They’re so soft—so squishy! Where to put a tag—and why bother? Questions like these moved scientists from the Monterey Bay Aquarium, the Monterey Bay Aquarium Research Institute (MBARI), Hopkins Marine Station and other institutions around the world to publish the first comprehensive how-to tagging paper for jellyfish researchers everywhere. This missing manual was long in the making
Tommy Knowles, a senior aquarist at Monterey Bay Aquarium, explains why. Historically, ocean researchers demonized jellies as “blobs of goo that hurt you,” and that interfered with scientific gear. That changed in the latter part of the 20th century as scientists grew keen to understand entire ecosystems, not just individual plants and animals. Knowing who eats what, how, where and when, they learned, is critical for conservation.
Jellyfish, however, remained a very under-appreciated member of the ecosystem for years, largely because so little was known about them.
“People didn’t know how to keep them alive in the lab or even on the boat,” says Knowles. Today, the field is coming into its own at a time when climate change has added urgency to the need to understand ecosystems in order to preserve ocean health.
A growing subject of interest
Understanding jellies is a concern for fisheries managers, too, since some jellyfish species prey upon the young and compete for food with the adults of commercially important fish. Other jellies impact tourism when blooms of stinging species foul beaches.
It’s not all negatives. We know that jellyfish play important roles in healthy marine ecosystems, by sheltering juvenile fish and crabs under their swimming bells, and nourishing hundreds of ocean predators. Jellies are a significant food source for ocean sunfish (the largest bony fish on the planet) and the endangered Pacific leatherback sea turtle, California’s state marine reptile.
As with other marine species that live and travel underwater—out of sight of human researchers—electronic data tags are useful tools for tracking jellies’ movements. Which gets back to the question: Just how do you tag a jellyfish?
In the 1990s, an Australian researcher wondered if box jellyfish sleep at night. He used early model radio tags developed for other species to discover that box jellies swam to the seafloor and rested there at night.
Rapid advances in tagging technology
Since then, tag technology has advanced rapidly, fostered by efforts like the ambitious research project, Global Tagging of Pelagic Predators, (GTOPP). While GTOPP primarily focused on birds, fishes and marine mammals, researchers did tag one invertebrate species, the Humboldt squid, which presented similar challenges to jellyfish.
A small but growing number of scientists continue to explore new and better ways to tag soft and squishy ocean drifters.
“What surprised me most was that you could do it!” says MBARI scientist Kakani Katija. She learned there’s more to the bell than meets the eye. Contrary to her expectation that it would be “all jelly and mucus, it actually has some heft and structure,” and could support a tag, she notes.
Jellyfish tags are similar to fitness trackers and dive computers, recording water temperature, depth, light and motion. Attachment methods include glue, suction cups and cable ties. The first two methods work well for the relatively small jellies tagged in Monterey Bay.
In other locations, researchers have been able to tag larger species by wrapping cable ties around the manubrium, where the swimming bell connects to the oral arms.
Field research is challenging
The hardest part of tagging jellyfish, says Senior Aquarist Wyatt Patry, can be finding them in the field.
The technique for success? According to Wyatt, “We read the ocean” scanning the bay for “slicks”—surface patches where food collects, concentrated by currents and wind.
Finding jellies is only the first hurdle.
“Sometimes the jellyfish are a little out of reach,” Tommy explains. “We can see them but they’re 20 feet down.” That’s when it’s time for a “jelly donut,” he says. Positioning themselves on top of the jelly, the team drives their boat in circles. “Doing donuts” creates an upwelling current, popping a smack (group of jellies) to the surface, Tommy says.
Sometimes, even the best laid plans can go awry. In the lab, the team practiced tagging Pacific sea nettles, a species commonly found in the Monterey Bay. But during an El Niño year, nettles were nowhere to be found. For three days in the field, the team tagged the next best thing—egg yolk jellies, Tommy says. (Though they were, he notes, much slimier to deal with than sea nettles.)
From their surface boat, the team followed radio signals transmitted by the jellyfishs’ tags. After two to six hours, the tags came loose and surfaced for retrieval. In the lab, researchers then downloaded the data.
Building the big picture
These and similar efforts are adding details to a larger research picture that has yet to fully emerge. Now that they’ve published a comprehensive guide for tagging still more species of jellyfish, and laying a foundation for improving this field of inquiry, a world of exploration awaits. And it’s a large field: So far, only nine of the 200-plus known jellyfish species have been tagged.
Working with captive jellyfish in the lab, Wyatt and Tommy are helping fellow researchers learn about the larval life stages of comb jellies, and about deep sea species as the Aquarium pioneers new methods of breeding and raising these delicately beautiful animals for exhibit.
For Tommy, it’s a challenge and a delight because, “Jellies are just so awesome!”
How to tag a jellyfish? A methodological review and guidelines to successful jellyfish tagging. Sabrina Fossette, Kakani Katija, Jeremy A. Goldbogen, Steven Bograd, Wyatt Patry, Michael J. Howard, Thomas Knowles, Steven H.D. Haddock, Loryn Bedell, Elliott L. Hazen, Bruce H. Robison, T. Aran Mooney, K. Alex Shorter, Thomas Bastian and Adrian C. Gleiss. J Plankton Res (2016) 38 (6): 1347-1363.