Ocean Acidification Affects Mussels at Early Life Stages

Shells protect themselves against environmental influences and enemies through a hard calcareous shell. Increased acidification makes it increasingly difficult for organisms to form their husks. A group of researchers from the Kiel University (Kiel University) and the GEOMAR Helmholtz Center for Ocean Research Kiel show that mussel larvae are sensitive to ocean acidification, resulting in reduced rates of calcification in a study published today in the international journal Nature Communications and shell resolution.

Mussels are popular seafood in northern Germany. The brown-black shells occur in tidal ranges of the seas. But like many creatures in the oceans, which protect themselves with a lime shell from enemies, the shells are endangered by, among other things, the increasing acidification of seawater. This is due to the absorption of additional carbon dioxide from the atmosphere, which is dissolved in seawater. The mussel is already very sensitive to a decline in pH in early life stages. An important reason for this are the enormous rates of calcification in the larval stage: between the first and second day of life they form calcareous shells, which correspond to the weight of the rest of the body. This is shown by a study by researchers from Kiel.

"For the first time, we used two methods to understand the calcification of one-to-two-day shelled larvae and their sensitivity to climate change," said Kirti Ramesh, first author of the study and PhD student in the Ecophysiology group at GEOMAR and Integrated School of Ocean Sciences (ISOS) of the Cluster of Excellence "Ocean of the Future". "With the help of fluorescent dyes and a special microscopy method, we were able to understand the deposition of calcium carbonate on living larvae and show that calcium carbonate is not formed intracellularly, as previously thought. It is more likely that calcium is absorbed directly from the seawater and transported to the shell via special proteins.

In the second step, the team studied the abiotic conditions directly under the shell shell. Calcium, pH and carbonate in tiny tubercles were measured with tiny, self - made glass microelectrodes. "For the first time, we have been able to show that the mussel larvae are able to increase the pH and the carbonate concentration below the shell, which then leads to higher rates of calcification," explains Drs. Frank Melzner, Head of the Ecophysiology Working Group at GEOMAR. "With increasing acidification, however, the pH values ​​below the shell also decrease, which leads to reduced calcification rates and, in the case of very high CO 2Concentrations, to shell solution and increased mortality leads, "Melzner continues. It is interesting, however, that the shells dissolve only at very low pH values. This suggests that organic constituents of the mussel shell contribute to acid resistance.

"With these results, we can establish a direct relationship between the rate of calcification of shellfish and the carbonate chemistry of seawater," explains Prof. Dr. med. Markus Bleich, Head of the Physiological Institute at Kiel University. The reason for the high sensitivity of mussel larvae to acidification is the limited ion regulation systems of the mussel larvae, continued Bleich.

What's next? "We use genetic and proteomic methods to look at which proteins play a role in the transport of calcium and carbonate, and which organics in the shell increase acid resistance. Findings from our laboratory show that some mussel populations, especially from the Baltic Sea, are more tolerant to ocean acidification. "We suspect that the key to increased acid resistance of mussel shells lies in the variation of organic shell constituents," says Melzner. Such tolerant populations could then be the winners of climate change.

This article has been republished from materials provided by Helmholtz Centre for Ocean Research Kiel. Note: material may have been edited for length and content. For further information, please contact the cited source.

Reference
Kirti Ramesh et al, Mussel larvae modify calcifying fluid carbonate chemistry to promote calcification, Nature Communications (2017). DOI: 10.1038/s41467-017-01806-8.