Marine Biology Blog

From early December we started to notice something amazing happening as darkness fell on the sandy shores of Gili Lankanfushi. Bright electric blue sparks lit up the beach as the waves gently lapped at the sand! This phenomenon, known as bioluminescence reached dramatic density and beauty on the few nights surrounding Christmas day 2022.

These neon drops of blue are often seen in certain parts of the Maldives at this time of year. However, this December was exceptional and unprecedented. Maldivians and tourists alike danced and covered themselves in the blue sparkling sand from the very North of the Maldives to the very south. It seems that this year there was a lot more of these glowing sea creatures washing up and over a much larger area than usual. Many of the hosts who have been working here at Gili Lankanfushi for many years had never seen anything like this on our shores.

There are many types of sea creatures that are capable of producing bright blue or green bioluminescent light, from fish and jellyfish to microscopic plankton. However, usually when we see these small blue sparkles in the sea or on the shore, it is being made by tiny plankton called dinoflagellates, or by ostracods, a type of tiny crustacean. These two types of organism are wildly different. Whilst dinoflagellates are a type of single-celled algae, ostracods are a type of multicellular animal. So which life form was behind the glow we saw this Christmas?

On the night of Boxing Day, our marine biologists crept down the beach to the waters edge armed with tweezers and carefully pinched the tiny drops of lightening blue out of the sand. Bringing the samples inside the lab, it was just possible to see the source of the neon light as tiny clear blobs of only 1 mm in diameter, with the naked eye. Under the microscope, these creatures were even more incredible! Still living, we were able to see that these clear blobs contained around 8-10 bubbles of lime green colour inside them. The little creatures were also clearly pulsing with life, with a dark patch marking its eye spot and dark lines marking appendages. This meant that we were able to identify these blobs as ostracods.

Ostracods are a type of crustacea (like crabs, lobsters, prawns and barnacles) that are also known as seed shrimp. They resemble tiny shrimps within an oval hard calcified shell. They usually have 8 pairs of soft appendages protruding from the shell for swimming, feeding and sensing. Ostracods can be planktonic (drifting with the current), but they can also live in the sediments and in seagrass.

Bioluminescence has evolved independently in different creatures over 100 times. However, the main way that light is made is the same for nearly all organisms. Indeed, for the ostracods, the light is made by a chemical reaction involving luciferin and luciferase. Luciferin is a type of small light-emitting compound. In different organisms, luciferins take different forms. In the presence of oxygen, luciferase, which is an enzyme (a type of active protein) can react with (oxidize) luciferin to release a photon of light.

When under threat, the ostracods release mucus containing the luciferin and luciferase, which flash bright blue as they react. The aim of expelling the light is to confuse predators as to the actual location of the ostracod. For some ostracods releasing this light is also part of their mating habits.

Here at Gili Lankanfushi, we found that when we scrabbled our feet in the sand at the shore, this activated the ostracods defense response, with streaks of blue entering the gentle waves as they lapped the shore. However, even more impressive was when we shook the clumps of dead seagrass that had washed up on the tide line. The ostracods must have been living in and attached to the seagrass as their density among the grass blades was phenomenal!

While this phase of nightly natural firework displays seems to have now ended, currents are ever bringing in new creatures to our shores. This week it’s the blue buttons (Porpita porpita). So while we enjoy what the changing winds and tides bring, we can eagerly await for bioluminescence season to return next Christmas!