Comb jellies, or ctenophores, are some of the most abundant organisms in the open ocean, and their voracious hunting satisfies their big appetites. But away from their deeper-water home, in the care of humans, they are fickle and finicky. When captured in jars, their fragile tentacles and gelatinous bodies are often damaged. In laboratory settings, they are intolerant of shifts in salinity and temperature, and sometimes refuse to feed.
For Providence College professor and marine ecologist Jack Costello and colleagues, this meant rethinking how they could learn more about the organisms in their natural environment.
“Our approach is to reverse the normal experimental process,” Costello said of his ctenophores study, which began at BIOS in January. Rather than force the animals into containers within land-based laboratories, he and other scientists are adapting their methods and equipment to observe these small, jellyfish-like creatures at sea. Wearing scuba or snorkeling gear, the scientists carry specialized cameras that capture high-speed, high-resolution images and use fluid-mechanic measurement methods that operate in situ.
Ctenophores (pronounced tee-no-fores) are widespread throughout the oceans, with a range of delicate shapes that resemble balls, bells, hearts, and ribbons. They move constantly, which triggers their huge appetites for zooplankton, egg larvae, and crustaceans, among other foods. Coastal dwelling ctenophores have been studied, Costello said, but their deeper-water relatives have not been widely researched, and without a better understanding of how they feed, it is difficult to know how they impact and influence the larger deeper-sea community.
The goal is to observe how the animals propel themselves through the water and determine how they feed, which includes understanding how they select their prey as well as the impact of their hunting on the surrounding planktonic community.
“If our preliminary consumption rates are a valid indication, they can eat a large number and a fairly diverse range of zooplankton prey,” Costello said. “Yet we have no quantification of these impacts so they remain invisible to trophic models for oceanic plankton. One of our goals is to find out whether this matters.”
For ctenophores, and many other deeper-ocean dwelling animals, this approach of meeting marine life on their own terms is overdue.
“We have reached the limits that conventional sampling methods can contribute to understanding many of the organisms that live in oceanic environments,” Costello said. “Our methods need to correspond to the animals’ world.”
Costello’s career centers on marine organism design—how does an animal’s shape influence how it moves and functions in its world? And how does the surrounding environment influence the organism? Much of his work, and that of his colleagues, over the past 25 years has concentrated on protozoans, fish, jellyfish and other gelatinous species, and their reliance on the fluids that surround them.
One year ago, Costello contacted BIOS faculty member and zooplankton ecologist Leocadio Blanco-Bercial to enquire about the possibility of working at BIOS during Costello’s sabbatical from his work in Rhode Island. The proximity of the island to the marine life-rich Gulf Stream appealed, and Costello quickly realized that the island offers quick and easy access to water hundreds of meters in depth, where ctenophores live. Two weeks after his arrival at BIOS in January, he had plans to go out and observe ctenophores with Blanco-Bercial.
“After a 20 minute boat ride, we can be in deeper water, up to 1,000 meters in depth,” he said. “This is what makes BIOS appealing.”
During Costello’s three-months at BIOS, he is joined by his wife Sue Costello, an architect who sometimes lends her artistic expertise to her husband’s science research through drawings and undersea renderings. “We talk about my work all the time, so she is well aware of the nuances and can quite concretely help me recreate, visually, the natural world in which I work,” he said.
Ctenophores are not the only delicate oceanic animals that will benefit from developing advanced in situ methods, Costello said. Similar techniques and approaches can be applied to other groups such as open sea mollusks, siphonophores (relatives of jellyfish that form colonies), marine snow (organic debris that falls to the seafloor from the upper water column), and large protists, such as radiolarians (single-celled crystalline organisms that drift through the ocean).
Costello’s work at BIOS is funded by the Biological Oceanography program at the National Science Foundation.