Research Highlight: Searching for the Source

The microscopic larvae of marine mussels are not very good swimmers, which puts the tiny mollusks at the mercy of the twisting turbulence of ocean currents. Thus for years marine ecologists presumed that different species of mussel larvae would be well mixed throughout the seas.
 
Proving such ideas has been difficult because of the complexities involved in tracking the origins and movements of the miniscule creatures, but recently a team of researchers at Scripps Institution of Oceanography at UC San Diego developed a method for doing just that.
 
Using a process called “elemental fingerprinting,” the researchers invented a system for using the chemical signature of seawater as a stamp for larvae identification.
 
The researchers installed a series of custom-built “homes” each filled with roughly 100,000 larvae along sites off San Diego’s beaches and bays. After a week the larvae were retrieved. Back at Scripps, the scientists used a specially designed mass spectrometer to analyze the chemical composition of the larvae’s shells, each roughly 100 microns in diameter, and the corresponding seawater. The researchers thus developed a distinct profile for each of the homes along the coast.
 
After a few weeks the researchers returned to collect week-old juvenile mussels. Because mussels retain their shells after settling, the researchers were able to chemically identify the origin of each mussel and whether they hailed from near or far. To their surprise, the researchers found that the larvae mostly stayed close to their original homes rather than traveling the great distances that were presumed.
 
Elemental fingerprinting can be seen as a “natural tag” for identifying the origins of larvae, said Scripps Professor Lisa Levin, who produced a paper on the method published in the Proceedings of the National Academy of Sciences with Bonnie Becker, Joel Fodrie, and Pat McMillan.
 
Levin believes the method could be useful not only in the basic science of evolution, but in applied areas such as the management and conservation of coastal resources, including the establishment of marine protected areas.
 
— Mario C. Aguilera