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

Kiko, Rainer; Hauss, Helena; Búchholz, Friedrich; Melzner, Frank

doi:10.5194/bgd-12-17329-2015

Cited by 11 publications

(6 citation statements)

References 65 publications

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“…While the total abundance of krill is probably underestimated by the comparatively slow and small plankton net, their vertical distribution in relation to the OMZ and the marked total decrease within the eddy compared to outside stations suggests that they are susceptible to OMZ conditions and may suffer from increased predation in the surface layer. This is in line with physiological observations, where a critical partial pressure of 2.4 and 6.2 kPa (29.6 and 64.2 µmol O 2 kg −1 ) was determined at subsurface (13 • C) and near-surface temperatures (23 • C), respectively, in Euphausia gibboides in the ETNA (Kiko et al, 2015). Calanoid copepods represent the largest group in terms of abundance and biomass and comprise approximately 100 species in Cabo Verdean waters (Séguin, 2010) with a wide range of physiological and behavioural adaptations.…”

Section: Shallow Omz Avoidance and Compression At The Surfacesupporting

confidence: 91%

“…Many zooplankton and nekton taxa perform diurnal vertical migrations (DVMs), usually spending the daylight hours in the mesopelagic OMZ and migrating into the productive surface layer at night. These taxa include for example euphausiids (Tremblay et al, 2011), sergestid and penaeid shrimp (Andersen et al, 1997), myctophid fishes (Kinzer and Schulz, 1985) as well as several large calanoid copepods (e.g. Pleuromamma species, Teuber et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Dead zone or oasis in the open ocean? Zooplankton distribution and migration in low-oxygen modewater eddies

Hauss¹,

Christiansen²,

Schütte³

et al. 2015

Preprint

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Abstract. The eastern tropical North Atlantic (ETNA) features a mesopelagic oxygen minimum zone (OMZ) at approximately 300–600 m depth. Here, oxygen concentrations rarely fall below 40 μmol O2 kg−1, but are thought to decline in the course of climate change. The recent discovery of mesoscale eddies that harbour a shallow suboxic (< 5 μmol O2 kg−1) OMZ just below the mixed layer could serve to identify zooplankton groups that may be negatively or positively affected by on-going ocean deoxygenation. In spring 2014, a detailed survey of a suboxic anticyclonic modewater eddy (ACME) was carried out near the Cape Verde Ocean Observatory (CVOO), combining acoustic and optical profiling methods with stratified multinet hauls and hydrography. The multinet data revealed that the eddy was characterized by an approximately 1.5-fold increase in total area-integrated zooplankton abundance. A marked reduction in acoustic target strength (derived from shipboard ADCP, 75kHz) within the shallow OMZ at nighttime was evident. Acoustic scatterers were avoiding the depth range between about 85 to 120 m, where oxygen concentrations were lower than approximately 20 μmol O2 kg−1, indicating habitat compression to the oxygenated surface layer. This observation is confirmed by time-series observations of a moored ADCP (upward looking, 300 kHz) during an ACME transit at the CVOO mooring in 2010. Nevertheless, part of the diurnal vertical migration (DVM) from the surface layer to the mesopelagic continued through the shallow OMZ. Based upon vertically stratified multinet hauls, Underwater Vision Profiler (UVP5) and ADCP data, four strategies have been identified followed by zooplankton in response to the eddy OMZ: (i) shallow OMZ avoidance and compression at the surface (e.g. most calanoid copepods, euphausiids), (ii) migration to the shallow OMZ core during daytime, but paying O2 debt at the surface at nighttime (e.g. siphonophores, Oncaea spp., eucalanoid copepods), (iii) residing in the shallow OMZ day and night (e.g. ostracods, polychaetes), and iv) DVM through the shallow OMZ from deeper oxygenated depths to the surface and back. For strategy (i), (ii) and (iv), compression of the habitable volume in the surface may increase prey-predator encounter rates, rendering zooplankton more vulnerable to predation and potentially making the eddy surface a foraging hotspot for higher trophic levels. With respect to long-term effects of ocean deoxygenation, we expect zooplankton avoidance of the mesopelagic OMZ to set in if oxygen levels decline below approximately 20 μmol O2 kg−1. This may result in a positive feedback on the OMZ oxygen consumption rates, since zooplankton respiration within the OMZ as well as active flux of dissolved and particulate organic matter into the OMZ will decline.

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Section: Shallow Omz Avoidance and Compression At The Surfacesupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Dead zone or oasis in the open ocean? Zooplankton distribution and migration in low-oxygen modewater eddies

Hauss¹,

Christiansen²,

Schütte³

et al. 2015

Preprint

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“…However, the difference between control and treatment decreased with incubation, revealing that copepods were excreting this compound. Our estimated rates are close to those reported in this zone in winter (P erez-Arag on et al 2011), but lower than those reported for other upwelling zones (Isla et al 2004;Fern andez-Urruzola et al 2016;Kiko et al 2015). In the second experiment, NH 1 4 decreased with incubation for both treatments and controls, which could be due to the high degree of lability of NH 1 4 in natural environments since it is actively used by phytoplankton and microbial communities.…”

Section: Nitrogen Excretion By Copepodssupporting

confidence: 82%

Nitrogen excretion by copepods and its effect on ammonia‐oxidizing communities from a coastal upwelling zone

Valdés

Fernández

Molina

et al. 2017

Limnology & Oceanography

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The role of zooplankton in microbial nitrogen turnover in marine environments is poorly understood. Here, we present results from two experiments designed to determine the excretion rate of ammonium and dissolved organic nitrogen (DON) by dominant copepods, Acartia tonsa and Paracalanus cf indicus, fed with two natural sized-fractioned diets (20-150 lm and < 20 lm), and its possible effects on the transcriptional activity of ammonia monooxygenase subunit A (amoA), a functional marker for ammonia-oxidizing archaea (AOA) and bacteria (AOB), as a response to the input of ammonium and DON by copepod excretion, during autumn and winter in central/southern Chile. Our results reveal that DON was the main excretion product, with rates up to 3.7 lmol L 21 h 21 . DON production increased in copepods fed with the small-sized food.Ammonium was also excreted, with rates up to 0.08 lmol L 21 h 21 in autumn and 0.4 lmol L 21 h 21 in winter, and rapidly consumed by the microbial community, decreasing down to 0.07 lmol L 21 between the initial time to 4 h. Ammonium consumption coincided with increased AOB and AOA amoA transcript copies in copepods fed with the larger-sized food, while a different microbial community, probably heterotrophic, reacted to nitrogen input via excretion by copepods fed with the smaller-sized food in autumn. AOA-A was transcriptionally active in winter with nearly zero ammonium concentration, suggesting that AOA outcompete AOB when ammonium becomes limited. We conclude that nitrogen excreted by copepods can be used directly by microbial communities, including nitrifying ones. Zooplankton excretion may thus provide significant remineralized nitrogen for new and regenerated production in the upper ocean.

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“…In the same study, NH + 4 production was not detected in spring, in contrast with our study, in which NH + 4 was the main compound excreted by copepods. Additionally, the NH + 4 excretion rates observed in the current study were higher than those reported in this area and were also in the range of those reported in other upwelling zones (Fernández-Urruzola et al, 2016;Kiko et al, 2016).…”

Section: Excretion Of Nitrogen and Phosphorus Compoundscontrasting

confidence: 52%

Dissolved Compounds Excreted by Copepods Reshape the Active Marine Bacterioplankton Community Composition

et al. 2017

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Copepods are important suppliers of bioreactive compounds for marine bacteria through fecal pellet production, sloppy feeding, and the excretion of dissolved compounds. However, the interaction between copepods and bacteria in the marine environment is poorly understood. We determined the nitrogen and phosphorus compounds excreted by copepods fed with two natural size-fractionated diets (<20-and 20-150-µm) in the upwelling zone of central/southern Chile in late summer and spring. We then assessed the biogeochemical response of the bacterial community and its structure, in terms of total and active cells, to enrichment by copepod-excreted dissolved compounds. Results revealed that copepods actively excreted nitrogen and phosphorus compounds, mainly in the form of ammonium and dissolved organic phosphorus (DOP), reaching excretion rates of 2.6 and 0.05 µmol L −1 h −1 , respectively. In both periods, the maximum excretion rates were associated with the 20-150-µm size fraction, but particularly during spring, when a higher organic matter quality was observed in excretion products compared to late summer. There were higher excretion rates of dissolved free amino acids (DFAAs) from copepods fed with the <20-µm size fraction, mainly histidine (HIS) in late summer and glutamic acid (GLU) in spring. A shift in the composition of the active bacterial community was observed between periods and treatments, which was associated with the response of the common seawater surface phyla Proteobacteria and Bacteroidetes. The specific bacterial activity (16S rRNA:rDNA) suggested a different response to the two size-fractionated diets. In late summer, Betaproteobacteria and Bacteroidetes were stimulated by the treatment enriched with excretion products derived from the 20-150-µm and <20-µm size fractions, respectively. In spring, Alphaproteobacteria were active in the treatment enriched with the excretion products of copepods fed with the <20-µm size fraction, whereas they were inhibited in the treatment enriched with excretion products in the 20-150-µm size fraction. Our findings indicate that different Valdés et al. Copepod Excretion and Bacterial Community Structure copepod diets can have a significant impact on the quantity and quality of their excretion compounds, which can subsequently generate shifts in the active bacterial composition. The bacterial response is probably associated with common-opportunistic sea surface microbes that are adapted to rapidly reacting to environmental offers.

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

Cited by 11 publications

References 65 publications

Dead zone or oasis in the open ocean? Zooplankton distribution and migration in low-oxygen modewater eddies

Dead zone or oasis in the open ocean? Zooplankton distribution and migration in low-oxygen modewater eddies

Nitrogen excretion by copepods and its effect on ammonia‐oxidizing communities from a coastal upwelling zone

Dissolved Compounds Excreted by Copepods Reshape the Active Marine Bacterioplankton Community Composition

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