Coastal Food Chains Research Articles

Spatial Variation in Mercury Accumulation in Bottlenose Dolphins (Tursiops spp.) in Southeastern U.S.A.

Bottlenose dolphins (Tursiops spp.) inhabit bays, sounds, and estuaries (BSEs) throughout the southeast region of the U.S.A. and are sentinel species for human and ecosystem-level health. Dolphins are vulnerable to the bioaccumulation of contaminants through the coastal food chain because they are high-level predators. Currently, there is limited information on the spatial dynamics of mercury accumulation in these dolphins. Total mercury (THg) was measured in dolphin skin from multiple populations across the U.S. Southeast Atlantic and Gulf of Mexico coasts, and the influence of geographic origin, sex, and age class was investigated. Mercury varied significantly among sampling sites and was greatest in dolphins in St. Joseph Bay, Florida Everglades, and Choctawhatchee Bay (14,193 ng/g ± 2196 ng/g, 10,916 ng/g ± 1532 ng/g, and 7333 ng/g ± 1405 ng/g wet mass (wm), respectively) and lowest in dolphins in Charleston and Skidaway River Estuary (509 ng/g ± 32.1 ng/g and 530 ng/g ± 58.4 ng/g wm, respectively). Spatial mercury patterns were consistent regardless of sex or age class. Bottlenose dolphin mercury exposure can effectively represent regional trends and reflect large-scale atmospheric mercury input and local biogeochemical processes. As a sentinel species, the bottlenose dolphin data presented here can direct future studies to evaluate mercury exposure to human residents in St. Joseph Bay, Choctawhatchee Bay, and Florida Coastal Everglades, as well as additional sites with similar geographical, oceanographic, or anthropogenic parameters. These data may also inform state and federal authorities that establish fish consumption advisories to determine if residents in these locales are at heightened risk for mercury toxicity.

INTERROGATING THE EFFECTS OF SAND MINING: A CASE STUDY OF AGILA DISTRICT, ADO LOCAL GOVERNMENT AREA, BENUE STATE, NIGERIA

This study is of believe that Illegal acts and discerning sand excavation/mining has become arisk to the ambiances. While theresearchrelied on personal geological observation on the mining sites, qualitative data were used from secondary literature. Using Agila’s river and coastal mining sites as a case study, the study revealed that it sparks to diversifications in river channels ways, physical ecosystem and food webs. As well it speeds up the river’scurrent and eventually eroding the river banks. Destroying the soil profile and removing the flora reduces the population of animals and eliminates habitat both the surface and subsurface resources. Sand dunes has played a vital aspect role in stoppage against heavy storms, erosion causes by some agents of transportations like winds, waves or floods. Numerous tiny habitants that are a component of the marine and coastal food chain and whose removal would pose some hazards to some other species rely on them for existence. The water tables in the surrounding areas decline as a result of sand mining, drying out the drinking water wells on the river embankments. Turbidity rises at the mining site as also the aquifers near the shore are affected by saline water intrusion. Sand mined areas loose scenic beauty, it emits radiation reliant on the component minerals, dust pollution, emits vibration/noise and it damages roads and some infrastructures. This researchinspected and reviewed the sand mining impacts on river, dune, marine, hydrological, biological and sociological environments with some case studies of the study area.

Climate Change as Observed in the Bay of Bengal

The Bay of Bengal covers a vast expanse of area, it being warmer, holds signatures of climate change. Its impact and the parameters have been studied in terms of rise in temperature, sea level change, increased rainfall, drought, heat waves, the intensity of tropical cyclones, ocean acidification and ocean productivity. In the last 45 years, sea surface temperature (SST) has risen by 0.2 to 0.3°C and is projected to rise further by 2.0 to 3.5°C by the end of this century. As a result, the sea level is expected to also rise 37 cm by 2050. The Bay of Bengal is witnessing an increase in the intensity of cyclones in the last two decades. Floods and droughts have increased over the years and are a growing threat to plant and animal life. Ocean acidification and increase in the sea surface temperature have made many fish species a major part of the coastal food chain vulnerable to its productivity. Hence, the collection of real time data and its continuous monitoring of the Bay of Bengal is essential to predict and project the future climate change to its accuracy both in space and time.

The Abundance and Distribution of Mangrove Gastropods from Kuala Selangor Nature Park, Selangor

This study reports on the abundance and distribution of mangrove gastropods from Kuala Selangor Nature Park, Malaysia (KSNP). The line transect method with quadrats (5m x 5m) was employed to sample the gastropods. Gastropods were collected from the leaves, branches, stems and roots of trees and the mangrove floor. Nineteen gastropod taxa from seven families were recorded from the Bruguiera, mixed (Bruguiera, Avicennia and Rhizophora), Avicennia and Rhizophora zones. Avicennia sp. recorded the largest Girth at Breast Height (GBH) (mean±sd=37.3±18.2 cm) while Bruguiera sp. recorded the smallest GBH (mean=22.36±8 cm). The overall density of the gastropods at KSNP was 0.85 no/m2. The gastropod density was higher at the Avicennia & Rhizophora zone (150-200m (closer to the mudflats) (0.064±0.084 no/m2) followed by the mixed zone (50-150m) (0.046±0.30 no/m2) and lowest at the Bruguiera zone (0-50m) (0.08±0.080 no/m2) (closer to the coastal bund). Gastropod density between sampling zones did not vary significantly (p>0.05) but generally increased from the bund towards the mudflat edge. Further studies of the role of gastropods in the coastal food chain, as bio-indicators of habitat change and as potential food source for local populace are needed.

Acartia tonsa Dana 1849 as a Model Organism: Considerations on Acclimation in Ecotoxicological Assays.

The copepod Acartia tonsa was standardized as model organism in acute toxicity bioassays due to its key position in coastal food chains and high sensitivity. Once bioassays are performed according to a protocol their results may become tools for the protection of aquatic ecosystems. However, there are divergences in bioassays methods using A. tonsa. This study aimed to investigate: (i) the need for acclimation of A. tonsa collected from the environment for use in acute toxicological bioassays; and (ii) differences in sensitivity between copepods collected from the environment and laboratory-grown copepods. Laboratory-grown copepods are more sensitive to SDS thanA. tonsa from theenvironment. The acclimation time of 30h helped organisms to recover from stress of collection/handling and changing environment/conditions. Therefore, laboratory-grown copepods showed to be more sensitive than organisms from environment; and for ecotoxicological bioassays acclimating A. tonsa collected from the environment for 30h can be adopted.

Elevated CO2 affects kelp nutrient quality: A case study of Saccharina japonica from CO2 -enriched coastal mesocosm systems.

Kelps provide critical services for coastal food chains and ecosystem, and they are important food source for some segments of human population. Despite their ecological importance, little is known about long-term impacts of elevated CO2 (eCO2 ) on nutrient metabolites in kelps and the underlying regulation mechanisms. In this study, the kelp Saccharina japonica was cultured in CO2 -enriched coastal mesocosm systems for up to 3months. We found that, although eCO2 significantly increased the growth rate, carbon concentrations, and C/N ratio of S.japonica, and it had no effect on total nitrogen and protein contents at the end of cultivation period. Meanwhile, it decreased the lipid, magnesium, sodium, and calcium content and changed the amino acid and fatty acid composition. Combining the genome-wide transcriptomic and metabolic evidence, we obtained a system-level understanding of metabolic response of S.japonica to eCO2 . The unique ornithine-urea cycle (OUC) and aspartate-argininosuccinate shunt (AAS), coupled with TCA cycle, balanced the carbon and nitrogen metabolism under eCO2 by providing carbon skeleton for amino acid synthesis and reduced power for nitrogen assimilation. This research provides a major advance in the understanding of kelp nutrient metabolic mechanism in the context of global climate change, and such CO2 -induced shifts in nutritional value may induce changes in the structure and stability of marine trophic webs and affect the quality of human nutrition resources.

Anthropogenic radioactive isotopes in Actiniaria from the Svalbard archipelago

The abundance of radionuclides in the Arctic Actiniaria has limited study despite their environmental importance in coastal food chains. Although the Arctic has incurred relatively little contamination by anthropogenic radionuclides as a result of nuclear weapons tests, there are still detectable levels of radionuclide activity observed in marine species. In this study of anthropogenic radionuclide activity in Actiniaria from Spitsbergen we observed levels of 90Sr from 0.92 Bq kg−1dw to 18 Bq kg−1dw and for 137Cs from 1.2 Bq kg−1dw to 12 Bq kg−1dw. The highest values of 90Sr and 137Cs were observed in organisms at stations close to seabird colonies and a river mouth, suggesting that fecal material and melting glaciers may be sources of radionuclides in the Arctic environment. The body mass of individual organisms affected bioaccumulation of 90Sr and 137Cs in Actiniaria, with radionuclide bioaccumulation occurring most intensively in the smaller specimens.

Biomagnificación de mercurio en la cadena trófica del Delfín Moteado del Atlántico (Stenella frontalis), usando el isótopo estable de nitrógeno como marcador ecológico

Se realizó una evaluación de las concentraciones del mercurio (Hg) y del isótopo estable de nitrógeno (δ15N) en la cadena trófica del Delfín Moteado del Atlántico (Stenella frontalis), incluyendo fitoplancton, zooplancton, peces planctívoros y sus principales presas (peces depredadores y una sola especie de cefalópodo), componentes de una cadena trófica tropical de la costa sureste de Brasil. Una de las presas del delfín, un pez depredador voraz, el pez sable (Trichiurus lepturus), presentó una concentración mediana del Hg 9,8 veces inferior que la del delfín. El valor de 15N es más bajo que al de su depredador. Los datos del isótopo han sugerido que ha habido diferencias significativas para el 15N a lo largo de la cadena trófica, en la que en el mayor depredador (delfín) se ha mostrado más pesado, seguido por el pez depredador y el pez bentófago, la corvina (Micropogonias furnieri). Se ha observado que el fitoplancton presentó el 15N más liviano, seguido por el zooplancton y el pez planctófago, el lebranche (Mugil liza). Este pez y el cefalópodo han mostrado la mediana más baja de Hg. Se han encontrado transferencias mayores que 1 en todos los vínculos de la cadena evaluada. Se ha obtenido una relación significativamente positiva entre la concentración del Hg (en logaritmo) y el nivel trófico (TL), incluyendo todas las especies investigadas, presentando una pendiente positiva (δ= 0,87). El factor de magnificación trófica (FMT= 7,44) indica que la concentración del Hg ha aumentado por TL, y también que toda la cadena trófica costera presentó un poder de biomagnificación de Hg dentro de un rango previamente reportado para ecosistemas costeros tropicales.

Does 'you are what you eat' apply to mangrove grapsid crabs?

In tropical mangroves, brachyuran crabs have been observed to consume high percentages of leaf litter production. However, questions concerning their ability to assimilate this low-quality food remain, as stable isotope analysis of C and N does not seem to support assimilation. Individuals of the common eastern Australian mangrove grapsid Parasesarma erythodactyla feeding on a mangrove leaf litter or mangrove+microphytobenthos diet developed a significantly higher hepatosomatic index than those with access to only sediment. Lipid biomarker analysis and feeding experiments using 13C and 15N-enriched mangrove leaf litter confirmed rapid assimilation of mangrove C and N by P. erythodactyla. Eight-week feeding experiments utilizing three food types (mangrove leaf litter, microphytobenthos and prawn muscle) established different food-specific trophic discrimination values (Δδ13C and Δδ15N) that are significantly different from those commonly applied to mixing model calculations. The mean Δδ13C(crab-mangrove) of +5.45‰ was close to the mean and median literature values for grapsid-mangrove pairs in 29 past studies (+5.2±1.8‰ and +5.6‰, respectively), suggesting that this large discrimination may generally be characteristic of detritivorous grapsid crabs. Solutions from the IsoConc mixing model using our determined trophic discrimination values suggest significantly higher and dominant contributions of mangrove C to the diet than those based on the global mean trophic discrimination values. Our results reaffirm the physiological capacity for and important mediating role of grapsid crabs in processing low-quality mangrove C in tropical estuaries, and caution against the use of global trophic discrimination values in stable isotope analysis of food-web data, especially those involving detritivores. While recent studies have questioned the trophic significance of mangrove detritus in coastal food chains, the contribution of this productive carbon source needs to be re-assessed in the light of these data.

Physico-chemical parameters of the SW and post NE monsoon (2009) seawater along the continental slope, Tamil Nadu, east coast of India, Bay of Bengal

Variations in sea water temperature, salinity, light intensity and availability of nutrients strongly influence the phytoplankton distribution that forms an important part of the coastal food chain. In this paper, we present the results of the physico-chemical parameters and nutrient concentrations in seawaters sampled during the 2009 South West (SW) and post North East (NE) monsoon periods along the continental shelf from Chennai to Nagapattinam, east coast, Tamil Nadu. This study was conducted to assess the status of the coastal biogeochemical environment and for this purpose, seawater samples were collected from the sea surface and also at varying depths (surface to 150m depth) at six different locations. The nutrient analyses and the CTD data reveal a distinct variation with water depth along the continental slope and also the physico-chemical properties of seawater are not homogenous. The observed values of nutrients for the post NE monsoon period are low compared to the SW monsoon period. Contour plots indicate seasonal and spatial variations in physico-chemical parameters along the continental shelf of the east coast of India. The data suggests that during the 2009 SW monsoon period, a significant increase of freshwater input into the Bay of Bengal could have elevated nutrient concentration compared to that observed during the post 2009 NE monsoon.

Growth form analysis of epiphytic diatom communities of Terra Nova Bay (Ross Sea, Antarctica)

Diatoms have been long collected from the Southern Ocean but almost no data exist for epiphytic communities, despite their high ecological significance as an important food source in Antarctic coastal food chains. Here, we present a first growth form analysis of diatoms associated with rhodophyte hosts from Terra Nova Bay, Ross Sea, Antarctica. We performed this study to gather baseline information on the species composition of epiphytic diatom communities, determine the influence of some environmental variables on the diatom distribution patterns, and assess the caveats that must be taken into account in terms of sampling design. Macroalgal material was collected during the Italian Antarctic expeditions between 1990 and 2004. Epiphytic diatoms were studied by means of scanning electron microscopy. In terms of growth forms, there were no significant differences between the diatom communities on the different macroalgal host species. Motile (mainly small-celled Navicula perminuta and other Navicula spp.) and adnate (Cocconeis spp.) diatoms dominated the community throughout the study period. Many of the macroalgal blades examined were also covered by epiphytic animals (calcareous bryozoans, hydroids) over most of their surface, with a significant effect on the associated diatom community structure. Our findings suggest that the bio-physicochemical characteristics of each sampling site affected the epiphytic diatom communities more than the substrate type provided by the macroalgal host or the sampling depth.

Use of multiple tools to assess the feeding preference of coastal dolphins

The feeding preferences of the coastal dolphins Pontoporia blainvillei and Sotalia guianensis in south-eastern Brazil (21o18′S–22o25′S) were assessed through the prey’s index of relative importance (IRI), total mercury concentration (Hgtot), and stable isotopic (δ15N and δ13C) to compare their efficiency in the discrimination of prey contribution to the predators’ diet. The IRI was the best tool to describe the dolphins’ preference, while Hgtot and δ15N seemed to be efficient as a trophic marker when the diet is made up of prey of varying sizes, as observed in S. guianensis. Both dolphins presented lighter δ15N than their prey species, which is an unusual pattern. However, as the sample size to isotope ratios analysis was small, especially to the dolphins, the results should be considered with caution, and further studies are necessary to corroborate these findings. The δ13C values characterized a typical coastal food chain, confirming the preferential area of these species.

Biodynamic modelling of the bioaccumulation of arsenic by the polychaete Nereis diversicolor

Environmental context Models that explain the uptake and bioaccumulation of an element in an aquatic ecosystem are valuable for predicting its potential ecotoxicity in coastal areas. Arsenic is a toxic element that is strongly adsorbed to sediments, offering a potential risk to deposit-feeding invertebrates, and ultimately to consumers higher up coastal food chains. This study uses biodynamic modelling to predict the uptake and accumulation of arsenic from water and sediment in a deposit-feeding polychaete worm that is a major source of food to fish and wading birds in estuaries. Abstract Arsenic (AsV) uptake and bioaccumulation from water and ingested sediment by the deposit-feeding polychaete Nereis diversicolor has been investigated using biodynamic modelling. Worms accumulated As from solution linearly at dissolved concentrations from 2 to 20 µg L–1 (uptake rate constant 0.057 l g–1 day–1 at 10°C, 16-psu salinity), and the As assimilation efficiency from ingested sediment was 28.9%. Efflux rate constants of As taken up from water and ingested sediment were 0.0488 and 0.0464 day–1 and did not differ significantly. Sediment As concentrations, ranging from very high to low, were measured at eight estuarine sites, and the model predicted accumulated As concentrations in resident N. diversicolor. Comparisons of predicted against independently measured As concentrations in locally collected worms showed that the model generally performed well, highlighting the potential of biodynamic modelling in predicting the uptake and therefore ecotoxicity of As in estuarine sediments.

Transferência trófica de mercúrio e selênio na costa norte do Rio de Janeiro

Trophic transfer of trace elements along marine food chains has been recognized as an important process influencing metal and metalloid bioaccumulation. The trophic transfer of mercury was observed between trophic levels from prey (considering fish with different feeding habits and squid) to top predator (dolphin) in a Northern coastal food chain of Rio de Janeiro. Selenium showed some evidence of trophic transfer between lower trophic levels. Dolphin presented the highest mercury concentrations whereas the benthic carnivorous fish showed the highest selenium concentrations. Mercury is biomagnified through the food chain while selenium does not present the same behavior.

Input of Nutritionally Rich Organic Matter from the Mississippi River to the Louisiana Coastal Zone

Isotopes have often been used to discern riverine subsidies to coastal food chains, but there are few direct measurements of nutritional quality of riverine particulates. We tested for nutritionally enriched organic matter in the Mississippi River suspended sediment and evidence for its delivery to Louisiana coastal sediments by measuring enzymatically hydrolysable amino acids (EHAA). Riverine suspended sediments contained EHAA concentrations of up to 5 mg g−1, higher than reported in any coastal sediment. Pigment concentrations indicated that EHAA in some river samples were dominated by phytoplankton, but many samples contained significant non-algal EHAA. Coastal sediments showed EHAA concentrations lower than riverine sediments but still higher than most reported shelf values. Incubation of riverine sediment showed losses of 28–34% of their EHAA over 6 days, similar to differences found between riverine and coastal sediments. EHAA concentrations decreased more rapidly than total nitrogen, indicating the relative lability of this pool of material in the studied region. These EHAA-enriched materials provide fuel for various coastal biota whose composition likely depends on factors such as disturbance regimes.

Survival and behaviour of juvenile red rock lobster, Jasus edwardsii, on rocky reefs with varying predation pressure and habitat complexity

The role of large predatory fish in coastal communities is generally unknown because of overfishing. In order to understand the direct and indirect impacts of these increased population sizes on coastal food chains, the effect of areas with more fish predators on the survival and behaviour of potential prey was assessed. Juvenile lobsters, Jasus edwardsii (10–20 mm carapace length), were tethered on rocky reefs inside and outside marine reserves in northeastern New Zealand to assess survival under differing predator densities. Since rocky reef habitats in northeastern New Zealand include zones of kelp forest and barren reef, a two-way factorial design was used to determine the effects of predators, habitat, and the interaction of these two factors on juvenile lobster survival. Overall, the results indicated that neither varying large fish density nor varying kelp density had direct impacts on the survival rate of juvenile lobsters. Laboratory manipulations demonstrated behavioural changes by juvenile lobsters such that when a large predatory fish was present, juvenile lobsters spent significantly less time moving, even when separated from the predator by a porous barrier. Thus areas with more fish predators may increase juvenile lobster survival but potentially at the cost of reduced feeding opportunities.

Perfluorinated Contaminants in Sediments and Aquatic Organisms Collected from Shallow Water and Tidal Flat Areas of the Ariake Sea, Japan: Environmental Fate of Perfluorooctane Sulfonate in Aquatic Ecosystems

Perfluorinated compounds (PFCs), such as perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), perfluorohexane sulfonate (PFHS), and perfluorooctane sulfonamide (PFOSA) are widely distributed in aquatic ecosystems. Despite studies reporting the occurrence of PFCs in aquatic organisms, the fate of PFCs in tidal flat and marine coastal ecosystems is not known. In this study, we determined concentrations of PFOS, PFOA, PFNA, PFHS, and PFOSA in sediments; benthic organisms, including lugworm, mussel, crab, clam, oyster, and mudskipper fish from tidal flat; and shallow water species, such as filefish, bream, flounder, shark, finless porpoise, gull, and mallard collected from the Ariake Sea, Japan. PFOS and PFOA were detected in most of the samples analyzed, followed by PFNA, PFOSA, and PFHS. In shallow water species, PFOS was the dominant contaminant, and elevated concentrations were found in higher trophic level species, such as marine mammals and omnivorous birds. These results suggest biomagnification of PFOS through the coastal food chain. In contrast, PFOA was the most abundant compound in tidal flat organisms and sediments. PFOA concentrations in sediments, lugworms, and omnivorous mudskippers in tidal flat were approximately 1 order of magnitude greater than the levels of PFOS. This indicates differences in exposure pattern and bioavailability of PFOS and PFOA between shallow water and tidal flat organisms. The accumulation profiles of PFCs were compared with those of organochlorines (polychlorinated biphenyls, PCB), organotin (tributyltin,TBT), and polycyclic aromatic hydrocarbons (PAHs) in tidal flat and shallow water samples collected from the Ariake Sea. Concentrations of PFCs in sediments and in tidal flat organisms were significantly lower than that found for PCBs, TBT, and PAHs. Nevertheless, PFOS concentrations in shallow water species were comparable to and/or significantly greater than those of other classes of contaminants. This implies that the aqueous phase is a major sink for PFCs, which is different from what was observed for nonpolar organic pollutants.

Speciation and bioavailability of mercury in well-mixed estuarine sediments

Despite regulations controlling anthropogenic mercury sources in North America, high levels of mercury in coastal fish and shellfish are an ongoing problem in Maritime Canada and the Northeastern United States. This study presents sediment core data from a macrotidal estuary located at the mouth of the Bay of Fundy showing stratigraphic profiles of total and methylmercury concentrations and potential methylation rates measured using stable mercury isotopes. The results show that in contrast to the expected methylmercury profile typically observed in unmixed sediments, methylmercury production occurs throughout the estimated 15-cm-thick active surface layer of these well-mixed sediments. The resulting large reservoir of methylmercury in these sediments helps to explain why mercury concentrations in organisms in this system remain high despite emissions reductions. Current management policies should take into account the expected delay in the response time of well-mixed estuarine systems to declines in mercury loading, considering the greater reservoir of historic mercury available in these sediments that can potentially be converted to methylmercury and biomagnify in coastal food chains.

Spatial and Temporal Variability in Nutrients and Suspended Material Processing in the Fier d'Ars Bay (France)

A net material flux study in an estuarine mudflat along the French Atlantic coast, confirmed the general hypothesis already shown in European salt marshes. Despite its small area, the system was not as homogeneous as first thought. The upper part of the bay imported both dissolved and particulate matter, whereas the lower part exported dissolved and imported particulate matter. Tidal dynamics and water residence time were suspected of enhancing these differences. Particulate mineral import represented more than 70% of the total suspended sediment, with export of silicate, dissolved organic carbon and chlorophyll a. It is assumed that phytoplankton and microphytobenthos were exported from the bay in a degraded form. A wide synthesis was conducted integrating the tidal physical dynamics, with the geomorphology of the system, to explain material flux differences between the two sampling sites. Differences of particulate material transport between European and North American systems were verified. New hypotheses relative to the functional role of phytoplankton and microphytobenthos in coastal food chains in European salt marshes were also investigated. In contrast to American systems, mineral particulate import was prevalent in European ecosystems, enhancing growth of small-celled phytoplankton and microphytobenthos. These latter, were sorbed onto sedimenting mineral particles, thus limiting losses from estuaries and explaining the major particulate retention in these systems.

The role of intertidal mudbanks in the diagenesis and export of dissolved and particulate materials from the Fly Delta, Papua New Guinea

Benthic processes and sedimentary structures of intertidal mudbanks within the Fly Delta, Papua New Guinea, were examined to assess their role in the storage, utilization and export of nutrients from the river delta to the adjacent Gulf of Papua. Three types of mudbanks were recognized based on interpretation of x-radiographs of sediment cores: a physically dominated, high sedimentation regime (one station), a biologically dominated, low-to-moderate sedimentation regime (one station) and a “transitional” regime (two stations). Meiofaunal (29–340 ind·10 cm -2) and macroinfaunal (174–6185 ind·m -2) densities varied widely, being lowest at the physically controlled site and dominated mainly by small deposit- and suspension-feeding polychaetes, amphipods, oligochaetes and nematodes. Infaunal biomass was low (0.17–1.38 g AFDW·m -2) across stations. Bacterial densities (0.14−1.5 × 10 10 cells·g −1 DM) were highest at the physically and biologically controlled sites. Bacterial C production was estimated from rates of protein ( 3H-leucine incorporation) and DNA ( 3H-thymidine incorporation) synthesis. The methods did not agree well, with rates of DNA synthesis (187–413 mg C·m -2·d -1) several times higher than production estimates derived from 3H-leucine incorporation (18–75 mg C·m -2·d -1). However, specific growth rates (μ) derived using both methods correlated strongly ( r = +0.90), with high rates across 20-cm depth horizons at all four stations. Levels of particulate organic C, total N, total P in the sediments and dissolved organic (DOC, DON, DOP) and inorganic (NH 4 +, NO 2 − + NO 3 −, Si(OH) 4 +, PO 4 3−) nutrients in the porewaters were low compared to other benthic habitats and generally varied little with sediment depth. The average stoichiometric ratio of solid-phase nutrients was low (atomic C:N:P = 42:6:1), suggesting that the material was in very early stages of diagenesis. Fluxes of dissolved inorganic and organic nutrients across the sediment-water interface were mostly undetectable and rates of O 2 consumption (145–206 mg C·m -2·d -1) and gross primary production (159–240 mg C·m -2·d -1) were low, as were Chl a (0.5–0.8 μg·g -1 DW) and phaeopigments (2.5–4.2 μg·g -1 DW). The two transitional stations had large quantities (482–1075 g DW · m -2) of deposited macroparticulate plant litter. It is proposed that the rapidly growing, bacterial communities in these sediments sequester and mineralize most of the labile organic matter deposited onto these mudbanks, leading to the observed lack of nutrient flux across the sediment-water interface and the general absence of vertical solid-phase and porewater nutrient profiles. Intertidal mudbanks of the Fly Delta therefore act as nutrient sinks rather than as net exporters of nutrients which may support coastal food chains in the adjacent Gulf of Papua.