Jellyfish can be both predator and prey as they drift through ocean currents. They eat almost anything they can get their hands on, following the traditional oceanic pattern of the giant eating the small. According to new research from the University of British Columbia on these gelatinous balls, jellyfish can become more nutritious as they get bigger.
As jellyfish grow, their size changes largely due to the possibility of encountering prey, the length and number of tentacles and their bells (the umbrella-like part of them). As a result, smaller jellyfish eat phytoplankton, microzooplankton and eggs, while larger jellyfish can eat all of these plus shrimp and even fish. However, jellyfish are also largely hunted by animals in and out of water. Jellyfish are important prey because they are easy to digest and easy to catch due to their high water content.
“Our study looked more closely at whether there was any information we could draw on jellyfish nutrition,” said Jessica Schaub, lead author and a doctoral student at UBC’s Institute of Oceans and Fisheries and Department of Earth, Ocean and Atmosphere. science.
“This information helps us understand the true value of jellyfish as food. We looked at what the energy that moves the food web might look like as it moves through jellyfish. What they eat, what they’re made of and how that can affect what she eats.” In Heriot Bay BC, for example, a moon jelly can often find itself eaten by other jellyfish, fish and other invertebrates.
Schaub and her team, which includes associate professor Dr. Brian Hunt, who heads the Pelagic Ecosystem Laboratory at the Institute of Oceans and Fisheries, looked at how jellyfish size, diet and nutritional quality interact. Nutritional quality can reflect the life history of an organism – the composition of a jellyfish can change in response to individual changes in diet and physiological changes.
During two one-day periods in July and September 2019, the team collected 150 moon jellyfish and measured their size. After drying them, they measured the jellyfish for specific compositional elements.
Schaub described what they discovered
“We first confirmed what was already known: jellyfish eat more prey as they grow, which means they also occupy a higher position in the food web as they grow,” she said. “We also found that some concentrations of ‘healthy fats’ increase as the jellyfish grow. We found some evidence that these changes may be influenced by their diet, and as they feed on larger prey with higher amounts of fatty acids, jellyfish accumulate more of these fatty acids.
“This means that larger jellyfish may be considered more nutritious,” Schaub said.
The study found size trends that highlight how important it is to consider jellyfish size when talking about marine food webs. Including these creatures will not only help their representation in food web models, but can also provide information for further studies.
Looking to the future, Schaub described what may come next.“Our recommendation for future studies on jellyfish predators is to consider size more closely. Feeding a young, small jellyfish is different than feeding a larger, older jellyfish.
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