ABSTRACT: We investigated the interactions between the cold-water coral Lophelia pertusa and its associated polychaete Eunice norvegica by quantifying carbon (C) and nitrogen (N) budgets of tissue assimilation, food partitioning, calcification and respiration using (13)C and (15)N enriched algae and zooplankton as food sources. During incubations both species were kept either together or in separate chambers to study the net outcome of their interaction on the above mentioned processes. The stable isotope approach also allowed us to follow metabolically derived tracer C further into the coral skeleton and therefore estimate the effect of the interaction on coral calcification. Results showed that food assimilation by the coral was not significantly elevated in presence of E. norvegica but food assimilation by the polychaete was up to 2 to 4 times higher in the presence of the coral. The corals kept assimilation constant by increasing the consumption of smaller algae particles less favored by the polychaete while the assimilation of Artemia was unaffected by the interaction. Total respiration of tracer C did not differ among incubations, although E. norvegica enhanced coral calcification up to 4 times. These results together with the reported high abundance of E. norvegica in cold-water coral reefs, indicate that the interactions between L. pertusa and E. norvegica can be of high importance for ecosystem functioning.
PLoS ONE 01/2013; 8(3):e58660. · 4.09 Impact Factor
ABSTRACT: The food webs of terrestrial soils and of freshwater and marine sediments depend on adjacent aboveground or pelagic ecosystems for organic matter input that provides nutrients and energy. There are important similarities in the flow of organic matter through these food webs and how this flow feeds back to primary production. In both soils and sediments, trophic interactions occur in a cycle in which consumers stimulate nutrient cycling such that mineralized resources are made available to the primary producers. However, aquatic sediments and terrestrial soils differ greatly in the connectivity between the production and the consumption of organic matter. Terrestrial soils and shallow aquatic sediments can receive organic matter within hours of photosynthesis when roots leak carbon, whereas deep oceanic sediments receive organic matter pos-sibly months after carbon assimilation by phytoplankton. This comparison has implications for the capacity of soils and sediments to affect the global carbon balance.
BioScience 01/2013; 63(1):35-42. · 4.62 Impact Factor
is an integrated software package for aquatic chemical model generation focused on ocean acidification and antropogenic CO2 uptake. However, the package is not restricted to the carbon cycle or the oceans: it calculates, converts, and visualizes
information necessary to describe pH, related CO2 air–water exchange, as well as aquatic acid–base chemistry in general for marine, estuarine or freshwater systems. Due to
the fact that it includes the relevant acid–base systems, it can also be applied to pore water systems and anoxic waters.
is implemented in the open source programming language
, which allows for a flexible and versatile application:
’s functionality can be used stand-alone as well as seamlessly integrated into reactive-transport models in the
modelling environment. Additionally,
provides a routine to simulate and investigate titrations of water samples with a strong acid or base, as well as a routine
that allows for a determination of total alkalinity and total carbonate values from recorded titration curves using non-linear
KeywordsAcid–base chemistry-pH modelling-Ocean acidification-Reactive-transport models-Marine estuarine and freshwater systems-CO2 air–sea exchange-In silico titration-TA determination
Aquatic Geochemistry 04/2012; 16(4):507-546. · 1.90 Impact Factor
ABSTRACT: The quantitative mapping of food web flows based on empirical data is a crucial yet difficult task in ecology. The difficulty
arises from the under-sampling of food webs, because most data sets are incomplete and uncertain. In this article, we review
methods to quantify food web flows based on empirical data using linear inverse models (LIM). The food web in a LIM is described
as a linear function of its flows, which are estimated from empirical data by inverse
modeling. The under-sampling of food webs implies that infinitely many different solutions exist that are consistent with a given
data set. The existing approaches to food web LIM select a single solution from this infinite set by invoking additional assumptions:
either a specific selection criterion that has no solid ecological basis is used or the data set is artificially upgraded
by assigning fixed values to, for example, physiological parameters. Here, we advance a likelihood approach (LA) that follows
a different solution philosophy. Rather than singling out one particular solution, the LA generates a large set of possible
solutions from which the marginal probability density function (mPDF) of each flow and correlations between flows can be derived.
The LA is exemplified with an example model of a soil food web and is made available in the open-source R-software. Moreover,
we show how stoichiometric data, stable isotope signatures, and fatty acid compositions can be included in the LIM to alleviate
the under-sampling problem. Overall, LIM prove to be a powerful tool in food web research, which can bridge the gap between
empirical data and the analysis of food web structures.
Ecosystems 04/2012; 13(1):32-45. · 3.49 Impact Factor
ABSTRACT: Trophodynamics of meso-zooplankton in the North Sea (NS) were assessed at a site in the southern NS, and at a shallow and
a deep site in the central NS. Offshore and neritic species from different ecological niches, including Calanus spp., Temora spp. and Sagitta spp., were collected during seven cruises over 14 months from 2007 to 2008. Bulk stable isotope (SI) analysis, phospholipid-derived
fatty acid (PLFA) compositions, and δ
13CPLFA data of meso-zooplankton and particulate organic matter (POM) were used to describe changes in zooplankton relative trophic
positions (RTPs) and trophodynamics. The aim of the study was to test the hypothesis that the RTPs of zooplankton in the North
Sea vary spatially and seasonally, in response to hydrographic variability, with the microbial food web playing an important
role at times. Zooplankton RTPs tended to be higher during winter and lower during the phytoplankton bloom in spring. RTPs
were highest for predators such as Sagitta sp. and Calanus helgolandicus and lowest for small copepods such as Pseudocalanus elongatus and zoea larvae (Brachyura). δ
15NPOM-based RTPs were only moderate surrogates for animals’ ecological niches, because of the plasticity in source materials from
the herbivorous and the microbial loop food web. Common (16:0) and essential (eicosapentaenoic acid, EPA and docosahexaenoic
acid, DHA) structural lipids showed relatively constant abundances. This could be explained by incorporation of PLFAs with
13C signatures which followed seasonal changes in bulk δ
13CPOM and PLFA δ
13CPOM signatures. This study highlighted the complementarity of three biogeochemical approaches for trophodynamic studies and substantiated
conceptual views of size-based food web analysis, in which small individuals of large species may be functionally equivalent
to large individuals of small species. Seasonal and spatial variability was also important in altering the relative importance
of the herbivorous and microbial food webs.
KeywordsCalanus–Compound-specific stable isotope analysis–GC-c-IRMS–North Sea–Phospholipids–Size-based food web–Stable isotopes–Zooplankton
Biogeochemistry 04/2012; · 3.07 Impact Factor
ABSTRACT: The diet of cavity sponges on the narrow fringing reefs of Curaçao, Caribbean was studied. The origin and resources of the
bulk food of these sponges, i.e., dissolved organic matter (DOM), were identified using stable carbon and nitrogen isotopes
and fatty acid biomarkers. We found that phytoplankton and its derived DOM from the adjacent open sea and from reef overlying
water is not the main source of food for most of the sponges examined nor is bacterioplankton. Interestingly, dual stable
isotope signatures (δ13Corg, δ15Norg) and fatty acid biomarkers appoint coral mucus and organic matter derived from crustose coralline algae (CCA) as probable
food sources for encrusting sponges. Mucus-derived DOM may contribute up to 66% to the diet of examined sponges based on results
of dual isotope mixing model analysis. The contribution of CCA (as purported representative for benthic algae) was smaller
with values up to 31%. Together, mucus- and CCA-derived substrates contributed for 48–73% to the diet of sponges. The presence
of the exogenous fatty acid 20:4ω6 in sponges, which is abundant in coral mucus of Madracis mirabilis and in CCA, highlights these reef-derived resources as sources of nutrition for DOM feeding cavity sponges. The relatively
high concentrations of exogenous 20:4ω6 in all sponges examined supports our hypothesis that the bulk of the food of the cavity
sponge community is reef-derived. Our results imply that cavity sponges play an important role in conserving food and energy
produced within the reef.
Marine Biology 04/2012; 158(7):1653-1666. · 2.28 Impact Factor
ABSTRACT: We report the results of a detailed investigation on the trophoecology of two dominant meiofaunal species at the Håkon Mosby
Mud Volcano (HMMV), a deep-sea cold methane-venting seep. Analyses of fatty acids (FAs) and their stable carbon isotopes were
used to determine the importance of chemosynthetic nutritional pathways for the dominant copepod species (morphologically
very similar to Tisbe wilsoni) inhabiting the volcano’s centre and the abundant nematode Halomonhystera disjuncta from the surrounding microbial mats. The strong dominance of bacterial biomarkers (16:1ω7c, 18:1ω7c and 16:1ω8c) coupled
with their individual light carbon isotopes signatures (δ
13C ranging from −52 to −81‰) and the lack of symbiotic relationships with prokaryotes (as revealed by molecular analyses and
fluorescent in situ hybridisation) indicated that chemosynthetically derived carbon constitutes the main diet of both species.
However, the copepod showed a stronger reliance on the utilisation of methanotrophic bacteria and contained polyunsaturated
FAs of bacterial origin (20:5ω3 and 22:6ω3 with isotope signatures δ
13C<−80‰). Instead, the FA profiles of H. disjuncta suggested that sulphide-oxidising bacteria constituted the main diet of this nematode. Therefore, HMMV can be regarded as
a persistent deep-sea cold seep, allowing a chemosynthesis-based trophic specialisation by the dominant meiofaunal species
inhabiting its sediments. The present investigation, through the determination of the fatty acid profiles, provides the first
evidence for trophic specialisation of meiofauna associated with sub-habitats within a cold seep.
Marine Biology 04/2012; 156(6):1289-1296. · 2.28 Impact Factor
ABSTRACT: The fate and transport of watershed-derived ammonium in a tidal freshwater marsh fringing the nutrient rich Scheldt River,
Belgium, was quantified in a whole ecosystem 15N labeling experiment. In late summer (September) we added 15N-NH4+ to the flood water entering a 3477m2 tidal freshwater marsh area, and traced the ammonium processing and retention in four subsequent tide cycles. In this paper
we present the results for the water-phase components of the marsh system and compare them to a similar experiment conducted
in spring/early summer (May). Changes in concentration and isotopic enrichment of NO3−+NO2−, N2O, N2, NH4+ and suspended particulate nitrogen (SPN) were measured in concert with a mass balance study. All analyzed N-pools were labeled,
and 49% of the added 15NH4+ was retained or transformed. The most important pool for 15N was nitrate, accounting for 17% of 15N-transformation. N2, N2O and SPN accounted for 2.4, 0.02 and 1.4%, respectively. The temporal and spatial patterns of 15N transformation in the water phase component of the system were remarkably similar to those observed in May, indicating good
reproducibility of the whole ecosystem labeling approach, but the absolute ammonium transformation rate was 3times higher
in May. While the marsh surface area was crucial for nitrification in May this was less pronounced in September. Denitrification,
on the other hand, appeared more important in September compared to May.
Biogeochemistry 04/2012; 80(3):289-298. · 3.07 Impact Factor
ABSTRACT: Organic matter (OM) remineralization may be considered a key function of the benthic compartment of marine ecosystems and
in this study we investigated if the input of labile organic carbon alters mineralization of indigenous sediment OM (OM priming).
Using 13C-enriched diatoms as labile tracer carbon, we examined shallow-water sediments (surface and subsurface layers) containing
organic carbon of different reactivity under oxic versus anoxic conditions. The background OM decomposition rates of the sediment
used ranged from 0.08 to 0.44μmolCmlws−1day−1. Algal OM additions induced enhanced levels of background remineralization (priming) up to 31% and these measured excess
fluxes were similar to mineralization of the added highly degradable tracer algal carbon. This suggests that OM priming may
be important in marine sediments.
Marine Biology 04/2012; 156(11):2277-2287. · 2.28 Impact Factor
ABSTRACT: Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the
Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the
1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m−2 d−1) decreasing seaward (22–37 mmol C m−2 d−1). A significant decrease of NIT was observed with regard to previous investigations although this process still represents
up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed
to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time
in the estuary with values ranging from −300 to 165 mmol C m−2 d−1. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published
benthic metabolic rates. A NEP of −39±8 mmol C m−2 d−1 was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from
June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure
applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the
inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much
lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m−2 d−1) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear.
Estuaries and Coasts 04/2012; 28(6):868-883. · 2.11 Impact Factor
ABSTRACT: Hypoxia represents one of the major causes of biodiversity and ecosystem functioning loss for coastal waters. Since eutrophication-induced hypoxic events are becoming increasingly frequent and intense, understanding the response of ecosystems to hypoxia is of primary importance to understand and predict the stability of ecosystem functioning. Such ecological stability may greatly depend on the recovery patterns of communities and the return time of the system properties associated to these patterns. Here, we have examined how the reassembly of a benthic community contributed to the recovery of ecosystem functioning following experimentally-induced hypoxia in a tidal flat. We demonstrate that organism-sediment interactions that depend on organism size and relate to mobility traits and sediment reworking capacities are generally more important than recovering species richness to set the return time of the measured sediment processes and properties. Specifically, increasing macrofauna bioturbation potential during community reassembly significantly contributed to the recovery of sediment processes and properties such as denitrification, bedload sediment transport, primary production and deep pore water ammonium concentration. Such bioturbation potential was due to the replacement of the small-sized organisms that recolonised at early stages by large-sized bioturbating organisms, which had a disproportionately stronger influence on sediment. This study suggests that the complete recovery of organism-sediment interactions is a necessary condition for ecosystem functioning recovery, and that such process requires long periods after disturbance due to the slow growth of juveniles into adult stages involved in these interactions. Consequently, repeated episodes of disturbance at intervals smaller than the time needed for the system to fully recover organism-sediment interactions may greatly impair the resilience of ecosystem functioning.
PLoS ONE 01/2012; 7(11):e49795. · 4.09 Impact Factor
ABSTRACT: The response of Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler, Calcidiscus leptoporus (G. Murray et V. H. Blackman) J. Schiller, and Syracosphaera pulchra Lohmann to elevated partial pressure of carbon dioxide (pCO2) was investigated in batch cultures. We reported on the response of both haploid and diploid life stages of these three species. Growth rate, cell size, particulate inorganic carbon (PIC), and particulate organic carbon (POC) of both life stages were measured at two different pCO2 (400 and 760 parts per million [ppm]), and their organic and inorganic carbon production were calculated. The two life stages within the same species generally exhibited a similar response to elevated pCO2, the response of the haploid stage being often more pronounced than that of the diploid stage. The growth rate was consistently higher at elevated pCO2, but the response of other processes varied among species. Calcification rate of C. leptoporus and of S. pulchra did not change at elevated pCO2, whereas it increased in E. huxleyi. POC production and cell size of both life stages of S. pulchra and of the haploid stage of E. huxleyi markedly decreased at elevated pCO2. It remained unaltered in the diploid stage of E. huxleyi and C. leptoporus and increased in the haploid stage of the latter. The PIC:POC ratio increased in E. huxleyi and was constant in C. leptoporus and S. pulchra. Elevated pCO2 has a significant effect on these three coccolithophore species, the haploid stage being more sensitive. This effect must be taken into account when predicting the fate of coccolithophores in the future ocean.
Journal of Phycology 11/2011; 47(6):1281 - 1291. · 2.07 Impact Factor
ABSTRACT: ABSTRACT: Dissolved organic nitrogen (DON) acts as a large reservoir of fixed nitrogen. Whereas DON utilization is common in the microbial community, little is known about utilization by macrophytes. We investigated the ability of the coexisting temperate marine macrophytes Zostera noltii, Cymodocea nodosa, and Caulerpa prolifera to take up nitrogen and carbon from small organic substrates of different molecular complexities (urea, glycine, L-leucine, and L-phenylalanine) and from dissolved organic matter (DOM) derived from algal and bacterial cultures (substrates with a complex composition). In addition to inorganic nitrogen, nitrogen from small organic substrates could be taken up in significant amounts by all macrophytes. Substrate uptake by the aboveground tissue differed from that of the belowground tissue. No relationships between carbon and nitrogen uptake of small organics were found. The preference for individual organic substrates was related to their structural complexity and C:N ratio. Upta
Marine Ecology Progress Series 04/2011; 427:71-81. · 2.71 Impact Factor
ABSTRACT: Biological particle mixing (bioturbation) and solute transfer (bio-irrigation) contribute extensively to ecosystem functioning in sediments where physical mixing is low. Macrobenthos transports oxygen and organic matter deeper into the sediment, thereby likely providing favourable niches to lower trophic levels (i.e., smaller benthic animals such as meiofauna and bacteria) and thus stimulating mineralisation. Whether this biological transport facilitates fresh organic matter assimilation by the metazoan lower part of the food web through niche establishment (i.e., ecosystem engineering) or rather deprives them from food sources, is so far unclear. We investigated the effects of the ecosystem engineers Lanice conchilega (bio-irrigator) and Abra alba (bioturbator) compared to abiotic physical mixing events on survival and food uptake of nematodes after a simulated phytoplankton bloom. The (13)C labelled diatom Skeletonema costatum was added to 4 treatments: (1) microcosms containing the bioturbator, (2) microcosms containing the bio-irrigator, (3) control microcosms and (4) microcosms with abiotic manual surface mixing. Nematode survival and subsurface peaks in nematode density profiles were most pronounced in the bio-irrigator treatment. However, nematode specific uptake (Δδ(13)C) of the added diatoms was highest in the physical mixing treatment, where macrobenthos was absent and the diatom (13)C was homogenised. Overall, nematodes fed preferentially on bulk sedimentary organic material rather than the added diatoms. The total C budget (µg C m(-2)), which included TO(13)C remaining in the sediment, respiration, nematode and macrobenthic uptake, highlighted the limited assimilation by the metazoan benthos and the major role of bacterial respiration. In summary, bioturbation and especially bio-irrigation facilitated the lower trophic levels mainly over the long-term through niche establishment. Since the freshly added diatoms represented only a limited food source for nematodes, the macrobenthic effect was more pronounced in niche establishment than the negative structuring effects such as competition.
PLoS ONE 01/2011; 6(3):e18078. · 4.09 Impact Factor
ABSTRACT: Ocean acidification, due to anthropogenic CO₂ absorption by the ocean, may have profound impacts on marine biota. Calcareous organisms are expected to be particularly sensitive due to the decreasing availability of carbonate ions driven by decreasing pH levels. Recently, some studies focused on the early life stages of mollusks that are supposedly more sensitive to environmental disturbances than adult stages. Although these studies have shown decreased growth rates and increased proportions of abnormal development under low pH conditions, they did not allow attribution to pH induced changes in physiology or changes due to a decrease in aragonite saturation state. This study aims to assess the impact of several carbonate-system perturbations on the growth of Pacific oyster (Crassostrea gigas) larvae during the first 3 days of development (until shelled D-veliger larvae). Seawater with five different chemistries was obtained by separately manipulating pH, total alkalinity and aragonite saturation state (calcium addition). Results showed that the developmental success and growth rates were not directly affected by changes in pH or aragonite saturation state but were highly correlated with the availability of carbonate ions. In contrast to previous studies, both developmental success into viable D-shaped larvae and growth rates were not significantly altered as long as carbonate ion concentrations were above aragonite saturation levels, but they strongly decreased below saturation levels. These results suggest that the mechanisms used by these organisms to regulate calcification rates are not efficient enough to compensate for the low availability of carbonate ions under corrosive conditions.
PLoS ONE 01/2011; 6(8):e23010. · 4.09 Impact Factor
ABSTRACT: Sea-surface warming, sea-ice melting and related freshening, changes in circulation and mixing regimes, and ocean acidification induced by the present climate changes are modifying marine ecosystem structure and function and have the potential to alter the cycling of carbon and nutrients in surface oceans. Changing climate has direct and indirect consequences on marine viruses, including cascading effects on biogeochemical cycles, food webs, and the metabolic balance of the ocean. We discuss here a range of case studies of climate change and the potential consequences on virus function, viral assemblages and virus-host interactions. In turn, marine viruses influence directly and indirectly biogeochemical cycles, carbon sequestration capacity of the oceans and the gas exchange between the ocean surface and the atmosphere. We cannot yet predict whether the viruses will exacerbate or attenuate the magnitude of climate changes on marine ecosystems, but we provide evidence that marine viruses interact actively with the present climate change and are a key biotic component that is able to influence the oceans' feedback on climate change. Long-term and wide spatial-scale studies, and improved knowledge of host-virus dynamics in the world's oceans will permit the incorporation of the viral component into future ocean climate models and increase the accuracy of the predictions of the climate change impacts on the function of the oceans.
FEMS microbiology reviews 11/2010; 35(6):993-1034. · 10.96 Impact Factor
ABSTRACT: A one-dimensional model that couples water-column physics with pelagic and benthic biogeochemistry in a 50-m-deep water column
is used to demonstrate the importance of the sediment in the functioning of shallow systems, the eutrophication status of
the system, and the system’s resilience to oligotrophication. Two physical scenarios, a well-mixed and a stratified water
column, are considered and both are run along a gradient of increasing initial pelagic-dissolved inorganic nitrogen (DIN)
concentration. Where the mixed layer extends to the bottom, more nutrients and less light are available for growth. Under
low to moderately eutrophic conditions (pelagic DIN <30 mmol m−3), this leads to higher productivity in well-mixed waters, while the stratified system is more productive under highly eutrophic
conditions. Under stratification, the build-up of nitrate and depletion of oxygen below the mixed layer does not notably change
the functioning of the sediment as a sink for reactive nitrogen. In sediments underlying well-mixed waters, sedimentary denitrification,
fueled mainly by in situ nitrification, is slightly more important (8–15% of total benthic mineralization) than under stratified
waters (7–20%), where the influx of bottom-water nitrate is the most important nitrate source. As a consequence of this less
efficient removal of reactive nitrogen, the winter DIN concentrations are higher in the stratified scenario. The model is
used to estimate the long-term benefits of nutrient reduction scenarios and the timeframe under which the new steady-state
condition is approached. It is shown that a 50% reduction in external nitrogen inputs ultimately results in a reduction of
60–70% of the original pelagic DIN concentration. However, as the efflux of nitrogen from the sediment compensates part of
the losses in the water column, system oligotrophication is a slow process: after 20 years of reduced inputs, the pelagic
DIN concentrations still remain 2.7 mmol m−3 (mixed) and 3.9 mmol m−3 (stratified) above the ultimate DIN concentrations.
KeywordsBenthic-pelagic coupling-Model-Nitrogen cycle-Denitrification-Eutrophication-Oligotrophication
05/2010: pages 239-254;