Bioluminescence in the Indian River Lagoon
It’s a summer thing here. As moderate temperatures in June give way to the sizzling days and muggy nights of July and August, there is magic happening in the lagoon when the sun goes down. At first, you may not notice it as more than a glimpse of something out of the corner of your eye but as you glide silently in the dark water by kayak, the little glimmers of blue-green light here and there become more frequent and pronounced. You sense the movement first, and it’s a little disconcerting in those moments before you realize what you are seeing. Fish are darting everywhere. Soon every dip of your paddle creates mesmerizing swirls of dazzling light leaving trails of shimmering ripples dancing in the dark. The water around and beneath you is alive and radiant, and you are in awe of this surreal encounter with one of nature’s most fascinating spectacles.
The Science Behind the Magic
Bioluminescence, the natural emission of light by living organisms, is a captivating phenomenon that illuminates the world’s oceans and estuaries like our Indian River Lagoon. These transitional zones, where freshwater meets and mixes with the salty sea, provide a unique environment for bioluminescent organisms to thrive. Understanding the science behind this phenomenon and its ecological significance can deepen our appreciation for these glowing wonders.
Drs. Edith Widder, CEO of the Ocean Research & Conservation Association (ORCA) in Vero Beach, and Francis Letendre, Senior Research Fellow at FAU Harbor Branch Oceanographic Institute in Fort Pierce have dedicated their careers to studying bioluminescence.
In the lagoon, Widder says the brightest bioluminescent displays are due to dinoflagellates, a group of phytoplankton that flash when agitated. These are single-celled organisms that contain chlorophyll and can photosynthesize food; they usually have two flagella, which are tail-like structures that help to propel the organism through the water. Comb jellies (Mnemiopsis leidyi) which are small gelatinous organisms similar to jellyfish but without the stinging tentacles, are also a source of bioluminescence in the lagoon.
“The bioluminescent dinoflagellates in the Indian River Lagoon are Pyrodinium bahamense, which is the same one responsible for the bioluminescent bays in Puerto Rico. P. bahamense prefers temperatures over 72⁰ F, which is why they are most prolific in the summer months locally. Blooms usually occur in the northern part of the Indian River Lagoon up around Merritt Island, but I have seen them as far south as Jensen Beach, which is where I took this picture in August 2004. Comb jellies also bloom but their numbers are fewer, and the light displays are less spectacular.”
(Photo courtesy of Dr. Edith Widder)
Both Letendre and Widder explain that bioluminescence in the dinoflagellates present in the IRL is an anti-predatory response known as aposematism, the display of bright color, or light in this case, to indicate toxicity to potential predators. This form of defense mechanism serves as a warning system, effectively reducing the likelihood of an attack by advertising the organism's harmful or distasteful nature which benefits both the predator and the prey. Predators learn to associate the warning colors with a negative experience, thus avoiding future encounters, while the prey avoids predation through this visual deterrence.
There are many examples of aposematism illustrated in a variety of species across different ecosystems. For instance, the vivid coloration of the poison dart frog in Central and South America warns predators of its highly toxic skin, which can be lethal if ingested. Similarly, the striking black and yellow bands of the monarch butterfly signal its unpalatability, a result of toxins accumulated from its milkweed diet. In the marine environment, the bright blue and yellow hues of the blue-ringed octopus serve as a stark warning of its potent venom.
Other occurrences of bioluminescence serve different purposes. Fireflies glow primarily for communication, particularly for mating purposes. Male fireflies use specific light patterns to attract females of the same species, and females respond with their own patterns if they are receptive. Bioluminescence is also employed by various organisms to enhance their hunting capabilities. One well-known example is the deep-sea anglerfish, which uses a bioluminescent lure extending from its head to attract prey in the dark ocean depths. This glowing lure mimics the appearance of small prey, enticing unsuspecting fish and other marine animals to come close enough for the anglerfish to capture them.
Lights in the Lagoon & Health Indicators
Bioluminescent organisms are native to the IRL and the intensity of the displays is always changing but what, if anything, those changes may indicate about the health of the estuary is still unknown. Widder says:
“I don’t think there has been any significant change in the bioluminescence in the lagoon over the last decade but, oddly, there has apparently been a change in the toxicity of the bioluminescent dinoflagellates. The first documented case of toxin production in these cells locally occurred in the mid-2000s. We don’t know why or whether it has any link to pollution. It’s something we’re studying.”
(Comb Jelly)
Letendre adds that “pollution can help certain populations of zooplankton overcompete the rest of the community, specifically gelatinous organisms.” He points out that the species of comb jellies here are native to the lagoon but highly invasive. "Increased pollution could see this organism increase in density and potentially spread further in Florida waters. These organisms are highly bioluminescent and trigger "bombs" of light when startled.” He also says “Increased bioluminescence from higher concentrations of dinoflagellates is also a concern since the species we have are responsible for red tide events and paralytic shellfish poisoning, which is a concern for food consumption in the IRL.”
But toxin production isn’t a concern for those who wish to enjoy the amazing experience of a night-time kayak excursion where every dip of your paddle produces an explosion of liquid light, and Widder reassures that the only danger to humans is the consumption of shellfish contaminated by the toxins.
Bioluminescence in any bay or estuarine environment is not just a beautiful natural phenomenon but a vital component of the ecosystem. Understanding and preserving our glowing waters ensures that future generations can continue to marvel at this natural wonder and benefit from its ecological and scientific contributions.
Learn more about research, citizen science projects, and volunteer opportunities with ORCA and FAU Harbor branch at their websites:
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