Deeper down, are coral reefs holding up better?

The next time you see a picture of a coral reef bleached ghost-white by warming seas, remember that there’s a good chance it was taken in the photic zone: the brightly lit layer of water that extends about 50 meters below the surface.

Australian marine biologist Tom Bridge wants to shift our focus deeper. Speaking at the World Science Festival in Brisbane, Australia, on Friday, he pointed out that two-thirds of all coral lives in the 50- to 700-meter (165 to 2,300 feet) range. That’s a habitat that reaches deeper than the height of New York’s One World Trade Center.

In particular, he wants to call our attention to the “mesophotic zone,” between 50 to 150 meters (165 to 492 feet), where enough sunlight reaches to sustain many of the same corals found higher up. “We have this sort of intermediate zone between the 50 to 150 meter depth range that’s really been ignored for a long period of time,” Dr. Bridge, the senior curator at Queensland Museum in Brisbane told the World Science Festival audience.

Studying this zone could do more than just fill a gap in scientific knowledge. The mesophotic’s greater depth and colder temperatures provide a buffer against climate change and other well-known threats facing reefs and studying it could change scientific methods for protecting the reefs overall.

“Sometimes these deeper areas are less vulnerable to these disturbances than shallow water habitats,” Bridge explained. In oceans, a transition layer called the “thermocline” separates warmer and colder waters. During one mesophotic research dive in Hawaii, recently described in Science magazine, the team reached waters as cold as 10 degrees Celsius, or 50 degrees F.

Along with the cold temperatures, scientists have other good reasons to stay in the shallows. Standard diving protocol involves pausing at regular intervals during an ascent.

To make enough time for these pauses, divers who go deep typically use a rebreather, which re-circulates exhaled air, rather than breathe compressed air from a scuba tank. Even then, a research dive at 100 meters (328 feet) might involve 20 minutes of work on the reef, followed by two hours of stops on the way up.

Despite the challenges, Bridge thinks studying the mesophotic could offer a more holistic – and encouraging – picture of Earth’s reefs. The same temperatures that chill divers to the bone could protect the mesophotic’s corals from the bleaching that occurs closer to the surface. They’re also farther removed from other threats, such as overfishing and coastal development.

Understanding if these traits make the mesophotic stronger would take more research. “Compared to what we know about shallow coral reefs, everything in the deep coral reefs is a big question mark,” Richard Pyle, an associate zoologist at Bishop Museum in Honolulu who specializes in deep-water coral climate, told Science magazine.

Bridge wants that to change. “A lot of the time it’s out of sight, out of mind…. If you can’t see it, it doesn’t become included in conservation plans and things like that.”


Scuba Diving In The Bahamas –

The Bahamas… if anyplace in the world is said to have multiple personalities, it would be the Bahamas. With over 3,000 islands and cays, there are many ways it can be different. The Commonwealth of the Bahamas is a part of the Commonwealth of Nations, formerly called the British Commonwealth. While they drive on the right-hand side of the road. The Commonwealth of the Bahamas and the British Overseas Territory Turks and Caicos inhabit the Lucayan Archipelago. The Archipelago is included in the West Indies, however, it is not a part of the Caribbean. However, most people including those from the Bahamas do consider it a part of the Caribbean. Many Bahamians look at their country as two distinct parts: the main islands and the Out Islands. Each with a different lifestyle and culture. For the tourist and more importantly the scuba diver two very different vacation experiences. The tourism industry is the largest employment sector with over 50% of the jobs being in this industry. Second is the finance sector.

Bahamas Main Islands

The Main Islands of the Bahamas are Grand Bahama Island and New Providence Island along with a few nearby cays and islands. The population of the Bahamas is about 400,000 and 80% of those people live in the Main Islands. Nassau, the capital of the Bahamas, is located on New Providence Island. This island and the connected small Paradise Island is home to over 70% of the countries population. Nassau is also the center of tourism in the Bahamas. You will find casinos, luxury shopping and hotel chains here. Nassau is the busiest cruise port in the world and 70% of the countries tourist are cruise ship passengers. Grand Bahama Island is the home of the city of Freeport and about 10% of the population.


Darby Island and Rudder Cut Cay, Exumas Photograph by Christina Hawkins

Darby Island and Rudder Cut Cay, Exumas
Photograph by Christina Hawkins

Diving Bahamas Main Islands

Diving in the Main Islands is legendary. There have been so many underwater scenes filmed around New Providence Island, including iconic scenes in James Bond movies, it is often called “Underwater Hollywood”. Many of the best dive sites are on the western edge of the island and are near the area known as the Tongue of the Ocean. The Tongue of the Ocean is a

The Tongue of the Ocean is a deep-water trench that is between Andros Island and New Providence Island. The reefs around New Province Island are generally in the 60 to 80-foot range. Whereas the floor of the Tongue of the Ocean is between 3,600 feet (1,100 m) to 6,600 feet (2,000 m) deep. The reefs benefit from the deep water as nutrients are brought from the depths. Sharks and other pelagic also visit the shallow reefs. Expect to see sharks on just about every dive. Looking over the edge of the reef into deep water you may see some of them way below you. There really is some great wall dives here.

Meanwhile, Grand Bahamas Island also has a great reputation for scuba diving. The Underwater Explorer Society (UNEXSO) has been in business for over 50 years and is considered the pioneer in shark feeding. They introduced hand feed of sharks in 1993 and are still doing it. They offer a range of shark diving and also diving with dolphins.

The Out Islands – Family Islands

Once you exclude the two main islands and their few nearby cays, the rest are what is called the Out Islands. You will also see them call the Family Islands. Only one percent of these 3,000 islands are considered inhabited. Many of the “uninhabited island” do have homes on them, often a single residence for a wealthy individual. Andros is the fifth largest island in the West Indies and largest of the islands in the Bahamas, many times the size of both of the Main Islands together. While ten percent of the country’s population live on the island, it’s large size means great portions of it are not inhabited.

Eleuthera and the Exuma Cays are also destinations know for its diving. The Exuma Cays start about 35 miles southeast of Nassau. The archipelago of about 365 cays and islands are separated into three sections and they span about 80 miles north to south. Resorts here are more relax and do not have the commercialism you will find in the Main Islands.

The Bimini Islands are the closest to the US mainland and may be the most known of the Family Islands. Here you will find a mix of small resorts and large scale resort complexes. The area is also considered one of the best sport fishing destinations in the world.


deans blue hole bahamas

Dean’s Blue Hole on Long Island Bahamas. A short distance from shore the Blue Hole drops to 663 feet (203 meters). Photograph by Christian Afonso

Diving the Family Islands

Diving the Family Islands/ Out Islands offers such a range of diving opportunities it hard to believe it is all the same country. Eleuthera and the Exuma Cays are on the eastern side of the Bahamas with direct access to the Atlantic Ocean. This can create some robust diving conditions. However, the western side of the islands are protected and can have calm conditions. This area is a favorite for those seeking a liveaboard destination.

Andros provides the diver many different options. As mentioned the Tongue of the Ocean is between this island and New Province Island. On the Andros side of the Tongue, you will find what is called the Andros Fringing Barrier Reef. This reef system is 190 miles long and is considered one of the healthiest reefs in the world. It extends from near the shoreline of Andros to the Tongue of the Ocean. Some marketing claims it is the third largest reef system in the world. This is hard to confirm as the reef does not meet the definition of a barrier reef nor a fringing reef but is somewhat a hybrid of the two. The reef’s many dive sites both along the wall and closer ashore give divers many types of dives to choose from.

Another aspect of diving Andros is that it has the largest concentration of blue holes in the world. Some of these blue holes are located on land providing an experience similar to the cenotes of Mexico. Others are located in shallow waters and allow divers to drop beyond recreational diving depths. Caver divers will find many underwater cave systems to keep themselves challenged.

Sharks are one of the big draws to the Bimini Islands. Located less than 60 miles from Florida, it is on the deep side of the Florida barrier reef. This deep water is a migratory route for many shark species including hammerheads and great whites. Florida has made shark feeding illegal in the states waters so many of the Florida dive operators have relocated its shark feeding to the waters off Bimini islands. Other large pelagic are found here and the wall diving is incredible.

You can spend years diving the Out Islands and still be amazed what you can find. The many shallow coral reefs and cays have created thousands of ship wrecks many still waiting to be discovered. Wall dives, ship wrecks, caves, coral reefs, drift dives are all waiting for you.



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