Scientists Finally Solve the Mystery Behind Basketball-Sized Octagons They Kept Finding on Arctic Seafloor
The stillness of deep waters allows the seemingly barren terrain of the seafloor to remain unperturbed for long periods. Myriads of deep-sea creatures come and go, brushing the floor, engraving it with patterns that sit there like perennial artifacts of the deep. These patterns may look like anything from squiggly trails to feeding pits, burrows, or circles of divots. In one instance, when researchers were mapping Fram Strait between Greenland and Svalbard, they came across a mysterious comb of octagons imprinted on the seafloor. Findings were published in the journal Proceedings Of The Royal Society B.
The examples of seafloor patterns have been captured by researchers zillions of times in the past. Known as “Lebesspuren,” the German word for “life traces,” these patterns are left behind by sea animals participating in various processes like feeding, exploring, mating, breeding, etc. In this particular investigation, researchers proposed that the behavioral octagon pattern on the seafloor suggested “prey handling.”
For this study, the researchers dipped their remotely operated vessels (ROVs) at a depth of 1,000 to 4,000 (3,280 to 13,100 feet). Back in the laboratory, they were flabbergasted when they spotted 106 odd octagonal structures popping out in 92 of the 5100 collected images. Some of the octagons were clumped together whereas others were in total isolation. Further analysis revealed that the octagons were most likely formed by “Dumbo octopuses,” known as Cirroteuthis muelleri in scientific terminology.
Defector explains that dumbo octopuses are “inkless, gelatinous, and immediately recognizable by a large pair of lop-eared fins on their heads.” Previous studies have shown that they typically feed on deep-sea fish and crustaceans. During this research, the team found that these deep-dwelling octopuses displayed unusual feeding sequences that they repeated to catch their prey. This sequence included spreading, enveloping, and retreating behaviors, along with frequent fin-flapping.
“First they swim slowly just above the seafloor with their arms curved to be parallel with the ground. They spread their webbed arms out and enveloped the ground below them. They rotate their fins, presumably to suck out whatever prey might be between them and the seafloor, and sometimes flap their fins faster. And finally, they take off from the seafloor to return to open water,” Defector elaborates on the feeding sequence. IFL Science explains that this sequence is “pelagic–benthic feeding.”
Adding to the paper, the researchers noted that the octopuses depicting this foraging behavior in the water column were not scared or disturbed when an ROV plummeted down to record its feeding process. Some octopods even expressed curiosity by drifting near to the camera and then drifting away in an umbrella posture. “The main ecological reasons are likely to avoid the threat from predators and to save energy by using passive transportation with ocean currents,” the researchers concluded. “These large-scale (over 2.5 km [1.6 miles]) vertical movements of megafauna should be considered in conservation strategies, and illustrate how deep-sea environments are ecologically connected.”