Bioturbation determines the response of benthic ammonia-oxidizing microorganisms to ocean acidification

Laverock, B. and Kitidis, V. and Tait, K. and Gilbert, J. A. and Osborn, A. M. and Widdicombe, S. (2013) Bioturbation determines the response of benthic ammonia-oxidizing microorganisms to ocean acidification. Philosophical Transactions of the Royal Society B: Biological Sciences, 368 (1627). n/a. ISSN 0962-8436

Full content URL: http://dx.doi.org/10.1098/rstb.2012.0441

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Abstract

Ocean acidification (OA), caused by the dissolution of increasing concentrations of atmospheric carbon dioxide (CO2) in seawater, is projected to cause significant changes to marine ecology and biogeochemistry. Potential impacts on the microbially driven cycling of nitrogen are of particular concern. Specifically, under seawater pH levels approximating future OA scenarios, rates of ammonia oxidation (the rate-limiting first step of the nitrification pathway) have been shown to dramatically decrease in seawater, but not in underlying sediments. However, no prior study has considered the interactive effects of microbial ammonia oxidation and macrofaunal bioturbation activity, which can enhance nitrogen transformation rates. Using experimental mesocosms, we investigated the responses to OA of ammonia oxidizing microorganisms inhabiting surface sediments and sediments within burrow walls of the mud shrimp Upogebia deltaura. Seawater was acidified to one of four target pH values (pHT 7.90, 7.70, 7.35 and 6.80) in comparison with a control (pHT 8.10). At pHT 8.10, ammonia oxidation rates in burrow wall sediments were, on average, fivefold greater than in surface sediments. However, at all acidified pH values (pH � 7.90), ammonia oxidation rates in burrow sediments were significantly inhibited (by 79-97; p < 0.01), whereas rates in surface sediments were unaffected. Both bacterial and archaeal abundances increased significantly as pHT declined; by contrast, relative abundances of bacterial and archaeal ammonia oxidation (amoA) genes did not vary. This research suggests that OA could cause substantial reductions in total benthic ammonia oxidation rates in coastal bioturbated sediments, leading to corresponding changes in coupled nitrogen cycling between the benthic and pelagic realms. © 2013 The Author(s) Published by the Royal Society. All rights reserved.

Keywords:Ocean acidification, Ammonia oxidation, Marine sediments, Bioturbation, Upogebia deltaura
Subjects:C Biological Sciences > C180 Ecology
C Biological Sciences > C161 Marine Biology
Divisions:College of Science > School of Life Sciences
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ID Code:11810
Deposited On:06 Sep 2013 09:28

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