Ammonium excretion and oxygen respiration of tropical copepods and euphausiids exposed to oxygen minimum zone conditions

• Published in: Biogeosciences
• Main Authors: R. Kiko, H. Hauss, F. Buchholz, F. Melzner
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2016
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Pacific; North Atlantic; Copepods
• Online Access: https://doi.org/10.5194/bg-13-2241-2016; https://doaj.org/article/9b6631f57c694b029af5e4fea36511b2

Calanoid copepods and euphausiids are key components of marine zooplankton communities worldwide. Most euphausiids and several copepod species perform diel vertical migrations (DVMs) that contribute to the export of particulate and dissolved matter to midwater depths. In vast areas of the global ocean, and in particular in the eastern tropical Atlantic and Pacific, the daytime distribution depth of many migrating organisms corresponds to the core of the oxygen minimum zone (OMZ). At depth, the animals experience reduced temperature and oxygen partial pressure ( p O 2 ) and an increased carbon dioxide partial pressure ( p CO 2 ) compared to their near-surface nighttime habitat. Although it is well known that low oxygen levels can inhibit respiratory activity, the respiration response of tropical copepods and euphausiids to relevant p CO 2 , p O 2 , and temperature conditions remains poorly parameterized. Further, the regulation of ammonium excretion at OMZ conditions is generally not well understood. It was recently estimated that DVM-mediated ammonium supply could fuel bacterial anaerobic ammonium oxidation – a major loss process for fixed nitrogen in the ocean considerably. These estimates were based on the implicit assumption that hypoxia or anoxia in combination with hypercapnia (elevated p CO 2 ) does not result in a down-regulation of ammonium excretion. We exposed calanoid copepods from the Eastern Tropical North Atlantic (ETNA; Undinula vulgaris and Pleuromamma abdominalis ) and euphausiids from the Eastern Tropical South Pacific (ETSP; Euphausia mucronata ) and the ETNA ( Euphausia gibboides ) to different temperatures, carbon dioxide and oxygen levels to study their survival, respiration and excretion rates at these conditions. An increase in temperature by 10 °C led to an approximately 2-fold increase of the respiration and excretion rates of U. vulgaris ( Q 10, respiration = 1.4; Q 10, NH 4 -excretion = 1.6), P. abdominalis ( Q 10, respiration = 2.0; Q 10, NH 4 -excretion = 2.4) and E. gibboides ( Q ...