Benthic System Research Articles

Variation in benthic long-term data of transitional waters: Is interpretation more than speculation?

Biological long-term data series in marine habitats are often used to identify anthropogenic impacts on the environment or climate induced regime shifts. However, particularly in transitional waters, environmental properties like water mass dynamics, salinity variability and the occurrence of oxygen minima not necessarily caused by either human activities or climate change can attenuate or mask apparent signals. At first glance it very often seems impossible to interpret the strong fluctuations of e.g. abundances or species richness, since abiotic variables like salinity and oxygen content vary simultaneously as well as in apparently erratic ways. The long-term development of major macrozoobenthic parameters (abundance, biomass, species numbers) and derivative macrozoobenthic indices (Shannon diversity, Margalef, Pilou’s evenness and Hurlbert) has been successfully interpreted and related to the long-term fluctuations of salinity and oxygen, incorporation of the North Atlantic Oscillation index (NAO index), relying on the statistical analysis of modelled and measured data during 35 years of observation at three stations in the south-western Baltic Sea. Our results suggest that even at a restricted spatial scale the benthic system does not appear to be tightly controlled by any single environmental driver and highlight the complexity of spatially varying temporal response.

Simulation of rapid ecological change in Lake Ontario

Lower trophic level processes are integral to proper functioning of large aquatic ecosystems and have been disturbed in Lake Ontario by various stressors including exotic species. The invasion of benthic habitats by dreissenid mussels has led to systemic changes and native faunal declines. Size-dependent physiological rates, spatial differences and connectivity, competition, and differential population dynamics among invertebrate groups contributed to the change and system complexity. We developed a spatially explicit, individual-based mechanistic model of the benthic ecosystem in Lake Ontario, with coupling to the pelagic system, to examine ecosystem dynamics and effects of dreissenid mussel invasion and native fauna losses. Benthic organisms were represented by functional groups; filter-feeders (i.e., dreissenid mussels), surface deposit-feeders (e.g., native amphipod Diporeia spp.), and deposit-feeders (e.g., oligochaetes and other burrowers). The model was stable, represented ecological structure and function effectively, and reproduced observed effects of the mussel invasion. Two hypotheses for causes of Diporeia loss, competition or disease-like mortality, were tested. Simple competition for food did not explain observed declines in native surface deposit-feeders during the filter-feeder invasion. However, the elevated mortality scenario supports a disease-like cause for loss of the native amphipod, with population changes in various lake areas and altered benthic biomass transfers. Stabilization of mussel populations and possible recovery of the native, surface-deposit feeding amphipod were predicted. Although further research is required on forcing functions, model parameters, and natural conditions, the model provides a valuable tool to help managers understand the benthic system and plan for response to future disruptions.

Bathymetric patterns in standing stock and diversity of deep-sea nematodes at the long-term ecological research observatory HAUSGARTEN (Fram Strait)

Abstract Bathymetric patterns in standing stocks and diversity are a major topic of investigation in deep-sea biology. From the literature, responses of metazoan meiofauna and nematodes to bathymetric gradients are well studied, with a general decrease in biomass and abundance with increasing water depth, while bathymetric diversity gradients often, although it is not a rule, show a unimodal pattern. Spatial distribution patterns of nematode communities along bathymetric gradients are coupled with surface-water processes and interacting physical and biological factors within the benthic system. We studied the nematode communities at the Long-Term Ecological Research (LTER) observatory HAUSGARTEN, located in the Fram Strait at the Marginal Ice Zone, with respect to their standing stocks as well as structural and functional diversity. We evaluated whether nematode density, biomass and diversity indices, such as H 0 , H inf , EG (50) , Θ − 1 , are linked with environmental conditions along a bathymetric transect spanning from 1200 m to 5500 m water depth. Nematode abundance, biomass and diversity, as well as food availability from phytodetritus sedimentation (indicated by chloroplastic pigments in the sediments), were higher at the stations located at upper bathyal depths (1200–2000 m) and tended to decrease with increasing water depth. A faunal shift was found below 3500 m water depth, where genus composition and trophic structure changed significantly and structural diversity indices markedly decreased. A strong dominance of very few genera and its high turnover particularly at the abyssal stations (4000–5500 m) suggests that environmental conditions were rather unfavorable for most genera. Despite the high concentrations of sediment-bound chloroplastic pigments and elevated standing stocks found at the deepest station (5500 m), nematode genus diversity remained the lowest compared to all other stations. This study provides a further insight into the knowledge of deep-sea nematodes, their diversity patterns and a deeper understanding of the environmental factors shaping nematodes communities at bathyal and abyssal depths.

The allochthonous material input in the trophodynamic system of the shelf sediments of the Gulf of Tigullio (Ligurian Sea, NW Mediterranean)

The organic allochthonous material input in the benthic system of a NW Mediterranean shelf area was studied using a three-pronged approach, focusing firstly on the evaluation of the sedimentary stable isotope ratios and organic matter (OM) composition, then on the OM recycling processes performed by the microbial organisms, and finally on the potential trophic relationships between the macrobenthic organisms. The highest allochthonous signal, indicating continental input, was observed within the 50-m isobath, while at the 80-m isobath the marine signal was higher, pointing to a rather low continental influence approximately 5 km from the shore. Heavier rainfall, often generating abrupt allochthonous inputs by river outfalls, led to a wider spread of fine sediment particles. Carbohydrates were the compounds that best represented the continental input and these compounds were associated with potential recycling activities by microbiota, pointing to the entry of these C-containing allochthonous materials into the microbial food web. The macrofaunal deposit-feeders used sedimentary OM characterised by a continental signature as a food source, although the isotopic ratios of the organisms also pointed to selective feeding on materials that had a marine signature, especially at our offshore sampling stations. Predators fed on deposit- or suspension-feeders, with a potential selection of the latter during the highest inputs of continental materials occurring in winter.

Modelling impacts and recovery in benthic communities exposed to localised high CO2

Regulations pertaining to carbon dioxide capture with offshore storage (CCS) require an understanding of the potential localised environmental impacts and demonstrably suitable monitoring practices. This study uses a marine ecosystem model to examine a comprehensive range of hypothetical CO2 leakage scenarios, quantifying both impact and recovery time within the benthic system. Whilst significant mortalities and long recovery times were projected for the larger and longer term scenarios, shorter-term or low level exposures lead to reduced projected impacts. This suggests that efficient monitoring and leak mitigation strategies, coupled with appropriate selection of storage sites can effectively limit concerns regarding localised environmental impacts from CCS. The feedbacks and interactions between physiological and ecological responses simulated reveal that benthic responses to CO2 leakage could be complex. This type of modelling investigation can aid the understanding of impact potential, the role of benthic community recovery and inform the design of baseline and monitoring surveys.

Assessment of long-term changes of ecosystem indexes in Tongoy Bay (SE Pacific coast): Based on trophic network analysis

Quantitative macroscopic's indexes have been used to compare three trophic models of the exploited benthic ecosystem of Tongoy Bay. In this system the primary productivity and benthic invertebrates are more important in the cycling of biomass. The models were built with a similar number of compartments for the years 1992, 2002 and 2012, using Ecopath with Ecosim (EwE). Odum and Ulanowicz's frameworks and ecological network analysis were then used to estimate the levels of maturity, growth and development of the system. Likewise, “keystoneness” indexes – at each time – were also estimated for the models. Our results show that Tongoy Bay exhibited an increase in maturity and development (“health”) in 2012 compared to past conditions, which was reflected by (1) an increase in the total system biomass, total system throughput, AMI, and absolute Ascendency, (2) higher flow and increased efficiency of transferred energy and its proportion at higher trophic levels, (3) an increase of recycling (FCI), (4) a reduction of NPP/R and NPP/B ratios of the system, and (5) an increase in the number of compartments trophically linked that comprise the keystone species complex. We argue that these results are a consequence of reduced fishing pressure on this benthic system in recent years. This study shows that the fishing would not only have a direct impact on exploited species, but would also affect the structure and functioning of the ecosystem. The information obtained could help to improve the management of fisheries resources, evaluating surveillance indicators that can show the putative changes of intervened ecosystems.

Subtle reproductive impairment through nitric oxide-mediated mechanisms in sea urchins from an area affected by harmful algal blooms.

The health of the sea urchin Paracentrotus lividus, a key species in the Mediterranean Sea, is menaced by several pressures in coastal environments. Here, we aimed at assessing the reproductive ability of apparently healthy P. lividus population in a marine protected area affected by toxic blooms of Ostreospsis cf. ovata. Wide-ranging analyses were performed in animals collected prior to and during the bloom, as well as at several times thereafter, during the reproductive season. Adults showed a low fertilization rate, along with high nitric oxide (NO) levels in the gonads and the nitration of the major yolk protein toposome, which is an important player in sea urchin development. Serious developmental anomalies were observed in the progeny, which persist several months after the bloom. NO levels were high in the different developmental stages, which also showed variations in the transcription of several genes that were found to be directly or indirectly modulated by NO. These results highlight subtle but important reproductive flaws transmitted from the female gonads to the offspring with the NO involvement. Despite a recovery along time after the bloom, insidious damages can be envisaged in the local sea urchin population, with possible reverberation on the whole benthic system.

Polychaete distribution on the southwestern Atlantic continental shelf

ABSTRACTDiversity and distribution of polychaetes on the southeastern Brazilian Shelf (SBS) adjacent to the city of Santos were studied. The study area is situated in the vicinity of Santos Bay with its estuarine complex and other small rivers along the coast. A total of 16,274 specimens belonging to 214 polychaete species were found at 21 sampling stations during two different periods. Two communities occur along the shelf and were related firstly to sediment characteristics. Prionospio dayi (Spionidae) was dominant in the inner shelf community that was characterized by well-sorted, very fine sand. The outer shelf community was found in muddy sediments with high organic matter content and was dominated by subsurface deposit feeders, like Petersenaspis capillata (Sternaspidae) and Leitoscoloplos kerguelensis (Orbiniidae), and by large carnivores such as Aglaophamus sp. (Nephtyidae) and Sigambra sp. (Pilargidae). A transition zone of mixed sediments presenting high diversity and richness was found between these communities. The characteristics of bottom water and food quality in the sediment were important to divide the inner shelf into two sub-areas. Nearshore sampling stations (A group) were more influenced by freshwater input, mainly during summer. This influence is not conspicuous at stations close to 30 m depth (B group). However the effect of South Atlantic Central Water mass (SACW) intrusion on the benthic system was observed on the inner shelf – B group during the summer. The summer intrusion of SACW onto the inner shelf may explain the higher quality of organic matter that resulted in an increase in polychaete abundance and richness.

Potential future fisheries yields in shelf waters: a model study of the effects of climate change and ocean acidification

Abstract. We applied a coupled marine water column model to three sites in the North Sea. The three sites represent different hydrodynamic regimes and are thus representative of a wider area. The model consists of a hydro-biogeochemical model (GOTM-ERSEM-BFM) coupled one way upwards to a size-structured model representing pelagic predators and detritivores (Blanchard et al., 2009). Thus, bottom-up pressures like changing abiotic environment (climate change, chemical cycling) will have an impact on fish biomass across the size spectrum. Here, we studied three different impacts of future conditions on fish yield: climatic impacts (medium emission scenario), abiotic ocean acidification impacts (reduced pelagic nitrification), and biotic ocean acidification impacts (reduced detritivore growth rate). The three impacts were studied separately and combined, and results showed that sites within different hydrodynamic regimes can respond very differently. The seasonally stratified site showed an increase in fish yields (occurring in winter and spring), with acidification effects of the same order of magnitude as climatic effects. The permanently mixed site also showed an increase in fish yield (increase in summer, decrease in winter), due to climatic effects moderated by acidification impacts. The third site, which is characterised by large inter-annual variability in thermal stratification duration, showed a decline in fish yields (occurring in winter) due to decline in the benthic system which forms an important carbon pathway at this site. All sites displayed a shift towards a more pelagic-oriented system.

Biodiversity and functioning of a subtropical coastal ecosystem: a contribution to an integrated managment

Biodiversity and functioning of a subtropical coastal ecosystem: a contribution to an integrated managment

Microbenthic community structure and trophic status of sediments in the Mar Piccolo of Taranto (Mediterranean, Ionian Sea).

This study aimed to assess the benthic ecosystem trophic status in a heavily polluted marine area and the response of the microbenthic community to multiple and diffuse anthropogenic impacts, integrating information coming from the active and resting (plankton's cysts) components of microbenthos. Two sampling campaigns were carried out in the period 2013-2014 and four sampling sites at different levels of industrial contamination were chosen within the first and second inlet of the Mar Piccolo of Taranto. The chemical contamination affected to a higher extent the active microbenthos than the resting one. In the central part of the first inlet, characterised by more marine features, thrives a very rich and biodiverse microbenthic community. In contrast, at the polluted site near the military navy arsenal, extremely low densities (9576 ± 1732 cellscm(-3)) were observed for active microbenthos, but not for the resting community. Here, the high level of contamination selected for tychopelagic diatom species, i.e., thriving just above the surface sediments, while the other life forms died or moved away. Following the adoption of a 10μmmesh, for the first time, resting spores produced by small diatoms of the genus Chaetoceros were found. Our results further indicate that although the Mar Piccolo is very shallow, the benthic system is scarcely productive, likely as a consequence of the accumulated contaminants in the surface sediments that probably interfere with the proper functioning of the benthic ecosystem.

Density dependence of growth and production in a Wadden Sea population of the cockle Cerastoderma edule

In suspension-feeding bivalves, growth rates generally remain at a high level over abroad range of numerical densities. However, data series on growth and production that cover awide density range in a natural marine benthic system appear to be scarce. A long-term monitoringstudy (1973-2013) of zoobenthos on tidal flats in the western Wadden Sea yielded twiceannualdata on numbers and weights of (among others) cockles Cerastoderma edule, allowingestimates of their annual and cohort production by the weight-increment summation method. Innearly all years, cockle densities did not exceed a few 100s m-2, and their individual weight incrementsshowed no significant relationship with density. Only the appearance of one exceptionallystrong year class in 2011 caused higher densities over an extensive area for >1 yr. Growth rates inall cockles were significantly reduced in the second growing season of this strong cohort, whentheir densities amounted to >500 m-2. Seasonal and annual survival did not show a significantrelationship with density. As a consequence of the reduction in growth of its members, productionof the single strong cohort was substantially less than expected on the basis of its initial abundance.In all smaller cohorts, the positive relationship between recruit numbers and cohort productionwas close to linear. However, when the higher density of the one strong year class wasincluded, an inverse-U shaped line would better characterize this relationship. Appearances ofvery strong bivalve cohorts are rare events in the Wadden Sea: bivalve stocks on the tidal flatsusually appear to be far below the carrying capacity of the area for suspension-feeding animals.

Use of dispersant in mudflat oil-contaminated sediment: behavior and effects of dispersed oil on micro- and macrobenthos.

The present study aimed to examine whether the use of dispersant would be suitable for favoring the hydrocarbon degradation in coastal marine sediments without impacting negatively micro- and macrobenthic organisms. Mudflat sediments, maintained during 286 days in mesocosms designed to simulate natural conditions, were contaminated or not with Ural blend crude oil (REBCO) and treated or not with third-generation dispersant (Finasol OSR52). While the dispersant did not lead to an increase of hydrocarbon biodegradation, its use enables an attenuation of more than 55 % of the sediment concentration of total petroleum hydrocarbons (TPH). Canonical correspondence analysis (CCA) correlating T-RFLP patterns with the hydrocarbon content and bacterial abundance indicated weak differences between the different treatments except for the mesocosm treated with oil and dispersant for which a higher bacterial biomass was observed. The use of the dispersant did not significantly decrease the macrobenthic species richness or macroorganisms' densities in uncontaminated or contaminated conditions. However, even if the structure of the macrobenthic communities was not affected, when used in combination with oil, biological sediment reworking coefficient was negatively impacted. Although the use of the dispersant may be worth considering in order to accelerate the attenuation of hydrocarbon-contaminated mudflat sediments, long-term effects on functional aspects of the benthic system such as bioturbation and bacterial activity should be carefully studied before.

Mass balanced trophic models and short-term dynamical simulations for benthic ecological systems of Mejillones and Antofagasta bays (SE Pacific): Comparative network structure and assessment of human impacts

Mass-balanced and dynamical multispecies trophic models were constructed for benthic systems of Mejillones and Antofagasta bays. We analysed data on biomass, P/B ratios, catches, food spectra, and the consumption and dynamics of commercial and non-commercial species or functional groups using the Ecopath with Ecosim framework. The biomass of the Rhodophyta group, which contributed 25.5% of the total system biomass, was the most abundant compartment in Mejillones bay, whilst the bivalve Transenella pannosa recorded the highest biomass (∼39%) in Antofagasta bay. Amongst the carnivores, the commercial gastropod Tais chocolata (∼2%) and the sea star Luidia magallanica (∼4%) were the compartment containing the highest biomass in Mejillones Bay and Antofagasta Bay, respectively. Based on the magnitudes of Pp/R, Relative Ascendency (A/C), Relative Overhead (Ov/C), Redundancy, Finn's cycling index and the system recovery time (SRT), the benthic system of Antofagasta Bay was more developed or mature and, in turn, less resistant against perturbations compared to Mejillones Bay. The outcomes of the mixed trophic impacts (MTI) indicate that the small epifauna carnivore (SEC) and the phytoplankton propagate the highest magnitudes of direct and indirect effects on the remaining compartments in the Mejillones and Antofagasta bays, respectively. According to the Ecosim short-term simulations (increasing 10, 30 and 50% the mortality by fishing and/or toxic substances) the snail Tegula spp. had the highest impact on the other compartments in Mejillones Bay, whilst the bivalve T. pannosa exhibited the highest impacts in Antofagasta Bay. Based on our results, we suggest that environmental studies should not only aim to promote and ensure the quality of physical components of nature, but should also consider the ecosystem properties and dynamics that emerge from complex networks.

Indicadores bioticos y fraccion de tamanos en la definicion de la macrofauna

El tamano de la abertura de malla en tamices para retener macrofauna bentonica, podria afectar la estimacion de los indicadores bioticos que describen el estado del sistema bentico submareal. El objetivo de este estudio fue determinar el efecto que tendria el limite inferior de abertura de la malla en las estimaciones de indicadores bioticos en dos centros de cultivo de mitilidos en el Seno de Reloncavi, Puerto Montt, Chile. Los datos fueron colectados desde muestras de sedimento obtenidas en estaciones ubicadas dentro y fuera (referencia) de los centros de cultivo. Se identifico y cuantifico la macrofauna bentonica con mallas de ≥500 µm y ≥1 mm. Se estimo el indice biotico marino (AMBI), la diversidad de Shannon-Wiener (log2) y riqueza de especies. Los resultados de ambos tamices se compararon mediante prueba t. La especie mas abundante en ambas localidades fue el poliqueto Chaetozone setosa , asignado al grupo ecologico GE IV, y la Clase Ostracoda, asignada segun expertos chilenos al grupo ecologico GE II. Solo se observo diferencias significativas en la riqueza de especies en las estaciones dentro del cultivo en el Centro 2. La caracterizacion de los sitios muestreados en terminos de indicadores bioticos permitio identificar que el estado ecologico del bentos de los centros de cultivo se encuentra dentro de los rangos aceptables segun limites establecidos para diversidad y AMBI. El uso de la malla de 500 µm aumento la abundancia de especies oportunistas respecto de lo observado con malla de 1 mm pero no cambio significativamente la clasificacion del estado ecologico.

Relationships between macrozoobenthos and habitat characteristics in an intensively used area of the Dutch coastal zone

Abstract Distribution patterns and species composition of macrozoobenthos were studied in the Dutch coastal zone in front of the Port of Rotterdam. Relationships between macrozoobenthic assemblages and environmental variables were determined using non-metric dimensional scaling (nMDS) based on 470 boxcore, bottom sledge, and sediment samples collected in spring 2006 and 2008 in a 2500-km2 research area. We investigated two types of benthic assemblages, infaunal assemblages sampled with a boxcorer and epifaunal assemblages sampled with a bottom sledge. Five main in- and epifaunal assemblages were distinguished using clustering techniques and nMDS ordinations. Macrozoobenthic species composition correlated with combinations of measured sediment variables and modelled hydrodynamic variables. Macrozoobenthic species richness and biomass were highest at 20 m deep areas with a grain size of 200 µm, elevated mud and sediment organic matter, and low mean bed shear stress. Considerable interannual differences in macrozoobenthic assemblage distribution were observed which resulted from more Echinoids, Phoronids, and jackknife clams. A distinct, highly productive and species-rich macrozoobenthic white furrow shell Abra alba assemblage coincided in a 8-m deepened shipping lane and near a disposal site for dredged fine sediment. This may be an indication that the benthic system can be changed by these human activities. Modelled bed shear stress is an important variable in addition to sediment variables in explaining distribution patterns in macrozoobenthos.

INFLUENCE OF SEDIMENT QUALITY ON THE BENTHIC COMMUNITIES OF ADMIRALTY BAY, KING GEORGE ISLAND, ANTARCTICA

Marine benthos is widely used in environmental impact studies, especially in coastal areas. In the summer of 2010, three areas of Martel Inlet and one in Mackellar Inlet were sampled in order to verify the marine environmental status near the Brazilian Station Comandante Ferraz (CF). In the shallow sublittoral zone (20 m depth), sediment samples were collected to analyze their physical characteristics, quality and indicators of anthropic activities (grain size, organic matter, phytopigments, linear alkylbenzenes, faecal sterols, microbiological indicators, hydrocarbons, persistent organic pollutants and metals) and to evaluate the meio- and macrofauna communities structure. Meiofauna densities were in the range of those found in previous studies in the bay and did not differ significantly among sampling sites. Nematodes were the dominant group. On the other hand, macrofauna densities were significantly higher in Mackellar Inlet, when comparing with some sites of Martel Inlet. Polychaetes, oligochaetes and bivalves were the dominant macrofauna taxa. Correlation analysis showed that different sediment characteristics could explain the abundance of the meiofauna or the macrofauna groups in a different way. Change in the meio- and macrobenthic community structure was detected at the site under the CF sewage outfall influence (lower density of meiofauna, different taxa composition of macro- and meiofauna), where relatively higher concentrations of linear alkylbenzenes and coprostanol, and densities of Escherichia coli and Clostridium perfringens were found. These results suggest some local impact of human activities on the benthic system in front of the Brazilian Research Station and contribute to the monitoring program under the scope of the INCT-APA (National Institute of Science and Technology - Antarctic Environmental Research).

Multiple stressors and multifunctionality: limited effects on an illuminated benthic system.

The bulk of experiments that study stressor effects on ecosystem functioning consider only individual functions one at a time, and such narrow focus may well bias our understanding of the overall impact on ecosystem functioning. We used data from six published experiments in which marine illuminated sediment systems were exposed to nutrient enrichment, toxicants, sedimentation and warming, either alone or in combination. Measured functions were primary production, community respiration, inorganic nitrogen and phosphorus fluxes, and autotrophic biomass. We calculated two indices of multifunctionality that simultaneously considered all six functions: (i) a weighted average level of the functions and (ii) the number of functions that simultaneously exceed a critical threshold level. Stressors affected individual functions both positively and negatively, but multifunctionality was generally unaffected by both single and joint stressors. The filtering capacity of coastal illuminated sediment systems thus appears resilient to exposure to moderate levels of multiple stressors, most probably due to the robustness of the benthic microalgal community. We recommend using a multifunctionality approach in future studies on cumulative stressor effects on ecosystem functioning, particularly when considering functions related to ecosystem services.

Anaerobic nitrification–denitrification mediated by Mn-oxides in meso-tidal sediments: Implications for N2 and N2O production

Field measurements in the Arcachon Bay (southwest France) indicated anaerobic production of NOx via nitrification, which was coupled to the reduction of Mn-oxides. To prove the occurrence of this process, laboratory microcosm experiments were set up. A 15N tracer-based approach was used to track if NOx produced through Mn-oxide-mediated anaerobic nitrification would be reduced to N2 via denitrification or anammox. We also hypothesized the generation of the potent greenhouse gas nitrous oxide (N2O) during nitrification–denitrification in the presence of Mn-oxides. The microcosms were prepared using sediment sectioned at varying depths (0–2.5, 2.5–4.5, 4.5–8.5, 8.5–12 and 12–17cm) during two sampling campaigns in October (fall) and January (winter). Labeling with 15NO3− revealed low N2 production originating from NO3− in the water column (Pw), which did not increase significantly on amendment with Mn-oxides during both sampling periods. However, for both seasons, a significant increase of N2 produced via nitrification (Pn) was observed upon addition of Mn-oxides reaching 76-fold enhancement at ≤2.5cm. To support these results, sediment slurries of October were subjected to amendment of 15NH4+, 14NO3− with or without addition of Mn-oxides. A substantial production of P15 (N2 production from 15NH4+) within 0–17cm provided further evidence on nitrification–denitrification mediated by Mn-oxides probably with minimal intervention of anammox. In organically rich sediments, anaerobic nitrification–denitrification mediated by Mn-oxides could play an important role in lowering re-mineralized NH4+ levels in the benthic system. As hypothesized, significant production of N2O through the pathway was observed revealing newer mechanisms leading to the generation of the radiative gas.

Influence of benthic macrofauna community shifts on ecosystem functioning in shallow estuaries

We identify how ecosystem functioning in shallow estuaries is affected by shifts in benthic fauna communities. We use the shallow estuary, Odense Fjord, Denmark, as a case study to test our hypotheses that (1) shifts in benthic fauna composition and species functional traits affect biogeochemical cycling with cascading effects on ecological functioning, which may (2) modulate pelagic primary productivity with feedbacks to the benthic system. Odense Fjord is suitable because it experienced dramatic shifts in benthic fauna community structure from 1998 to 2008. We focused on infaunal species with emphasis on three dominating burrow-dwelling polychaetes: the native Nereis (Hediste) diversicolor and Arenicola marina, and the invasive Marenzelleria viridis. The impact of functional traits in the form of particle reworking and ventilation on biogeochemical cycles, i.e. sediment metabolism and nutrient dynamics, was determined from literature data. Historical records of summer nutrient levels in the water column of the inner Odense Fjord show elevated concentrations of NH4+ and NO3- (DIN) during the years 2004-2006, exactly when the N. diversicolor population declined and A. marina and M. viridis populations expanded dramatically. In support of our first hypothesis, we show that excess NH4+ delivery from the benthic system during the A. marina and M. viridis expansion period enriched the overlying water in DIN and stimulated phytoplankton concentration. The altered benthic-pelagic coupling and stimulated pelagic production may, in support of our second hypothesis, have feedback to the benthic system by changing the deposition of organic material. We therefore advice to identify the exact functional traits of the species involved in a community shift before studying its impact on ecosystem functioning. We also suggest studying benthic community shifts in shallow environments to obtain knowledge about the drivers and controls before exploring deep-water environments.