Deep sea lanternfish help transmit parasites to sperm whales and giant squid, new research shows.
These parasitic worms, known as Anisakis brevispiculata, infect dwarf and pygmy sperm whales, strange and poorly-understood creatures found worldwide. The study, published recently in Deep-Sea Research Part I, sheds light on these mysterious creatures—as well as the parasites, closely related species of which can infect humans and cause severe symptoms.
“Anisakis are pervasive everywhere in the ocean,” and yet very little is known about them, says Francisco Aznar, associate professor in zoology, in the Marine Zoology Unit at the University of Valencia in Spain and one of the study coauthors.
Lanternfish are bioluminescent, producing light in the dark, deep sea habitat where they spend their daylight hours. Many species migrate toward the surface during the night, possibly following zooplankton or smaller prey fish. These daily migrations allow lanternfish, which are abundant throughout the ocean, to act as a link between deep sea zooplankton and top predators which stay closer to the surface, the study authors say.
From the Bottom to the Top
There are many different types of anisakis worms, some which infect a succession of three or more hosts, jumping from one to another.
Most start their lives after hatching from eggs by infecting crustaceans. At this point, they are either eaten by fish or other smaller sea life, though the exact path of many of these parasite species is not completely understood.
Finally, the worms end up in the guts of marine mammals—especially whales or dolphins—where they feed, mate, and spend the rest of their lives releasing eggs, expelled in feces. These eggs hatch and are ingested by crustaceans.
While the parasite specific to dwarf and pygmy sperm whales hasn’t been found in humans, some closely related anisakis species can infect people via raw or undercooked fish or seafood. While the worms cannot reproduce or even survive for too long in humans, an unlucky bite of sushi can still lead to symptoms such as vomiting, diarrhea, and severe abdominal pain, and may require surgery in the worst cases. Even cooked fish infected with the parasite can cause allergic reactions.
Whale of a Problem
According to Aznar, it is more difficult to tell what type of symptoms whales have.
While many cases likely lead to nothing serious, Mercedes Fernandez, one of Aznar’s coauthors and colleague at the University of Valencia, says that extreme infections can lead to stomach inflammation and ulcers. Severe infections may even lead to perforations in the stomach, and death, she says.
The parasite had been found in dwarf sperm whales, but the vector was unknown until researchers in India sent Aznar some samples from lanternfish in the Arabian Sea.
“They found these worms and they didn’t know what these animals were,” he says, adding that the Indian Ocean is “like a black hole for knowledge” on cetaceans. An examination of the DNA revealed some of the worms were nearly identical to those found in the pygmy sperm whale.
Many questions remain. For one, it’s unclear whether the sperm whales directly prey on lanternfish, or whether the lanternfish transmit the parasites first to deep water squid after being eaten.
Since sperm whales are known to eat squid, the parasite might use the latter to get to its final goal. While lanternfish have been discovered in the stomachs of pygmy or dwarf sperm whales, the cetaceans tend to prefer squid. As a result, Aznar says that the lanternfish found may have just been inside the stomach of squid rather than eaten directly by the whales.
Isaure de Buron-Connors, a biology professor at the College of Charleston in South Carolina who studies parasites but was not involved in Fernandez’ and Aznar’s research says that the paper brings valuable new information to the table, especially since the study of parasites is often neglected.
“We don’t know anything,” she says. “My colleagues would joke that there are parasites only where there are parasitologists.”
She says that information about these parasites is critical because it could be important in managing and conserving ocean species, especially since parasites can affect host behavior or performance in such ways as making creatures feed more, or swim faster or slower.
“All of that is going to affect the ecosystem,” she says.