Scientists Discover Hidden Barriers Shaping the Life of Deep-Sea Creatures

Marine scientists at The University of Western Australia have uncovered a fascinating discovery that could change our understanding of oceanic barriers. In a study published in the journal Deep Sea Research, researchers have shown that certain deep-sea jellyfish species, such as those from the genus Botrynema, face an invisible barrier in the North Atlantic. This “soft barrier” appears to separate jellyfish that can survive in warmer, predator-filled waters from those restricted to the Arctic’s icy depths.
The Mysterious Botrynema Jellyfish and Its Global Distribution
Botrynema jellyfish, part of the Trachymedusae group, are a unique species that live their entire lives as free-swimming medusae without the usual attached “polyp” stage. The study, published in the journal Deep Sea Research, and led by marine scientists at The University of Western Australia, reveals that these jellyfish are typically found in the Arctic and subarctic regions of the North Atlantic. For years, scientists believed that these jellyfish were confined to cold waters, especially a subspecies called Botrynema brucei ellinorae. This subspecies was thought to be restricted to the polar regions, but new findings suggest that their distribution might be more complex.
The breakthrough came when a Botrynema jellyfish was spotted in the deep waters off Florida—far south of its expected range. Researchers were able to capture and genetically analyze this specimen, discovering that it was genetically similar to the Arctic individuals. This led the researchers to question how these jellyfish, typically confined to the cold Arctic waters, could end up so far south, in the warmer, predator-rich waters near Florida.
Understanding the “Soft Barrier” in the North Atlantic Drift
Upon analyzing the distribution of Botrynema jellyfish, the researchers identified a distinct pattern in their locations. The knobbed and knobless morphs of Botrynema brucei ellinorae appear in different regions of the Atlantic. The knobbed form, which has a small bump on top of its bell, is found across a wider range of latitudes, including temperate and subtropical waters. In contrast, the knobless form is much more restricted, mainly inhabiting the Arctic Ocean and parts of the subarctic North Atlantic.
Dr. Javier Montenegro, the lead author of the study, explained,
“It could keep specimens without a knob confined to the north while allowing the free transit of specimens with a knob further south, with the knob possibly giving a selective advantage against predators outside the Arctic and sub-Arctic regions.”
This observation points to a possible adaptation mechanism that might explain the distribution differences between the two morphs. The knobbed morph might have evolved in a way that gives it a better chance of survival in the warmer, more predator-rich waters of the southern Atlantic, while the knobless form is better suited for the harsher Arctic conditions.
The Role of Deep-Sea Currents in Jellyfish Migration
A significant aspect of this study is the role that ocean currents play in the distribution of marine species. In the North Atlantic, cold water sinks near Greenland and then flows southward along the Deep Western Boundary Current. This deep-sea current, part of the ocean’s conveyor belt, transports water—and potentially species—thousands of miles. According to the researchers, Botrynema jellyfish could be drifting along these currents without actively swimming, explaining how they can appear in far-off regions such as Florida without having to travel through more favorable surface waters.