The ocean is mysterious but alluring. You know so much is happening beneath that shimmery surface, yet it's out of reach.

Take this octopus, for example. French photographer Gabriel Barathieu captured the image during low tide in the lagoons surrounding the island of Mayotte in the Indian Ocean. The photo — with the perfectly posed creature that seems to dance for the camera — earned him top honors in the 2017 Underwater Photographer of the Year contest.

"Both balletic and malevolent, this image shows that the octopus means business as it hunts in a shallow lagoon," said judge Alex Mustard. "The way it moves is so different from any predator on land, this truly could be an alien from another world. It was taken in knee deep water, showing that underwater photography is open to anyone who is prepared to dip their toe in the water."

About 4,500 images were entered by photographers from 67 countries in the acclaimed competition, which started in 1965.

'Out of the Blue'

'Out of the Blue' by Nick Blake (U.K.)
British Underwater Photographer of the Year, 2017: 'Out of the Blue' was shot in a freshwater sinkhole in Mexico. (Photo: Nick Blake/UPY 2017)

Nick Blake was named British Underwater Photographer of the Year for this photo taken in a freshwater sinkhole in Mexico, known as Chac Mool Cenote.

"The light show flickered on and off as the sun was periodically covered by cloud and as it reappeared, I beckoned to my buddy and dive guide, Andrea Costanza of ProDive, to edge into the illumination of some of the stronger beams, completing the composition," Blake said.

"My journey from diver to underwater photographer has brought many amazing photographic opportunities."

'Oceanic in the Sky'

'Oceanic in the Sky' by Horacio Martinez (Argentina)
'Oceanic in the Sky' features an oceanic whitetip shark and earned Martinez the Up and Coming Underwater Photographer of the Year award. (Photo: Horacio Martinez/UPY 2017)

Argentinian photographer Horacio Martinez was named Up and Coming Underwater Photographer of the Year for this image he took in Egypt of an oceanic whitetip shark.

"We were on the last dive of the day and I ventured a tad deeper to get closer portraits of the oceanic whitetips, when I noticed this shark patrolling in the distance. I took a few shots to expose for the sun beams and the surface, and was pleased by the dreamlike effect," Martinez explains. "Oceanics are great subjects for close ups as they are anything but shy. Yet, every now and then it is great to try and capture their apparent loneliness, their wandering, and their independence in the big blue."

'Orca Pod'

 'Orca Pod' by Nicholai Georgiou (UK)
Most Promising British Underwater Photographer of the Year was awarded for 'Orca Pod,' which captured an up-close encounter with orcas. (Photo: Nicholai Georgiou/UPY 2017)

Nicholai Georgiou was named Most Promising British Underwater Photographer for this image taken during a week he spent free-diving with wild orcas in northern Norway in winter.

"Orcas are easily the most beautiful, intelligent and confident animals I’ve ever had the honor of spending time with," Georgiou says. "The days are quite short in winter and the water was around 5 degrees but we wore a thick wetsuit and of course with orca around, the cold was quickly forgotten. The light had a really nice color from the setting sun as this graceful pod of orca swam by nice and close. It was a moment which will be hard to top."

Commented Rowlands: "Most underwater photographers would be happy to get a shot of a single killer whale in its environment but Nicholai had the composure not to panic and time the shot perfectly as a pod of killer whales passed by heading into the setting sun. I'm jealous."

'One in a Million'

'One in a Million' by Ron Watkins (U.S.)
Winner of the Wide Angle category 'One in a Million' is right in the middle of a jellyfish bloom. (Photo: Ron Watkins/UPY 2017)

American photographer Ron Watkins was heading to Alaska to look for salmon sharks, but it was his image of jellyfish that earned him the top spot in the competition's wide-angle category.

"We came across an enormous moon jellyfish bloom that stretched for several hundred meters," Watkins says. "It was surreal and more dense than anything I had ever experienced including Jellyfish Lake in Palau. I came across this Lion's Mane Jellyfish rising from the bloom towards the surface and positioned myself directly over it to capture this image."

Judge Mustard explains part of the image's appeal: "Most photographers would swim up to the subject, probably shooting it from below, Ron found a far more striking composition with this top down view, making use of the moon jellies as a background."

'Prey?'

 'Prey?' by So Yat Wai (Hong Kong)
Winner of the macro category, 'Prey?' focuses on a larvae mantis shrimp ready to pounce. (Photo: So Yat Wai)

Photographer So Yat Wai of Hong Kong was the winner in the macro category for this photo taken during a blackwater dive in Anilao in the Philippines.

"Even though the larvae mantis shrimp (left) is very small, it still a predator which uses its raptorial appendages to hunt. Has it spotted the prey and is ready to pounce?"

"This shot works on so many levels," says Rowlands. "Like a Sci Fi encounter in outer space, the fortuitous (for once) backscatter creates a perfect starry background, which makes the main subject seem huge and menacing. Perfect composition leaves you in no doubt and you can only fear for the 'little fella' on the right."

'Your home and my home'

'Your home and my home' by Qing Lin (Canada)
Winner of the behavior category, 'Your home and my home,' features colorful clownfish with their isopod companions. (Photo: Qing Lin/UPY 2017)

Clownfish are the focus of Qing Lin's image, which is the winner in the competition's behavior category. Lin was looking at the parasitic isopods that like to hang out in the mouths of the fish.

"Perhaps because of the isopods, clown anemonefish often open their mouths. These three particular fish were very curious. As I approached, they danced about the camera lens. It took me six dives, patience and luck to capture the exact moment when all three fish opened their mouths to reveal their guests."

'Face to face'

'Face to face' by ifj. Lorincz Ferenc (Hungary)
Winner of the portrait category: 'Face to face' gets up close and personal with a bat fish. (Photo: ifj. Lorincz Ferenc/UPY 2017)

Hungarian photographer Lorincz Ferenc won the portrait category for this up-close and personal image of a bat fish taken at Rash Mohamed National Park in Egypt. He was trying to photograph a large school of fish, but gave up because there were divers swimming by all the time.

"Not so far from the others I noticed a crevice in a rock, which fish used as a cleaning station, and slowly, very slowly, I swam into the gap, switching places with the cleaning fish," Ferenc says. "This made it possible to photograph this bat fish front on."

Rowlands is a big fan of the results.

"Here is a great example of what really works as a portrait. The eye contact is immediate and they are pin sharp but it is the mouth and lips which deliver the character. The lighting and color contrast lifts the subject from the background and, for me, the four little fish in the background are the icing on the cake."