A siphonophore swimming through the water column. Full video is available on AGU's YouTube channel. Credit: Monterey Bay Aquarium Research Institute.
New videos of fragile, spindly deep-sea creatures called physonect siphonophores reveal how their specialized jet-powered members propel their colonies through the world's oceans. The findings could help reveal new information about these elusive creatures and inform designs of novel underwater vehicles.
Siphonophores are marine organisms, similar to jellyfish. They are long, thin colonies made up of dependent, specialized individual organisms that perform different functions, including some that move the colony around in the water.
Siphonophores propel themselves in a way similar to jellyfish, but instead of just one round bell that contracts to propel them through the water, a siphonophore has many smaller bells. The bells contract and jet out water in a wave-like pattern, like the legs of a centipede, to move the colony through the water.
But just how the siphonophores coordinate their movements isn't well understood, said Shirah Strock, a student at Roger Williams University who, under the supervision of Associate Professor of Environmental Science Sean Colin, is studying video footage of wild siphonophore colonies collected in collaboration with the Monterey Bay Aquarium Research Institute. Strock will present the findings on 1 March at the 2022 Ocean Sciences Meeting, taking place online everywhere from 24 February to 4 March.
"Siphonophores, like other very delicate oceanic gelatinous zooplankton, are difficult to study so very little is known about their role in the oceanic ecosystem," said Colin. "These types of studies can also help inform engineers who are interested in designing new novel underwater vehicles inspired by multi-jet animals."
The videos were shot using high-resolution cameras mounted on small remotely operated vehicles (ROVs). The mini-ROVs allow the cameras to track and gently follow the siphonophores without disturbing them. In the wild, some siphonophore species are more than 50 meters long - longer than a blue whale - which makes their method of coordinated propulsion all the more intriguing and difficult to study.
"I'm trying to learn about their swimming patterns, how long they are contracting each bell and how long they wait between each contraction," said Strock. Her analysis has focused on how long each bell contracts, how much time there is between pulses, and how often each bell pulses.
"These three variables help us understand things like thrust and give us a general idea about how the animal is swimming," Strock said.
Previous researchers have studied lab specimens of siphonophores, but these studies are less useful because the creatures are in a confined space, Strock said. The video footage of siphonophore colonies in the wild allows for a more nuanced analysis of their movements.
Among the observations Strock will be presenting is how the bells of the same species contract their bells differently in videos taken off coast of Panama compared to videos shot in the cooler waters of Monterey Bay, California.
"One species in two different locations has different patterns," Strock observed. She suspects it's related to the different temperatures of the two locations.
