Find out more: Exploring the underwater phenomenon of blue holes
A rare “blue hole” has been discovered in the Arabian Gulf by environment chiefs in Abu Dhabi.
The underwater sinkhole lies just off Al Dhafra and is about 12 metres deep, 200 metres wide and has an area of about 45,000 square metres.
The Environment Agency Abu Dhabi said it was a “recent discovery in a routine inspection” and was being monitored as part of regular surveys and assessments.
It provides a unique habitat for fish such as grouper, sweetlips, emperor fish and jackfish, and holds at least 10 types of coral species, which form a reef at the edges of the hole.
The agency said it was significant because it “provides a glimpse of how historic reefs used to look in Abu Dhabi".
Experts will conduct an environmental assessment survey of the unique ecosystem to learn more about its geological composition. This will involve mapping the area and analysing seawater.
The agency will also conduct scientific and topographic surveys.
Similar holes can be found around the world. The deepest blue hole, the Yongle, lies in the South China Sea and reaches 300 metres beneath the seabed.
Other famous blue holes include the “Great Blue Hole” in Belize; “Gozo’s Blue Hole” in Malta; the Blue Hole at Dahab in Egypt and “Dean’s Blue Hole” in the Bahamas.
“These unique structures attract divers from all over the world and are home to fringing reefs and diverse fish species, and at their depths, they host diverse microbial communities,” said the Environment Agency Abu Dhabi.
Sinkholes of this type were usually formed in limestone rock during the Ice Age when sea levels were low. Water eroded the stone over time and left an opening that water rushed into as sea levels climbed.
Ocean Photography Awards 2021 - in pictures
Scroll below to see stunning images of ocean life taken this year.
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Winner of Ocean Photographer of the Year, Aimee Jan: A green turtle, surrounded by glass fish in Ningaloo Reef, Western Australia. 'I was out snorkelling when one of my colleagues told me there was a turtle under a ledge in a school of glass fish, about 10 metres down,' says Jan. 'When I dived down to look, the fish separated around the turtle perfectly. I said to her: ‘I think I just took the best photo I have ever taken’.' -
Second place in Ocean Photographer of the Year, Henley Spiers: 'Diving amidst the barrage of gannets, I witness the violent synchronicity of these impressive seabirds as they embark on fishing dives,' says Spiers of this photo taken in the UK's Isle of Noss. 'They hit the water at 60 miles per hour (96kmh), an impact they can only withstand thanks to specially evolved air sacs in the head and chest. The bird’s agility transfers from air to sea where it also swims with incredible speed.' -
Third place in Ocean Photographer of the Year, Matty Smith: 'A hawksbill turtle hatchling just 3.5cm long and a few minutes old takes its first swim,' says Smith of his photo taken in Lissenung Island, Papua New Guinea. 'It had emerged from an egg just minutes earlier with approximately 100 of its siblings. They quickly made their way into the ocean to disperse as rapidly as they could and avoid predation from birds and fish. I had to work quickly for this shot.' -
Winner of Ocean Adventure Photographer of the Year, Ben Thouard: Surfer Matahi Drollet catches a wave known as Teahupo’o in Tahiti, French Polynesia -
Second place in Adventure Photographer of the Year, Ben Thouard: A wave known as Teahupo’o, as seen from below, in Tahiti, French Polynesia -
Third place in Ocean Adventure Photographer of the Year, Sebastien Pontoizeau: A freediver duck dives to capture a photograph of a humpback whale off the coast of Reunion Island -
Nominee in Adventure Photographer of the Year, Steve Woods: Sea lions swarm a diver off Vancouver Island, Canada -
Winner of Collective Portfolio Award, Stefan Christmann: In late spring, the emperor penguin colony almost mainly consists of chicks in Antarctica -
Winner of Collective Portfolio Award, Stefan Christmann: When both parents are foraging, their chicks gather in creches, or mini huddles -
Winner of Collective Portfolio Award, Stefan Christmann: A lone chick standing on the ice shelf, as the sea ice broke up too early, in Antarctica -
Winner of Collective Portfolio Award, Stefan Christmann: Male emperor penguins huddling during polar night in Antarctica, to stay warm as a group -
Second place in Collective Portfolio Award, Matty Smith: A southern bobtail squid performs a spectacular display on the seabed at night -
Second place in Collective Portfolio Award, Matty Smith: Pacific Man o’ War, a colourful marine invader, under an apocalyptic red sky -
Second place in Collective Portfolio Award, Matty Smith: The Porpita porpita siphonophore appears like a miniature spinning galaxy on the ocean surface -
Third place in Collective Portfolio Award, Alex Kydd: A rare encounter with a fever of cownose rays on the Ningaloo Reef, Western Australia -
Third place in Collective Portfolio Award, Alex Kydd: A freediver falls through an ocean full of moon jellyfish in Raja Ampat, West Papua -
Winner of Community Choice Award, Phil de Glanville: Surfer Jack Robinson rides the famous break known as ‘The Right’, home to some of the heaviest waves in the world in Denmark, Western Australia -
Winner of Conservation Photographer of the Year, Kerim Sabuncuoglu: A dead moray eel on an abandoned fishing line in Bodrum, Turkey -
Highly Commended in Conservation Photographer of the Year, Thien Nguyen: Anchovy fishing boats photographed from above along the coastline of Phu Yen province, Vietnam -
Winner of Exploration Photographer of the Year, Martin Broen: Speleothems cast long shadows at cenote Dos Pisos in Quintana Roo, Mexico -
Third place in Exploration Photographer of the Year, Matty Smith: A portrait of a squid, taken in Bushrangers Bay, Australia
