Fine-scale vertical distribution of macroplankton and micronekton in the Eastern Tropical North Pacific in association with an oxygen minimum zone

Maas, Amy E.; Frazar, Sarah L.; Outram, Dawn M.; Seibel, Brad A.; Wishner, Karen F.

doi:10.1093/plankt/fbu077

Cited by 46 publications

(38 citation statements)

References 61 publications

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“…1). This picture is broadly consistent with in situ net data, for example from the Arabian Sea and the ETNP, indicating diel migration of zooplankton and micronekton, including abundant euphausiids and myctophid fish, in and out of the oxygen-deficient layers (25)(26)(27).…”

Section: Dvm Association With Anoxic Waterssupporting

confidence: 87%

“…2). Given the uncertainties in the DVM depth estimate as determined by the acoustic method, and roundoff errors associated with the climatological O 2 concentrations, this is essentially consistent with the main DVM stationary depths lying within anoxic waters wherever they occur, consistent with observations (25)(26)(27). It is within these regions that an intensification of anammox by DVM could be anticipated.…”

Section: Dvm Association With Anoxic Waterssupporting

confidence: 79%

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Enhancement of anammox by the excretion of diel vertical migrators

Bianchi

Babbin

Galbraith

2014

Proc. Natl. Acad. Sci. U.S.A.

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Measurements show that anaerobic ammonium oxidation with nitrite (anammox) is a major pathway of fixed nitrogen removal in the anoxic zones of the open ocean. Anammox requires a source of ammonium, which under anoxic conditions could be supplied by the breakdown of sinking organic matter via heterotrophic denitrification. However, at many locations where anammox is measured, denitrification rates are small or undetectable. Alternative sources of ammonium have been proposed to explain this paradox, for example through dissimilatory reduction of nitrate to ammonium and transport from anoxic sediments. However, the relevance of these sources in open-ocean anoxic zones is debated. Here, we bring to attention an additional source of ammonium, namely, the daytime excretion by zooplankton and micronekton migrating from the surface to anoxic waters. We use a synthesis of acoustic data to show that, where anoxic waters occur within the water column, most migrators spend the daytime within them. Although migrators export only a small fraction of primary production from the surface, they focus excretion within a confined depth range of anoxic water where particle input is small. Using a simple biogeochemical model, we suggest that, at those depths, the source of ammonium from organisms undergoing diel vertical migrations could exceed the release from particle remineralization, enhancing in situ anammox rates. The contribution of this previously overlooked process, and the numerous uncertainties surrounding it, call for further efforts to evaluate the role of animals in oxygen minimum zone biogeochemistry.anammox | denitrification | oxygen minimum zone | diel vertical migration W ater column oxygen minimum zones (OMZs), where oxygen concentrations plummet to submicromolar levels (1), are responsible for approximately one-third of the total removal of fixed nitrogen from the oceans (2, 3). Several processes mediated by specialized prokaryotes convert fixed inorganic nitrogen (NH 4 + , NO 2 − , and NO 3 − ) to N 2 in anoxic waters. Canonical denitrification, consisting of dissimilatory NO 3 − reduction to NO 2 − (DNRN) followed by the further oxidation of organic matter with NO 2 − (the denitrification step), was long considered the dominant fixed N removal pathway in anoxic waters. Over the last decade, anammox has gained attention as a major sink of fixed N in nearly anoxic waters (O 2 < 10 mmol·m −3 ) (4, 5).Stoichiometric considerations would suggest a close coupling between denitrification and anammox (6, 7). Under anoxic conditions, the NH 4 + liberated by the remineralization of organic matter through DNRN and denitrification should accumulate in the water column because conventional (aerobic) nitrification cannot proceed. However, this accumulation is not observed in the cores of anoxic waters, where observed NH 4 + concentrations are generally much less than 1 mmol·m −3 (8). In these regions, oxidation of NH 4 + with NO 2 − by anammox is thought to be the major sink of NH 4 + (9). Given that no significant NH 4 + acc...

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Section: Dvm Association With Anoxic Waterssupporting

confidence: 87%

Section: Dvm Association With Anoxic Waterssupporting

confidence: 79%

Enhancement of anammox by the excretion of diel vertical migrators

Bianchi

Babbin

Galbraith

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Similarly, a lower species richness of euphausiids occurs in the eastern Pacific Ocean [11], which has well-known oxygen minimum zones [67]. Bentheuphausia amblyops is usually found below 500 m [7], and has been found at the lower oxyclines in the Costa Rica Dome [68]. Euphausia sibogae has also been reported to tolerate oxygen minimum zones in the northern Indian Ocean, typically occurring around 300-400 m during the day, but migrating to the surface waters at night [7,9].…”

Section: Discussionmentioning

confidence: 99%

Species Richness, Taxonomic Distinctness and Environmental Influences on Euphausiid Zoogeography in the Indian Ocean

Sutton

Beckley

2017

Diversity

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Abstract:Although two thirds of the world's euphausiid species occur in the Indian Ocean, environmental factors influencing patterns in their diversity across this atypical ocean basin are poorly known. Distribution data for 56 species of euphausiids were extracted from existing literature and, using a geographic information system, spatially-explicit layers of species richness and average taxonomic distinctness (AveTD) were produced for the Indian Ocean. Species richness was high in tropical areas of the southern Indian Ocean (0-20 • S), and this high richness extended southwards via the Agulhas and Leeuwin boundary currents. In contrast, the land-locked northern Indian Ocean exhibited lower species richness but higher AveTD, with the presence of the monotypic family Bentheuphausiidae strongly influencing the latter result. Generalised additive modelling incorporating environmental variables averaged over 0-300 m depth indicated that low oxygen concentrations and reduced salinity in the northern Indian Ocean correlated with low species richness. Depth-averaged temperature and surface chlorophyll a concentration were also significant in explaining some of the variation in species richness of euphausiids. Overall, this study has indicated that the patterns in species richness in the Indian Ocean are reflective of its many unusual oceanographic features, and that patterns in AveTD were not particularly informative because of the dominance by the family Euphausiidae.

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“…We previously noted the presence of zooplankton boundary layers (sharp peaks of high zooplankton biomass and abundances of certain fish and copepod indicator species) at the upper and lower edges (oxyclines) of the OMZ core at several of these sites (Costa Rica Dome, Tehuantepec Bowl), and how the lower oxycline biomass peak shifted depth by tracking oxygen 60 concentration (Wishner et al, 2013). These peaks of zooplankton concentration in the water column were also locations of active trophic processing (Williams et al, 2014), life history events (diapause depths) for some species (Wishner et al, 2013), and predator concentrations (Maas et al, 2014). On the 2017 cruise, horizontally-sequenced transects and tows at three different depths within the OMZ exhibited considerable submesoscale physical and biological variability (including km-scale features of oxygen); zooplankton abundance differences were associated with oxygen differences of only a few µM (Wishner et al, 2018).…”

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confidence: 97%

Ocean Deoxygenation and Copepods: Coping with Oxygen Minimum Zone Variability

Wishner¹,

Seibel²,

Outram³

2019

Preprint

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Abstract. Increasing deoxygenation (loss of oxygen) of the ocean, including expansion of oxygen minimum zones (OMZs), is a potentially important consequence of global warming. We examined present day variability of vertical distributions of copepod species in the Eastern Tropical North Pacific (ETNP) living in locations with different water column oxygen profiles and OMZ intensity (lowest oxygen concentration and its vertical extent in a profile). Copepods and hydrographic data were collected in vertically-stratified day and night MOCNESS tows (0&#8211;1000&#8201;m) during 4 cruises over a decade (2007&#8211;2017) that sampled 4 ETNP locations: Costa Rica Dome, Tehuantepec Bowl, and 2 oceanic sites further north (21&#176;&#8211;22&#176;&#8201;N) off Mexico. The sites had different vertical oxygen profiles: some with a shallow mixed layer, abrupt thermocline, and extensive very low oxygen OMZ core, and others with a more gradual vertical development of the OMZ (broad mixed layer and upper oxycline zone) and a less extensive OMZ core where oxygen was not as low. Copepod species (including examples from the genera Eucalanus, Pleuromamma, and Lucicutia) demonstrated different distributional strategies and physiologies associated with this variability. We identified sets of species that (1) changed their vertical distributions and depth of maximum abundance associated with the depth and intensity of the OMZ and its oxycline inflection points, (2) shifted their depth of diapause, (3) adjusted their diel vertical migration, especially the nighttime upper depth, or (4) expanded or contracted their depth range within the mixed layer and upper part of the thermocline in association with the thickness of the aerobic epipelagic zone (habitat compression concept). The upper ocean to mesopelagic depth range encompasses a complex interwoven ecosystem characterized by intricate relationships among its inhabitants and their environment. It is a critically important zone for oceanic biogeochemical and export processes and hosts key food web components for commercial fisheries. Among the zooplankton, there will likely be winners and losers with increasing ocean deoxygenation as species cope with environmental change. Changes in individual copepod species abundances, vertical distributions, and life history strategies may create potential perturbations to these intricate food webs and processes. Present day variability provides a window into future scenarios and potential effects of deoxygenation.

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Fine-scale vertical distribution of macroplankton and micronekton in the Eastern Tropical North Pacific in association with an oxygen minimum zone

Cited by 46 publications

References 61 publications

Enhancement of anammox by the excretion of diel vertical migrators

Enhancement of anammox by the excretion of diel vertical migrators

Species Richness, Taxonomic Distinctness and Environmental Influences on Euphausiid Zoogeography in the Indian Ocean

Ocean Deoxygenation and Copepods: Coping with Oxygen Minimum Zone Variability

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