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Marine biologists have discovered a dense population of mussels (the vent mussel Bathymodiolus brevior, a common, edible bi-valve “shellfish”), carpeting the sides of a submarine volcano, which has survived–despite the highly acidic environment–for the past 40 years. The results of this study were reported in a recent, on-line edition of the Journal Nature Geoscience.

The acidification of ocean habitats due to increased absorption of CO2 (which reacts with water to form carbonic acid) has become an issue of great concern over the past decade. Shellfish and other marine species (like corals and snails) that make their “homes” or shells from carbonates of calcium (CaCO3), are vulnerable to more acidic waters. A lower ph (generally below 8 on the ph scale) marine environment makes calcium ions less available to these creatures to fabricate their fortifications against nature’s predators and chemical forces. The result of this acidic exposure in shellfish is typically a much thinner shell, thus making the creature more susceptible to predation and even disease (as in the case of many corals; see: One Third of Reef-Building Corals Face Extinction Risk ).

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But this particular variety has been doing relatively well, despite the continuous spewing of liquid carbon dioxide from the volcano.  The ph range along the northwest side of the volcano was found to be between 5.36 and 7.29, which is considered too acidic for most calcium metabolizing species. Researchers Verena Tunnicliffe and colleagues studied a population of mussels living around the base of Eifuku volcano which is part of the Mariana Arc in the Pacific Ocean. In a comparison study, the researchers analyzed shell thickness in related species found in more hospitable waters. On average, the shell thickness of the mussels near the volcano (a higher acid locale) were only half the thickness of the higher ph-dwelling counterparts (high ph, above 7 on the ph scale; means lower acidity).

These findings are remarkable and a bit counter-intuitive to researchers who see acidification of ocean waters to be a generally bad thing for the ocean’s calcareous creatures. However,  a species that is more adaptive (such as the mussel) to a harsher environment can benefit by a decrease in its natural (but less adaptive) predator population. In this case, that would see to be the bottom-feeding crabs who are seemingly less tolerant of the acidic waters. The lack of crabs in these chemically harsher waters has proven advantageous to the mussel population, despite their thinning shells.

This is the team’s current theory.  New predators could eventually move into the habitat and pose a new threat to the mussels. More tests and follow up studies will determine if this advantage is long-term, or, if the acidic waters (or their consequent effects) will ultimately win out.

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