Jellyfish to dominate Arctic waters as climate warms, study finds

Jellyfish are among the few groups of organisms that will benefit from climate change. Already, cnidarians are spreading further north, and by the end of the 21st century, according to the latest research, they may dominate the waters of the Arctic Ocean.

Progressive climate change negatively impacts many marine organisms. However, jellyfish may benefit from rising water temperatures—especially in the Arctic region. Scientists at the Alfred Wegener Institute for Polar and Marine Research (AWI) in Germany reached these conclusions, which were published in the journal Limnology and Oceanography.

Researchers used computer modelling to understand how marine ecosystems will change in the future. They introduced eight Arctic jellyfish species into the simulation and examined how rising temperatures, the retreat of sea ice, and other environmental changes affect their occurrence. The modelling employed a climate scenario in which greenhouse gas emissions remain at a moderate to high level.

In the future, gelatinous zooplankton (composed of simple invertebrates such as predatory cnidarians, comb jellies, or filter-feeding tunicates) may be one of the few groups of organisms to benefit from global warming. Numerous studies have confirmed that these animals thrive due to rising water temperatures, overfishing, and excess nutrients in seas and oceans. Combined, these three factors may cause marine ecosystems to be dominated by jellyfish. Many researchers have already warned of the impending "gelification of the oceans."

"Climate change may give gelatinous zooplankton an advantage over their food competitors, such as fish. And this will affect the entire food web and fish populations," explained the study's lead author, Dmitrii Pantiukhin, from the Arctic Jellies (ARJEL) research group specializing in Arctic jellyfish at the Alfred Wegener Institute.

He added that many jellyfish feed on fish larvae and eggs, which can slow down or prevent the recovery of fish populations already dwindling due to global warming and intensive fishing. "The Arctic Ocean is warming the fastest of all the oceans in the world. About 10 percent of the world's fish catch comes from the Arctic," he reminded.

"Anyone interested in the fate of fish should keep an eye on jellyfish," noted Pantiukhin.

During the study, the AWI team combined three-dimensional species distribution models with oceanographic data from the Earth's climate model (MPI-ESM1.2) developed at the Max Planck Institute in Germany.

"Simulations of species distribution in the ocean are often two-dimensional, like a map. However, jellyfish population sizes depend on water depth. So, we created three-dimensional species occurrence models. By combining them with the Earth's climate model, we calculated how the distribution of the eight main jellyfish species might change by 2050-2099," explained Dr. Charlotte Havermans, head of the ARJEL research group.

The modelling results indicated that the habitats of seven out of the eight studied species could soon significantly expand towards the North Pole—they will occupy areas twice as large. Most significantly, nearly three times, the habitat of the lion's mane jellyfish (Cyanea capillata) may increase.

Only one species included in the study, Sminthea arctica, would occupy a slightly smaller area than today by the end of the 21st century. Rising Arctic Ocean temperatures would force this jellyfish to retreat to greater depths.

"The predicted expansion of jellyfish habitats could have a huge, cascading impact on the entire food web," warned Dmitrii Pantiukhin.