When the sun sinks below the horizon, the ocean doesn’t go dark – it comes alive. Beneath the waves, tiny plankton spark like embers, jellyfish pulse in glowing colours and deep-sea creatures ignite the darkness with bursts of living light.
Bioluminescence
Bioluminescence turns the ocean into a silent fireworks display, powered not by fire, smoke or sparks but by chemistry, evolution and survival. These mesmerising displays can be used to attract a mate or prey, act as defence or used for communication and are spectacular to witness.
Bioluminescence is the natural production of light by living organisms, through chemical reactions involving luciferin, luciferase and oxygen. Luciferin is the light emitting molecule, while luciferase is the enzyme that catalyses the reaction. So, when luciferase reacts with oxygen, it produces light, often referred to as ‘cold light’ as it generates very little heat during the process. Marine organisms produce blue or green light as these lights travel through water.
Pyrosomes
These fascinating creatures are not just a single organism but a colony of zooids working in harmony, sometimes in the thousands. Their tubular structure, all organisms working together, allows them to propel through the water, filtering the water as they move, consuming plankton and other small particles. The nature of them being filter feeders helps to keep the ocean ecosystem in balance.
They are large in size, reaching 60 feet in length, which is the size of a standard cricket pitch. It is thought that one of the reasons pyrosomes use bioluminescence is for intraspecific communication. The light waves can be a way for zooids to communicate with each other within a colony.
Firefly Squid
Found in the Western Pacific Ocean off the coast of Japan, they are named after the Japanese word ‘hotaru-ika’ which means ‘firefly squid’. As they can produce bioluminescence through light producing organs located on their tentacles.
These tiny squid (about 3 inches long), spend most of their lives in deep ocean waters, about 200m-400m down. But in the spring, they will come closer to the shore to lay their eggs. This annual spawning event, where millions of squids light up the bay, attracts tourists and is celebrated in local festivals.
Firework Jellyfish
These jellyfish do not fail to astound, as they truly are fireworks of the sea, living in the deep depths of the ocean, 1,200m – 1,500m down. Their unique light display is dependent on the species. Some will create swirling patterns others will pulse rhythmically and a few can even produce circular wave effects. Not all species will glow the same colour. Some rare firework jellyfish can shift seamlessly from colour to colour, including deep blues, reds and greens. They do this via their internal chemistry, but also external factors have an influence, including salt levels, temperature and even the moon’s phase. Scientists study firework jellyfish in areas, take note of the colour changes, informing the current health of the ocean before other detection methods may signal environmental problems.
It is thought that they perform these colourful light displays as a form of defence. When they feel threatened, they can release glowing particles into the water. These flashes and bright lights confuse predators, giving the jellyfish time to drift away.
These spectacular jellyfish, in 2008, won a Nobel prize in chemistry. Due to the protein in their tissues, which glow under ultraviolet light, which scientists refer to as green fluorescent protein or GFP. This GFP has now become a standard laboratory tool used as part of genetic engineering as well as assisting fundamental research.
This is just a small example of the many wonderous creatures who light up the oceans. These radiant displays can dazzle predators, attract mates, or lure prey, turning survival into a breathtaking show. Just like fireworks in the night sky, these glowing creatures remind us of the beauty and wonder hidden beneath the ocean’s surface.