PMID- 23980243 OWN - NLM STAT- MEDLINE DCOM- 20140414 LR - 20240318 IS - 1471-2970 (Electronic) IS - 0962-8436 (Print) IS - 0962-8436 (Linking) VI - 368 IP - 1627 DP - 2013 TI - Bioturbation determines the response of benthic ammonia-oxidizing microorganisms to ocean acidification. PG - 20120441 LID - 10.1098/rstb.2012.0441 [doi] LID - 20120441 AB - 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