Microbial gardening in the ocean's twilight zone: Detritivorous metazoans benefit from fragmenting, rather than ingesting, sinking detritus

• Published in: BioEssays 2014-12, Vol.36 (12), p.1132-1137
• Main Authors: Mayor, Daniel J., Sanders, Richard, Giering, Sarah L. C., Anderson, Thomas R.
• Format: Article
• Language: English
• Subjects: carbon cycling; detritus; Insights & s; mesopelagic; Metazoa; microbial loop; nutrition; Plankton; polyunsaturated fatty acid; zooplankton
• ISSN: 0265-9247; 1521-1878
• DOI: 10.1002/bies.201400100

Sinking organic particles transfer ∼10 gigatonnes of carbon into the deep ocean each year, keeping the atmospheric CO2 concentration significantly lower than would otherwise be the case. The exact size of this effect is strongly influenced by biological activity in the ocean's twilight zone (∼50–1,000 m beneath the surface). Recent work suggests that the resident zooplankton fragment, rather than ingest, the majority of encountered organic particles, thereby stimulating bacterial proliferation and the deep‐ocean microbial food web. Here we speculate that this apparently counterintuitive behaviour is an example of ‘microbial gardening’, a strategy that exploits the enzymatic and biosynthetic capabilities of microorganisms to facilitate the ‘gardener's’ access to a suite of otherwise unavailable compounds that are essential for metazoan life. We demonstrate the potential gains that zooplankton stand to make from microbial gardening using a simple steady state model, and we suggest avenues for future research. Zooplankton in the ocean's twilight zone typically consume nutritionally poor detritus. We speculate that these animals fragment large detrital particles to stimulate the growth of microorganisms. This ‘gardening’ of microbes exploits their enzymatic and biosynthetic pathways to produce biomass that can be harvested as an energy‐rich and nutritious food source.