn coral, a critically endangered species diminished throughout the Caribbean. We found ourselves in a dense thicket, amazed as we watched grunts and snappers jostle for space among the broad branches, as if in a game of musical chairs. This is exactly what we hoped to see; we were inside a liquid time capsule, transported back to a world of coral draped in fish, what the Caribbean looked like to our eyes decades ago.

Noel López, a dive master who has observed these waters for two decades, guided us to a deeper reef where we encountered four species of grouper, including a goliath the size of a stove. The reef seemed even more crowded with large fish and sharks than on our first visit.

The Crown Jewels Gardens of the Queen National Park, about 850 square miles of islands and reefs, is one of the most unspoiled environments in the Caribbean. Cuba limits the number of divers and fishermen allowed to visit but could face pressure to increase access. Coral reef CUBA FLORIDA (U.S.) Havana GARDENS OF THE QUEEN NATIONAL PARK 200 mi 200 km NG MAPS SOURCES: IUCN and UNEP-WCMC, World Database on PRotected Areas (2016); Worldfish center; world resources institute; Nature conservancy The Crown Jewels Miami FLORIDA (U.S.) Gulf of Mexico Gardens of the Queen National Park, about 850 square miles of islands and reefs, is one of the most unspoiled environments in the Caribbean. Cuba limits the number of divers and fishermen allowed to visit but could face pressure to increase access. CUBA Havana AREA ENLARGED Golfo de Ana María CAYMAN ISLANDS (U.K.) Cayos Cinco Balas 100 mi Caribbean Sea 100 km Coral reef Cayos de las Doce Leguas Cayos Pingües GARDENS OF THE QUEEN NATIONAL PARK Cayo Anclitas Jon Bowen, NG STAFF. Sources: IUCN and UNEP-WCMC, World Database on PRotected Areas (2016); Worldfish center; world resources institute; Nature conservancy Cayos los Indios Cayos Laberinto de las Doce Leguas 10 mi 10 km

One morning we entered the mangroves and swam through a flooded forest filled with clouds of silversides. We ventured out to open water to dive with dozens of sleek silky sharks, which formed a perfect carousel around us. At dusk we returned to the mangroves and submerged into the dark water with powerful lights. We followed an American crocodile, hunting silent as a submarine. To encounter such abundant prey and super predators in a single system, let alone a single day, was incredible.

This oasis in the ocean flourishes, marine scientist Fabián Pina Amargós emphasizes, because Cuba actively protects the preserve, where tides and currents help retain nutrients and larvae. So far the marine ecosystem has proven resilient to coral bleaching, but it faces the same threat that other reefs do as the ocean warms, acidifies, and rises.

As the U.S. embargo draws to an end, the romance of Cuba’s waters is sure to lure more Americans. There’s an urgent need to strike a balance between ecotourism and conservation. Cubans know what’s at stake: the living crown jewels of the Caribbean.

View Images Silversides swirl through mangroves like a river in the sea. The dense forest of roots offers welcome shelter for the finger-size fish, which form large schools to try to confuse predators. Mangroves enhance reefs by providing a nursery area for vulnerable creatures and by trapping sediment that can smother coral. They also store carbon that might otherwise contribute to global warming.

View Images A critically endangered hawksbill sea turtle hatchling (Eretmochelys imbricata), about three inches long, paddles away from shore under the protective cover of dusk. Cuba banned the harvest of sea turtles in 2008.

In the Mangroves Submerged in the sun-dappled mangrove waters, American crocodiles glide past schools of silversides and turtle grass — and come face to face with photographer Jennifer Hayes.

View Images Sunset casts a golden glow over corals flourishing off the country’s southern coast. Named by Christopher Columbus in honor of Queen Isabella, this remote set of keys, mangroves, and reefs appears nearly unchanged by time and human hand.

View Images A submerged American crocodile (Crocodylus acutus) rises from an evening slumber in a bed of turtle grass to return to the labyrinth of mangrove roots that offer near-impenetrable shelter. Scientists consider crocodiles the engineers of the mangrove ecosystem because they create pathways that improve nutrient circulation. Increasing numbers of super predators, such as crocodiles and sharks, are key indicators of a balanced ecosystem.