Production Of Particulate Organic Matter Research Articles

Ability of grazing fish to generate particulate organic matter derived from autochthonous primary production

AbstractGrazing fish play a role of controlling autochthonous primary production and converting it to secondary production by consuming benthic algae. Moreover, they will also provide autochthonous particulate organic matter (POM) for freshwater ecosystems by dislodging the benthic algal matrix while feeding. However, it has not been confirmed whether grazing fish induce POM production during their feeding on benthic algae. To verify this POM production during grazing by fish, short‐term (90 min) feeding experiments were conducted by introducing grazing fishPlecoglossus altivelisinto indoor aquaria with benthic algal mats. We found that the fish can generate POM by feeding on benthic algae. Although POM was generated in the aquaria where the fish had not grazed on the benthic algal mats at all, the concentration of POM in the aquaria increased with the frequency of the acts of scraping benthic algae by the fish. Furthermore, we observed that the fish egested faeces which corresponded to about 44% on average of the ingested benthic organic matter. In some cases, the fish generated POM that corresponded to 88% of the removed (dislodged and ingested) benthic organic matter through their feeding and defecation. This study suggested that grazing fish have a function of providing autochthonous POM to freshwater ecosystems both via dislodging benthic algae during feeding and through egestion of consumed benthic algae.

Bacterial reworking of particulate organic matter in a dynamic marginal sea: Implications for carbon sequestration

Concentrations of particulate organic carbon (POC) and total hydrolyzable amino sugars (THAS) were measured along a transect of the dynamic South Yellow Sea (SYS) to investigate the bioreactivity and bacterial reworking of particulate organic matter (POM). Results showed that POM bioavailability was linked with primary production, as revealed by the significant correlation between chlorophyll-a concentrations and the diagenetic indicator glucosamine/galactosamine (GlcN/GalN). Production of bioavailable POM could rapidly stimulate microbial activity, generating hot spots of heterotrophic alteration. Lower GlcN/GalN ratios (<3) observed in the entire SYS indicate that POM underwent extensive microbial alteration. In particular, extremely low GlcN/GalN ratios (∼0.7) were found in the Yellow Sea Cold Water Mass, reflecting high bacterial alteration of POM. Estimates based on the bacterial biomarker muramic acid showed that on average ∼13% of POM in the SYS was of bacterial origin. Elevated bacterial contributions were found in both nearshore and offshore areas. Strong mixing in the nearshore and the presence of cyclonic eddies in offshore waters may increase the residence time of POM in the water column and thus promote bacterial transformation of POM. Overall, our findings indicate that bacterial reworking of POM varies with productivity and that the extensive bacterial transformation of the remaining POM observed in the water column probably enhances long-term carbon sequestration.

Calibration of temperature-dependent ocean microbial processes in the cGENIE.muffin (v0.9.13) Earth system model

Abstract. Temperature is a master parameter in the marine carbon cycle, exerting a critical control on the rate of biological transformation of a variety of solid and dissolved reactants and substrates. Although in the construction of numerical models of marine carbon cycling, temperature has been long recognised as a key parameter in the production and export of organic matter at the ocean surface, its role in the ocean interior is much less frequently accounted for. There, bacteria (primarily) transform sinking particulate organic matter (POM) into its dissolved constituents and consume dissolved oxygen (and/or other electron acceptors such as sulfate). The nutrients and carbon thereby released then become available for transport back to the surface, influencing biological productivity and atmospheric pCO2, respectively. Given the substantial changes in ocean temperature occurring in the past, as well as in light of current anthropogenic warming, appropriately accounting for the role of temperature in marine carbon cycling may be critical to correctly projecting changes in ocean deoxygenation and the strength of feedbacks on atmospheric pCO2. Here we extend and calibrate a temperature-dependent representation of marine carbon cycling in the cGENIE.muffin Earth system model, intended for both past and future climate applications. In this, we combine a temperature-dependent remineralisation scheme for sinking organic matter with a biological export production scheme that also includes a dependence on ambient seawater temperature. Via a parameter ensemble, we jointly calibrate the two parameterisations by statistically contrasting model-projected fields of nutrients, oxygen, and the stable carbon isotopic signature (δ13C) of dissolved inorganic carbon in the ocean with modern observations. We additionally explore the role of temperature in the creation and recycling of dissolved organic matter (DOM) and hence its impact on global carbon cycle dynamics. We find that for the present day, the temperature-dependent version shows a fit to the data that is as good as or better than the existing tuned non-temperature-dependent version of the cGENIE.muffin. The main impact of accounting for temperature-dependent remineralisation of POM is in driving higher rates of remineralisation in warmer waters, in turn driving a more rapid return of nutrients to the surface and thereby stimulating organic matter production. As a result, more POM is exported below 80 m but on average reaches shallower depths in middle- and low-latitude warmer waters compared to the standard model. Conversely, at higher latitudes, colder water temperature reduces the rate of nutrient resupply to the surface and POM reaches greater depth on average as a result of slower subsurface rates of remineralisation. Further adding temperature-dependent DOM processes changes this overall picture only a little, with a slight weakening of export production at higher latitudes. As an illustrative application of the new model configuration and calibration, we take the example of historical warming and briefly assess the implications for global carbon cycling of accounting for a more complete set of temperature-dependent processes in the ocean. We find that between the pre-industrial era (ca. 1700) and the present (year 2010), in response to a simulated air temperature increase of 0.9 ∘C and an associated projected mean ocean warming of 0.12 ∘C (0.6 ∘C in surface waters and 0.02 ∘C in deep waters), a reduction in particulate organic carbon (POC) export at 80 m of just 0.3 % occurs (or 0.7 % including a temperature-dependent DOM response). However, due to this increased recycling nearer the surface, the efficiency of the transfer of carbon away from the surface (at 80 m) to the deep ocean (at 1040 m) is reduced by 5 %. In contrast, with no assumed temperature-dependent processes impacting production or remineralisation of either POM or DOM, global POC export at 80 m falls by 2.9 % between the pre-industrial era and the present day as a consequence of ocean stratification and reduced nutrient resupply to the surface. Our analysis suggests that increased temperature-dependent nutrient recycling in the upper ocean has offset much of the stratification-induced restriction in its physical transport.

Nitrogen isotopic fractionation of particulate organic matter production and remineralization in the Prydz Bay and its adjacent areas

During the 29th Chinese National Antarctic Research Expedition, spatial variations in nitrogen isotopic composition of particulate nitrogen (δ15NPN) and their controlling factors were examined in detail with regard to nitrate drawdown by phytoplankton and particulate nitrogen (PN) remineralization in the Prydz Bay and its adjacent areas. To better constrain the nitrogen transformations, the physical and chemical parameters, including temperature, salinity, nutrients, PN and δ15NPN in seawater column were measured from surface to bottom. In addition, the nitrogen isotopic fractionation factor of nitrate assimilation by phytoplankton in the mixed layer, and the nitrogen isotopic fractionation factor of PN remineralization below the mixed layer were estimated using Rayleigh model and Steady State model, respectively. Our results showed that suspended particles had its lowest δ15NPN in the surface layer, which was due to the preferential assimilation of 14N in nitrate by phytoplankton. The δ15NPN in the mixed layer of the Prydz Bay and its adjacent areas decreased from the inner shelf to the outer basin, ascribing to the effect of isotope fractionation during phytoplankton assimilation. In mixed layer, the spatial distribution of δ15NPN associated with particulate organic matter (POM) production can be well interpreted according to Rayleigh model and Steady State model. The nitrogen isotope fractionation factor during phytoplankton assimilating nitrate was estimated as 10.0%o by Steady State model, which was more reasonable than that calculated by Rayleigh model. These results validate the previous reports of fractionation factor during nitrate assimilation by phytoplankton. Increasing δ15NPN with depth below the euphotic zone correlated with the decreasing PN contents, and it was attributed to preferential remineralization of 14N in PN by bacteria. In subsurface and deep layer, the δ15NPN distributions also conformed to Rayleigh model and Steady State model during PN remineralization, with a fractionation factor of about 3.6% and 3.2%, respectively. It is the first time to estimate the fractionation factor during POM production and remineralization in the Prydz Bay and its adjacent areas. Such fractionation may provide a useful tool for the follow-up study of the nitrogen dynamics in the Southern Ocean.

Spectral and isotopic characteristics of particulate organic matter in a subtropical estuary under the influences of human disturbance

Abstract Particulate organic matter (POM) in the coastal zone plays an important role in global carbon cycle, yet its spectral properties under human disturbance are not well understood. This study investigated the source and dynamics of POM in a typical coastal area (Minjiang Estuary, China) under the influences of estuarine mixing, urbanization and dam construction, based on spectral and isotopic analysis. The yield of particulate organic carbon from the watershed (0.38 g m−2 yr−1) was in part limited by the historical decrease in sediment discharge downstream hydropower station. The absorption and fluorescence indices of POM suggested an important contribution from biological production with a low humic content. The importance of river and estuarine production was supported by elemental and isotopic analysis, in particular for N-bound constituents of POM. Three humic-like and two protein-like fluorescent components were identified from POM using fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). They showed weak correlations with salinity, suggesting non-conservative behaviors of fluorescent POM during the estuarine mixing. Principal component analysis (PCA) identified two principal factors, which were related to the level of chromophoric POM (PC1) and biological production (PC2), respectively. The PCA results indicated stronger influence of biological production in the estuarine zone and potential effect of sediment re-suspension and/or wastewater discharge in the urban zone. Overall, our results demonstrated significant influences of human disturbance on the flux, source and dynamics of POM in the coastal zone, which could be assessed by spectral and stable isotopic analysis.

Effects of fish culture on particulate organic matter in a reservoir-type river as revealed by absorption spectroscopy and fluorescence EEM-PARAFAC

Dam construction and fish culture can change the biogeochemical processes in river, yet their impact on the spectral properties of particulate organic matter (POM) remains to be studied. This was investigated in a reservoir-type river (Minjiang river, SE China) using absorption spectroscopy and fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Five fluorescent components were identified from POM with PARAFAC. Four components C1–C4 were affected by the seasonal variations of rainfall and runoff, indicating the influences of hydrological condition and terrestrial inputs. The Chlorophyll a concentration (Chl a) correlated significantly with the humic-like C3 (p < 0.05) and the protein-like C4 (p < 0.01), indicating phytoplankton was an important source of C3 and C4. The Chl a and fluorescence intensities of C3–C4 were higher in the fish culture zones than in other areas, and the absorption coefficient a300 and C1–C4 were lower downstream the dam. These results indicated that fish farming in the reservoir probably promoted the production of POM. The a300 and C1 per unit mass of suspended particulate matter (a300/TSM and C1/TSM) correlated significantly with the median particle size (p < 0.01), which might be related to the contribution of micro-phytoplankton. The absorption spectra of POM showed a shoulder peak at ∼280 nm, and its intensity correlated significantly and positively with Chl a (p < 0.01). These results indicated that the peak was probably derived from phytoplankton production. Our results have implications for better understanding the influences of human activities on the dynamics of river POM.

Sediment-Associated Phytoplankton Release From the Seafloor in Response to Wind-Induced Barotropic Currents in the Bering Strait

Bering Strait is the single gateway between the Arctic and Pacific Oceans, and has localized strong currents, which can reach up to 100 cm s−1. Although massive spring phytoplankton blooms and the subsequent production of particulate organic matter that sinks to the seafloor are observed in the surrounding regions of the Bering Strait, the impact of the locally strong current on the horizontal and vertical transport of the particles remains unclear. Therefore, we conducted year-round mooring measurements from 2016 to 2017 by focusing on near-bottom processes associated with ocean currents. Our time-series analysis showed that high-turbidity events, triggered by strong barotropic currents, occurred near the seafloor in all seasons. Consequently, the fluorescence sensor detected highly concentrated chlorophyll a in the resuspended sediment; however, the amount of chlorophyll a release was seasonal, with large and small amounts being released during the warm and cold seasons, respectively. The small amounts of chlorophyll a may be attributed to small amounts of phytoplankton in the sediment owing to less input of fresh phytoplankton from the overlaying water column and organic matter decomposition in the sediments under no-light conditions. The barotropic currents were modulated by surface winds associated with an intercontinental atmospheric pattern having a 5000-km spatial scale on a timescale of 6 days. The locally strong ocean current in the Bering Strait, driving the upward transport of sediment and the subsequent horizontal transport, may play a vital role in supplying particulate organic matter/phytoplankton/nutrients to the downstream region of the southern Chukchi Sea where the formation of biological hotspots is reported.

Leaf traits drive plant diversity effects on litter decomposition and FPOM production in streams.

Biodiversity loss in riparian forests has the potential to alter rates of leaf litter decomposition in stream ecosystems. However, studies have reported the full range of positive, negative and no effects of plant diversity loss on decomposition, and there is currently no explanation for such inconsistent results. Furthermore, it is uncertain whether plant diversity loss affects other ecological processes related to decomposition, such as fine particulate organic matter production or detritivore growth, which precludes a thorough understanding of how detrital stream food webs are impacted by plant diversity loss. We used a microcosm experiment to examine the effects of plant diversity loss on litter decomposition, fine particulate organic matter production, and growth of a dominant leaf-shredding detritivore, using litter mixtures varying in species composition. We hypothesized that plant diversity loss would decrease the rates of all studied processes, but such effects would depend on the leaf traits present in litter mixtures (both their average values and their variability). Our findings partly supported our hypotheses, showing that plant diversity loss had a consistently negative effect on litter decomposition and fine particulate organic matter production (but not on detritivore growth) across litter mixtures, which was mediated by detritivores. Importantly, the magnitude of the diversity effect and the relative importance of different mechanisms underlying this effect (i.e., complementarity vs. selection) varied depending on the species composition of litter mixtures, mainly because of differences in litter nutritional quality and trait variability. Complementarity was prevalent but varied in size, with positive selection effects also occurring in some mixtures. Our results support the notion that loss of riparian plant species is detrimental to key stream ecosystem processes that drive detrital food webs, but that the magnitude of such effects largely depends on the the order of species loss.

Effects of intrapopulation phenotypic traits of invasive crayfish on leaf litter processing

The impact of invasive alien species (IAS) on an ecosystem is primarily studied at the species level, whereas the functional impacts of their genetic and phenotypic traits are poorly investigated. We used two laboratory based experiments to assess how intrapopulation phenotypic traits (size, sex, and number of claws) of the invasive red swamp crayfish Procambarus clarkii affect invertebrate shredders and leaf processing. Leaf consumption was significantly affected by the size and number of claws but not by the sex of the crayfish. Bigger animals presented a higher overall consumption but, in contrast, the mass of leaves consumed per unit crayfish body mass decreased with size. Indeed, the production of particulate organic matter followed the same trend, suggesting that the higher metabolic needs of smaller animals are responsible for their higher feeding activity on leaf litter. Claw loss in P. clarkii also led to increased leaf consumption and may be related to increased energy requirements for claw regeneration. Our results highlight the importance of also considering the phenotypic traits within populations for better understanding the impacts of IAS on ecosystem processes.

Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; tolerance in phytoplankton productivity

Abstract. High-latitude oceans are anticipated to be some of the first regions affected by ocean acidification. Despite this, the effect of ocean acidification on natural communities of Antarctic marine microbes is still not well understood. In this study we exposed an early spring, coastal marine microbial community in Prydz Bay to CO2 levels ranging from ambient (343 µatm) to 1641 µatm in six 650 L minicosms. Productivity assays were performed to identify whether a CO2 threshold existed that led to a change in primary productivity, bacterial productivity, and the accumulation of chlorophyll a (Chl a) and particulate organic matter (POM) in the minicosms. In addition, photophysiological measurements were performed to identify possible mechanisms driving changes in the phytoplankton community. A critical threshold for tolerance to ocean acidification was identified in the phytoplankton community between 953 and 1140 µatm. CO2 levels ≥ 1140 µatm negatively affected photosynthetic performance and Chl a-normalised primary productivity (csGPP14C), causing significant reductions in gross primary production (GPP14C), Chl a accumulation, nutrient uptake, and POM production. However, there was no effect of CO2 on C : N ratios. Over time, the phytoplankton community acclimated to high CO2 conditions, showing a down-regulation of carbon concentrating mechanisms (CCMs) and likely adjusting other intracellular processes. Bacterial abundance initially increased in CO2 treatments ≥ 953 µatm (days 3–5), yet gross bacterial production (GBP14C) remained unchanged and cell-specific bacterial productivity (csBP14C) was reduced. Towards the end of the experiment, GBP14C and csBP14C markedly increased across all treatments regardless of CO2 availability. This coincided with increased organic matter availability (POC and PON) combined with improved efficiency of carbon uptake. Changes in phytoplankton community production could have negative effects on the Antarctic food web and the biological pump, resulting in negative feedbacks on anthropogenic CO2 uptake. Increases in bacterial abundance under high CO2 conditions may also increase the efficiency of the microbial loop, resulting in increased organic matter remineralisation and further declines in carbon sequestration.

Effects of human land use on the terrestrial and aquatic sources of fluvial organic matter in a temperate river basin (The Meuse River, Belgium)

The impact of human activities on the concentrations and composition of dissolved organic matter (DOM) and particulate organic matter (POM) was investigated in the Walloon Region of the Meuse River basin (Belgium). Water samples were collected at different hydrological periods along a gradient of human disturbance (50 sampling sites ranging from 8.0 to 20,407 km2) and during a 1.5 year monitoring of the Meuse River at the city of Liège. This dataset was completed by the characterization of the DOM pool in groundwaters. The composition of DOM and POM was investigated through elemental (C:N ratios), isotopic (δ13C) and optical measurements including excitation emission matrix fluorescence with parallel factor analysis (EEM–PARAFAC). Land use was a major driver on fluvial OM composition at the regional scale of the Meuse Basin, the composition of both fluvial DOM and POM pools showing a shift toward a more microbial/algal and less plant/soil-derived character as human disturbance increased. The comparison of DOM composition between surface and groundwaters demonstrated that this pattern can be attributed in part to the transformation of terrestrial sources by agricultural practices that promote the decomposition of soil organic matter in agricultural lands and subsequent microbial inputs in terrestrial sources. In parallel, human land had contrasting effects on the autochthonous production of DOM and POM. While the in-stream generation of fresh DOM through biological activity was promoted in urban areas, summer autochthonous POM production was not influenced by land use. Finally, soil erosion by agricultural management practices favored the transfer of terrestrial organic matter via the particulate phase. Stable isotope data suggest that the hydrological transfer of terrestrial DOM and POM in human-impacted catchment are not subject to the same controls, and that physical exchange between these two pools of organic matter is limited.

Long-term effects of fungicides on leaf-associated microorganisms and shredder populations-an artificial stream study.

Leaf litter is a major source of carbon and energy for stream food webs, while both leaf-decomposing microorganisms and macroinvertebrate leaf shredders can be affected by fungicides. Despite the potential for season-long fungicide exposure for these organisms, however, such chronic exposures have not yet been considered. Using an artificial stream facility, effects of a chronic (lasting up to 8 wk) exposure to a mixture of 5 fungicides (sum concentration 20 μg/L) on leaf-associated microorganisms and the key leaf shredder Gammarus fossarum were therefore assessed. While bacterial density and microorganism-mediated leaf decomposition remained unaltered, fungicide exposure reduced fungal biomass (≤71%) on leaves from day 28 onward. Gammarids responded to the combined stress from consumption of fungicide-affected leaves and waterborne exposure with a reduced abundance (≤18%), which triggered reductions in final population biomass (18%) and in the number of precopula pairs (≤22%) but could not fully explain the decreased leaf consumption (19%), lipid content (≤43%; going along with an altered composition of fatty acids), and juvenile production (35%). In contrast, fine particulate organic matter production and stream respiration were unaffected. Our results imply that long-term exposure of leaf-associated fungi and shredders toward fungicides may result in detrimental implications in stream food webs and impairments of detrital material fluxes. These findings render it important to understand decomposer communities' long-term adaptational capabilities to ensure that functional integrity is safeguarded. Environ Toxicol Chem 2017;36:2178-2189. © 2017 SETAC.

Sponge waste that fuels marine oligotrophic food webs: a re‐assessment of its origin and nature

AbstractIt has recently been realized that sponges take up much of the dissolved organic matter (DOM) available in the water of reefs. The energy derived from this DOM is suggested to be invested in renewing the sponge filter cells (choanocytes) every few hours, generating an outflow of detrital particulate organic matter (POM) that is rapidly ingested by other invertebrates. By this DOM‐to‐POM recycling, sponges are proposed to fuel the food web of oligotrophic marine communities, including reefs, caves and deep‐sea environments. In four species studied herein by electron microscopy, the POM found in the outgoing aquiferous canals had a complex composition, with large between‐species differences. It may include choanocytes (0–52%), and also mesohyl cells, such as archeocytes (9–20%) and spherulous, and granular cells with inclusions (27–90%). Exocytosed vesicles also occurred. Surprisingly, to end up into the outgoing canals, the internal mesohyl cells squeezed between the epithelial cells (endopinacocytes) of the canal wall. Mesohyl cells were also able to transfer their inclusions to the endopinacocytes, which in turn extruded their acquired vesicle loads into the canal lumen. The unanticipated abundant participation of mesohyl cells and endopinacocytes in the production of POM appears to be an ordinary process that occurs continuously in the sponges, mostly related to elimination of digestion leftovers and excretion by‐products. Therefore, POM is generated by sponges irrespective of whether the primary food source is particulate (evidence from this study) or DOM (previous literature). Altogether, these results indicate that the cellular mechanisms behind the relevant organic‐matter recycling carried out by sponges are more diverse than initially anticipated. The varying ratios of choanocytes/mesohyl cells in the POM across species suggest that different sponge species may impact differently the energetics of food webs of the respective oligotrophic habitats where they dominate.

Food type and temperature constraints on the fitness of a dominant freshwater shredder

Freshwaters receive a large amount of materials and biologically available energy from their surrounding catchments. In particular, small forested streams are dependent on allochthonous organic matter inputs. However, since the middle 20th century large areas of forests in the Iberian Peninsula have been converted to eucalypt plantations, impairing invertebrate communities and stream energy fluxes. In addition, the dependence of organismal metabolic rates on temperature may influence invertebrate life cycles and development, and ultimately the riparian-stream system. We tested the effects of two food resources (alder and eucalypt) under two different temperatures (9 vs. 14°C) on the life history parameters and elemental composition of Brillia bifida (Chironomidae), a numerically dominant shredder in forested streams of NW Spain. Our results showed: (i) warmer temperature accelerated the development of B. bifida larvae (i.e., three times faster at warm than at cold temperature), (ii) Brillia's growth rate when fed on eucalypt leaves was only 30% of what it was on alder leaves, and (iii) both factors together modified larvae stoichiometry and nutrient fluxes (i.e., through fine particulate organic matter production). The observed elemental imbalances suggest, to some extent, a deviation from the “strict homeostasis” assumption for heterotrophs. Differential effects observed on larval development, growth and elemental composition point out that food type and temperature are influencing B. bifida performance, and this fact may reach other trophic compartments through detritivore-mediated nutrient cycling.

Changes in epilithic diatom communities and periphytic biomass downstream of a reservoir on a Mediterranean river (Calabria region, S Italy)

Diatom community structure and morphotype classification were studied and periphyton biomass, course particulate organic matter (CPOM), hydrogeomorphological parameters, and nutrient concentrations were measured at 4 stations downstream of the Cecita dam (Mucone River) and at 3 control sites located on different tributaries of the Mucone River in May, August, and November 2005. The lowest values of current velocities and the highest amounts of sand deposition and CPOM accumulation were detected at the stations closest to the dam. Downstream, the confluence with the first permanent tributary (Cerreto River) of the Mucone showed a "rhythral" morphology, similar to that of the control sites. Multivariate analysis showed that the community was constantly segregated into 2 groups: G1 (stations upstream of the Cerreto inflow), dominated by early colonizers, adapted to both high and low current velocity and tolerating burial and light deficiencies; and G2 (all other stations), where the prevailing taxa were species typical of stable environments with high values of flow and abundance of coarse substrates. Genus-based morphotype classification failed to detect any differences between the 2 groups. Biomass levels were higher at station G2 than G1, while accumulation of CPOM downstream of the reservoir promoted fine particulate organic matter production and a switch from autotroph to heterotroph dominated biofilms.

Effect of CO2, nutrients and light on coastal plankton. II. Metabolic rates

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 22:43-57 (2014) - DOI: https://doi.org/10.3354/ab00606 Theme Section: Environmental forcing of aquatic primary productivity Effect of CO2, nutrients and light on coastal plankton. II. Metabolic rates J. M. Mercado1,*, C. Sobrino2, P. J. Neale3, M. Segovia4, A. Reul4, A. L. Amorim1, P. Carrillo5, P. Claquin6, M. J. Cabrerizo5, P. León1, M. R. Lorenzo4, J. M. Medina-Sánchez7, V. Montecino8, C. Napoleon6, O. Prasil9, S. Putzeys1, S. Salles1, L. Yebra1 1Centro Oceanográfico de Málaga, Instituto Español de Oceanografía, Puerto Pesquero s/n, 29640 Fuengirola, Málaga, Spain 2Department of Ecology and Animal Biology, Faculty of Sciences, University of Vigo, 36310 Vigo, Spain 3Smithsonian Environmental Research Center, Edgewater, Maryland 21037, USA 4Department of Ecology, Faculty of Sciences, University of Málaga, 29071 Málaga, Spain 5Instituto del Agua, Universidad de Granada, Granada, Spain 6Université Caen Basse-Normandie, BIOMEA FRE3484 CNRS, 14032 Caen Cedex, France 7Departamento de Ecología, Facultad de Ciencias, Universidad de Granada, Granada, Spain 8Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Santiago, Chile 9Laboratory of Photosynthesis, CenterAlgatech, Institute of Microbiology ASCR, 37981 Trĕboň, Czech Republic *Corresponding author: jesus.mercado@ma.ieo.es ABSTRACT: We conducted a microcosm experiment aimed at studying the interactive effects of high CO2, nutrient loading and irradiance on the metabolism of a planktonic community sampled in the Western Mediterranean near the coast of Málaga. Changes in the metabolism of phytoplankton and bacterioplankton were observed for 7 d under 8 treatment conditions, representing the full factorial combinations of 2 levels each of CO2, nutrient concentration and solar radiation exposure. The initial plankton sample was collected at the surface from a stratified water column, indicating that phytoplankton were naturally acclimated to high irradiance and low nutrient concentrations. Nutrient addition combined with high irradiance resulted in a significant increase in primary production. Nitrate uptake by phytoplankton was also stimulated under high nutrient conditions. High nutrients, high irradiance and the combination of low CO2 and high irradiance positively affected bacterial production. Light was the main factor affecting the respiration rates of the community, which were higher at the high light level. After 7 d of incubation, nutrient loading was the only factor that significantly affected the amount of particulate organic carbon (POC) accumulated in the microcosms. Therefore, the changes in metabolic rates produced at high CO2 had no effect on net production of particulate organic matter. If these results are extrapolated to the natural environment, it could be hypothesized that high levels of CO2 will have a limited impact on biological pump activity in the northern Alboran Sea since it is assumed that POC export towards deeper layers determines the potential for carbon sequestration. KEY WORDS: Acidification · Bacterioplankton · Nutrients · Phytoplankton · Primary productivity · Respiration · UVR Full text in pdf format PreviousNextCite this article as: Mercado JM, Sobrino C, Neale PJ, Segovia M and others (2014) Effect of CO2, nutrients and light on coastal plankton. II. Metabolic rates. Aquat Biol 22:43-57. https://doi.org/10.3354/ab00606 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 22. Online publication date: November 20, 2014 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2014 Inter-Research.

Stable isotope ratios reveal food source of benthic fish and crustaceans along a gradient of trophic status in the East China Sea

The East China Sea (ECS) receives large quantities of particulate organic matter (POM) and inorganic nutrients transported from the Changjiang (Yangtze River), which have produced high productivity in the northwestern ECS. This study evaluated potential contributions of terrigenous POM (allochthonous food source) and nutrient-induced marine production (autochthonous source) to the ECS benthic ecosystem by analyzing stable isotopic compositions of phytoplankton, zooplankton, benthic crustaceans and fish. Benthic consumers exhibited δ13C values similar to those of their autochthonous food sources (i.e., phytoplankton and zooplankton), revealing their major reliance on marine production. In contrast, the δ13C values of benthic fish (−19.6‰ to −13.5‰) and crustaceans (−18.9‰ to −15.0‰) were much higher than that of terrigenous POM (−25.7‰), which generally accounted for less than 20% of the most fish diet. Phytoplankton and zooplankton generally exhibited higher δ13C values at eutrophic and highly productive inshore sites than at oligotrophic offshore sites. This enrichment of inshore δ13C values was mainly attributed to lower photosynthetic fractionation during algal blooms, an effect that was further enhanced during flood period of the Changjiang. The δ13C values of demersal fish assemblages were also significantly higher at inshore sites and decreased seaward. However, fish δ15N values and their estimated trophic levels showed relatively small spatial variation. The disproportionate variations in δ13C and δ15N values suggested that the enriched C isotopic signatures derived from an elevated δ13C baseline of the inshore food web instead of trophic enrichment of the isotopic ratios. The significantly positive correlations between concentrations of chlorophyll a and nutrients versus fish δ13C provided further evidence for the use of pelagic algal bloom materials by inshore consumers. The isotopic and oceanographic survey data suggested that inorganic nutrients discharged from the Changjiang River nourish benthic consumers in the ECS and play an important role in linking marine benthic ecosystems to local pelagic primary production as well as to the adjacent terrestrial watershed.

Spatial and temporal variability in the chemical properties of the oxic and suboxic layers of the Black Sea

The Black Sea, a land-locked deep basin with sulfide bearing waters below 150–200m, has been subject to anthropogenic pressures since the 1970s. Large inputs of nutrients (nitrate — N, phosphate — P, silicate — Si) with high N/P but low Si/N ratios and subsequent development of intensive eutrophication over the basin have changed vertical distributions and inventories of nutrients and redox-sensitive metals in the oxic, suboxic and anoxic layers. Chemical data sets obtained between 1988 and 2010, and older data from before 1970 were evaluated to assess spatial/temporal variations of the dissolved oxygen (O2), nutrients and dissolved/particulate manganese (Mnd, Mnp) in the water column from the lower salinity, oxygenated surface waters through the SubOxic Layer (SOL; O2<20μM; H2S<1μM) to the anoxic, sulfidic water interface. Correlations were observed between salinity and nutrients (nitrate, silicate) in the nearshore waters off the Danube delta and in the southwestern (SW) coastal waters which had low Si/N ratios. Surface waters from the western central gyre were consistently depleted in nitrate and phosphate with low N/P but higher Si/N molar ratios throughout the year. Chemical profiles obtained recently in the Rim Current and western central gyre displayed very similar vertical features through the halocline to the sulfidic water interface. However, in the SW coastal margin, lateral intrusion of O2 and nutrients by the Bosporus Plume resulted in formation of secondary maxima of nitrate, nitrite and O2 in the SOL, and local deepening of the first appearance of anoxic, sulfidic waters. Before the mid 1960s, nitrate-enriched major rivers fed the Black Sea with high N/P ratios (>50). The surface waters over the basin were rich in silicate (25–70μM), but poor in nitrate (<0.1μM) and phosphate (0.05–0.3μM), resulting in very high Si/N (>500) but very low N/P (<1.0) ratios. After the mid 1970s, construction of dams, especially on the Danube River, resulted in lower Si concentrations. At this time the increased loads of anthropogenic nitrate and phosphate by the major rivers resulted in lower Si/N, but still high N/P molar ratios, which enhanced eutrophication (production of particulate organic matter, POM) drastically in the coastal waters. This led to reductions in the surface Si/N ratio by up to 500-fold in the western basin while the N/P ratio increased. The enhanced POM export increased the nitrate inventory and thus N/P ratios of the NW shelf waters spreading over the whole basin. The increased export of POM decreased the Si inventory of the upper layer down to the boundary of sulfidic waters. This export also increased O2 consumption and removal of nitrate to N2 form by denitrification in the oxic/suboxic interface, leading to seasonal/decadal changes in the boundaries of the nitracline and main oxycline and changes in the slopes of the nitrate-phosphate and Apparent Oxygen Utilization (AOU)-nitrate regressions in the steep oxycline down to the SOL. These slopes are much smaller than those observed in the lower layer of Marmara Sea fed by the Black Sea outflow. The enlargement of SOL by ~15–20m after the 1970s modified the vertical features of nitrate, phosphate and manganese (Mnd, Mnp) species in the redox gradient zone.

Particulate nutrient fluxes over a fringing coral reef: Source‐sink dynamics inferred from carbon to nitrogen ratios and stable isotopes

We examined spatial and temporal variations in particulate organic matter (POM) dynamics over a fringing coral reef (Ningaloo Reef) in Western Australia during the austral autumn and spring. Total POM concentrations generally did not differ between seasons or reef zones, but the composition of POM, in terms of carbon isotope ratios (δ13C‐POM), carbon to nitrogen ratios (C : N), and fatty acids, changed consistently in water flowing across the reef. Both δ13C‐POM and C : N increased from the fore reef to the reef flat and lagoon, −23.0‰ to −20.1‰ and 7.31 to 8.34, respectively. Average rates of net POM uptake by the reef community were highest over the reef crest (4 to 30 mmol N m−2 d−1 and 6 to 130 mmol C m−2 d−1), with a Bayesian isotope model confirming independent measurements of high uptake rates of allochthonous POM (oceanic phyto‐ and zooplankton). In contrast, over the reef flat, net release of POM was observed (−4 to −5 mmol N m−2 d−1 and −50 mmol C m−2 d−1), with gross release rates (estimated as −6 to −8 mmol N m−2 d−1 and −30 to −90 mmol C m−2 d−1) indicating that the release of autochthonous POM may be of similar magnitude to allochthonous uptake. Examining POM dynamics in terms of gross fluxes reinforces the dependence of coral reef systems on oceanographic processes for allochthonous POM supply, as well as highlighting the potential for autochthonous POM production to supply nutrients to benthic and pelagic communities downstream.

Foam fractionation efficiency of a vacuum airlift—Application to particulate matter removal in recirculating systems

The accumulation of particulate organic matter (POM) in recirculating aquaculture systems (RAS) has become an important issue with the intensification of finfish production. The objective of this study was to assess the foam fractionation efficiency of a vacuum airlift in different conditions (POM concentrations, airflow rates, bubble sizes, water renewal rates and feed addition). In sea water, the vacuum airlift allowed removing 20% of the initial POM concentration per hour (foam fractionation efficiency), corresponding to a 20.7-fold concentration factor between the tank and the foam. In rearing conditions, efficiency increased with decreasing water renewal rate or increasing POM concentration. An increase in airflow rate from 10 to 80Lmin−1 in the vacuum airlift significantly decreased foam fractionation efficiency when feed was added to the water. The impact of feeding was only observed with high airflow rates where bubble coalescence occurred. Calculated POM production by fish ranged between 15.9 and 23.5gh−1 and was equivalent to estimations based on feed conversion ratio (FCR). This indicated that all the POM produced was extracted by the vacuum airlift.