glowing mermaid
Image via Piqsels

Do mermaids glow? Here is a case for bioluminescence among the merfolk.

Mermaids are a humanoid cryptid often depicted as half human and half fish. Specifically, human from the waist up and fish from the waist down. 

Depictions and stories of mermaids have existed for over 30,000 years. A concise summary is available at Sirenas Meditterranean Academy. 

With sightings all over the planet, varying both geographically and temporally, numerous and diverse characteristics have been propagated with respect to the merfolk. A perfect example is the dichotomy of good versus evil; bringers of storms in the Mediterranean versus creators of beauty in East Asia; beautiful guides of treacherous waters versus grotesque consumers of wayward sailors. 

Despite the differences, there are also many similarities: human faces and torsos combined with fish tales; the ability to transition from water to land; and universal communication. Most notably, all merfolk are given, if not fully, semi-magical powers. 

Given that most god-like mythical beings have a glow or aura about them, should mermaids also glow? While not all sea creatures glow, some certainly due through the process of bioluminescence. 

Of all the ocean going creatures, nothing excites the imagination quite like bioluminescence. A simple chemical reaction (similar to the one fireflies use to light up during the summer) is at work. However, unlike fireflies, underwater luminescence has several uses. According to Smithsonian, there are three main reasons to use bioluminescence: feeding, protection, and attracting mates. 

Bioluminescence for Feeding

Bioluminescence is used by deep sea fish to lure prey to within striking distance. 

In the case of the lantern fish, it can lure prey directly into its mouth. 

Image Credit: Christopher Glenn (Flickr)

According to the legends, mermaids eat wayward sailors that they charm over the sides of their ships. Specifically, they are regarded as so beautiful that the sailors willingly jump overboard. 

This beauty would seem to negate the need for bioluminescence as a method of gathering food. Looking deeper we see that the mermaid would need a way to isolate its prey from the rest of the crew. Shouting loudly or banging on the ship would likely disturb at least several crew members and hence increase the chances of a mermaid being killed or captured. 

A faint glow just beneath the waves might be just enough to peak the interest of a single sailor without raising alarm, thus isolating the mermaid’s prey and preserving its safety. 

Bioluminescence for Protection

Contrary to common sense, using light for protection is a form of underwater camouflage. By dispensing light on the underside of the body and leaving the sunlight/moonlight above, an animal can become nearly invisible from below. 

Applying this to mermaids reveals how they could avoid shark attacks despite appearing as a silhouette of a seal or turtle. Save Our Sharks explains why sharks attack humans, but is equally, if not more, appropriate for potential merfolk attacks. 

Bioluminescence for Mating

The predominant theories surrounding mermaids are that they travel in pods, much like dolphins, of around 30 to 50 merfolk. This would appear to eliminate the necessity of light as a method of finding a partner. 

The only source attributing luminescent qualities to mermaids is the wiki fandom for the show Sirens, which states that they glow red as part of the reproductive process. 

Do Mermaids Glow?

Tallying the possible uses, we see two scenarios in which bioluminescence would be actively beneficial and one which, at minimum, would not be a hindrance. So, why is there so little evidence for the existence of this trait amongst the merfolk? 

The recent photographing of a glowing kitefin shark provides the perfect answer. Despite understanding many things about the kite shark, including its lifespan, evolutionary history, and closest relatives, bioluminescence has only ever been a suspected capability of theirs. 

Image Credit: Jérôme Mallefet

That a species could be “understood” and yet have no active proof of the ability to light itself up, despite literally tons of captures, explains the lack of evidence. Further, tons of shark are processed and turned into food, leather and other commodities. Yet nobody had ever managed to photograph the glow, until recently. 

One final piece of evidence exists: a large glowing vertebrate with a length approximately that of a mermaid has a similar range to the most common mermaid sightings is likely more than a coincidence. 

Taken as a whole, we should add mermaids to the list of glowing cryptids. Further, we may be able to utilize this new assumption in a future search to find the merfolk.


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