Surf's up: Turbulence tells sea urchins to settle down

Apr 09, 2013
Top: The larva of the purple sea urchin drifts in the ocean for a month before settling on a rock. Bottom: Then the larvae change shape and grow spines as they prepare to settle down on a rocky shore. Credit: Brian Gaylord/UC Davis photos

(Phys.org) —Tumbling in the waves as they hit a rocky shore tells purple sea urchin larvae it's time to settle down and look for a spot to grow into an adult, researchers at the University of California, Davis, Bodega Marine Laboratory have found. The work is published April 8 in the journal Proceedings of the National Academy of Sciences.

"How these animals find their way to the right habitat is a fascinating problem," said Brian Gaylord, professor of evolution and ecology at UC Davis and a researcher at the Bodega Marine Lab. "The response allows them to tell that they're in the right neighborhood."

Like most shoreline animals, purple sea urchins (Strongylocentrotus purpuratus) have a two-stage life cycle. The young are microscopic, look completely different from adults and drift in the upper levels of the ocean for about a month before settling on a rocky shore and transforming into the familiar spiny adult.

"Once they decide to settle, they attach to a rock and undergo body remodeling into a juvenile sea urchin with spines," Gaylord said.

Over short distances, the can respond to chemical traces in the water, especially substances that might be given off from a rock thick with algae or other food for the growing urchins.

But how do the larvae know they are close enough to the right shoreline habitat to start searching for such signals?

On the California coast, rocky headlands—the urchins' preferred environment—are interspersed with long stretches of beach that experience lower levels of turbulence. The larvae don't have the resources to swim for miles along a beach looking for a nice slimy rock, but when carried by currents near a wave-swept rocky reef, the high turbulence tells them to begin a finer-scale search, the researchers found.

Gaylord and co-authors Jason Hodin of Stanford University's Hopkins Marine Station and Matthew Ferner of San Francisco State University used a device called a Taylor-Couette cell to see how urchin larvae responded to being churned by shear forces comparable to those in waves breaking on a rocky shore.

The Taylor-Couette cell consists of one rotating cylinder inside another, with a layer of fluid in between. When the cylinders spin relative to each other, they set up shear forces in the fluid. Scientists more typically use the device for studying fluid dynamics, especially the transition where flows becomes chaotic and turbulence appears.

Gaylord and his colleagues took the urchin larvae for a spin through a Taylor-Couette cell then exposed them to potassium, known to act as a that triggers larvae to begin settling.

Larvae that had been exposed to turbulence responded to the chemical signal earlier in development than those that had not—in fact, they responded at a stage at which it had previously been believed larvae could not settle.

Especially telling was that neither turbulence nor the chemical signal alone promoted settling at this earlier developmental stage.

The experiment shows that the shift from living free in the ocean to living on a rock is a two-step process, Gaylord said. In the first step, exposure to turbulence initiates an abrupt transition to a state in which the larvae are "competent to settle." A chemical signal triggers the second step, actual settlement, and the larvae then complete their transformation into juvenile sea urchins.

It's not yet clear how the larvae detect turbulence, Gaylord said. That might happen through receptors that respond to stretching or flexing. The two-step settlement process might occur in other species that settle on shorelines, he said.

Explore further: Lost sea lion in California found mile from water

Related Stories

Purple sea urchin metamorphosis controlled by histamine

Apr 26, 2012

Now that hay fever season has started, sufferers are well aware of the effect of histamines. However it is easy to forget that histamine is also a neurotransmitter involved in controlling memories, regulating ...

Sea urchins cope with rising CO2 levels

Apr 09, 2013

(Phys.org) —Increasing levels of carbon dioxide (CO2) in the atmosphere are causing oceans to become more acidic. This situation poses a threat to marine organisms with shells made of calcium carbonate, ...

On 'Earth week,' world is no longer our oyster

Apr 20, 2010

The world is no longer our oyster. As we prepare to celebrate Earth Day on April 22, we can add another species, one of widespread ecological and economic importance, to the list of the beleaguered.

Recommended for you

Orchid named after UC Riverside researcher

8 hours ago

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

10 hours ago

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

10 hours ago

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 0

More news stories

Deadly human pathogen Cryptococcus fully sequenced

Within each strand of DNA lies the blueprint for building an organism, along with the keys to its evolution and survival. These genetic instructions can give valuable insight into why pathogens like Cryptococcus ne ...

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...