Boating on coastal waters, under a star-filled sky, can reveal yet another natural light source, biological light (=bioluminescence). As kids in our backyard, we captured fireflies, put them into a jar and watched in amazement as they lit up a spot on our picnic table. Lightning bugs, in reality beetles, produce their glow by creating a chemical reaction between an enzyme (luciferase) and a compound called luciferin. On land, some species of mushrooms, glow worms, a few breeds of snails and a variety of different fireflies are sources of biological light. In fresh water, other than a snail (Latia) found in New Zealand streams, there are few, if any other, widely known examples of light producing organisms.
However, in contrast, the world’s oceans are host to a huge number of residents that produce their own light. These include certain bacteria, algae, worms, crustaceans, sea stars, jellyfish, comb jellies, sharks and aproximately1,500 species of fish. Beginning in 1930, William Beebe and Otis Barton made a series of deep dives in the waters off Bermuda. Crammed into a 57-inch-wide, steel hull bathysphere, they were lowered by a single cable into a world that had never experienced by any other human. Peering out their single 3-inch thick window, they were witness to a cornucopia of strange creatures that lit up the otherwise dark seas. There were long thin transparent creatures, siphonophores, described by Beebe as “lovely as the finest lace,” “flying snails that swam with a pair of flapping fleshy wings,” glowing jellyfish and strange-looking fishes equipped with glowing lights. On August 15,1934, the explorers descended to 3,028 feet, a record that stood 15 years. The bathysphere used by the explorers, is now on permanent display outside the Wildlife Conservation Society’s New York Aquarium at Coney Island.
In Long Island Sound and along the much of the western Atlantic, the sea walnut, a 3 to5-inch long comb jelly, is a common source of biological light. The nearly transparent creature paddles itself slowly through the water, using its eight rows of tiny beating combs (=cilia). A flash from an underwater camera reflecting off the combs, makes the creature shimmer in a rainbow of colors. But the sea walnut’s biological light, a blue-greenish glow, is only visible at night. It is often triggered in the wake of a boat’s hull. And it is also important to note that comb jellies are not equipped with stinging cells. Despite their similar name and jelly-like body structure, they are not related to jellyfishes.
Sea walnuts are most common on Long Island Sound, f rom May through December. Throughout the world’s seas, there are an estimated 100 to 150+ different species of comb jellies. Some are coastal species while others inhabit mid-water or deep oceans. Near shore at Nantucket Island, MA, microscopic size, single-cell algae, dinoflagellates, are responsible for a great deal of the watery burst of light. Known locally as “sea sparkles,” their display can easily be viewed along the beach, in the breaking waves. The glow from the huge number of dinoflagellates, estimated at 700,000 per single gallon of water, light up the nighttime waters of Puerto Rico’s Mosquito Bay (Isla de Vieques). The breathtaking display, an experience of a lifetime, can be seen on tours aboard clear-bottom kayaks at the Puerto Rico site or at Florida’s Indian River Lagoon and the Merritt Island Wildlife Refuge. It is recommended that the best time to experience the display of biological light is during as “New Moon” phase. For more information, go to Google and enter bioluminescence tours Florida or Puerto Rico.
Why do oceanic creatures produce a biological light? Some use the light to attract a mate, distinguish between gender, bait a prey or distract or ward-off a predator Anglerfish use a lighted “fishing rod” to lure prey toward their mouth and some deep-sea squids can cast off a lighted arm to confuse a predator. Biological light is also used as counter-illumination, matching the background light from the ocean surface. The technique helps mask them from predators hunting below them.
In November, 1918, a U-boat sailed through a bioluminescent bloom, giving away its position. It resulted in its sinking by Allied ships. It was the last German submarine to be sunk during World War l.