New system developed by Scripps researchers

March 21, 2007

Tracing the origins of marine animals can be extremely difficult, especially in the free-flowing, soup-like conditions of the ocean, but obtaining this information is vital not only for understanding these organisms but for managing and conserving them as well. Scientists at Scripps Institution of Oceanography at UC San Diego have developed a novel approach for tracing the life roots of marine larvae, some of the most difficult organisms to track due to their microscopic sizes.

In a study published in the Proceedings of the National Academy of Sciences (PNAS), Bonnie Becker, Lisa Levin, Joel Fodrie and Pat McMillan describe a new process for studying mussel larvae through "elemental fingerprinting," a method in which chemical signatures in ocean water are used to construct geographical birthplace maps and baseline profile information about the tiny creatures.

"Elemental fingerprinting is a sort of natural tag," said Levin, a professor in the Integrative Oceanography Division at Scripps. "Basically, the water itself creates a chemical tag and we use that information to figure out where larvae come from."

Developing the new approach involved several labor-intensive steps, including establishing-or "outplanting" as Becker calls it-a series of larval "homes" made of PVC pipe and mesh in 18 locations off San Diego's beaches and bays. Each home contained approximately 100,000 mussel larvae. After a week, the homes and larvae were retrieved along with water samples from each site.

The chemical composition of the minuscule larval shells, roughly 100 microns in diameter, was then examined using a powerful analytical instrument (called a "laser ablation inductively coupled plasma mass spectrometer") housed at Scripps Oceanography's Unified Laboratory Facility. By analyzing the chemical makeup within the shells in each larval home and the corresponding seawater, the researchers were able to construct a reference map in which each of the locations could be individually identified with a distinct chemical signature.

Several weeks later the researchers returned to each site and collected week-old juvenile mussels, typically less than two millimeters in size, in an effort to investigate whether they traveled there from near or far sites. Because mussels retain their larval shells after settling, the scientists were able to establish the chemical fingerprint of each shell and thereby trace its geographic origin. In doing so they could then say whether mussels traveled far from their birthplaces or stayed closer to home.

For much of the 20th century, marine ecologists have believed that mussel larvae are transported long distances and dispersed broadly across the marine environment because of ocean currents and the larvae's poor swimming abilities. Different populations of mussels, it was thought, would be well mixed in the ocean "blender" and relational ties would span vast regions.

The new study found the opposite. Rather than mixing throughout San Diego's beaches and bays, the mussels stayed within 20 to 30 kilometers (12 to 18 miles) of their point of origin, with many typically keeping to a mostly northern or mostly southern source.

One surprise emerged in that the two closely related mussel species studied, Mytilus californianus and Mytilus galloprovincialis, were shown to have somewhat different movement patterns.

The researchers say that elemental fingerprinting can be a way to develop "high resolution" information about larval sources, including where populations thrive and fail. It opens the door to studying other organisms with free-floating planktonic larvae, whereas previous approaches limited studies to species with more static ocean bottom broods.

A challenge remains, however, in integrating this approach for the management and conservation of coastal resources, including the establishment of marine protected areas and understanding how habitats are connected.

"This result will affect our understanding of how species evolve, interact and are distributed and alter our strategies to protect them effectively," the authors note.

"This research also holds important implications for the basic science of evolution, including how populations come to differ, because we don't know a lot about how populations are connected," said Levin.

Future studies using chemical fingerprinting will include collaborations with Scripps physical oceanographers who model ocean circulation to more deeply probe how physical processes influence larval development.
Becker, the PNAS study's lead author, is a graduate of Scripps and now an assistant professor at the University of Washington, Tacoma.

Funding for the research was provided by the Cabrillo National Monument Foundation, the University of California Marine Science Council, the U.S. Office of Naval Research and the National Science Foundation.

University of California - San Diego

Related Mussels Articles from Brightsurf:

Small mussels in the Baltic are getting even smaller
Blue mussels in the Baltic Sea are getting smaller with time but bigger in numbers, according to a new study from Stockholm University.

Future ocean conditions could cause significant physical changes in marine mussels
Scientists from the University of Plymouth showed increased temperature and acidification of our oceans over the next century could have a range of effects on an economically important marine species

Laundry lint can cause significant tissue damage within marine mussels
Research by the University of Plymouth showed that ingesting lint caused significant abnormality within the mussels' gills, as well as atrophy or deformities leading to loss of definition in digestive tubules

Insight from sports medicine leads to discovery about mussels in acidifying ocean
Feeding rates of blue mussels slow down under ocean acidification conditions, and the cause may be the slowing beat of gill cilia, similar to a known response in human lung cells.

Decreased iron levels in seawater make mussels loosen their grip
Mussels secrete sticky plaques that help them attach to wet surfaces, such as rocks on the beach.

Neanderthals ate mussels, fish, and seals too
Over 80,000 years ago, Neanderthals fed themselves on mussels, fish and other marine life.

Genetic variation gives mussels a chance to adapt to climate change
Existing genetic variation in natural populations of Mediterranean mussels allows them to adapt to declining pH levels in seawater caused by carbon emissions.

Contamination by metals can increase metabolic stress in mussels
The researchers propose that this evidence should be used as input to public policy with the aim of mitigating the impacts of human activities on coastal and marine ecosystems.

Australia's got mussels (but it could be a problem)
One of the world's most notorious invasive species has established itself on Australia's coastlines, according to research from The University of Queensland.

Gimme shelter: Seven new leech species call freshwater mussels home
The frequent presence of leeches with a hidden lifestyle in the mantle cavity of freshwater mussels has been recorded since the second half of the 19th century.

Read More: Mussels News and Mussels Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to