Zooplankton and the Ocean Carbon Cycle (original) (raw)
Related papers
Journal of Geophysical Research: Biogeosciences
Marine zooplankton forms an important component of the ocean ecosystem. It serves as a link between primary producers and higher trophic levels (Steinberg & Landry, 2017). Although zooplankton consists of a large variety of taxa from unicellular flagellates to multicellular organisms like copepods, it can be classified into five different size classes; nano (2-20 μm, e.g., flagellates), micro (20-200 μm, e.g., ciliates), meso (0.2-20 mm, e.g., copepods), macro (2-20 cm, e.g., krill) and mega (0.2-2 m, e.g., jellyfish; Sieburth et al., 1978). These different size classes of zooplankton have distinct functions in the ecosystem. For example, microzooplankton consume almost 60% of the daily primary production as major grazers of phytoplankton (Calbet, 2008; Landry & Calbet, 2004), while mesozooplankton and macrozooplankton produce fast sinking particulate matter as fecal pellets, which can contribute the highest share to carbon flux (Turner, 2002, 2015). These groups also prefer different prey. While meso-and macrozooplankton prefer larger prey items such as diatoms and smaller zooplankton, microzooplankton prefer smaller organisms such as smaller phytoplankton (
2007
The objective of the present study was to study the dynamics of protozoan and metazoan zooplankton food webs in coastal NE Atlantic waters exposed to variable nutrient input. Data were derived from a mesocosm experiment (7 units, 40 m 3 , 12 m deep) receiving variable nutrient input. The food web included 3 autotrophic groups based on size, and 4 functional heterotrophic groups mainly based on trophic position. Inverse modelling was used to construct networks of carbon flows for the planktonic food web. Heterotrophic nanoplankton, microplankton and mesoplankton (HNP, CIL and COP, respectively) were found to be equally important contributors to grazing and carbon release during undisturbed summer situations. The release of dissolved organic carbon by zooplankton was comparable to that of phytoplankton. Autotrophic food was generally more important for zooplankton than heterotrophic (mean 75%). Assimilation and growth efficiencies (AE and GE, respectively) of zooplankton groups in undisturbed situations were in the range of 33 to 69% and 10 to 41%, respectively. Values were inversely related to gross primary production (GPP). Sedimentation rates of carbon were low. High nutrient input rates increased food availability and most CIL and COP carbon flows. HNP did not respond, and neither did its food, that is, bacteria and picoautotrophs. The response in biomass was generally lower than that for the flows. Values of AE and GE of the zooplankton during high nutrient input and food availability varied between 11 and 29% and 5.7 and 19%, respectively, and throughout were lower than at low nutrient input. The sedimentation rate of particulate carbon increased strongly, resulting in an enhanced organic input rate in deep water.
2018
A thesis submitted to the School of Environmental Sciences of the University of East Anglia in partial fulfilment of the requirements for the degree of Doctor of Philosophy July 2018 This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that use of any information derived therefrom must be in accordance with current UK Copyright Law. In addition, any quotation or extract must include full attribution.
Mucospheres produced by a mixotrophic protist impact ocean carbon cycling
Nature Communications, 2022
Mixotrophic protists (unicellular eukaryotes) that engage in both phototrophy (photosynthesis) and phago-heterotrophy (engulfment of particles)—are predicted to contribute substantially to energy fluxes and marine biogeochemical cycles. However, their impact remains largely unquantified. Here we describe the sophisticated foraging strategy of a widespread mixotrophic dinoflagellate, involving the production of carbon-rich ‘mucospheres’ that attract, capture, and immobilise microbial prey facilitating their consumption. We provide a detailed characterisation of this previously undescribed behaviour and reveal that it represents an overlooked, yet quantitatively significant mechanism for oceanic carbon fluxes. Following feeding, the mucospheres laden with surplus prey are discarded and sink, contributing an estimated 0.17–1.24 mg m−2 d−1 of particulate organic carbon, or 0.02–0.15 Gt to the biological pump annually, which represents 0.1–0.7% of the estimated total export from the euph...
Limnology and Oceanography, 2017
Anthropogenic atmospheric loading of CO 2 raises concerns about combined effects of increasing ocean temperature and acidification, on biological processes. In particular, the response of appendicularian zooplankton to climate change may have significant ecosystem implications as they can alter biogeochemical cycling compared to classical copepod dominated food webs. However, the response of appendicularians to multiple climate drivers and effect on carbon cycling are still not well understood. Here, we investigated how gelatinous zooplankton (appendicularians) affect carbon cycling of marine food webs under conditions predicted by future climate scenarios. Appendicularians performed well in warmer conditions and benefited from low pH levels, which in turn altered the direction of carbon flow. Increased appendicularians removed particles from the water column that might otherwise nourish copepods by increasing carbon transport to depth from continuous discarding of filtration houses and fecal pellets. This helps to remove CO 2 from the atmosphere, and may also have fisheries implications.
Small copepods (<2 mm) are the most abundant metazoans in the world’s oceans, a keystone in pelagic food webs. Small copepods are considered to be omnivorous, feeding on unicellular protists and phytoplankton, with carnivorous feeding –i.e. preying on zooplankton- restricted to larger copepods and cyclopoid copepods. We developed a PCR based technique that detected a diverse range of zooplankton species (eight families of decapods, bivalves, fish, and also other copepods) within the digestive tract of copepods traditionally considered to be “herbivorous”. This finding provides evidences that a significant component of copepod diets has been overlooked owed to the methodologies traditionally been carried out –visual inspection and pigments analysis. Such predatory behaviour extends the trophic role of small copepods in upwelling food webs, affecting the mesozooplankton communities through intraguild predation. Furthermore, this study helps to explain the discrepancies found between quantified phyto/microzooplankton ingestion and metabolic demands of copepods. In order to infer the consequences of this overlooked predatory behaviour to the flux of Carbon in the whole pelagic ecosystem, we screened the literature to obtain an estimate of weight specific ingestion rates (WSIR) based on their averaged weight for adult calanoid (n=121) and cyclopoid copepods (n=41), in the field (n=125) and under laboratory conditions (n=37). By multiplying the estimated WSIR by the standing stock of adult copepods in the upper 100 m of the ocean -assuming that i) copepods are approximately 80% of the total zooplankton biomass ii) only 50% are adults and iii) calanoids comprise between 30 to 40% of total copepods (the rest being cyclopoid copepods) - our carbon budget estimates show that on a global scale, copepods process, between 3.41 - 3.70 up to 20.75 - 21.87 gigaton (Gt) C yr-1 through zooplankton predation based on field and laboratory measured WSIR, respectively. This conservative field estimate reveals that copepods are channeling 31.28 - 33.95% more carbon towards upper trophic levels than previous estimates focused on phytoplankton and microzooplankton consumption (10.9 Gt C yr-1). Hence, copepod intrigued predation should definitely be considered in oceanic biogeochemical cycles and ecosystem models.
Deep Sea Research Part II: Topical Studies in Oceanography, 2002
Ingestion by mesozooplankton and micronekton was monitored during two of the ANTARES cruises in the Indian sector of the Southern Ocean in spring and summer. The composition of the mesozooplankton populations varied in space and with season. Copepods always dominated in number and biomass, but salps and pteropods were present in the northern part of the transect in summer. Five species of large copepod (Calanus simillimus, Calanoides acutus, Rhincalanus gigas, Calanus propinquus and Metridia gerlachei) dominated the biomass with a North-South gradient. Smaller species (Oithona spp., Ctenocalanus citer, Clausocalanus laticeps) were also present. Biomass showed a definite trend with highest levels towards the polar front zone and permanent open-ocean area. Feeding activity was monitored either for the total population (summer) or specific individuals (spring). In summer, depending on the area considered, grazing rates by mesozooplankton appeared to have a significant impact on phytoplankton primary production. In the northern part of the transect (polar front zone or PFZ), salps and to a minor extent pteropods and copepods contributed mostly to the feeding pressure. Maximum intensity was observed in the Coastal Antarctic Zone (CCSZ) where Euphausia superba (adults and calyptopis larvae) could ingest more than 100% of the daily primary production. In spring, the impact of copepods dominated the zooplankton community. Small calanoids and young stages of large species of copepods rather than adult stages were the dominant contributors to grazing pressure. In summer, respiration rates of the dominant copepod species showed that energy expenditure exceeded by far chlorophyll ingestion. This is generally interpreted as the consequence of ingestion of alternate non-chlorophyll food source. The inverse correlation between the biomass of microzooplankton and the area of maximum difference between grazing and respiration confirmed that in summer the protozoans are strongly controlled by the copepod community.
Progress in Oceanography, 2014
Exploring climate and anthropogenic impacts on marine ecosystems requires an understanding of how trophic components interact. However, integrative end-to-end ecosystem studies (experimental and/or modelling) are rare. Experimental investigations often concentrate on a particular group or individual species within a trophic level, while tropho-dynamic field studies typically employ either a bottom-up approach concentrating on the phytoplankton community or a top-down approach concentrating on the fish community. Likewise the emphasis within modelling studies is usually placed upon phytoplankton-dominated biogeochemistry or on aspects of fisheries regulation. In consequence the roles of zooplankton communities (protists and metazoans) linking phytoplankton and fish communities are typically under-represented if not (especially in fisheries models) ignored. Where represented in ecosystem models, zooplankton are usually incorporated in an extremely simplistic fashion, using empirical descriptions merging various interacting physiological functions governing zooplankton growth and development, and thence ignoring physiological feedback mechanisms. Here we demonstrate, within a modelled plankton food-web system, how trophic dynamics are sensitive to small changes in parameter values describing zooplankton vital rates and thus the importance of using appropriate zooplankton descriptors. Through a comprehensive review, we reveal the mismatch between empirical understanding and modelling activities identifying important issues that warrant further experimental and modelling investigation. These include: food selectivity, kinetics of prey consumption and interactions with assimilation and growth, form of voided material, mortality rates at different age-stages relative to prior nutrient history. In particular there is a need for dynamic data series in which predator and prey of known nutrient history are studied interacting under varied pH and temperature regimes.
Modeling the Impact of Macrozooplankton on Carbon Export Production in the Southern Ocean
Journal of Geophysical Research: Oceans, 2021
The biological carbon pump plays an essential role in the cycling of carbon in the oceans (Honjo, 2004; Volk & Hoffert, 1985). It is driven by a large variety of organisms that are part of a complex ecosystem. The export of organic carbon from the surface to deeper layers proceeds via several pathways including the formation of aggregates and fecal pellets that sink gravitationally, and the downwelling of dissolved compounds (Boyd et al., 2019; Steinberg & Landry, 2017). Marine carbon cycle models are used to assess carbon fluxes in the ocean ecosystems to gain a deeper understanding of the carbon cycle. However, the complexity of marine ecosystems and the processes relevant for carbon export cannot be fully reflected in these models (Laufkötter et al., 2016). For example, zooplankton is still represented by a single variable in many global ocean biogeochemical models (Séférian et al., 2020), despite the large diversity and traits of zooplankton. A handful of models represent three plankton functional types (PFTs) of zooplankton (Le Quéré et al., 2016; Stock et al., 2020). One of the zooplankton PFTs is macrozooplankton, defined as the size class of 2-20 cm, which reaches high biomass and shows a patchy distribution (Moriarty et al., 2013). Groups being classified as macrozooplankton
Large deep-sea zooplankton biomass mirrors primary production in the global ocean
Nature Communications, 2020
The biological pump transports organic carbon produced by photosynthesis to the meso- and bathypelagic zones, the latter removing carbon from exchanging with the atmosphere over centennial time scales. Organisms living in both zones are supported by a passive flux of particles, and carbon transported to the deep-sea through vertical zooplankton migrations. Here we report globally-coherent positive relationships between zooplankton biomass in the epi-, meso-, and bathypelagic layers and average net primary production (NPP). We do so based on a global assessment of available deep-sea zooplankton biomass data and large-scale estimates of average NPP. The relationships obtained imply that increased NPP leads to enhanced transference of organic carbon to the deep ocean. Estimated remineralization from respiration rates by deep-sea zooplankton requires a minimum supply of 0.44 Pg C y−1 transported into the bathypelagic ocean, comparable to the passive carbon sequestration. We suggest that...