Manta Magic: An acrobatic performance beneath the waves

People generally don’t realize that only a handful of marine biologists spend their daily lives in the ocean. The rest of us tend to work in labs, offices, or from home. For us, the moments we can get to the ocean (usually for holidays or fieldwork) are treasured.

With ocean habitats degrading and marine life increasingly under threat, these fleeting moments of connecting with the ocean are even more special. For me, one particular moment that will stay with me forever is a manta ray night dive I went on in 2017.

I was in Hawai’i supporting my mum, who was competing in the Ironman World Championships on the Big Island. I did a bit of research before the trip for things to do while my mum was training, and found that the island has a resident population of reef mantas. There are three spots around the island that you can visit for a night dive (or a snorkel) to see these mantas feeding.

On the night of the trip, our boat set off into the sunset, accompanied by a pod of dolphins playing in the waves at the bow. I’d never been in the water with anything bigger than a turtle before, so I was really excited to see a manta ray!

After we kitted up, we descended down the mooring line and finned towards the bottom of the ocean. We’d each been given a torch to be able to see, but as we got nearer to the feeding station the ocean became more and more lit up.

Directed by the guide, we all sat cross-legged in a circle on the seabed and were given a rock to place on our laps. We pointed our torches upwards, and lights shone from the surface and the seabed all around us.

I settled into my spot, readjusted my rock, and then I looked up… Being a scientist, I’m not a very spiritual person, but the scene that met my eyes was…  ethereal. Over thirty manta rays danced above me, to music I couldn’t hear. Shoals of silver fish gathered, shimmering and moving as one.

The ocean was so well-lit that it created the feeling of being inside an aquarium. With nothing but the sound of our bubbles, it was comparable to being inside a hushed cathedral, or watching the sunrise on a secluded beach. So serene, and completely mesmerizing.

The graceful acrobats performed somersaults in the water. Swimming in large chains and groups, they often synchronized their barrel rolls and loop-to-loops—filtering as much of their prey as possible from the water column. Despite so many being in the water, they always managed to just avoid colliding with each other, and us… I can’t count the number of times I’d look up to see one swimming over me, just inches from my head. They were so agile.

What I found really interesting about the night dive is how the lights work. Phytoplankton are basically tiny plants that live near the surface of the ocean. When the sun goes down, they can be attracted to artificial lights—like the ones used by the tour operators. Another kind of plankton, called zooplankton, usually comes to the surface at night to feed on the phytoplankton under the cover of darkness. With their prey concentrating around the lights, it makes for an easy meal. So mantas come to these feeding stations to eat this thick soup of zooplankton.

There are few moments in life that are truly memorable, and this manta ray night dive was definitely one of them. It was pure ocean magic.

On our way back to shore, I was reflecting on how lucky I was to have experienced this underwater show, and also wondering how manta rays are affected by climate change. I was just about to start my master’s degree in tropical marine biology, and I didn’t have the answers yet.

Over the next year, I learnt about all the various ways manta rays are threatened by human activity. A more obvious, and very significant threat, is the gill raker trade. But climate change also plays a role. I learnt that ocean warming is altering the distribution and composition of zooplankton, manta rays’ main prey. Climate change is also severely threatening coral reefs, where manta rays feed and visit cleaning stations.

I often think back to this dive, and hope that we can tackle climate change so that other people can experience the same connection with the ocean.