Breathing sediments: microbes, waves, and hidden animal pumps

Funnell, G
Vopel, K
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Kay Vopel and Greig Funnell look into the mechanisms and creatures that help maintain the seabed’s life-support system.

Aquatic sediment provides an important ecosystem service: the decomposition of organic matter and the associated regeneration of nutrients for algae and plants. In coastal marine ecosystems, more than half of the nutrients available for primary production in the water column and at the sediment surface can be supplied by the sedimentary processes of aerobic and anerobic decomposition. The most important (and abundant) players in this service are aerobic and anaerobic bacteria, which transform organic into inorganic matter using oxidants such as oxygen and nitrate. 49710

Fluid-dynamic animal pumps on the sediment surface of Mahurangi Harbour. (Click for enlargement and details)(Photos: K. Vopel) 49711

Kay Vopel uses a microelectrode mounted onto a micromanipulator to measure oxygen concentrations in the sediment immediately surrounding a buried echinoderm. (Photo: G. Funnell)

To supply the bacteria with oxidants, the sediment breathes, just like we do to supply our cells. When we breathe, we transport oxygen into our lungs and from there into the bloodstream by air flow and molecular diffusion. We draw our diaphragm down to inhale air and up to exhale. This maintains an oxygen concentration in the alveoli of our lungs that is sufficiently high to let oxygen molecules diffuse from the alveoli into our blood. A similar principle applies to aquatic sediment.

Water & Atmosphere, vol.13(2), pp.16 - 17
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