A team of researchers has just discovered a new behavior that baby sea stars use to get around. Sea star larvae spin water to form complicated vortices, allowing them to survive and find food. The findings are in a paper that was just published in the journal Nature Physics.
Sea stars, also known as starfish (though they are not fish), are well-known marine invertebrates. Their larval stages aren’t quite as recognizable, however. Sea star larvae are so tiny that it can be difficult or even impossible to study them without microscopes. The larvae barely resemble their parents and drift through the ocean, subsisting on phytoplankton. Eventually, they’ll settle somewhere and develop into their star-shaped adult forms. The larvae get around by using cilia, hair-like structures that can be used for movement or to pull food closer. This is an understudied area, however, and researchers had yet to examine the hydrodynamics of these movements.
Researchers from the Stanford School of Engineering studied the ciliary bands of sea star larvae in an effort to better understand larval movement. The team used cameras fitted with microscopes to observe sea star larvae in their laboratory. The animals were kept in aquariums and fed phytoplankton so that the team could watch how the larvae moved. Right away, the team noticed something special about their movements. The larvae were using their cilia to create whirls of water called vortices. As the animals swirled the water around, it propelled them forward while dragging food close to their mouths. The behavior may seem overly complex but the authors point out that it must strike a balance between energy required and survival to have evolved this way.
The team’s findings provide new insights into how sea star larvae survive the most dangerous part of their lives. They use their cilia to create vortices that function in both movement and feeding. The research team plans to study the larval movements of other marine invertebrates in the near future.
Gilpin, W. Prakash, VN. Prakash, M. Vortex arrays and ciliary tangles underlie the feeding–swimming trade-off in starfish larvae. Nature Physics (2016).