Fecal Pellet Production Research Articles

The Role of Zooplankton Community Composition in Fecal Pellet Carbon Production in the York River Estuary, Chesapeake Bay

Zooplankton play a key role in the cycling of carbon in aquatic ecosystems, yet their production of carbon-rich fecal pellets, which sink to depth and can fuel benthic community metabolism, is rarely quantified in estuaries. We measured fecal pellet carbon (FPC) production by the whole near-surface mesozooplankton community in the York River sub-estuary of Chesapeake Bay. Zooplankton biomass and taxonomic composition were measured with monthly paired day/night net tows. Live animal experiments were used to quantify FPC production rates of the whole community and dominant individual taxa. Zooplankton biomass increased in surface waters at night (2- to 29-fold) due to diel vertical migration, especially by Acartia spp. copepods. Biomass and diversity were seasonally low in the winter and high in the summer and often dominated by Acartia copepods. Whole community FPC production rates were higher (3- to 65-fold) at night than during the day, with the 0.5–1 mm size class contributing 2–26% to FPC production in the day versus 40–70% at night. An increase in the relative contribution of larger size fractions to total FPC production occurred at night due to diel vertical migration of larger animals into surface waters. Community FPC production was highest in fall due to increased diversity and abundance of larger animals producing larger fecal pellets, and lowest in summer likely due to top-down control of abundant crustacean taxa by gelatinous predators. This study indicates that zooplankton FPC production in estuaries can surpass that in oceanic systems and suggests that fecal pellet export is important in benthic-pelagic coupling in estuaries.

Sublethal effects of microplastic and oil co-exposure on biological rates and lipid profiles of keystone Arctic copepods

Microplastics (MPs) and petroleum hydrocarbons are contaminants of emerging concern in the Arctic, but little is known about their co-exposure effects. In this study, we present the first assessment of the sublethal impacts resulting from combined exposure to microplastics and oil in three key Arctic copepod species. Specifically, we investigated the effects of a 5-day exposure to oil alone (1 μL L−1) and in combination with MPs (polyethylene microspheres, 20 μm, 20 MP mL−1) and dispersant (Corexit 9500, 0.05 μL L−1) on the biological functions and lipid profiles of the planktonic copepods Metridia longa, Calanus finmarchicus, and Calanus glacialis. Exposure to oil alone caused a significant reduction (34–58%) in fecal pellet production, but neither microplastics nor dispersant increased the negative effect of oil on fecal pellet production. C. glacialis and C. finmarchicus exposed to the studied pollutants for 5 days produced eggs with delayed hatching and lower hatching success. The highest hatching inhibition (50%) was observed in eggs of C. glacialis exposed to oil plus MPs and dispersant for five days. This indicates that maternal transfer of oil components to eggs negatively affects embryonic development and hatching. Lipid content and fatty acids profiles varied among the studied copepod species but were not affected by the tested pollutants after five days of exposure. By microscopical observation of fecal pellets, ingestion of small oil droplets and MPs was confirmed in all species, but the estimated ingestion of MPs was low (<25 MPs cop−1 d−1, <0.2% of total offered MPs) suggesting avoidance of MP consumption in copepods. Our results indicate that virgin MPs did not increase the toxicity of oil to the studied Arctic copepods under co-exposure conditions, and dispersants can slightly increase certain adverse effects of oil (hatching). However, environmentally relevant concentrations of oil alone can negatively impact Arctic keystone copepods and potentially the biological carbon pump. These findings emphasize the need to reduce petrogenic pollution and the risk of oil spills in the sensitive Arctic ecosystem.

Temporal and vertical variations in carbon flux and export of zooplankton fecal pellets in the western South China Sea

The enhancement of particulate organic carbon transfer to the deep sea by zooplankton fecal pellets constitutes a crucial component of the marine biological carbon pump. Here, we investigated time-series variations in characteristic and flux of zooplankton fecal pellets at different water depths of two sediment-trap mooring stations from May 2021 to May 2022 in the western South China Sea. The results show that numerical fluxes of fecal pellets were 0.75 ± 0.60 × 104, 0.63 ± 0.63 × 104, and 0.38 ± 0.29 × 104 pellets m−2 d−1 at 500 m, 1170 m, and 1380 m water depth, respectively, corresponding to their carbon fluxes of 0.10 ± 0.06, 0.09 ± 0.04, and 0.10 ± 0.04 mg C m−2 d−1. Both numerical and carbon fluxes of fecal pellets exhibited clear seasonal variations, with two peaks occurred in August and early November at all water depths. The fecal pellets have distinct morphological types (spherical, cylindrical, and ellipsoidal) and their contributions to the numerical and carbon fluxes were different. At all water depths, ellipsoidal and spherical pellets accounted for 96.0% of the numerical flux and 72.1% of the carbon flux. Cylindrical pellets were rare in quantity, accounting for 4.0% of numerical flux, but their carbon contribution accounted for 27.9% of the total fecal pellet carbon flux. The proportional fractions of zooplankton fecal pellets contributed to the overall particulate organic carbon from 0.7% to 28.2% in the western South China Sea, and fell in a reasonable range around the world. Multiple mechanisms, including East Asian monsoon climate and zooplankton community structure may be responsible for the production and fate of fecal pellets as well as their contribution to the settling particulate organic carbon.

Sex-specific epigenetics drive low GPER expression in gastrointestinal smooth muscles in type 2 diabetic mice

Type 2 diabetes mellitus (T2D) causes gastroparesis, delayed intestinal transit, and constipation, for unknown reasons. Complications are predominant in women than men (particularly pregnant and postmenopausal women), suggesting a female hormone-mediated mechanism. Low G-protein coupled estrogen receptor (GPER) expression from epigenetic modifications may explain it. We explored sexually differentiated GPER expression and gastrointestinal symptoms related to GPER alterations in wild-type (WT) and T2D mice (db/db). We also created smooth muscle-specific GPER knockout (GPER KO) mice to phenotypically explore the effect of GPER deficiency on gastrointestinal motility. GPER mRNA and protein expression, DNA methylation and histone modifications were measured from stomach and colon samples of db/db and WT mice. Changes in gut motility were also evaluated as daily fecal pellet production patterns. We found that WT female tissues have the highest GPER mRNA and protein expressions. The expression is lowest in all db/db. GPER downregulation is associated with promoter hypermethylation and reduced enrichment of H3K4me3 and H3K27ac marks around the GPER promoter. We also observed sex-specific disparities in fecal pellet production patterns of the GPER KO mice compared to WT. We thus, conclude that T2D impairs gut GPER expression, and epigenetic sex-specific mechanisms matter in the downregulation.

Cumulative Impacts of Oil Pollution, Ocean Warming, and Coastal Freshening on the Feeding of Arctic Copepods.

The Arctic is undergoing rapid changes, and biota are exposed to multiple stressors, including pollution and climate change. Still, little is known about their joint impact. Here, we investigated the cumulative impact of crude oil, warming, and freshening on the copepod species Calanus glacialis and Calanus finmarchicus. Adult females were exposed to ambient conditions (control; 0 °C + 33 psu) and combined warming and freshening: 5 °C + 27 psu (Scenario 1), 5 °C + 20 psu (Scenario 2) for 6 days. All three conditions were tested with and without dispersed crude oil. In Scenario 1, fecal pellet production (FPP) significantly increased by 40-78% and 42-122% for C. glacialis and C. finmarchicus, respectively. In Scenario 2, FPP decreased by 6-57% for C. glacialis, while it fluctuated for C. finmarchicus. For both species, oil had the strongest effect on FPP, leading to a 68-83% reduction. This overshadowed the differences between climatic scenarios. All variables (temperature, salinity, and oil) had significant single effects and several joint effects on FPP. Our results demonstrate that Arctic copepods are sensitive to environmentally realistic concentrations of crude oil and climate change. Strong reductions in feeding can reduce the copepods' energy content with potential large-scale impacts on the Arctic marine food web.

A biogeochemical model of mineral-based ocean alkalinity enhancement: impacts on the biological pump and ocean carbon uptake

Minimizing anthropogenic climate disruption in the coming century will likely require carbon dioxide removal (CDR) from Earth’s atmosphere in addition to deep and rapid cuts to greenhouse gas emissions. Ocean alkalinity enhancement—the modification of surface ocean chemistry to drive marine uptake of atmospheric CO2—is seen as a potentially significant component of ocean-based CDR portfolios. However, there has been limited mechanistic exploration of the large-scale CDR potential of mineral-based ocean alkalinity enhancement, potential bottlenecks in alkalinity release, and the biophysical impacts of alkaline mineral feedstocks on marine ecology and the marine biological carbon pump. Here we a series of biogeochemical models to evaluate the gross CDR potential and environmental impacts of ocean alkalinity enhancement using solid mineral feedstocks. We find that natural alkalinity sources—basalt and olivine—lead to very low CDR efficiency while strongly perturbing marine food quality and fecal pellet production by marine zooplankton. Artificial alkalinity sources—the synthetic metal oxides MgO and CaO—are potentially capable of significant CDR with reduced environmental impact, but their deployment at scale faces major challenges associated with substrate limitation and process CO2 emissions during feedstock production. Taken together, our results highlight distinct challenges for ocean alkalinity enhancement as a CDR strategy and indicate that mineral-based ocean alkalinity enhancement should be pursued with caution.

Twenty‐year trends of Centropages typicus (Copepoda, Calanoida) reproduction, feeding, population abundance and structure in the Gulf of Naples (Western Mediterranean Sea)

AbstractCentropages typicus is a temperate calanoid copepod occurring in Atlantic and Mediterranean coastal waters, where its reproductive biology and population dynamics are well‐known. C. typicus has also been suggested as a key species for monitoring the impact of environmental changes on copepod secondary production. The aim of this study is to investigate the seasonal and interannual reproductive (egg production and egg hatching success) and feeding (fecal pellet production) traits, population abundance and structure (sex ratio) of C. typicus over a 20‐year period at the Long‐Term Ecological Research site MareChiara (LTER‐MC) in the Gulf of Naples (Central Tyrrhenian Sea, Western Mediterranean Sea), identifying specific trends and patterns. At a seasonal scale, egg production and hatching success were tightly linked with maxima in February–March, driving the juvenile and adult springtime population peaks but showing a poor correlation with phytoplankton abundance, pointing to an omnivorous diet. At a multiannual scale, an observed decrease in the population is backed up by a reduction in egg production, despite an increase in hatching success. The results of this study provide new elements to comprehend the links between C. typicus functional traits, population dynamics, and environmental factors and highlight the importance of running LTER series to monitor the trends in natural environments.

High trophic level feedbacks on global ocean carbon uptake and marine ecosystem dynamics under climate change.

Despite recurrent emphasis on their ecological and economic roles, the importance of high trophic levels (HTLs) on ocean carbon dynamics, through passive (fecal pellet production, carcasses) and active (vertical migration) processes, is still largely unexplored, notably under climate change scenarios. In addition, HTLs impact the ecosystem dynamics through top-down effects on lower trophic levels, which might change under anthropogenic influence. Here we compare two simulations of a global biogeochemical-ecosystem model with and without feedbacks from large marine animals. We show that these large marine animals affect the evolution of low trophic level biomasses, hence net primary production and most certainly ecosystem equilibrium, but seem to have little influence on the 21st-century anthropogenic carbon uptake under the RCP8.5 scenario. These results provide new insights regarding the expectations for trophic amplification of climate change through the marine trophic chain and regarding the necessity to explicitly represent marine animals in Earth System Models.

The Outsized Role of Salps in Carbon Export in the Subarctic Northeast Pacific Ocean.

Periodic blooms of salps (pelagic tunicates) can result in high export of organic matter, leading to an "outsized" role in the ocean's biological carbon pump (BCP). However, due to their episodic and patchy nature, salp blooms often go undetected and are rarely included in measurements or models of the BCP. We quantified salp-mediated export processes in the northeast subarctic Pacific Ocean in summer of 2018 during a bloom of Salpa aspera. Salps migrated from 300 to 750m during the day into the upper 100m at night. Salp fecal pellet production comprised up to 82% of the particulate organic carbon (POC) produced as fecal pellets by the entire epipelagic zooplankton community. Rapid sinking velocities of salp pellets (400-1,200md-1) and low microbial respiration rates on pellets (<1% of pellet C respired day-1) led to high salp pellet POC export from the euphotic zone-up to 48% of total sinking POC across the 100m depth horizon. Salp active transport of carbon by diel vertical migration and carbon export from sinking salp carcasses was usually <10% of the total sinking POC flux. Salp-mediated export markedly increased BCP efficiency, increasing by 1.5-fold the proportion of net primary production exported as POC across the base of the euphotic zone and by 2.6-fold the proportion of this POC flux persisting 100m below the euphotic zone. Salps have unique and important effects on ocean biogeochemistry and, especially in low flux settings, can dramatically increase BCP efficiency and thus carbon sequestration.

The role of biological processes in muddy sediments

Muddy sediments are inhabited by diverse communities of animals that burrow, construct and irrigate tubes, ingest and egest sediments, and produce hard structures such as shells and exoskeletons. These infaunal animals mix sediments through bioturbation and modify the physical properties of sediments. Bulk density can be increased through compaction along burrow walls and production of compact fecal pellets or decreased by excavation of burrows and mixing of compacted sediments. Burrows and other biogenic structures can increase heterogeneity and consequently sound attenuation. Characterization of infauna using functional groups based on how their activities and body types affect their sediment environments can simplify the diversity of these animals. Some species, such as those that build tubes from shell fragments, have a disproportionately large impact on acoustics. Both infaunal and microbial communities feed on and modify the organic matter in muds, which may affect grain-grain interactions. Understanding the effects of biological processes on acoustics is important in interpreting acoustic data both in the upper layer of sediments and in deeper layers in which paleo-biological activities are preserved as well as in using acoustics as a tool for studying infaunal communities and their activities.

Impact of a Dinophysis acuminata Bloom on the Copepod Acartia clausi: First Indications

Faecal pellet production and content along with egg production of the dominant copepod species Acartia clausi were studied in the Thermaikos Gulf (NW Aegean Sea) during a pre-bloom and a bloom of the toxic dinoflagellate Dinophysis acuminata. Both faecal pellet production (6.8–8.6 ind−1 d−1) and egg production (15.8–47.6 ind−1 d−1) appeared unrelated to the D. acuminata bloom. Less than 11% of the copepod faecal pellets contained one or two D. acuminata cells, almost intact, whereas the other material in the pellets was broken into small pieces or amorphous shapes. The toxin outflux seemed to be insignificant when compared to the mean toxin concentration from the whole D. acuminata population. Finally, the potential grazing impact of A. clausi on D. acuminata during the study period was low.

Heteromastus similis Southern, 1921 (Polychaeta: Capitellidae) in Mar Chiquita brackish coastal lagoon, Argentina

This paper analyzes the spatial and vertical distribution and describes biological and ecological features o f the capitellid polychaete. He leromas lus similis, in the southern part of Mar Chiquita coastal lagoon, Argentina. Sampling was carried out in three intertidal sand-muddy areas from April 1993 to April 1994. Sediment composition and organic matter content were analysed in two different depths. Feeding activity of this head-down deposit feeder occurs below aerobic sediment layers. Galleries are not ventilated, remaining as grey-black as the sourrounding sediments. Average densities vary markedly between upper and lower layers, and over time. Juveniles are frequently recorded in gregarious settlements. Feeding type, morphology of juveniles and habitat are similar to those of other capitellids. Size, faecal pellet production and food availability for H. similis are compared w-ith the northern H. jiliformis.

Fine-scale vertical distribution and diel migrations ofPyrosoma atlanticumin the northern California Current

AbstractBlooms of the colonial pelagic tunicate Pyrosoma atlanticum in 2014–2018 followed a marine heatwave in the eastern Pacific Ocean. Pyrosome blooms could alter pelagic food webs of the northern California Current (NCC) by accelerating the biological pump via active transport, fecal pellet production and mortality events. Although aggregations of P. atlanticum have the potential to shape marine trophic dynamics via carbon export, little is known about pyrosome vertical distribution patterns. In this study, we estimated the distribution of P. atlanticum in the NCC along transects off of Oregon (45°N and 124°W) and northern California (41°N and 124°W), USA during February and July 2018. Depth-stratified plankton tows provided volume-normalized pyrosome abundance and biovolume estimates that complemented fine-scale counts by a vertically deployed camera system. Pyrosomes were numerous offshore during February, especially off Oregon. Colonies were distributed non-uniformly in the water column with peak numbers associated with vertical gradients in environmental parameters, notably density and chl-a. Vertical distributions shifted over the 24-h period, indicative of diel vertical migration. Understanding the vertical distribution of these gelatinous grazers in the NCC gives insight to their behavior and ecological role in biologically productive temperate ecosystems as conditions become more favorable for recurring blooms.

Calanus finmarchicus basin scale life history traits and role in community carbon turnover during spring

Abstract The copepod Calanus finmarchicus was investigated in four Subpolar Basins, Labrador, Irminger, Iceland, and Norwegian Seas, during spring, covering the time of ascent, grazing, and initiation of reproduction in the area. Lipid content, spawning activity, and stage composition and vital rates, such as egg and faecal pellet production were measured and linked to environmental parameters. Specific egg- and faecal pellet production rates varied with diatom biomass and were negatively correlated with temperature. Comparison of the various biological indicators revealed different life history traits C. finmarchicus has adopted in the different basins. In Labrador Sea, the females have invested in large eggs compared to the remaining basins. Labrador and Irminger Sea C. finmarchicus invest in size that we propose to be adaptation to cope with warmer overwintering habitats resulting in larger potential lipid storage capacity, while the Iceland and Norwegian Sea females can invest their remaining lipid storage in spring to fuel lipid-driven egg production. Grazing pressure on the phytoplankton community was estimated and compared between copepod and two dominating groups of protozooplankton; ciliates and heterotrophic dinoflagellates. Despite approximately the same biomass in the upper 100 m, the grazing impact of the protozoan grazers was an order of magnitude higher than the C. finmarchicus dominated mesozooplankton. This illustrates the importance to also include the smallest grazers when studying the spring bloom in high latitude marine ecosystems if the fate of the primary production should be fully understood.

Leaf litter morphological traits, invertebrate body mass and phylogenetic affiliation explain the feeding and feces properties of saprophagous macroarthropods

Saprophagous macroarthropods are important actors in litter decomposition as they process large amounts of litter and transform it into fecal pellets that differ in chemical and physical properties compared to ingested litter. When having a choice among several litter types, saprophagous macroarthropods exhibit feeding preferences depending on their nutritional requirements and body size. However, how these preferences affect feces properties is not well known. We compared the feeding preferences, production of fecal pellets and their properties for six widespread saprophagous macroarthropods species feeding on a litter mix of four common tree species from Mediterranean forests. The six animal species showed different feeding preferences that were not correlated to litter nutritional quality. Instead, we suggest that the use as microhabitat of the leaves of one litter species with tubular shape by macroarthropods induced its higher consumption despite having the lowest nutritional value. Larger species consumed less litter per unit of body mass and had a more diverse diet composition. Furthermore, feces properties could not be linked to the diet composition, but always had higher nutritional value and water holding capacity compared to the leaf litter. The three woodlice species consistently produced feces with higher tannin concentration, higher specific area, and lower water holding capacity than that of the three millipede species. Our study calls for the consideration of other leaf litter properties than the generally studied physical and chemical ones, as well as quantifying the difference between millipede and woodlice feces properties that may have functional implication for nutrient cycling.

Effects of Microalgal Food Quantity on Several Productivity-Related Parameters of the Calanoid Copepod Bestiolina similis (Calanoida: Paracalanidae)

The optimization of copepod feeding protocol is paramount to improve culture productivity and to maintain favorable water quality parameters overtime, as well as saving operational costs by preventing the production of unnecessary quantities of microalgae. The influence of microalgal feeding concentration on major parameters related to culture productivity of the calanoid copepod Bestiolina similis (Paracalanidae) was investigated in a series of laboratory experiments. B. similis was fed eight different concentrations (0, 150, 300, 600, 900, 1,200, 1,500 and 1,800 μgC l–1) of a mixed microalgal diet consisting of Tahitian strain of Isochrysis species, Pavalova 50 and Tetraselmis chuii at 1:1:1 carbon ratio. The results indicate that female daily and cumulative egg production over lifespan, egg hatching rate, naupliar and copepodite survival and development, adult female life expectancy, population growth and fecal pellet production rate (FPPR) were all significantly affected by microalgae feeding ration. Conversely, no significant influence could be established between microalgae food concentration and egg diameter or adult sex ratio. Feeding rations as low as 150 μgC l–1 led to lower egg hatching rates, survival and development, adult female life expectancy and population growth compared with the higher microalgae rations tested. Feeding concentration ≤ 900 μgC l–1 significantly limited female daily egg and fecal pellet production rate, as well as their cumulative egg production over lifespan, when compared to a level of 900 μgC l–1. Bestiolina similis fed with 1,200 μgC l–1 significantly improved female egg and fecal pellet production when compared to the lower treatments and was responsible for the highest female lifespan egg production and population growth observed among all treatments. Feeding rations as high as 1,500 μgC l–1 and 1,800 μgC l–1 did not lead to significant improvement in any of the parameters measured. This is likely due to a saturation effect at high food concentration which is known to decrease calanoid copepods feeding efficiency. Finally, B. similis FPPR, used as a proxy for ingestion, was found to saturate at a microalgae concentration of 783.4 μgC l–1 using a non-linear Michael-Menton (2 parameters), indicating that CVI female ingestion did not increase significantly above this concentration. Based on the above results it is recommended that B. similis cultures should be fed at a concentration of 1,200 μgC l–1, and not above, as rations &amp;gt; 1,200 μgC l–1 will not significantly improve any of the productivity-related parameters observed in this study. Feeding rations should never be below 783.40 μgC l–1 as this is the threshold level below which adult female ingestion rates become limiting.

Krill and salp faecal pellets contribute equally to the carbon flux at the Antarctic Peninsula

Krill and salps are important for carbon flux in the Southern Ocean, but the extent of their contribution and the consequences of shifts in dominance from krill to salps remain unclear. We present a direct comparison of the contribution of krill and salp faecal pellets (FP) to vertical carbon flux at the Antarctic Peninsula using a combination of sediment traps, FP production, carbon content, microbial degradation, and krill and salp abundances. Salps produce 4-fold more FP carbon than krill, but the FP from both species contribute equally to the carbon flux at 300 m, accounting for 75% of total carbon. Krill FP are exported to 72% to 300 m, while 80% of salp FP are retained in the mixed layer due to fragmentation. Thus, declining krill abundances could lead to decreased carbon flux, indicating that the Antarctic Peninsula could become a less efficient carbon sink for anthropogenic CO2 in future.

Diel metabolic patterns in a migratory oceanic copepod

Diel vertical migration of zooplankton profoundly impacts the transport of nutrients and carbon through the water column. Despite the acknowledged importance of this active flux to ocean biogeochemistry, these contributions remain poorly constrained, in part because daily variations in metabolic rates are not considered or are modeled as simple functions of temperature. To address this uncertainty, we sampled the subtropical copepod Pleuromamma xiphias at 4- to 7-h intervals throughout the daily migration and measured rates of oxygen consumption, ammonium excretion, fecal pellet production and metabolic enzyme activity. No significant patterns were detected in rates of oxygen consumption or ammonium excretion for freshly caught animals over the diel cycle. Fecal pellet production was highest during mid-night, consistent with several hours of feeding near the surface. Surface feeding resulted in fecal pellet production at depth in the morning, providing direct evidence that active flux of particulate organic carbon occurs in this region. Electron transport system activity was highest during the afternoon, contrary to our prediction of reduced daytime metabolism. Activity of both glutamate dehydrogenase and citrate synthase increased during early night, reflecting higher capacity for excretion and aerobic respiration, respectively. Overall, these results show that activities of metabolic enzymes vary during diel vertical migration. The surprising observation of elevated afternoon enzyme activity coupled with daytime fecal pellet and ammonium production suggests that additional characterization of the daytime activity of migratory zooplankton is warranted.

Should we account for mesozooplankton reproduction and ontogenetic growth in biogeochemical modeling?

Mesozooplankton play a key role in marine ecosystems as they modulate the transfer of energy from phytoplankton to large marine organisms. In addition, they directly influence the oceanic cycles of carbon and nutrients through vertical migrations, fecal pellet production, respiration, and excretion. Mesozooplankton are mainly made up of metazoans, which undergo important size changes during their life cycle, resulting in significant variations in metabolic rates. However, most marine biogeochemical models represent mesozooplankton as protists-like organisms. Here, we study the potential caveats of this simplistic representation by using a chemostat-like zero-dimensional model with four different Nutrient-Phytoplankton-Zooplankton configurations in which the description of mesozooplankton ranges from protist-type organisms to using a size-based formulation including explicit reproduction and ontogenetic growth. We show that the size-based formulation strongly impacts mesozooplankton. First, it generates a delay of a few months in the response to an increase in food availability. Second, the increase in mesozooplankton biomass displays much larger temporal variations, in the form of successive cohorts, because of the dependency of the ingestion rate to body size. However, the size-based formulation does not affect smaller plankton or nutrient concentrations. A proper assessment of these top-down effects would require implementing our size-resolved approach in a 3-dimensional biogeochemical model. Furthermore, the bottom-up effects on higher trophic levels resulting from the significant changes in the temporal dynamics of mesozooplankton could be estimated in an end-to-end model coupling low and high trophic levels.

Fecal pellet production by mesozooplankton in the subarctic Northeast Pacific Ocean

AbstractMesozooplankton fecal pellets sinking from the sea‐surface constitute an important component of the biological carbon pump, which is variable in part due to differences in zooplankton community composition on various scales. Particulate organic carbon production as fecal pellets by the entire mesozooplankton community has, until now, not been directly measured. We measured fecal pellet carbon (FPC) production rates of the mesozooplankton community separated into five size classes (0.2 to &gt; 5.0 mm), and rates of key taxa, in the upper 100 m of the subarctic Northeast Pacific Ocean, August–September, 2018. We scaled up FPC production rates to total FPC production in the epipelagic zone, which was 2.8‐fold higher at night than day due to diel vertical migration. Despite its lower total biomass, the smallest size class (0.2–0.5 mm) contributed more FPC than other size classes (up to 81.6%), due to high weight‐specific FPC production rates (3.0 μgFPC mgDW−1 h−1). The pelagic tunicate Salpa aspera had the highest individual FPC production rate (7.5 μgFPC ind−1 h−1) and when present, contributed most to community FPC production (up to 82.3%). While the large copepod Neocalanus cristatus dominated the 2.0–5.0 mm fraction (up to ~ 100% by biomass), its FPC production rate was low (0.4 μgFPC mgDW−1 h−1), likely due to minimal feeding and gut shrinkage preceding diapause. Comparison of FPC production with export recorded in sediment traps suggests high attenuation of smaller pellet classes in the epipelagic (86%). Our results provide direct measurements of mesozooplankton FPC production in a “low‐production, low‐export” region.