- Tracing Environmental Change via Scallops
“You are what you eat” is true not just for people — it also works for scallops, members of the large family of marine bivalve mollusks. Scallops are a potential treasure trove for environmental scientists because their shells are grown layer by layer, incidentally recording environmental conditions reflected in the materials they have digested. Some researchers are trying to read that shell-encased record in species such as the Pecten maximus, or great scallop, which is found in a wide range of waters.
“The aim is to use this kind of archive in ‘unknown’ temperate ecosystems, where there is no regular monitoring of environmental conditions,” explained Aurélie Barats, an associate professor at the University of Nice in France.
The shell of a juvenile great scallop (upper left) records manganese concentration during its daily growth (upper right). This record can be read with laser-ablation inductively coupled plasma mass spectrometry, if proper calibration is performed (bottom sequence, left to right). Because these scallops are found around the world, they could serve as environmental monitors where otherwise there are none. Courtesy of Aurélie Barats, University of Nice.
However, deciphering that archive in enough detail has been challenging. Now scientists from Université de Pau et des Pays de l’Adour and from Université de Bretagne Occidentale in Plouzané, both in France, have shown that it is possible to trace the ebb and flow of manganese input in juvenile scallops using laser-ablation inductively coupled plasma mass spectrometry. The shells can be used to evaluate coastal environment changes that occur daily. At the time of the research, Barats was a graduate student at the Université de Pau et des Pays de l’Adour
The researchers obtained shells of juvenile great scallops that were collected from the Bay of Seine on the northern coast of France. Using the 266-nm beam from a laser device made by Cetac Technologies of Omaha, Neb., to ablate the scallop shell material, they fed the material into an inductively coupled plasma mass spectrometer from Thermo Fisher Scientific Inc. of Waltham, Mass. The result was a chronological and quantitative elemental profile obtained from the daily calcite growth layer in the shells. They compared the information from the scallops with that from other environmental monitors. They describe their work in the Jan. 1 issue of Environmental Science & Technology.
They focused on manganese content of the shells because it is highly mobile and plays an important role in reduction/oxidation, or redox, processes. Thus, it serves as an elemental indicator of environmental conditions.
The data showed that, in a four-month period spanning late spring to summer, the manganese content from the shells strongly correlated with inputs from the Seine River. In late summer, the correlation broke down somewhat, a consequence of redox oscillations in the highly turbid part of the water.
Other researchers have tried to extract similar information in other locations and with various shelled species. Their results showed some significant concentration differences that are explainable partly by variations in ecosystems and partly by the physiological differences between the shells of scallops and mussels, the other animals tested.
However, some of the differences result from the analytical methods. Some researchers have had to drill, mill and dissolve samples because they lack a laser ablation unit. “Not everyone can have access to such an apparatus,” Barats said.
With proper calibration, she continued, correlation of readings is possible. She noted that the use of a laser with a lower wavelength, such as 213 nm, would provide a simpler method for quantitative analysis. It also would help sensitivity, precision and repeatability, improvements also possible with a femtosecond laser.
More work in the environmental area of the scallop shells is planned but must wait for additional funding. The ability to study this archive would make it possible to reconstruct even those events that took place long ago.
“This may also be a great tool to investigate ancient shells found in archaeological sites, to have some idea of environmental changes,” Barats explained.
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