Drifting along in marine currents, jellyfish can be both predator and prey, eating nearly anything they can capture, but also being consumed by larger marine predators. According to a recent study led by the University of British Columbia (UBC) investigating the relationship between jellyfish size, diet, and nutritional quality, jellyfish may get more nutritious as they grow and are able to consume a larger variety of prey.
While smaller jellyfish eat phytoplankton, microzooplankton, and eggs, larger ones can also eat shrimps and even fish. Yet, since they are easy to catch and digest due to their high water content, these animals are also an important nutritional source in marine food webs. For instance, in Heriot Bay, British Columbia, the moon jellyfish (Aurelia labiata) are frequently eaten by other jellyfish, fish, and various invertebrates.
“Our study looked more closely to see if there was any information we could draw about nutrition in jellyfish,” said lead author Jessica Schaub, a PhD student in Oceanography at UBC. “This information helps us understand the true value of jellyfish as food. We looked at how the energy that moves through a food web might look as it moves through jellyfish. What they eat, what they are composed of, and how this might affect what eats them.”
The scientists collected 150 moon jellyfish and measured their size, along with specific compositional elements. The analysis revealed that jellyfish eat bigger prey as they grow, which leads to higher concentrations of healthy fats.
“We found some evidence that these changes might be influenced by their diet, and as they feed on bigger prey with higher levels of fatty acids, the jellyfish accumulate more of these fatty acids. This means bigger jellyfish might be considered more nutritious,” Schaub explained.
“Our recommendation for future studies on jellyfish predators is to consider size more thoroughly. Feeding on a young, small jellyfish is different than feeding on a larger and older jellyfish,” she concluded.
The study is published in the journal Ecosphere.
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