Glowing dolphins: The brilliance of bioluminescence off our coasts

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Marine biologist Vanessa Pirotta was instrumental in filming dolphins swimming in bioluminescence for the first time – and the experience was unforgettable.

This article is suited to students in years 5, 6, 7, 8, and 10 studying Biological, Chemical and Physical Sciences by covering photosynthesis, chemical reactions, and light energy.

Try the student activity below to learn more about bioluminescence and make your own glow in the dark slime.

Word Count / Video Length: 971 / 2:48 mins

Dolphins swimming through bioluminescence. Credit: Dean Cropp, Author provided

One of the largest migrations on earth takes place in the ocean every night.

Billions of tiny marine organisms known as zooplankton rise to the surface to feed on phytoplankton– tiny microscopic creatures which make their own food using the sunlight.

Certain species of phytoplankton (dinoflagellates e.g. Noctiluca scintillans) congregate in large numbers, sometimes turning the ocean an electric blue colour, a phenomenon called bioluminescence or sea sparkle.

They trigger their bioluminescence as a warning signal to predators, but it can also be caused when they’re disturbed in the water.

But bioluminescence isn’t only found in the oceans.

On land, there are fireflies. They produce their own light to attract prey and signal potential mates. There are also glow worms and certain species of mushrooms that glow in the dark.

Bioluminescence in all its elusive glory

It took me many years to finally see bioluminescence in the ocean.

I had heard about it from fellow scientists and travelled all the way to Antarctica and back and never saw it.

It was only in 2018, living aboard a boat in the Galapagos Islands, when I flushed the toilet at night. To my surprise, the entire bowl lit up and glowed! This was my rather odd yet amazing first encounter with bioluminescence.

Thankfully, this wouldn’t be my last.

I teamed up with underwater cinematographer and explorer Dean Cropp who came across bioluminescence as he sailed down the east coast of Australia.

At 4 am one morning, Dean and his crew witnessed dolphins glowing in the dark as they surfed the bow wave of his sailing catamaran.

Grabbing his camera he captured the unique light show on film for the first time.

This caught the interest of Plimsol, a documentary production house in the UK, and Netflix who set us the challenge: to predict, find and again film dolphins swimming underwater in bioluminescence off Sydney.

We sat down to plan the adventure. By combining what was known about bioluminescence in the scientific literature, and keeping an eye on the forecast, we concluded our best chance would be mid-summer. And so we waited for the perfect night to see things that glow – low wind and a new moon phase, when the moon is lowest and the night is at its darkest.

Bright blue, glowing dolphins

It was around 10 pm on a warm summer’s night when Dean’s boat sailed through the heads of Sydney.

As we travelled, Dean and the team prepared the camera equipment- highly light-sensitive cameras with an ISO setting of 85000, underwater housings and a specially modified camera stabiliser system. I remained on the bow, ready to spot bioluminescence and dolphins.

The sea became darker as we headed further east off Sydney. Then, it started to glow very lightly with only small amounts of bioluminescence where the bow disturbed the surface.

Bioluminescence in Sydney in the wake of the boat. Credit: Vanessa Pirotta

Hours passed. Nothing.

You can plan everything, but sometimes nature just doesn’t play ball.

There was nothing to do other than wait for similar conditions to come around again, a new moon phase and low winds.

Weeks later we left the wharf for a second time and the water sparkled lightly- this was promising.

As we headed offshore the ocean lit up. I had never seen it like this. The wake of our boat was electric. It reminded me of the movie Avatar. Now, all we needed were the dolphins.

It was around 2 am when something caught my eyes. It looked like a float at the surface, then it darted towards our boat.

As I looked down, bioluminescence illuminated a pod of dolphins riding the bow of our boat. It was strangely disorientating and electrifying at the same time.

Dean used an ultra-low light camera to film the dolphins swimming underwater illuminated only by the surrounding bioluminescence – something which had never been done before until now.

I had a front-row seat holding the monitor in my hands. I screamed with delight (very un-professionally) every time a bright blue glowing dolphin came into view. It was surreal.

Predicting bioluminescence is tricky

Trying to predict when bioluminescence is going to happen can be tricky, but when we got it right it was absolutely amazing. Any disturbance, the movement of the boat, the dolphins swimming through the water, even baitfish resulted in their bright illumination from a sea of dinoflagellates.

Having the tools to capture events like this is one step closer to observing marine life from another perspective and allows us to ask new questions.

For example, could dolphins use bioluminescence to advance hunting success in combination with echolocation (biological sonar)?

Already we have seen advances in technologies in the marine environment which has allowed us to learn more about marine animals in ways we would have never thought possible – think drones collecting whale snot and technology in your mobile phones to track seal movements in Antarctica.

A new generation of tools to study bioluminescence could open a whole new understanding of our oceans.

We need to conserve darkness

But as the world changes, so does bioluminescence. Artificial light is thought to reduce the effectiveness of bioluminescence by dinoflagellates. With more background light they appear less bright, and that could increase their risk from predators.

Atmospheric light levels can also be a signal to marine life to rise to the surface – they’ll only rise when it’s dark enough to provide safety. Therefore too much light from above and these organisms may stay deeper for longer, reducing their feeding time.

Bioluminescence is truly one of the most amazing natural wonders I have ever seen. And the glow-in-the-dark dolphins off Sydney serve as a visually beautiful reminder of how incredible our ocean is. We just need to make sure we conserve what darkness we have left – for our sake and theirs.

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Years: 5, 6, 7, 8, 10


Biological Sciences –  Ecosystems, Cells, Living Things

Chemical Sciences – Chemical Reactions

Physical Sciences – Energy

Additional: Careers, Technology

Concepts (South Australia):

Biological Sciences –  Interdependence and Ecosystems, Diversity and Evolution, Form and Function

Chemical Sciences – Change of Matter

Physical Sciences – Energy


6, 8 & 10