Decaying Jellyfish Responsible for Changes to Coastal Ecosystems, Study Finds

A swarm of jellyfish swim in coastal waters. (Via Pixabay)

(CN) — Scientists have found that a handful of marine bacteria strains are being fueled largely by decaying jellyfish blooms. These bacteria function like an oceanic clean-up crew, keeping the dissolved organic matter released by these jellyfish inside the water column food web, but they can also wreak havoc on coastal ecosystems.

Jellyfish play an important role in many marine ecosystems. Researchers studied their dependent microbial populations in a new study released Thursday in the journal Frontiers in Microbiology. They’re seeking to better understand the bacterial response to these jellyfish blooms, and the resulting effects on other nearby marine life.

“When jellyfish blooms decay, the sinking detritus is likely to be a temporary but significant source of food for marine microorganisms,” said Tinkara Tinta, researcher at the Marine Biology Station Piran in Slovenia, and lead author of the study, in a statement. “We show that organic matter leaching from decaying jellyfish is rapidly consumed by a few opportunistic fast-growing bacteria that in turn will provide food for other marine animals in the water column.”

Jellyfish, which themselves feed on phytoplankton, zooplankton and fish larvae, can bloom and decay over a relatively short time frame. By consuming what these jellyfish blooms leave behind, the bacteria are actively recycling leftover organic matter and making it available to the next generation. 

Without their services, that organic matter could slowly leech out of the local ecosystem, potentially resulting in local population decline further up the food chain.

Researchers collected 27 dying jellyfish specimens in the Gulf of Trieste, in the northern Adriatic Sea, during a bloom in the spring of 2018. They evaluated each specimen’s overall condition, state of decay and activity levels before transporting them to the laboratory via first-class accommodations in a Ziplock bag.

Not long after their arrival, the jellyfish were freeze-dried for a week, weighed, then pooled and pulverized with a mortar and pestle to preserve their biochemical properties and to obtain homogenous “dry jellyfish material,” avoiding biases stemming from variations in size among individuals.

The researchers dissolved this jellyfish material in vials of artificial sea water containing ambient bacterial community, and mixed in bacterial inoculum to kickstart growth, while comparing with bottles of plain sea water as a control.

“We identified a small number of key microbes that consumed the jellyfish detritus very quickly, rapidly multiplying in the process. Temporarily, these bacteria will form an important component of the water column food web, feeding plankton that are then consumed by larger marine animals. These findings also imply the amount of food reaching the seafloor, the organic material from jellyfish detritus, is effectively reduced by just a few strains of bacteria in the water column,” Tinta said.

As it turns out, increasing numbers of jellyfish blooms across the globe have also proven problematic. Likely fueled in part by warmer waters brought on by climate change, these blooms can take a toll on critical infrastructure nearby and cause headaches back on land. 

They can also raise concentrations of inorganic nutrients which may lead to undesirable phytoplankton blooms in coastal waters, especially throughout temperate waters during late spring and summer.

“Large jellyfish blooms block cooling intakes of coastal power and desalinization plants, interfere with ship operations, and cause damage to the tourism, fishing and aquaculture industries,” said Gerhard Herndl, co-author of the study, and a professor at the University of Vienna in Austria. “It is therefore important to fully understand the role and impact of these blooms on the marine ecosystem. To date, very few studies have examined the link between jellyfish detritus and its most probable consumers and degraders, marine microorganisms.”

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