A Limestone Home: How Methane helps Create Habitats for Microbes and Animals

durch Prof. Tina Treude (for FB2/MG)

Mittwoch 15.10.2025, 13:15 → 14:30 Europe/Berlin

8A-002 - Hörsaal Ostufer / Lecture Hall East (GEOMAR - Standort Ostufer / GEOMAR - East Shore)

At marine cold seeps, a unique group of microbes known as anaerobic methanotrophs (ANME) thrive by consuming methane in environments where oxygen is absent. In this process, ANME oxidize methane, turning it into bicarbonate, which accumulates in sediment porewaters. As the concentration of bicarbonate builds up and becomes oversaturated, it leads to the formation of authigenic carbonates or limestone. Over time, the accumulated carbonates solidify into structures called chemoherms—large, mound-like formations made of minerals, which can become eroded, causing them to protrude from the sediment and rise into the water column (Fig. 1).

These protruding chemoherms serve as important habitats. The inside of the chemoherms offers a safe refuge for the ANME (Fig. 2), protecting them from oxygen, which they cannot tolerate. Meanwhile, the outer surface of these structures, which is sometimes spongy and porous, creates a surface where other organisms, like aerobic microbes and animals, can colonize and find shelter.

In this way, the ANME not only sustain themselves by metabolizing methane, but their activity also creates a physical structure—the chemoherm—that acts as a habitat for other organisms. Thus, by producing these carbonates through their metabolic processes, ANME essentially become "foundation species," laying the groundwork for diverse ecosystems in these methane-rich environments.

This presentation will focus on methane-seep carbonate datasets obtained from two major submersible-supported expeditions to methane seeps off the coast of Southern California and in the Aleutian Trench off Alaska. Our findings reveal that: (1) anaerobic methanotrophy within protruding chemoherms is influenced by the surrounding oxygen levels, (2) aerobic microorganisms colonizing the exterior of the carbonates facilitate carbonate dissolution, and (3) animals living on or within the chemoherms exhibit distinct carbon isotopic signatures, linking them to methanotrophic processes at the chemoherms. Based on observations of chemoherms at water depths ranging from 700 to 5000 meters, we hypothesize that the distribution of protruding chemoherms is confined to depths above the lysocline, thus setting a lower depth limit for this unique deep-sea habitat.