This aerial view shows the RV Rachel Carson inside a moon jelly aggregation on August 25, 2021, in Quartermaster Harbor. The concentration of tiny marine life known as copepods inside the moon jelly aggregation was as low as a quarter of the levels in other parts of the bay.

A GoPro camera shows moon jellies below the water in Sinclair Inlet on August 25, 2021. Moon jellies tend to aggregate in protected bays. New research suggests that when populations spike the moon jellies can consume a significant amount of the zooplankton in those waters.

A view of the ocean’s surface on August 25, 2021, in Sinclair Inlet shows a pack of moon jellies during the sampling cruise. Other types of jellyfish, like lion’s mane or egg-yolk jellyfish, also have population spikes in summer but don’t congregate in a single area like moon jellies.

Researchers rinse a plankton net (hanging in background) that was used to sample moon jellies. The team lowered the net into the water and raised it straight up, then counted the moon jellies trapped inside to measure their concentration. The highest concentration was about 10 jellies per cubic meter of water. The team used a smaller net and a similar technique to count the zooplankton.