I have spent the better part of two days trying to learn about glowing shrimp puke. ScienceOnline made me do it.
A few days ago, during a quick tour organized by the annual science communication conference, North Carolina Museum of Natural Sciences exhibit director Roy Campbell pointed out a tiny invertebrate in the gloomy recesses of the institution’s deep sea exhibit. He said this crustacean was one of the jewels of the tour – a representation of a shrimp named Acanthephyra purpurea that spews a bioluminescent cloud from its mouth when attacked. The burst of bright barf is enough to put would-be predators off their tea.
We didn’t have time to dally around the submarine diorama. The tour proceeded through the rest of the museum at a breakneck pace, but I kept wondering about the shrimp. How does defensive retching actually work?
You would think that the internet would hold a wealth of information about such an unusual animal. At the very least, a vomiting shrimp should be a YouTube sensation. But my internet trawls came up mostly empty. Dr. SkySkull, one of the other tour attendees, turned up a composite image of the shrimp, a viperfish, and a glowing cloud of expelled gunk on the NOAA Ocean Explorer website, but that was just about all.
I contacted marine biologist Steven Haddock at the Monterey Bay Aquarium Research Institute to get the skinny on this shrimp. As it turns out, “vomiting shrimp” is a misnomer. The bright blue bioluminescent cloud the shrimp expels isn’t regurgitated stomach contents. Instead, Haddock explained, “The luminous fluid probably originates in the hepatopancreas” – an organ that plays roles similar to the liver and pancreas in us – “and, depending on the species [of shrimp], can come from the mouth or nearby organs.” Haddock also shared a quote from a 1985 paper by researcher Peter Herring which noted that “[The bioluminescent fluid] is always associated with a hepatopancreas which is luminescent if macerated.”
As Haddock pointed out, other shrimp are equally capable of such beautifully gross feats. Other species among several shrimp genera – such as Heterocarpus, Systellaspis, and Oplophorus – also squirt lovely luminous clouds. And, despite their different family relationships, the same chemical compounds underlie their light-emitting abilities.
Marine biologist Edith Widder surveyed the various forms of lights in the deep in a 2010 review published in Science. The squirting shrimp actually joins most light-emitting marine life in relying on blue light – the part of the spectrum that travels furthest through seawater. But the shrimp’s store of spew isn’t blue when it’s stored inside the crustacean’s body. When discharged into the water, a chemical compound in the fluid – luciferin – reacts with oxygen to produce light and the enzyme luciferase. The whimsical Lucifer prefix doesn’t denote anything particularly devilish, but rather the “light-bringing” aspects of these building blocks of bioluminescence.
Different creatures possess different flavors of luciferin. The structure of luciferin in bacteria – whether living alone or in the glowing organs of some fish and squid – are structurally different from those utilized by other clades, such as the subgroup our peculiar shrimp belongs to. In all, bioluminescence has evolved independently at least 40 times, although exactly how this happened in each lineage remains in the realm of hypothesis.
In the case of Acanthephyra, the particular variety of chemical compound is used to confuse or distract predators. (In the video above, a similarly-equipped shrimp uses the defense to protest its appearance on Japanese television.) Where the bioluminescent material comes from, however, is not exactly clear. I asked Haddock if the shrimp produced the compounds themselves, or obtained it through the food they ate (perhaps smaller bioluminescent creatures.) He replied that some shrimp, such as a close relative of Acanthephyra called Systellaspis, have been found to synthesize the organic compounds necessary for bioluminescence inside their bodies. “The luciferase almost certainly originates in the shrimp,” Haddock said, “and the luciferin is likely to as well.”
So we’re left with the question of what to call Acanthephyra purpurea. “Vomiting shrimp” does not fit, nor does the alliterative “spewing shrimp.” The alternative “fire-breathing shrimp” suggested by the NOVA video above just makes me wonder how a true flamethrowing shrimp would avoid flash-frying itself. And, of course, any name we might pick could easily apply to the various other shrimp species that also squirt their away from danger. I went in search of a crustacean species with an upset stomach, and I found a variety of gushing, glowing shrimp.
Haddock, S., Moline, M., & Case, J. (2010). Bioluminescence in the Sea Annual Review of Marine Science, 2 (1), 443-493 DOI: 10.1146/annurev-marine-120308-081028
Inouye, S., Watanabe, K., Nakamura, H., Shimomura, O. (2000). Secretional luciferase of the luminous shrimp Oplophorus gracilirostris: cDNA cloning of a novel imidazopyrazinone luciferase FEBS Letters, 481 (1), 19-25 DOI: 10.1016/S0014-5793(00)01963-3
Widder, E. (2010). Bioluminescence in the Ocean: Origins of Biological, Chemical, and Ecological Diversity Science, 328 (5979), 704-708 DOI: 10.1126/science.1174269