Walk the beach or peer into a tidepool anywhere along the northeastern U.S. coast, and you'll find shells stacked on top of one another. They're most likely common Atlantic slipper shells, a species of marine snail.
Scientists took a closer look at these ubiquitous snails, and discovered that how their larvae swim is key to the species' seeming residence in every nook and cranny along the coast. And to how the snails may be able to invade new territory.
Equipped with high-speed, high-resolution video, the researchers discovered how the larvae of these marine snails swim, a behavior that determines individual dispersal and ultimately, survival.
Researchers at the Woods Hole Oceanographic Institution (WHOI) and Stony Brook University grew Atlantic slipper limpet larvae, which can become slightly larger than a grain of rice, and recorded videos of them swimming.
In previous studies, it was thought that the larvae swim faster when they beat their hair-like cilia faster. However, this new research shows that's not the case.
"I was very surprised when I saw that there was no relationship between cilia beat frequency and how fast these animals swim," says Karen Chan, a WHOI scientist and the lead author of a paper published today in the journal PLOS ONE.
The larvae control how fast they swim by subtly shifting the position of their velar lobes--flat, disc-shaped wings fringed with cilia.
The ability to make small movements with these velar lobes, akin to how a bird adjusts the angle of its wings while soaring, demonstrates complex neuromuscular control.
"This careful study tells us a lot about how organisms interact with the marine environment, knowledge we need in a time of environmental change," says David Garrison, program director in the National Science Foundation's Division of Ocean Sciences, which funded the research.
The Atlantic slipper shell is a marine snail native to the northeastern United States. It has become an invasive species elsewhere in the world, especially in Europe.
The slipper shell has many common names, including Atlantic slippersnail, boat shell and quarterdeck shell. It is known in the United Kingdom as the common slipper limpet. The species is a medium-sized sea snail, a marine gastropod mollusk in the family Calyptraeidae, the slipper snails and the cup-and-saucer snails.
Paper co-author Dianna Padilla of Stony Brook University collected the snails from the North Shore of Long Island, N.Y. She grew the larvae in her lab, which were then sent to WHOI for video analysis.
Houshuo Jiang, a scientist at WHOI and collaborator on the project, says the goal is to understand the limpet's role in shaping the marine ecosystem.
With support from NSF, Jiang built a customized, vertically-oriented optical system that can magnify and record high-speed, high-resolution video of microorganisms swimming in seawater at 2,000 frames per second.
"Much more can be observed in great detail using this setup than looking through a microscope," Jiang says.
Jiang found that in a single day, slipper shell larvae could vary their speed from swimming one body length per second to four body lengths per second.
"What this means is they have a lot of control over how fast they swim," Chan says. How they swim can determine where they go.
And where they might turn up next.
"These results show the flexibility these little animals have," says Padilla, "which is likely what makes them so successful in their environment."
In addition to NSF, the Croucher Foundation, the Royal Swedish Academy of Sciences and WHOI provided support for the project.