The Flamingo tongue snail:  Predator and parasite

By Corinne Pita (University of Michigan) and Julia de los Reyes (Yale University), The School for Field Studies Center for Marine Resource Studies, South Caicos ~ Photos By Dr. C.E. O’Brien

It’s easy to conjure images of predation: a lion pouncing on its prey, an owl hunting for mice, a spider entwining a fly in its web. Similarly, one can picture classic examples of parasitism: a tapeworm, fleas on a dog, the tick that ruined a summer camping trip. In nature, however, there exist complex relationships that don’t fit neatly into these simple examples, and some that even blur the lines between predation and parasitism. 

One example of this is the relationship between sea fans and the flamingo tongue, a curious little snail that is both predator and parasite. This relationship can be seen throughout the clear blue waters of the Turks & Caicos Islands, where the common sea fan and flamingo tongue are found in abundance.

A flamingo tongue snail perches on a small gorgonian during a night dive near South Caicos.

The common sea fan, Gorgonia ventalina, is a species of coral abundant in near-shore reefs throughout the Caribbean and Western Atlantic, easily identified by its purple color and wispy, fan-like shape. Often seen swaying in the ocean current, G. ventalina is a member of a group of similarly wispy corals known as gorgonians and is broadly classified as an octocoral, meaning that its polyps—the hundreds of tiny animals that together comprise a large coral—have eight small tentacles. These tentacles are used to catch its food: tiny bits of floating plankton. While they are predators of plankton, sea fans are themselves the prey of various marine predators, each armed with unique adaptations to easily consume sea fans.

The flamingo tongue, also known as Cyphoma gibbosum, is a marine mollusc present throughout the tropical western Atlantic Ocean on shallow gorgonian-dominated reefs. The characteristically beautiful patterns present on C. gibbosum make them easily visible when they take residence on sea fans and other octocorals like sea plumes and sea rods. These patterns can differ greatly between individuals, so much so that scientists once thought that different shell patterns indicated the existence of multiple species! C. gibbosum is most often seen with orange spots outlined in black, but other patterns such as “fingerprint” (elongated orange lines outlined in black) and “broken spots” (similar spot pattern with black outlines partially dissipating) also exist.

While these different characteristics caused scientists in the 18th and 19th centuries to declare these flamingo tongues different species, today we have DNA analysis to tell us this is not the case. However, the reason for the difference in shell patterns is actually unknown, even today, and various hypotheses as to the reason for this disparity are being investigated. One possible explanation is in-process species divergence, which is the hypothesis that C. gibbosum is in the middle of becoming separate species since morphological differences tend to precede genetic differences. Such a hypothesis implies that we are witness to a stage in species divergence where morphological differences have occurred but not genetic. To prove this, further study demonstrating a mating preference between flamingo tongues with the same pattern would be needed. 

Then there’s the supergene hypothesis, which the belief that flamingo tongues have a supergene, or a strongly linked set of DNA sequences that don’t often get separated over generations and which code for certain morphological features. This scenario can result in common and rare morphologies within a species, the common ones here being the spotted orange and black circle pattern, and the rare being the fingerprint and broken spot patterns. Many other hypotheses exist for the differences in patterning, but all point to one fact:  C. gibbosum is a much more diverse and multi-faceted species than meets the eye.

What’s more, beyond the eye-catching coloration of C. gibbosum lies a violent and intriguing story. At first glance, the spotted snail perched on the swaying sea fan looks innocent—serene, even. However, a closer look reveals a complicated picture of both predation and parasitism. C. gibbosum is a predator in that it consumes G. ventalina and other soft coral polyps for sustenance. Because of this, the flamingo tongue is classified as a “tissue-stripping tropical corallivore.” But the flamingo tongue also lives on its prey. How is it possible for an organism to maintain long-term residency on something it chooses to eat? The answer is that C. gibbosum rarely kills its hosts, eating it slowly enough that the prey is able regenerate its lost tissues.

What this means is that C. gibbosum may not be a true predator, but instead can be classified as an exoparasite, a parasite that affects its prey from the outside. Unlike some other parasites such as tapeworms or ringworms, flamingo tongues do their damage without entering their hosts. Flamingo tongues benefit from their sea fan’s continued functionality, purposely inducing only small amounts of damage on their prey/hosts. By not causing total mortality in their prey/host, flamingo tongues have found a way to gain a long-lasting home as well as a reusable food source. Indeed, all life stages of this species are dependent on their host:  C. gibbosum individuals lay their eggs on gorgonians, from which free-floating larvae develop after a week, settling back onto gorgonian colonies as juveniles.

This flamingo tongue has the “fingerprint” pattern. Note the coral polyps it has eaten.

Another interesting aspect of this relationship involves chemical warfare: Sea fans have evolved toxins to ward off predation, which are effective against many of their potential predators. Known as allelochemicals, these substances are known in part for their bad taste, but more so for their toxicity to many potential consumers. While this scary-sounding collection of chemicals seems like it would be too much for a little flamingo tongue, this stubborn mollusc has evolved resistance to host chemical defenses such as these. Recent studies have suggested that marine consumers like the flamingo tongue can tolerate toxin-laden prey through the presence of special enzymes, biological catalysts that respond to specific chemical signatures. While they serve many purposes, enzymes in the flamingo tongue and other marine consumers are believed to be able to neutralize the toxins in sea fans to keep them from inflicting their catastrophic effects.

With these methods allowing C. gibbosum to consume their toxic prey, these molluscs don’t just survive, but thrive on their poisonous diet, going so far as to assimilate the sea fan’s toxicity into their own tissues. This gives the flamingo tongue a poisonous defense mechanism against its own predators that its bright-orange color then advertises. Warning coloration such as this is referred to as aposematic coloration, and is meant to signal to potential predators that it’s off the menu. This is an incredible example of coevolution, a phenomenon in which organisms evolve in response to each other, with the flamingo tongue having evolved to thrive on a diet that its prey had evolved to ward off other grazers, and to even co-opt its prey’s defense mechanism as its own. This ancient “evolutionary arms race” is what we must thank for the beautiful coloration adored by snorkelers throughout the tropical western Atlantic and Caribbean. 

So, what’s the deal with C. gibbosum:  If it is both a predator and parasite of corals, is it a threat to our dwindling coral reefs? Or does it play a key role in these complex coral communities? The answer likely lies somewhere in the middle.

Research suggests that these gorgonian-munching snails may help maintain coral reef diversity by creating space for other types of coral to settle and flourish. Thus, by eating sea fans and other octocorals, flamingo tongues help cultivate the diverse community structure of healthy reefs. However, if there is a change in population dynamics, this healthy natural balance can be dramatically shifted, having devastating impacts on sea fan corals. For example, a 2008 outbreak of C. gibbosum in Puerto Rico wiped out more than 90% of the sea fans around the remote reefs around Mona Island.

This flamingo tongue has its mantle mostly retracted, exposing the unpatterned white shell beneath.

One factor that can lead to this imbalance is overfishing—despite the snail’s toxicity, there are species of fish, primarily pufferfish and invertebrates such as lobster, that consume it. These snail predators indirectly maintain coral health by keeping the parasitic species in check. For example, a study in the Florida Keys found that C. gibbosum populations in areas where large predators were removed increased to nearly 20 times their original size, leading to extensive damage to the sea fans. Here, the relationship between flamingo tongues, sea fans, large predators, and the greater coral community demonstrates the precarious balance of nature, a precisely interwoven web vulnerable to human-mediated shifts. While most imagine predation and parasitism as something of violence and destruction, it’s important to recognize the delicate interplay of these relationships that help to maintain balance in nature, and how necessary it is to uphold their existence moving forward in our changing world.

In case you were hoping to collect one of these beauties for your shell collection, beware:  These mystifying patterns are only present in live flamingo tongues, as they are created by a part of the mollusc’s body known as the mantle, a soft covering that lies over the shell. When the snail dies, or when it retracts into its shell for protection, that distinct coloration disappears, leaving just a plain orange cream-colored shell in its place. As a result, flamingo tongues are best admired alive and from a distance and should be in their natural habitat. This way, everyone who visits our Islands will have the chance to experience the beauty of the flamingo tongue’s shell for generations to come.

For detailed article references or more information about The School for Field Studies, contact Director Heidi Hertler on South Caicos at hhertler@fieldstudies.org or visit www.fieldstudies.org.