An international team of researchers, led by Brazilian biologist Dr Angela Sanseverino, has presented a study that shows methane from lakebeds to be present in tissues of tropical freshwater fish.

Methane (CH 4 ) is an organic carbon compound containing the fundamental building block of nearly all living material: carbon. It provides an important source of energy and nutrients for bacteria. Methane is produced in oxygen-free environments and is found in abundance at the bottom of lakes.

The study, published in the journal PLoS-ONE, provides new evidence that methane-derived carbon can be an important carbon source for the whole aquatic food web, up to the fish level.

Dr Sanseverino’s team has studied a combination of two biomarkers: a stable isotope that indicates the presence of methane along with a specific fatty acid from methane-oxidizing bacteria.

The study was carried out on fish and other parts of the food web from a lake in the Pantanal, inland Brazil.

“This is the first time we can say with any great certainty that methane from the lake bed has ended up in fish tissue via the food chain”, said co-author Dr David Bastviken of the Linköping University, Sweden.

“Isotopic studies have been carried out in the past, but they have been more uncertain as they only related to one biomarker. We now have two independent biomarkers presenting the same results. This considerably increases the certainty of our findings.”

“It is like opening a black box. It turns out that carbon, which we thought was lost forever, can return to the food chain.”

Methane is taken up by methane oxidizing bacteria, which in turn are eaten by zooplankton and other aquatic organisms. These organisms eventually end up in fish stomachs, meaning that food webs not only feed off organic carbon from plants in the lake or from the surrounding land; but also from deep-lying and oxygen-free, yet carbon-rich, sediment stores where methane is formed.

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Bibliographic information: Sanseverino AM et al. 2012. Methane Carbon Supports Aquatic Food Webs to the Fish Level. PLoS-ONE 7(8): e42723; doi: 10.1371/journal.pone.0042723