zooplankton :: Ocean Carbon & Biogeochemistry

Studying marine ecosystems and biogeochemical cycles in the face of environmental change

Archive for zooplankton

Turning a spotlight on grazing

Posted by mmaheigan

· Thursday, July 23rd, 2020

Microscopic plankton in the surface ocean make planet Earth habitable by generating oxygen and forming the basis of marine food webs, yielding harvestable protein. For over 100 years, oceanographers have tried to ascertain the physical, chemical, and biological processes governing phytoplankton blooms. Zooplankton grazing of phytoplankton is the single largest loss process for primary production, but empirical grazing data are sparse and thus poorly constrained in modeling frameworks, including assessments of global elemental cycles, cross-ecosystem comparisons, and predictive efforts anticipating future ocean ecosystem function. As sunlight decays exponentially with depth, upper-ocean mixing creates dynamic light environments with predictable effects on phytoplankton growth but unknown consequences for grazing.

Figure caption: Rates (d⁻¹) of phytoplankton growth (μ), grazing mortality (g), and biomass accumulation (r) under four mixed layer scenarios simulated using light as a proxy of (a) sustained deep mixing, (b) rapid shoaling, (c) sustained shallow mixing, and (d) rapid mixed layer deepening. Error bars represent one standard deviation of the mean of duplicate experiments. Grazing was measured but not detected in the sustained deep mixing and rapid shoaling conditions, denoted with x.

Using data from a spring cruise in the North Atlantic, authors of a recent study published in Limnology & Oceanography compared the influences of microzooplankton predation and fluctuations in light availability—representative of a mixing water column—on phytoplankton standing stock. Data from at-sea incubations and light manipulation experiments provide evidence that phytoplankton’s instantaneous and zooplankton’s delayed responses to light fluctuations are key modulators of the balance between phytoplankton growth and grazing rates (Figure 1). These results suggest that light is a potential, remotely retrievable predictor of when and where in the ocean zooplankton grazing may represent an important loss term of phytoplankton production. If broadly verified, this approach could be used to systematically assess sparsely measured grazing across spatial and temporal gradients in representative regions of the ocean. Such data will be essential for enhancing our predictive capacity of ocean food web function, global biogeochemical cycles and the many derived processes, including fisheries production and the flow of carbon through the oceans.

Authors:
Françoise Morison (University of Rhode Island)
Gayantonia Franzè (University of Rhode Island, currently Institute of Marine Research, Norway)
Elizabeth Harvey (University of Georgia, currently University of New Hampshire)
Susanne Menden-Deuer (University of Rhode Island)

Modern OMZ copepod dynamics provide analog for future oceans

Posted by mmaheigan

· Thursday, July 23rd, 2020

Global warming increases ocean deoxygenation and expands the oxygen minimum zone (OMZ), which has implications for major zooplankton groups like copepods. Reduced oxygen levels may impact individual copepod species abundance, vertical distribution, and life history strategy, which is likely to perturb intricate oceanic food webs and export processes. In a study recently published in Biogeosciences, authors conducted vertically-stratified day and night MOCNESS tows (0-1000 m) during four cruises (2007-2017) in the Eastern Tropical North Pacific, sampling hydrography and copepod distributions in four locations with different water column oxygen profiles and OMZ intensity (i.e. lowest oxygen concentration and its vertical extent in a profile). Each copepod species exhibited a different vertical distribution strategy and physiology associated with oxygen profile variability. The study identified sets of species that (1) changed their vertical distributions and maximum abundance depth associated with the depth and intensity of the OMZ and its oxycline inflection points, (2) shifted their diapause depth, (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) (Figure 1). Distribution depths for some species shifted by 10’s to 100’s of meters in different situations, which also had metabolic (and carbon flow) implications because temperature decreased with depth. This observed present-day variability may provide an important window into how future marine ecosystems will respond to deoxygenation.

Figure caption: Schematic diagram showing how future OMZ expansion may affect zooplankton distributions, based on present-day responses to OMZ variability. The dashed line indicates diel vertical migration (DVM) and highlights the shoaling of the nighttime depth as the aerobic habitat is compressed. The lower oxycline community and the diapause layer for some species, associated with a specific oxygen concentration, may deepen as the OMZ expands.

Authors:
Karen F. Wishner (University of Rhode Island)
Brad Seibel (University of South Florida)
Dawn Outram (University of Rhode Island)

Tiny, but effective: Gelatinous zooplankton and the ocean biological carbon pump

Posted by mmaheigan

· Wednesday, March 25th, 2020

Barely visible to the naked eye, gelatinous zooplankton play important roles in marine food webs. Cnidaria, Ctenophora, and Urochordata are omnipresent and provide important food sources for many more highly developed marine organisms. These small, nearly transparent organisms also transport large quantities of “jelly-carbon” from the upper ocean to depth. A recent study in Global Biogeochemical Cycles focused on quantifying the gelatinous zooplankton contribution to the ocean carbon cycle.

Figure 1. Processes and pathways or gelatinous carbon transfer to the deep ocean.

Using >90,000 data points (1934 to 2011) from the Jellyfish Database Initiative (JeDI), the authors compiled global estimates of jellyfish biomass, production, vertical migration, and jelly carbon transfer efficiency. Despite their small biomass relative to the total mass of organisms living in the upper ocean, their rapid, highly efficient sinking makes them a globally significant source of organic carbon for deep-ocean ecosystems, with 43-48% of their upper ocean production reaching 2000 m, which translates into 0.016 Pg C yr^-1.

Figure 2. Mass deposition event of jellyfish at 3500 m in the Arabian Sea (Billett et al. 2006).

Sediment trap data have suggested that carbon transport associated with large, episodic gelatinous blooms in localized open ocean and continental shelf regions could often exceed phytodetrital sources, in particular instances. These mass deposition events and their contributions to deep carbon export must be taken into account in models to better characterize marine ecosystems and reduce uncertainties in our understanding of the ocean’s role in the global carbon cycle.

Links:

Jellyfish Database Initiative http://jedi.nceas.ucsb.edu, http://jedi.nceas.ucsb.edu-dmo.org/dataset/526852 )

Authors:
Mario Lebrato (Christian‐Albrechts‐University Kiel and Bazaruto Center for Scientific Studies, Mozambique)
Markus Pahlow (GEOMAR)
Jessica R. Frost (South Florida Water Management District)
Marie Küter (Christian‐Albrechts‐University Kiel)
Pedro de Jesus Mendes (Marine and Environmental Scientific and Technological Solutions, Germany)
Juan‐Carlos Molinero (GEOMAR)
Andreas Oschlies (GEOMAR)

Krillin’ it with poop: Highlighting the importance of Antarctic krill in ocean carbon and nutrient cycling

Posted by mmaheigan

· Tuesday, February 4th, 2020

Scientists have long known the role of Antarctic krill (Euphausia superba) in Southern Ocean ecosystems. Evidence is gathering about krill’s biogeochemical importance through releasing millions of faecal pellets in swarms and stimulating primary production through nutrient excretion. Here, we explore and synthesise the known impacts that this highly abundant and rather large species has on the environment. Krill exemplify how metazoa can play a dominant role in shaping ocean biogeochemistry, thus providing additional motivation for protecting certain harvested species.

Figure 1: The ecological roles of krill in Southern Ocean biogeochemical cycles, including releasing faecal pellets, excreting nutrients whilst grazing, and larval krill migrating throughout the water column, shedding exoskeletons, and feeding on the seabed.

A review published in Nature Communications uncovers at least 13 possible pathways by which Antarctic krill either influence the carbon sink or release fertilizing nutrients (Figure 1). Their large size (up to 7 cm) and swarming nature (millions of krill aggregate) enable krill to strongly impact ocean biogeochemistry. Swarms release large numbers of faecal pellets, overwhelming detritivores and resulting in a large sink of faecal carbon. Krill may physically mix nutrients from the deep ocean and become a decades-long carbon store in whale biomass. Antarctic krill larvae, which live near the sea-ice, undergo deeper diel vertical migrations compared to adult Antarctic krill (400 m vs. 200 m), so any carbon respired or faecal pellets released by larvae could remain in the deep ocean longer than those released by adult krill at a shallower depth; the larval krill contribution to carbon export has not been quantified. Furthermore, it is currently unknown how many krill larvae are removed from the Antarctic krill fishery as by-catch. Perhaps the biggest challenge in constraining the role of krill (adult and larvae) in biogeochemical cycles is our limited capacity to quantify the abundance and biomass of Antarctic krill, since shipboard sampling methods (nets or acoustics) have limited spatial and temporal coverage. Ultimately, the Southern Ocean is an important physical AND biological sink of carbon, and we must consider the role krill and other animals have in this cycle.

Figure 2: Processes in the biological carbon pump including the sinking of dead phytoplankton aggregates, zooplankton, krill and fish faecal pellets and dead animals. Microbial remineralisation is depicted through the return of particulate organic carbon to dissolved organic carbon (DOC) and eventually carbon dioxide.

Authors:
Emma Cavan (Imperial College London and University of Tasmania)
Anna Belcher (British Antarctic Survey)
Angus Atkinson (Plymouth Marine Laboratory)
Simeon Hill (British Antarctic Survey)
So Kawaguchi (Australian Antarctic Division)
Stacey McCormack (University of Tasmania)
Bettina Meyer (Alfred Wegener Institute for Polar and Marine Research and University of Oldenburg)
Stephen Nicol (University of Tasmania)
Lavenia Ratnarajah (University of Liverpool)
Katrin Schmidt (University of Plymouth)
Deborah Steinberg (Virginia Institute of Marine Science)
Geraint Tarling (British Antarctic Survey)
Philip Boyd (University of Tasmania and Antarctic Climate and Ecosystems Cooperative Research Centre)

Zooplankton-fueled carbon export is changing in the North Atlantic Ocean

Posted by mmaheigan

· Monday, June 10th, 2019

Zooplankton-mediated carbon export is an important, but variable and relatively unconstrained part of the biological carbon pump—the processes that fix atmospheric carbon dioxide in organic material and transport it from the upper sunlit ocean to depth. Changes in the biological pump impact the climate system, but are challenging to quantify because such analyses require spatially and temporally explicit information about biological, chemical, and physical properties of the ocean, where empirical observations are in short supply.

A recent study in Nature, Ecology and Evolution focused on copepods in the northern half of the North Atlantic Ocean, where the Continuous Plankton Recorder (CPR) time series program has documented surface plankton abundance and taxonomic composition for nearly six decades. Copepods transport carbon passively by producing sinking fecal pellets while feeding near the sea surface, and actively via daily and seasonal migrations to deeper waters where carbon is released through respiration, defecation, and mortality. Using allometry, metabolic theory, and an optimal behavior model, the authors examined patterns of passive and active carbon transport from 1960 to 2014 and sensitivity of carbon export to different model inputs.

Figure caption: Spatial distribution and change, from 1960 to 2014, of modeled copepod-mediated carbon flux: top left – mean passive carbon flux (sinking fecal pellets), bottom left – change in passive carbon flux, top right – mean active carbon flux (respiration plus fecal pellets produced during diel vertical migration), bottom right – change in active carbon flux.

The authors observed that from southern Iceland to the Gulf of Maine, copepod-mediated carbon transport has increased over the last six decades, with the highest rates around 30 mgC m^-2 y^-1 each decade for passive flux, and 4 mgC m^-2 y^-1 each decade for active flux. Meanwhile, it has decreased across much of the more temperate central northern North Atlantic with highest rates around 69 mgC m^-2 y^-1 each decade for passive flux and 8 mgC m^-2 y^-1 each decade for active flux. This pattern is largely driven by changes in copepod population distributions and community structure, specifically the distributions of large and abundant species (e.g. Calanus spp.). These results suggest that shifts in species distributions driven by a changing global climate are already impacting ecosystem function across the northern North Atlantic Ocean. These shifts are not latitudinally uniform, thus highlighting the complexity of marine ecosystems. This study demonstrates the importance of these sustained plankton measurements and how plankton-mediated carbon fluxes can be mechanistically implemented in next-generation biogeochemical models.

Authors:
Philipp Brun (Technical University of Denmark and Swiss Federal Research Institute)
Karen Stamieszkin (University of Maine, Bigelow Lab and Virginia Institute of Marine Science)
Andre W. Visser (Technical University of Denmark)
Priscilla Licandro (Sir Alister Hardy Foundation for Ocean Science, Plymouth Marine Laboratory, and Stazione Zoologica Anton Dohrn, Italy)
Mark R. Payne (Technical University of Denmark)
Thomas Kiørboe (Technical University of Denmark)

Also see OCB2019 plenary session: The effect of size on ocean processes (allometry) and implications for export (Thursday, June 27, 2019)

Zooplankton vertical migrations represent a significant source of carbon export in the ocean

Posted by mmaheigan

· Friday, March 15th, 2019

Huge numbers of tiny marine animals, known as zooplankton, migrate between the surface ocean and the twilight zone (200 – 1,000 m below the surface) everyday; it is the largest migration event anywhere on the planet. How much carbon do these animals transport with them and how much do they leave behind sequestered in the deep ocean? In a recent publication in Global Biogeochemical Cycles, Archibald et al. (2019) used a simple model to estimate the magnitude of carbon flux into the twilight zone from zooplankton vertical migrations and observed that it was a significant contributor to carbon export on a global scale. The study also revealed strong regional patterns in migration-mediated carbon flux, with the greatest impact on export occurring at subtropical latitudes (Figure 1).

Figure 1. Percent increase in the modeled carbon export flux out of the surface ocean as a result of zooplankton vertical migrations.

Migrating zooplankton also consume significant amounts of oxygen at depth, generating a local maximum in the oxygen utilization profile at depth within the migration layer. By including the effect of the metabolism of migrating zooplankton, the model is able to produce a more detailed picture of oxygen utilization over the twilight zone. The model in this study effectively simulates the complex phenomenon of zooplankton vertical migrations, providing a simple framework that will allow researchers to investigate how this key component of the global carbon cycle might change under future climatic conditions. For example, if increased stratification leads to a greater representation of small cells in phytoplankton communities, then zooplankton migration-mediated carbon export is expected to make up a proportionally larger fraction of the total carbon export flux.

Authors:
Kevin M. Archibald (Woods Hole Oceanographic Institution and Massachusetts Institute of Technology)
David A. Siegel (University of California, Santa Barbara)
Scott C. Doney (University of Virginia)

Artificial light from sampling platforms changes zooplankton behavior

Posted by mmaheigan

· Monday, November 26th, 2018

When designing sampling we make generally accepted assumptions that what we collect is representative of what is “normal” or naturally occurring at the place, time, and depth of collection. However, a recent study in Science Advances revealed that this might not be true. During round-the-clock shipboard sampling, lights used at night can actually be a form of pollution that disrupts the diel cycle of zooplankton vertical migration.

Effect of light pollution on krill from a ship (left), diel vertical migration in natural dark conditions (middle) and effect of moonlight (right). Figure by Malin Daase (UiT).

Using a Autonomous Surface Vehicle the authors documented zooplankton behavioral patterns of light avoidance never previously seen. The study compared results from high Arctic polar night (unpolluted light environment for an extended time), to near ship samples. During months of near constant darkness in the Arctic, there was still a diel vertical migration of zooplankton limited to the upper 30 m of the water column and centered around the local sun noon. Contrasting the results from light-polluted and unpolluted areas, the authors observed that the vast majority of the pelagic community exhibit a strong light-escape response in the presence of artificial light (both ship light and even headlamps from researchers in open boats). This effect was observed down to 100 m depth and 190 m from the ship. These results suggest that artificial light from traditional sampling platforms may bias studies of zooplankton abundance and diel migration within the upper 100 m. These findings underscore the need for alternative sampling methods such as autonomous platforms, particularly in dim-light conditions, to collect more accurate and representative physical and biological data for ecological studies. In addition to research cruises and sampling, anthropogenic light pollution from predicted increases in shipping, oil and gas exploration, and light-fishing are anticipated to impact the diel rhythms of zooplankton behavior all around the globe.

Authors:
Jørgen Berge (Norwegian University of Technology and Science; UiT The Arctic University of Norway)
Martin Ludvigsen (Norwegian University of Technology and Science; University Centre in Svalbard)
Maxime Geoffroy (UiT The Arctic University of Norway, Memorial University of Newfoundland)
Jonathan H. Cohen (University of Delaware)
Pedro R. De La Torre (Norwegian University of Technology and Science)
Stein M. Nornes (Norwegian University of Technology and Science)
Hanumant Singh (Northeastern University)
Asgeir J. Sørensen (Norwegian University of Technology and Science)
Malin Daase (Norwegian University of Technology and Science)
Geir Johnsen (Norwegian University of Technology and Science; Norwegian University of Technology and Science)

Lasers shed light on giant larvacean filtration impact on the ocean’s biological pump

Posted by mmaheigan

· Thursday, January 4th, 2018

To accurately assess the impacts of climate change, we need to understand how atmospheric carbon is transported from surface waters to the deep sea. Grazers and filter feeders drive the ocean’s biological pump as they remove and sequester carbon at various rates. This pump extends down into the midwater realm, the largest habitat on earth. Giant larvaceans are fascinating and enigmatic occupants of the upper 400 m of the water column, where they build complex filtering structures out of mucus that can reach diameters greater than 1 m in longest dimension (Figure 1A). Because of the fragility of these structures, direct measurements of filtration rates require us to study them in situ. We developed DeepPIV, an ROV-deployable instrument (Figure 1B) to directly measure fluid motion and filtration rates in situ (Figure 1C).

Figure 1. (A) Traditional view of a giant larvacean illuminated by white ROV lights. (B) DeepPIV instrument is seen attached to Monterey Bay Aquarium Research Institute’s (MBARI) MiniROV. (C) DeepPIV-illuminated interior view of a giant larvacean house, where particle motion in ambient seawater serves as a proxy for fluid motion. White arrows in (A) and (C) indicate larvacean head/trunk; white arrow in (B) indicates DeepPIV.

The filtration rates we measured for giant larvaceans are far greater than for any other zooplankton filter feeder. When combined with abundance data from a 22-year time series, the grazing impact of giant larvaceans indicates that within 13 days, they can filter the total volume of water within their habitable depth range (~100-300 m; based on maximum abundance and measured filtration rates). Our results reveal that the contribution of giant larvaceans to vertical carbon flux is much greater than previously thought. Small larvaceans, which are present in the water column in even larger quantities than giant larvaceans, may also have a measurable impact on carbon fluxes. New technologies such as DeepPIV are yielding more quantitative observations of midwater filter feeders, which is improving our understanding of the roles that deep-water biota play in the long-term removal of carbon from the atmosphere.

Read the full journal article: http://advances.sciencemag.org/content/3/5/e1602374.full

Authors: (All at MBARI)
Kakani Katija
Rob E. Sherlock
Alana D. Sherman
Bruce H. Robison

Zooplankton play a key and diverse role in the ocean carbon cycle

Posted by mmaheigan

· Thursday, December 7th, 2017

How does the enormous diversity of zooplankton species, life cycles, size, feeding ecology, and physiology affect their role in ocean food webs and cycling of carbon?

In the 2017 issue of Annual Review of Marine Science, Steinberg and Landry review the fundamental and multifaceted roles that zooplankton play in the cycling and export of carbon in the ocean. Carbon flows through marine pelagic ecosystems are complex due to the diversity of zooplankton consumers and the many trophic levels they occupy in the food web–from single-celled herbivores to large carnivorous jellyfish. Zooplankton also contribute to carbon export processes through a variety of mechanisms (mucous feeding webs, fecal pellets, molts, carcasses, and vertical migrations).

Figure 1. Pathways of cycling and export of carbon by zooplankton in the ocean.

Climate change and other stressors are already affecting zooplankton abundance, distribution, and life cycles, and are predicted to result in widespread changes in zooplankton carbon cycling in the future. These changes will affect both the larger marine food web that depends upon zooplankton for food (fish) or recycled products for growth (primary producers) and the amount of carbon exported into the deep sea–where far from contact with the atmosphere it no longer contributes to global warming.

Authors:

Deborah K. Steinberg, Virginia Institute of Marine Science, The College of William and Mary
Michael R. Landry, Scripps Institution of Oceanography

Tiny marine animals strongly influence the carbon cycle

Posted by mmaheigan

· Thursday, August 31st, 2017

What controls the amount of organic carbon entering the deep ocean? In the sunlit layer of the ocean, phytoplankton transform inorganic carbon to organic carbon via a process called photosynthesis. As these particulate forms of organic carbon stick together, they become dense enough to sink out of the sunlit layer, transferring large quantities of organic carbon to the deep ocean and out of contact with the atmosphere.

However, all is not still in the dark ocean. Microbial organisms such as bacteria, and zooplankton consume the sinking, carbon-rich particles and convert the organic carbon back to its original inorganic form. Depending on how deep this occurs, the carbon can be physically mixed back up into the surface layers for exchange with the atmosphere or repeat consumption by phytoplankton. In a recent study published in Biogeosciences, researchers used field data and an ecosystem model in three very different oceanic regions to show that zooplankton are extremely important in determining how much carbon reaches the deep ocean.

Figure 1. Particle export and transfer efficiency to the deep ocean in the Southern Ocean (SO, blue circles), North Atlantic Porcupine Abyssal Plain site (PAP, red squares) and the Equatorial Tropical North Pacific (ETNP, orange triangles) oxygen minimum zone. a) particle export efficiency of fast sinking particles (Fast PEeff) against primary production on a Log10 scale. b) transfer efficiency of particles to the deep ocean expressed as Martin’s b (high b = low efficiency). Error bars in b) are standard error of the mean for observed particles, error too small in model to be seen on this plot.

In the Southern Ocean (SO), zooplankton graze on phytoplankton and produce rapidly sinking fecal pellets, resulting in an inverse relationship between particle export and primary production (Fig. 1a). In the North Atlantic (NA), the efficiency with which particles are transferred to the deep ocean is comparable to that of the Southern Ocean, suggesting similar processes apply; but in both regions, there is a large discrepancy between the field data and the ecosystem model (Fig. 1b), which poorly represents particle processing by zooplankton. Conversely, much better data-model matches are observed in the equatorial Pacific, where lower oxygen concentrations mean fewer zooplankton; this reduces the potential for zooplankton-particle interactions that reduce particle size and density, resulting in a lower transfer efficiency.

This result suggests that mismatches between the data and model in the SO and NA may be due to the lack of zooplankton-particle parameterizations in the model, highlighting the potential importance of zooplankton in regulating carbon export and storage in the deep ocean. Zooplankton parameterizations in ecosystem models must be enhanced by including zooplankton fragmentation of particles as well as consumption. Large field programs such as EXPORTS could help constrain these parameterisation by collecting data on zooplankton-particle interaction rates. This will improve our model estimates of carbon export and our ability to predict future changes in the biological carbon pump. This is especially important in the face of climate-driven changes in zooplankton populations (e.g. oxygen minimum zone (OMZ) expansion) and associated implications for ocean carbon storage and atmospheric carbon dioxide levels.

Authors:
Emma L. Cavan (University of Tasmania)
Stephanie A. Henson (National Oceanography Centre, Southampton)
Anna Belcher (University of Southampton)
Richard Sanders (National Oceanography Centre, Southampton)

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.

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