APR 07, 2021 4:27 PM PDT

Scientists Discover a Crab-Dissolving Parasite

WRITTEN BY: Tiffany Dazet

Parasites abound throughout the natural world. While not all of them cause the host's death, this newly discovered parasitic ciliate dissolves and destroys common West Coast crabs. According to the study by researchers at Scripps Institution of Oceanography (UC San Diego), this single-celled parasite eats the crabs' muscle and connective tissue, thereby dissolving and killing the animal. The study was published this week in the Journal of Eukaryotic Microbiology.

According to an article from Scripps, the crabs infected by this parasite were five times more likely to die than those that were uninfected, increasing the local mortality of striped shore crabs by 22 percent. In a quote to Scripps, senior author of the study and ecologist Ryan Hechinger said, "It is also very possible that populations of the crabs we like to eat are actually getting hammered by this or a similar parasite without us even knowing it." Due to the potential ecological implications of these parasites, Hechinger continues, "We really need to survey these other crabs."

Scripps reports that striped shore crabs are integral pieces of the West Coast shoreline food chains, providing a food source for birds. While humans do not consume striped shore crabs, the researchers are concerned that the parasite could spread to fishery species. According to Scripps, Pacific rock crabs could become infected since some of their habitat overlaps with the striped shore crabs.

The researchers were also astounded by the parasite's method of infection, as well as its feeding stage. Scripps reports that the parasite makes a temporary mouth out of its skin, something not seen with any other ciliate species. First study author and Scripps Oceanography Ph.D. candidate Dan Metz stated, "This parasite really eats these crabs from the inside out. It has five distinct stages living inside the crab. There's a huge feeding state that forms a gigantic mouth, something never seen before." Metz compares the feeding states to a "furry basking shark swimming around in a crab's blood."

Because this research team discovered the new species, they had the privilege of naming it. The genus name—Lynnia—honors late ciliate biologist Denis Lynn. Metz said, "He contributed so much to the biology of ciliates, including important work on species closely related to this new genus we found." The species name—graspolytica—means "crab dissolving" and refers to its host (Pachygrapsus crassipes) and parasitic pathology.

Source: Scripps Institute of Oceanography

About the Author
  • Tiffany grew up in Southern California, where she attended San Diego State University. She graduated with a degree in Biology with a marine emphasis, thanks to her love of the ocean and wildlife. With 13 years of science writing under her belt, she now works as a freelance writer in the Pacific Northwest.
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