Pelagic Production Research Articles

Long-Term Surveys Show Invasive Overbite Clams (Potamocorbula amurensis) are Spatially Limited in Suisun Marsh, California

Author(s): Baumsteiger, Jason; Schroeter, Robert E.; O'Rear, Teejay; Cook, Jonathan D.; Moyle, Peter B. | Abstract: The overbite clam (Potamocorbula amurensis) is a major invasive species in the San Francisco Estuary, California, and has been implicated in the decline of pelagic productivity and native fish species. Little is known of its impact on Suisun Marsh, a large brackish tidal region of the estuary. We looked at the abundance and spatial distribution of clams in the marsh, including examining the influence of water quality, using long-term (1988–2015) otter trawl surveys. Temporal trends indicated that overbite clam abundance has been increasing, but adult clams were spatially restricted to a single large slough (Suisun). Clams were absent from most interior channels, limiting their overall effect on the marsh aquatic ecosystem. Abiotic variables, particularly salinity, proved important predictors of overbite clam abundance, although the variables examined alone could not explain overbite clam distributions. We propose that connectivity, detritus loads, and/or predation pressure may work in conjunction with abiotic variables to cause poor survival rates for recruits in interior marsh sites, keeping the distribution limited. Overall results are encouraging for restoration projects in brackish tidal marshes that need to deal with overbite clams.

Heterogeneity in food-web interactions of fish in the Mwanza Gulf, Lake Victoria: a quantitative stable isotope study

Stable isotope analyses and derived population-level metrics were used to quantitatively analyse spatial and seasonal heterogeneity in the fish trophic dynamics in relation to environmental variables in Mwanza Gulf, Lake Victoria (Tanzania). The fish community in Lake Victoria, including the top predator Nile perch, is generally omnivorous with a heavy reliance on invertebrates. This is in contrast to findings based on stomach content analyses of Nile perch, which showed a stronger reliance on fish. We tested two hypotheses: (1) during the rainy seasons multiple carbon sources influence the food-web structure inside the Gulf, leading to increased carbon ranges and trophic diversity. (2) During dry periods, the food-web structure mainly relies on pelagic primary production, reducing carbon ranges and trophic diversity. Carbon sources indeed varied seasonally and spatially, affecting the fish community at the highest trophic levels. With the onset of rains, carbon sources became spatially highly differentiated with enriched δ13C values of fish in shallow water inside the Gulf and depleted δ13C values in open waters. Metrics associated with niche size correlated significantly with seasonally varying environmental variables, while δ13C ranges correlated with spatially varying environmental variables.

Benthic primary producers are key to sustain the Wadden Sea food web: stable carbon isotope analysis at landscape scale.

Coastal food webs can be supported by local benthic or pelagic primary producers and by the import of organic matter. Distinguishing between these energy sources is essential for our understanding of ecosystem functioning. However, the relative contribution of these components to the food web at the landscape scale is often unclear, as many studies lack good taxonomic and spatial resolution across large areas. Here, using stable carbon isotopes, we report on the primary carbon sources for consumers and their spatial variability across one of the world's largest intertidal ecosystems (Dutch Wadden Sea; 1460km2 intertidal surface area), at an exceptionally high taxonomic (178 species) and spatial resolution (9,165 samples from 839 locations). The absence of overlap in δ13 C values between consumers and terrestrial organic matter suggests that benthic and pelagic producers dominate carbon input into this food web. In combination with the consistent enrichment of benthic primary producers (δ13 C-16.3‰) relative to pelagic primary producers (δ13 C -18.8) across the landscape, this allowed the use of a two-food-source isotope-mixing model. This spatially resolved modelling revealed that benthic primary producers (microphytobenthos) are the most important energy source for the majority of consumers at higher trophic levels (worms, molluscs, crustaceans, fish, and birds), and thus to the whole food web. In addition, we found large spatial heterogeneity in the δ13 C values of benthic primary producers (δ13 C -19.2 to -11.5‰) and primary consumers (δ13 C -25.5 to -9.9‰), emphasizing the need for spatially explicit sampling of benthic and pelagic primary producers in coastal ecosystems. Our findings have important implications for our understanding of the functioning of ecological networks and for the management of coastal ecosystems.

Life history differences and latitudinal variation in recruitment in two species of arctic-boreal perciform fishes, the fish doctor Gymnelus viridis and the Arctic shanny Stichaeus punctatus

Growth and recruitment were examined in two arctic-boreal, shallow water marine perciform species: the fish doctor Gymnelus viridis (Zoarcidae) and the Arctic shanny Stichaeus punctatus (Stichaeidae). G. viridis ranges in the Canadian Arctic from northern Hudson Bay to northern Ellesmere Island, whereas S. punctatus has a more southerly range from Nova Scotia coastal waters to northern Hudson Bay. At Nuvuk Islands in northeastern Hudson Bay, where the two species are sympatric in shallow water, they had comparable juvenile growth rates but temporal variation in 0+ recruitment was substantially greater in S. punctatus. This difference may stem from their contrasting early life histories. S. punctatus spawns large numbers of small demersal eggs that hatch into pelagic larvae, whereas G. viridis spawns small numbers of large demersal eggs that hatch directly into demersal juveniles with no pelagic stage, suggesting that recruitment in G. viridis should be less sensitive to yearly variation in the onset of the ice-free period in Hudson Bay and the subsequent pulse of pelagic invertebrate production. Relative to Nuvuk, recruitment variation in G. viridis was found to be greater at Resolute, Cornwallis Island, close to its northern range limit, whereas recruitment variation in S. punctatus was not evident in Newfoundland, closer to its southern range limit.

Marine micronutrient vectors: seabirds, marine mammals and fishes egest high concentrations of bioactive metals in the subantarctic island ecosystem

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 563:13-23 (2017) - DOI: https://doi.org/10.3354/meps11978 Marine micronutrient vectors: seabirds, marine mammals and fishes egest high concentrations of bioactive metals in the subantarctic island ecosystem S. R. Wing1,*, L. C. Wing1, O. A. Shatova1, R. Van Hale2 1Department of Marine Science and 2Department of Chemistry, University of Otago, PO Box 56, Dunedin 9054, New Zealand *Corresponding author: steve.wing@otago.ac.nz ABSTRACT: We investigated concentrations of bioactive metals (Mn, Fe, Co, Ni, Cu, Zn, As, Cd) in organic matter source pools: suspended particulate organic matter and macroalgae, and macrozooplankton from the vicinity of the Snares Islands, situated adjacent to the Subtropical Frontal Zone south of New Zealand. Further we sampled egested material from 6 coastal fishes, 8 seabirds and 2 pinniped species with rookeries on the islands. Analysis of δ15N and δ13C from basal organic matter sources, zooplankton, fish muscle tissue and egesta of fishes, seabirds and pinnipeds was used to estimate trophic position for each group. We found a food web heavily dependent on pelagic productivity culminating with New Zealand fur seals and Hooker’s sea lions. We compared multivariate concentration profiles of metals in the egesta of 4 trophic level groups from the Snares Islands with 4 similar trophic groups from the Auckland Islands. Results indicated more variation in concentration of bioactive metals in egesta among trophic level groups, than among islands. These results demonstrated that several potentially limiting micronutrients (Mn, Fe, Co, Zn) are bioaccumulated in the egesta of upper trophic levels of subantarctic food webs. The variance in concentration patterns of bioactive metals is more coincident with differences in food web structure than differences in water mass type surrounding the 2 islands. The patterns observed have important implications for understanding the interactions between food web architecture, biological vectors and productivity around the subantarctic islands of the Southern Ocean. KEY WORDS: Southern Ocean · Iron · Seabird · Fish · Marine mammal · Nutrient vector Full text in pdf format PreviousNextCite this article as: Wing SR, Wing LC, Shatova OA, Van Hale R (2017) Marine micronutrient vectors: seabirds, marine mammals and fishes egest high concentrations of bioactive metals in the subantarctic island ecosystem. Mar Ecol Prog Ser 563:13-23. https://doi.org/10.3354/meps11978 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 563. Online publication date: January 20, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Relación entre la producción primaria y bacteriana pelágicas en dos lagunas húmicas vegetadas

In this study, we show that depth-integrated pelagic primary production (PP) can exceed bacterioplankton production (BP) in vegetated humic shallow lakes, giving as a result an autotrophic water column, despite light restrictions and availability of organic carbon for lake bacteria. Intuitively, these conditions should favor the development of a heterotrophic water column. Instead, during our survey, BP represented between 1.3 to 5% of PP most of the time. Only once, during late summer, BP was ~71% of PP. Although we cannot conclude about the mechanisms behind the observed results, previous surveys and experimentation in the wetland allow us to hypothesize that autotrophic conditions were favored by: i) the shallow nature of the lakes, which compensates for light attenuation by organic matter when integrating production in the water column, ii) the presence of anaerobic anoxygenic photosynthetic bacteria below the macrophyte cover, and iii) high predation rates on bacterioplankton by heterotrophic flagellates below the floating plants.

The Arctic Marine Pulses Model: linking annual oceanographic processes to contiguous ecological domains in the Pacific Arctic

The Pacific Arctic marine ecosystem extends from the northern Bering Sea, across the Chukchi and into the East Siberian and Beaufort seas. Food webs in this ecosystem are short, a simplicity that belies the biophysical complexity underlying trophic linkages from primary production to humans. Existing advective and pelagic-benthic coupling models describe processes that connect certain aspects of marine food webs, but do not offer a comprehensive approach to understanding the Pacific Arctic ecosystem. In the course of the Synthesis of Arctic Research (SOAR) project, the Arctic Marine Pulses (AMP) model was developed that depicts seasonal biophysical ‘pulses’ across a latitudinal gradient by linking processes in four previously-defined contiguous ecological domains, including the: (i) Pacific Arctic domain; (ii) Seasonal Ice Zone domain; (iii) the Marginal domain (i.e., the shelf break and slope); and (iv) Riverine Coastal domain. Some of the biophysical processes included in the AMP model, such as pelagic-benthic coupling on the broad shelves of the northern Bering and Chukchi seas and advection and upwelling of zooplankton along the western Beaufort shelf (i.e. the krill trap), have been the focus of long-term studies. Other aspects such as biological processes associated with shifts in seasonal sea-ice phenology and trophic responses to riverine outflow have received less attention. The AMP model provides an annual spatiotemporal framework to guide research on dynamic ecosystem processes during the recent period of rapid biophysical changes in the Pacific Arctic. The model aims to encourage integrated research to track seasonal sea-ice and current-flow dynamics, coincident with variability in nutrients, benthic and pelagic production, and upper-trophic species occurrence to provide a foundation for the development of predictive human-inclusive ecosystem models for the Pacific Arctic region. We suggest that the AMP model, with its focus on phenology, might facilitate communication between conventional science approaches to marine research and seasonal-cycle based indigenous knowledge of marine ecosystems. The goal of improving our understanding of the state and variability of the Pacific Arctic marine ecosystem is a shared one and we conclude with views on how the AMP model can support that goal while contributing to the development of a pan-Arctic ecosystem model.

Palaeoenvironmental vs. evolutionary control on size variation of coccoliths across the Lower-Middle Jurassic

Size is an easily quantifiable trait probing the respective influence of evolution and palaeoenvironment on organisms through time. After the stressed period that spanned across western Tethys epicontinental seas during the early Toarcian, the following rebuilding of a restored water column ecosystem is coeval with the size increase of the Lotharingius genus coccoliths, one of the main pelagic producers at that time. In order to quantitatively assess the coccolith size evolution during a time span of ~10myr, measurements of seven morphospecies of Lotharingius across the Toarcian and early Aalenian were performed. This study was carried out on a total of 5500 specimens from samples retrieved from two distinctive palaeoenvironmental settings in the western Mediterranean Tethys: three sections from the Lusitanian Basin in Portugal and one section from the Causses Basin in southern France. For each specimen, coccolith length, width and central area length and width were measured using specific measurement software. Statistical and data analysis tools were used in order to evaluate significant resemblances and/or differences between different size groups and samples. Two main clusters are acknowledged from this study. Small-sized Lotharingius is <4μm and large-sized Lotharingius is >4μm. In addition to common evolutionary processes, changes in palaeoenvironmental conditions were taken into account to explain such a size distribution. Although background evolution pushed the Lotharingius genus toward larger sizes, palaeoenvironmental conditions seemed to play an important role in the Toarcian-early Aalenian morphological evolution of this taxon. The production of larger coccoliths profited from stable environmental conditions, whereas smaller morphotypes dominated during periods marked by stress. The transition from small to large Lotharingius was synchronous in the two investigated western Tethys basins at the Bifrons-Gradata (or Variabilis) ammonite zone boundary (middle Toarcian), thus representing an important event for the Lower Jurassic calcareous nannofossil biostratigraphy.

A geochemical perspective on the impact of development at Alta Lake, British Columbia, Canada

Small, temperate lakes are important to communities across Canada, but commonly lack the long-term water quality records that are required to assess the impact of development and environmental change. We measured a combination of bulk sediment geochemistry and stable isotopes of carbon and nitrogen in a 210Pb- and 14C-dated sediment core from Alta Lake, Whistler, British Columbia. Channel avulsion at AD 1754 ± 81 on the 21-Mile Creek alluvial fan resulted in increased deposition of organic matter with a signal of autochthonous production. A decrease in δ13C beginning at AD 1949 ± 17 indicates an increase in pelagic productivity relative to benthic productivity and/or sewage input to Alta Lake. A corresponding increase in δ15N indicates an increase in sewage-derived nutrients during the same time period. These changes were synchronous and coincide with the onset of rapid development in the Whistler Valley. Increased metal deposition (Cu, As, and Zn) during the same period resulted from watershed disturbance during highway construction. Cu, As, and Zn concentrations correlated positively with C concentrations and negatively with Ti and K, suggesting removal of metals from the water column is closely related to autochthonous organic matter deposition. Fe/Mn ratios and Mo concentrations were expected to respond to hypolimnetic oxygen availability in response to decreased flushing rate and increased productivity following the loss of inflow from 21-Mile Creek, but did not display a clear time-stratigraphic signal. Collectively, these data suggest that the combination of bulk geochemistry and stable isotopes was an effective suite of variables for inferring environmental change and the effects of development on Alta Lake.

Asymmetrical competition between aquatic primary producers in a warmer and browner world.

In shallow lakes, pelagic and benthic producers engage in spatially asymmetrical resource competition. Pelagic producers intercept the flux of light to the benthic habitat and benthic producers intercept the flux of sediment-derived nutrients to the pelagic habitat. In boreal and subarctic regions, climate change is affecting this interaction both directly through warming and indirectly through increased loading with colored dissolved organic matter (cDOM) from the catchment ("brownification"). We use a dynamical ecosystem model to explore the consequences of these changing environmental conditions for lake primary production and compare model predictions with the results of an experiment in which we manipulated water temperature and cDOM supply in a 2×2 factorial design. The experiment was performed in field mesocosms large enough to harbor reproducing fish populations and was run over an entire growing season. In agreement with model predictions, benthic algal production and biomass declined and pelagic algal production and biomass increased with browning. Pelagic nutrient concentrations diverged over time between low and high cDOM treatments, suggesting that browning alleviated pelagic algal nutrient limitation by shading benthic competitors and preventing them from intercepting the release of nutrients from the sediment. Warming considerably reduced benthic and pelagic algal production as well as pelagic algalbiomass and total phosphorus. The warming results are only in partial accordance with model expectations, but can be explained by an indirectly inferred, positive response of macrophyte production (which was not included in the model) to warming. Our study suggests that lake ecosystem responses to climate change are mediated by cross-habitat feedbacks between benthic and pelagic producers.

Sedimentary record and anthropogenic pollution of a complex, multiple source fed dam reservoirs: An example from the Nové Mlýny reservoir, Czech Republic

While numerous studies of dam reservoirs contamination are reported world-wide, we present a missing link in the study of reservoirs sourced from multiple river catchments. In such reservoirs, different point sources of contaminants and variable composition of their sedimentary matrices add to extremely complex geochemical patterns. We studied a unique, step-wise filled Nové Mlýny dam reservoir, Czech Republic, which consists of three interconnected sub-basins. Their source areas are located in units with contrasting geology and different levels and sources of contamination. The aim of this study is to provide an insight into the provenance of the sediment, including lithogenic elements and anthropogenic pollutants, to investigate the sediment dispersal across the reservoir, and to assess the heavy metal pollution in each basin. The study is based on multi-proxy stratigraphic analysis and geochemistry of sediment cores. There is a considerable gradient in the sediment grain size, brightness, MS and geochemistry, which reflects changing hydrodynamic energy conditions and primary pelagic production of CaCO3. The thickness of sediments generally decreases from proximal to distal parts, but underwater currents can accumulate higher amounts of sediments in distal parts near the thalweg line. Average sedimentation rates vary over a wide range from 0.58cm/yr to 2.33cm/yr. In addition, the petrophysical patterns, concentrations of lithogenic elements and their ratios made it possible to identify two main provenance areas, the Dyje River catchment (upper basin) and the Svratka and Jihlava River catchments (middle and lower basin). Enrichment factors (EF) were used for distinguishing the anthropogenic element contribution from the local background levels. We found moderate Zn and Cu pollution (EF ~2 to 5) in the upper basin and Zn, Cu and Pb (EF ~2 to 4.5) in the middle basin with the peak contamination in the late 1980s, indicating that the two basins have different contamination histories.

Trophic interactions and food web structure of a subantarctic marine food web in the Beagle Channel: Bahía Lapataia, Argentina

Basic ecological knowledge regarding the importance of different sources of primary production and how it is transferred among consumer species is required to properly manage and conserve subpolar ecosystems that are particularly vulnerable to environmental changes. We used carbon (δ13C) and nitrogen (δ15N) stable isotope analysis to establish a baseline of species interactions and food web structure for the nearshore marine community in Bahia Lapataia, Argentina, an ecosystem that faces many threats, including a recent invasion of exotic chinook salmon. Primary producers and other organic sources (e.g., particulate organic matter) available to the food web were isotopically distinct and had a wide range in δ13C (−31.3 to −5.3 ‰) and δ15N (−0.5 to 13.1 ‰) values. Consumers also showed a wide range of isotope values with mean δ13C and δ15N values ranging from −20.8 to −12.3 ‰ and from 10.5 to 19.6 ‰, respectively. A cluster analysis of these isotope data correctly identified functional groups and expected interactions among species based on independent information. Using Bayesian isotope mixing models, we estimated that the proportional contribution of benthic production, in particular through grazing and the consumption of detritus, was a more important source of energy for primary and secondary consumers than pelagic production. Using stable isotope analysis to continually monitor species interactions and food web structure may prove to be a valuable research and management tool for assessing ecological consequences of different threats in this and other subpolar ecosystems.

Do benthic meiofaunal and macrofaunal communities respond to seasonality in pelagial processes in an Arctic fjord (Kongsfjorden, Spitsbergen)?

This study explores whether the marked seasonality in pelagic productivity and phytodetritus fluxes to the sea bottom in an Arctic fjord is reflected in variability of benthic communities in terms of taxonomic composition and standing stocks. Three stations located along the Kongsfjorden (west Spitsbergen) axis were visited in four seasons (May, August, October and January), and meiofauna and macrofauna was sampled. The elusive seasonal variability in benthic attributes contrasted with the clear seasonal effects in organic matter productivity and vertical fluxes (with diatom bloom-related peak in spring). No consistent differences in meiofaunal and macrofaunal density, diversity or composition among the four seasons were detected by PERMANOVA tests. Possible responses to spring food supply in meiofaunal reproduction timing were demonstrated in variability in individual size of Nematoda (decline in October after the maximum in August), Harpacticoida (decline in May and increase till October) and macrobenthic Crustacea (minimum in May). The spatial patterns shaped by the environmental gradients related to glacial inputs, the faunal impoverishment in inner basin and a shift in dominants along the fjord axis, were clearly designated and stable throughout the year. The resilience of Arctic fjordic benthic community to marked seasonality in pelagic phytodetritus fluxes may be related to organic matter reserves in sediments (large enough to sustain the detritus feeders on a year-round basis), inclusion of macroalgal carbon into the diet and common employment of lecithotrophic larva or direct development by polar benthos.

A comparison between late summer 2012 and 2013 water masses, macronutrients, and phytoplankton standing crops in the northern Bering and Chukchi Seas

Survey data from the northern Bering and Chukchi sea continental shelves in August–September 2012 and 2013 reveal inter-annual differences in the spatial structure of water masses along with statistically significant differences in thermohaline properties, chemical properties, and phytoplankton communities. We provide a set of water mass definitions applicable to the northern Bering and Chukchi continental shelves, and we find that the near-bottom Bering-Chukchi Summer Water (BCSW) was more saline in 2012 and Alaskan Coastal Water (ACW) was warmer in 2013. Both of these water masses carried higher nutrient concentrations in 2012, supporting a larger chlorophyll a biomass that was comprised primarily of small (<10µm) size class phytoplankton, so the classical relation between higher nutrient loads and larger phytoplankton does not hold for this region in late summer. The distributions of phytoplankton biomass and size structure reveal linkages between the wind fields, seafloor topography, water mass distributions and the pelagic production. The water mass structure, including the strength and location of stratification and fronts, respectively, differed primarily because of the August regional wind field, which was more energetic in 2012 but was more persistent in direction in 2013. High concentrations of ice in winter and early spring in 2012 and 2013 resembled conditions of the 1980s and early 1990s but the regional ice retreat rate has accelerated in the late 1990s and 2000s so the summer and fall ice concentrations more closely resembled those of the last two decades. Our data show that wind forcing can shut down the Alaskan Coastal Current in the NE Chukchi Sea for periods of weeks to months during the ice-covered winter and during the summer when buoyancy forcing is at its annual maximum. We hypothesize that a decrease in salinity and nutrients from 2012 to 2013 was a consequence of a decreased net Bering Strait transport from 2011 to 2012. Biological ramifications of an accelerated ice melt-back, restructuring of shelf flow pathways, and inter-annually varying Bering Strait nutrient fluxes are mostly unknown but all of these variations are potentially important to the Arctic ecosystem. Our results have implications for the total magnitude and seasonal evolution of primary productivity, secondary production, and the fate of fresh water, heat, and pelagic production on the Bering-Chukchi shelves.

Is colonization of sea ice by diatoms facilitated by increased surface roughness in growing ice crystals?

Colonization by ice algae at the bottom of the sea ice is important ecologically as these algae are the major carbon source for zooplankton and the Polar food chains from early spring and until ice break-up several months later. At that time, ice algae can seed the water column promoting the pelagic production. We collected a time-series of ice growth, surface roughness, ice algae biomass (Chl-a), photosynthetic performance, primary production, irradiance, species composition, under ice ADCP data, nutrients, and ice algae spatial distribution in Kangerlussuaq, Greenland. A significant increase in biomass, primary production, and photosynthetic performance was observed at the bottom of the first-year sea ice. This colonization was not related to any change in light or nutrient availability, but instead occurred over a few days after which all parameters remained stable and constant. Colonization was concurrent with active ice growth associated with a period of very cold air temperatures as low as minus 35 °C. This new ice growth featured ice crystals and dendrites that significantly increased the surface roughness of the bottom, which facilitated the colonization. The dendrites are about 0.5 mm high and with a similar distance between the crests. The species composition of ice algae was similar in the water below and at the ice bottom, though biomass remained significantly lower in the water, and was dominated by Fragilariopsis oceanica and Navicula vanhoeefi. It is concluded that the colonization of the bottom of the sea ice is solely related to the increase in surface roughness initiated in the growing ice.

Carbon sources and trophic relationships of ice seals during recent environmental shifts in the Bering Sea.

Dramatic multiyear fluctuations in water temperature and seasonal sea ice extent and duration across the Bering-Chukchi continental shelf have occurred in this century, raising a pressing ecological question: Do such environmental changes alter marine production processes linking primary producers to upper trophic-level predators? We examined this question by comparing the blubber fatty acid (FA) composition and stable carbon isotope ratios of individual FA (δ¹³CFA) of adult ringed seals (Pusa hispida), bearded seals (Erignathus barbatus), spotted seals (Phoca largha), and ribbon seals (Histriophoca fasciata), collectively known as "ice seals," sampled during an anomalously warm, low sea ice period in 2002-2005 in the Bering Sea and a subsequent cold, high sea ice period in 2007-2010. δ¹³C(FA) values, used to estimate the contribution to seals of carbon derived from sea ice algae (sympagic production) relative to that derived from water column phytoplankton (pelagic production), indicated that during the cold period, sympagic production accounted for 62-80% of the FA in the blubber of bearded seals, 51-62% in spotted seals, and 21-60% in ringed seals. Moreover, the δ¹³CFA values of bearded seals indicated a greater incorporation of sympagic FAs during the cold period than the warm period. This result provides the first empirical evidence of an ecosystem-scale effect of a putative change in sympagic production in the Western Arctic. The FA composition of ice seals showed clear evidence of resource partitioning among ringed, bearded, and spotted seals, and little niche separation between spotted and ribbon seals, which is consistent with previous studies. Despite interannual variability, the FA composition of ringed and bearded seals showed little evidence of differences in diet between the warm and cold periods. The findings that sympagic production contributes significantly to food webs supporting ice seals, and that the contribution apparently is less in warm years with low sea ice, raise an important concern: Will the projected warming and continuing loss of seasonal sea ice in the Arctic, and the associated decline of organic matter input from sympagic production, be compensated for by pelagic production to satisfy both pelagic and benthic carbon and energy needs?

The effect of summer monsoon on pelagic and littoral food webs in a large regulated reservoir (Lake Paldang, Korea): A stable isotope approach

To investigate the effect of summer monsoon-derived inputs of particulate organic matter (POM) on patterns of stable isotopes in the food web in a reservoir, we traced dietary sources of carbon and nitrogen in pelagic zooplankton and herbivorous littoral zoobenthos following a monsoonal disturbance in Lake Paldang, a large regulated reservoir in Korea. Carbon and nitrogen stable isotopes were analyzed in POM, zooplankton, sedimentary organic matter, zoobenthos, and piscivorous fishes in pre- and post-summer monsoon periods. Sharp depletion of 13C and enrichment of 15N of POM along with elevated POC/Chl a ratios occurred following the summer monsoon period, reflecting the rapid reduction of phytoplankton biomass and a pulsed supply of terrestrial organic detritus. Herbivorous zooplankton δ13C values, which were initially similar to POM δ13C values in the pre-summer monsoon period, decreased to nearly that of terrestrial organic matter, providing isotopic evidence of allochthonous contribution to zooplankton in the post-summer monsoon period. In contrast, herbivorous zoobenthos in the littoral area and higher fishes appeared to have a similar stable isotope composition between the pre- and post-summer monsoon period. Our findings indicate that although monsoon storms dramatically decrease phytoplankton biomass, the augmented allochthonous material after the summer monsoon offsets this effect temporarily by subsidizing pelagic zooplankton production. Allochthonous subsidies to herbivorous littoral zoobenthos and piscivorous fishes are relatively limited.

&amp;lt;i&amp;gt;Couplerlib&amp;lt;/i&amp;gt;: a metadata-driven library for the integration of multiple models of higher and lower trophic level marine systems with inexact functional group matching

Abstract. End-to-end modelling is a rapidly developing strategy for modelling in marine systems science and management. However, problems remain in the area of data matching and sub-model compatibility. A mechanism and novel interfacing system (Couplerlib) is presented whereby a physical–biogeochemical model (General Ocean Turbulence Model–European Regional Seas Ecosystem Model, GOTM–ERSEM) that predicts dynamics of the lower trophic level (LTL) organisms in marine ecosystems is coupled to a dynamic ecosystem model (Ecosim), which predicts food-web interactions among higher trophic level (HTL) organisms. Coupling is achieved by means of a bespoke interface, which handles the system incompatibilities between the models and a more generic Couplerlib library, which uses metadata descriptions in extensible mark-up language (XML) to marshal data between groups, paying attention to functional group mappings and compatibility of units between models. In addition, within Couplerlib, models can be coupled across networks by means of socket mechanisms. As a demonstration of this approach, a food-web model (Ecopath with Ecosim, EwE) and a physical–biogeochemical model (GOTM–ERSEM) representing the North Sea ecosystem were joined with Couplerlib. The output from GOTM–ERSEM varies between years, depending on oceanographic and meteorological conditions. Although inter-annual variability was clearly present, there was always the tendency for an annual cycle consisting of a peak of diatoms in spring, followed by (less nutritious) flagellates and dinoflagellates through the summer, resulting in an early summer peak in the mesozooplankton biomass. Pelagic productivity, predicted by the LTL model, was highly seasonal with little winter food for the higher trophic levels. The Ecosim model was originally based on the assumption of constant annual inputs of energy and, consequently, when coupled, pelagic species suffered population losses over the winter months. By contrast, benthic populations were more stable (although the benthic linkage modelled was purely at the detritus level, so this stability reflects the stability of the Ecosim model). The coupled model was used to examine long-term effects of environmental change, and showed the system to be nutrient limited and relatively unaffected by forecast climate change, especially in the benthos. The stability of an Ecosim formulation for large higher tropic level food webs is discussed and it is concluded that this kind of coupled model formulation is better for examining the effects of long-term environmental change than short-term perturbations.

CO2 Saturation and Trophic Shift Induced by Microbial Metabolic Processes in a River-Dominated Ocean Margin (Tropical Shallow Lagoon, Chilika, India)

ABSTRACTAn effort has been made for the first time in Asia's largest brackish water lagoon, Chilika, to investigate the spatio-temporal variability in primary productivity (PP), bacterial productivity (BP), bacterial abundance (BA), bacterial respiration (BR) and bacterial growth efficiency (BGE) in relation to partial pressure of CO2 (pCO2) and CO2 air–water flux and the resultant trophic switchover. Annually, PP ranged between 24 and 376 µg C L−1 d−1 with significantly low values throughout the monsoon (MN), caused by light limitation due to inputs of riverine suspended matter. On the contrary, BP and BR ranged from 11.5 to 186.3 µg C L−1 d−1 and from 14.1 to 389.4 µg C L−1 d−1, respectively, with exceptionally higher values during MN. A wide spatial and temporal variation in the lagoon trophic status was apparent from BP/PP (0.05–6.4) and PP/BR (0.10–18.2) ratios. The seasonal shift in net pelagic production from autotrophy to heterotrophy due to terrestrial organic matter inputs via rivers, enhanced the bacterial metabolism during the MN, as evident from the high pCO2 (10,134 µatm) and CO2 air–water flux (714 mm m−2 d−1). Large variability in BGE and BP/PP ratios especially during MN led to high bacteria-mediated carbon fluxes which was evident from significantly high bacterial carbon demand (BCD >100% of PP) during this season. This suggested that the net amount of organic carbon (either dissolved or particulate form) synthesized by primary producers in the lagoon was not sufficient to satisfy the bacterial carbon requirements. Lagoon sustained low to moderate autotrophic–heterotrophic coupling with annual mean BCD of 231% relative to the primary production, which depicted that bacterioplankton are the mainstay of the lagoon biogeochemical cycles and principal players that bring changes in trophic status. Study disclosed that the high CO2 supersaturation and oxygen undersaturation during MN was attributed to the increased heterotrophic respiration (in excess of PP) fuelled by allochthonous organic matter. On a spatial scale, lagoon sectors such as south sector, central sector and outer channel recorded “net autotrophic,” while the northern sector showed “net heterotrophic” throughout the study period.

Accounting for littoral primary production by periphyton shifts a highly humic boreal lake towards net autotrophy

Abstract The prevailing view that many humic lakes are net heterotrophic is commonly based on pelagic measurements alone. Poor light conditions in humic lakes are assumed to constrain littoral primary production (PP), such that the littoral zone has been considered an insignificant contributor to whole‐lake PP. However, that assumption is based on models and inferences from pelagic processes which do not take littoral zone structure into account. Many lakes have an extensive ring of aquatic vegetation lying near the water surface, which provides substratum for epiphytic algae under well‐illuminated conditions. We measured both pelagic and littoral PP and community respiration (CR) in Mekkojärvi, a small, highly humic headwater lake, in southern Finland throughout the open water season in 2012. We used a 14C incorporation technique to measure pelagic PP, while littoral PP was determined using changes in dissolved inorganic carbon concentrations during in situ incubations. We then estimated whole‐lake PP and CR for both the littoral and pelagic zones. We found that littoral PP usually dominated whole‐lake PP, contributing &gt;90% to total PP in summer. A mean pelagic production to respiration ratio (GPP : CR) of 0.4 clearly indicated strong net heterotrophy, but a value of 2.2 for the littoral zone indicated strong autotrophy. For both habitats combined, the mean whole lake GPP : CR was 1.6, indicating net autotrophy. We suggest that littoral PP can contribute significantly to whole‐lake PP even in highly humic lakes, and that the littoral contribution can shift some lakes which have been considered net heterotrophic to metabolic balance or even net autotrophy during the ice‐free period. Small humic lakes like Mekkojärvi with rings of littoral vegetation are widespread, especially in the boreal zone, and at least for similar lakes, evaluating lake metabolism from pelagic measurements alone is likely to be misleading.