Glow and Behold! Underwater LED Surveys Reveal Rare Marine Species

Typically reserved for psychedelic ‘60s posters and funky lava lamps, fluorescence adopts a new important role in the discovery of mysterious marine species. By following the lead of a new tourism trend, scientists in Australia have developed a creative and colorful way to detect lesser-known lifeforms under the sea.

We are surrounded and often outnumbered by that which we cannot see. Cryptic species, identified as such due to their likeness to their surroundings, elusive behavior, and small size, are both the most abundant and comparatively least researched in any given ecosystem. Detectability, or the extent to which something is easily observed, therefore presents a major variable in conservation science.

Before determining population trends, true conservation status, and risk of extinction, scientists must first acquire a wealth of data regarding a species’ abundance and geographical distribution. This task is especially important when attempting to fit the globally recognized ranking criteria outlined by the International Union for Conservation of Nature (IUCN). As a result of these lofty data requirements, extinction-risk assessments in common fishes are typically based on the readily available information derived from fisheries and other commercial sources, while rare species most at risk are left with the label “data deficient”.  With the development of new sampling technologies, the problem of data deficiency has been partially solved for terrestrial species. Auditory and acoustic surveys have been designed for organisms that are difficult to see but easy to hear such as birds, bats, and frogs. For large yet sneaky felines like jaguars and snow leopards, camera trapping and hair sampling is now providing researchers with consistent data on species abundance and distribution. Despite these advancements, however, cryptic marine species remain underrepresented and understudied, with surveying methods relying heavily on inefficient and potentially biased visual counts dependent on the expertise of the surveyor. That is, until now.

See biofluorescent diving in action in this video highlighting the reefs around Koh Tao, Thailand.

With the expansion of recreational fluorescence diving, a new technological market has arisen for underwater gear such as blue LED torches and camera filters. At a relatively affordable price, certified divers can take a nighttime dip into an environment where biofluorescent creatures abound, and cryptic species reveal themselves in a kaleidoscope of color. Capitalizing on this growing trend, Dr. Maarten De Brauwer and his team from Curtin University packed their blue LED torches and sojourned to the coral reefs of Indonesia, a region containing the greatest number of marine fish species in the world. Focusing in particular on two rare species of pygmy seahorses (Hippocampus bargibanti and H. denise), the team completed underwater biofluorescence census (UBC) surveys at 63 sites with the goal of investigating which cryptically patterned fish species emit biofluoresence, and whether or not this new methodology is appropriate for estimating the population density of cryptic marine species.

Although the pygmy seahorses were rarely encountered (only 39 in total), the surveys revealed that all of the individuals identified fluoresced in the red and green spectrum. The brightness of the red fluorescence along each seahorse’s tail allowed for increased detectability against the dark background of the seafans on which they cling. For H. bargibanti, nearly double the number of individuals was detected using the fluorescence method when compared to non-fluorescent surveys. This increase of detectability was also found during Brauwer’s assessment of a more abundant fish, the largemouth triplefin, as nearly three times more individuals were detected in UBC transects versus the traditional visual method.

Pygmy seahorse H. bargibanti (pictured) is considered a cryptic species for its ability to blend in with its environment, its secretive behavior, and its small size.

The results of the study therefore demonstrated that the UBC method was indeed effective at finding cryptic species that are otherwise difficult to detect and quantify. The diversity of the research sites and recorded species also indicated that biofluorescence is ubiquitous in cryptic marine life, demonstrating that the new methodology is applicable across a wide range of taxa and geographic locations.

The implications of such a study are immense, as increased data for data deficient species such as the pygmy seahorses spotlighted in this study may lead to their proper identification as vulnerable, threatened, or even endangered. By establishing the abundance, distribution, and conservation status of such species, especially under the IUCN criteria, scientists and policymakers will be better equipped to implement effective protective measures, as well as facilitate the research and conservation initiatives needed to ensure the survival of these mysterious marine species.

Want to know more? Find the full research article here!

De Brauwer et al. (2017) Biofluorescence as a survey tool for cryptic marine species. Conservation Biology 32(3): 706-715.

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