A mysterious oceanic barrier is stopping some deep-sea jellyfish in the Arctic from reaching the Atlantic Ocean, a new study has found.
The animals, members of the jellyfish subspecies Botrynema brucei ellinorae, inhabit depths between 3,300 and 6,600 feet (1,000 to 2,000 meters) and can be divided into two groups based on whether individual specimens have a knob on their umbrella-like bell structure.
“This jellyfish […] has two different shapes depending on which area it occurs in — one with a distinctive knob at the top and one without,” study lead author Javier Montenegro, a biologist at the University of Western Australia, said in a statement.
The sea creature’s anatomy somehow influences its worldwide distribution: jellyfish with the distinctive knob live across all oceans and latitudes, while those without a knob have only ever been documented in the Arctic and sub-Arctic, Montenegro said.
For the study, Montenegro and his colleagues examined observational and photographic records of B. brucei ellinorae going back more than 120 years. The researchers then mapped the distribution of the jellyfish subspecies by combining these records with genetic analyses. They published their results in the online version of the journal Deep Sea Research on July 3.
Genetic data indicated that specimens of B. brucei ellinorae with and without knobs in the Arctic and sub-Arctic were almost identical to specimens with knobs in the western Atlantic. This suggested that, despite strong genetic similarities, knobless jellyfish were unable to leave the frigid waters.
So how does the animal’s shape determine its distribution? It appears that access to the Atlantic is blocked by a barrier — not a physical obstacle, but a biological one, or one determined by local geography.
“The differences in shape, despite strong genetic similarities across specimens, above and below 47 degrees north, hint at the existence of an unknown deep-sea bio-geographic barrier in the Atlantic Ocean,” Montenegro said.
This barrier is located within the North Atlantic Drift, a warm ocean current that extends northward from the Gulf Stream, but it’s unclear if the current…
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