Effect of oil and dispersants on the growth of Mussels

Mussels (Mytilus edulis L.) were exposed to North Sea crude oil, microencapsulated oil and dispersants, singly and in combination, and growth rates measured at 24–48 h intervals.Exposure to microencapsulated pure oil (2·0–2·1 mg litre⁻¹) and to microencapsulated mixtures of oil (2·2−2·5 mg litre^-1+5 % of the different dispersants (FINASOL OSR 5, COREXIT 9527, DISPOLENE 36 S) gave approximately the same reduction in growth rate (80–90%) within 170h.Oil chemically dispersed with DISPOLENE 36 S and a pure oil mechanically dispersed in water were significantly less toxic. In high concentrations (2 mg litre⁻¹) all disperants are toxic, DISPOLENE 36 S ssignificantly more than the others.Mussels exposed for 170 h to microencapsulated oil and to microencapsulated oil dispersant mixtures recovered to control growth within 300 h in clean seawater, while in those given pure oil-in-water suspension, the recovery was slower.It is concluded that the toxicity of oil is mainly related to size and concentration of oil particles, while the effect of 5% dispersants added is negligible.     

The influence of dissolved petroleum hydrocarbon residues on natural phytoplankton biomass

The effect of dissolved petroleum hydrocarbons in the environment on phytoplankton biomass measured as chlorophyll a was studied near the oil tanker route in the southern Bay of Bengal. In the transect from 5° N, 77° E to 5° N, 87° E the concentrations of dissolved petroleum hydrocarbons were negatively correlated with phytoplankton biomass, whereas in the 0° N, 87° E to 1° N, 79° E transect they were positively correlated with phytoplankton biomass. The mean petroleum hydrocarbon concentrations in the two transects were 12·12 ± 4·67 μg litre⁻¹ and 11·23 ± 4·5 μg litre⁻¹, respectively.It is surmised that the effect of dissolved petroleum hydrocarbons on phytoplankton biomass varies depending on the nature rather than the quantity of petroleum hydrocarbons present. Culture studies with unialgal Nitzschia sp. in seawater collected from selected stations in the study area as well as in artificial seawater spiked with the water-soluble petroleum hydrocarbon fraction of light Arabian Crude support this.     

Effects of mercury on the prosobranch mollusc Crepidula fornicata: Acute lethal toxicity and effects on growth and reproduction of chronic exposure

Exposure to a mercury-equilibrated algal suspension containing 0·25, 0·42 and 1 μg Hg litre⁻¹ as mercuric chloride in solution reduced the growth and condition of pairs of adults of the slipper limpet Crepidula fornicata in a 16-week period. Reproduction rates and larval survival to settlement were also reduced over the first three spawnings when the exposed pairs reached sexual maturity. The adult and larval 96-h LC₅₀s were 330 and 60 μg Hg litre⁻¹, respectively, as mercuric chloride in solution, indicating that a ‘safety factor’ of 10⁻¹ needs to be applied to adult data to protect the most sensitive stage in the life cycle. However, the chronic exposure of the maturing adults showed that levels of inorganic mercury below the ‘safe’ concentration derived from the adult 96 h LC₅₀ affected growth and reproductive success.     

Relationships between macroalgal biomass and nutrient concentrations in a hypertrophic area of the Venice Lagoon

Macroalgae biomass and concentrations of nitrogen, phosphorus and chlorophyll a were determined weekly or biweekly in water and sediments, during the spring-summer of 1985 in a hypertrophic area of the lagoon of Venice. Remarkable biomass production (up to 286 g m⁻² day⁻¹, wet weight), was interrupted during three periods of anoxia, when macroalgal decomposition (rate: up to 1000 g m⁻² day⁻¹) released extraordinary amounts of nutrients. Depending on the macroalgae distribution in the water column, the nutrients released in water varied from 3·3 to 19·1 μg-at litre⁻¹ for total inorganic nitrogen and from 1·8 to 2·7 μg-at litre⁻¹ for reactive phosphorus. Most nutrients, however, accumulated in the surficial sediment (up to 0·640 and to 3·06 mg g⁻¹ for P and N respectively) redoubling the amounts already stored under aerobic conditions, Phytoplankton, systematically below 5 mg m⁻³ as Chl. a, sharply increased up to 100 mg m⁻³ only after the release of nutrients in water by anaerobic macroalgal decomposition. During the algal growth periods, the N:P atomic ratio in water decreased to 0·7, suggesting that nitrogen is a growth-limiting factor. This ratio for surficial sediment was between 6·6 and 13·1, similar to that of macroalgae (8·6–12·0).     

Ammonium input to the sea via large sewage outfalls-Part 2: Effects of ammonium on growth and photosynthesis of southern California phytoplankton cultures

Cultures of six marine phytoplankton were grown at ammonium concentrations ranging up to 200 μg-atom NH₄---N litre⁻¹. Only the growth of dinoflagellates, Gymnodinium splendens and Gonyaulax polyedra was inhibited at the two highest concentrations used. In 3-h photosynthetic ¹⁴CO₂ uptake experiments, only Gymnodinium was inhibited at concentrations of NH₄---N greater than 100 μg-atom litre⁻¹. We conclude that the increased ammonium concentrations found near Southern California sewage outfalls would not be inhibiting to phytoplankton in the vicinity of such outfalls.     

Butyltins in marine waters of The Netherlands in 1988 and 1989; Concentrations and effects

Specific effects of tributyltin (TBT) on Crassostrea gigas—valve thickening, and Nucella lapillus—imposex, were measured on local populations, relatively clean unaffected species from England were transferred to the Netherlands and exposed during six weeks to ambient TBT concentrations. Near marinas 50% of the exposed species were sterile after six weeks. In general, no dissolved butyltins were detected in the Rhine and Scheldt estuaries. In 1988 TBT concentrations in marinas ranged from 120 to 4000 ng litre⁻¹. In sediments (fraction <60 μm) and suspended particulate matter TBT concentrations reached up to 1200 ng g⁻¹. TBT concentrations in mussel tissue ranged from <1 to 2300 ng g⁻¹ based on a dry weight. In 1989 concentrations of dissolved TBT ranged from <0·1 to 7200 ng litre⁻¹. In 1989 a seasonal study in the marina of Colijnsplaat showed that dissolved butyltins increased from April to the end of May due to the launching of freshly painted boats, and decreased afterwards.     

Non-volatile Hydrocarbon Chemistry Studies Around a Production Platform on Australia's Northwest Shelf

In September 1994 and 1995, scientists from the Australian Institute of Marine Science (AIMS) and the Australian Geological Survey Organization (AGSO) conducted surveys aboard the RV Lady Basten to determine the dispersion, fates and effects of produced formation water (PFW) discharged from the ‘ Harriet A ’ oil production platform near the Montebello Islands. This report is one of four related papers and describes the non-volatile hydrocarbon chemistry studies. The dispersion of the PFW into dissolved and particulate fractions of seawater were measured using moored high volume water samplers, surface screen samplers and moored and drifting sediment traps. Bio-accumulation was studied using transplanted oysters, and dispersion measured into sediment with benthic grabs.Results showed enrichment in non-volatile hydrocarbons in surface microlayer samples to a distance of 1·8 km in the direction of tidal flow. Concentrations in surface microlayers near the platform varied by an order of magnitude and corresponded to when a surface slick was visible or not visible. Concentrations of oil in seawater ranged from 2·0 to 8·5 μg l⁻¹at near stations to 1·3 μg l⁻¹at 1·8 km. Water column samples showed the processes of desorption from particles for soluble components occur within the range of 1·8 km. Most particulate hydrocarbons drop out of suspension within c. 1 to 2 km from the platform. Fluxes of particulate hydrocarbons through the water column at c. 1 km, as estimated by moored sediment traps in 1995, were 138 to 148 ng cm⁻²day⁻¹. A decrease in sediment concentrations within c. 1 km of the platform was measured as 2·45±1·29 μg g⁻¹dry wt (n=15) in 1994 to 0·86±0·54 μg g⁻¹dry wt (n=21) in 1995, after the platform installed a centrifugal separator in the discharge treatment process. Thus the residence time of this relatively low molecular weight oil was estimated in the coarse aerobic sands surrounding the platform to be less than one year. Oysters suspended near the platform bio-accumulated hydrocarbons and other lipophilic organics in their tissues. Uptake rates and bio-concentration factors of hydrocarbons indicated potential toxicity at the near-field stations within c. 1 km radius.A mass balance was constructed to show the partitioning of the input of hydrocarbons from the PFW into the surrounding marine ecosystem. The rates of dissipation processes were estimated as follows: dilution from tidal currents>degradation in the water column>sedimentation>evaporation. The calculations based on maximum concentrations measured in the environmental samples accounted for 85% of the daily input suspended within a 1 km radius.It is estimated that the potential zone of toxic influence in the water column extends to a distance of approximately 1 km. Concentrations of oil in sediments were too low to indicate potential toxicity. By the collaborative application of oceanographic and geochemical techniques to marine environmental problems, we endeavour to provide effective feedback to the oil industry to gauge the effectiveness of their operational strategies in minimizing impact in these pristine regions.     

The effects of paraquat on microsomal oxygen reduction and antioxidant defenses in ribbed mussels (Geukensia demissa) and wedge clams (rangia cuneata)

The hepatopancreae of the ribbed mussel, Geukensia demissa, and the wedge clam, Rangia cuneata, were examined for their ability to catalyze the reduction/oxidation cycling of the bipyridyl herbicide paraquat. In vitro studies indicated a dose-dependent increase in the rate of superoxide anion (O₂⁻) generation in microsomal fractions supplemented with NADPH; the highest concentration of paraquat employed (4 mm) elicited an 81 % increase in cytochrome c reduction in G. demissa and a 135% increase in R. cuneata. In both .species, cytochrome c reduction was inhibited by the addition of exogenous superoxide dismutase (SOD). For in vivo studies, a single application of paraquat (0·5, 1·0 or 2·0 mm) was added to aerated salt-water aquaria containing G. demissa. Biochemical analyses of antioxidant enzymes, reduced glutathione (GSH) and lipid peroxidation were performed in hepatopancreatic tissue after exposures of 6, 12, 24 and 36 h. Results support the hypotheses that these bivalves can activate redox cycling compounds and demonstrate in vivo responses typical of oxidative stress as observed in other organisms.     

Some effects of copper on the veliger larvae of the mussel Mytilus edulis and the Scallop Pecten maximus (Mollusca, Bivalvia)

During 1983 and 1985 several batches of laboratory reared veliger larvae of Mytilus edulis and Pecten maximum here subjected to a rank of concentrations of added copper (CuCl₂) over a 15-day period. M. edulis larvae were less sensitive, measured both as mortality (15-day LC₅₀) of 400 μglitre⁻¹) and reduced growth, than P. maximus larvae (15-day LC₅₀ of 85μg litre⁻¹). Both species appeared less sensitive to Cu than other bivallve larvae previously studied. Veliger larvae of M. edulis are from 7 to 10 times more tolerant of Cu than juveniles or adults and this unexpected finding is discussed in relation to the recent literatures on Cu toxicity and accumulation in mussels.     

Evidence on the interaction of mercury and selenium in the shrimp Palaemon elegans

The interaction of selenium with mercury was studied in the shrimp Palaemon elegans. The release of ²⁰³HgCl₂ (5·0 μg Hg per gramme body weight) from shrimp pretreated with selenium (SeO₂ doses of 1·97, 3·95 and 7·90 μg Se per gramme fresh weight) was significantly decreased compared with the control group to which only 5·0 μg Hg/g had been administered.In the presence of HgCl₂ (5·0 μg Hg per gramme fresh weight) the release of ⁷⁵Se also diminished significantly at the higher stable Se pretreated dose (7·90 μg Se/g) while, at a lower selenium concentration, the release was not statistically different. Analyses for stable Hg and Se confirmed the decrease in rate of selenium loss in the presence of mercury which had been demonstrated with radiotracers.A dose of 7·9 μg Se per gramme fresh weight injected 12 h before exposure of the shrimp to the various mercuric chloride solutions did not produce a significant difference in the 24 h LC₅₀ compared with the group not pretreated with selenium. However, during exposure to mercury at 3·8 mg/litre, the median lethal time (LT₅₀) for the shrimp pretreated for 4 days with sublethal selenium (6·9 and 10·5 mg Se/litre) was delayed (19·2 and 33·2 h) compared with the group which was not pretreated. The results are discussed in relation to the role of selenium in the acutely toxic effects of inorganic mercury.     

Sublethal effects of hydrogen sulfide in sediments on the Urchin Lytechinus pictus

Laboratory exposures of the urchin Lytechinus pictus to sediment dosed with varying concentrations of hydrogen sulfide (H₂S), but without elevated organic material, were conducted. Changes in mortality, behavior, growth and gonad production were measured during 49 days' flow through exposures. Hydrogen sulfide concentrations of 165·8 μ liter⁻¹ in pore water caused significant changes in all parameters measured. Concentrations as low as 32·9 μ liter⁻¹ caused significant decreases in wet weight and male gonad production. A concentration of 91·8 μ liter⁻¹ caused the mortality rate to increase 100-fold over control exposures (0·63 μ liter⁻¹). Sublethal effects on growth and gonad production could have been caused by either direct biochemical inhibition by H₂S or secondarily through behavioral modifications. Hydrogen sulfide concentrations above 165·8 μ liter⁻¹ are common near sewage outfalls and could contribute to changes in species composition and sediment toxicity that occur there.     

Settleable and Non-Settleable Suspended Sediments in the Ogeechee River Estuary, Georgia, U.S.A.

Suspended particle dynamics were investigated in the Ogeechee River Estuary during neap tide in July 1996. Samples were operationally separated into ‘ truly suspended ’ (settling velocity <0·006 cm s⁻¹) and ‘ settleable ’ (settling velocity >0·006 cm s⁻¹) fractions over the course of a tidal cycle to determine whether these two fractions were comprised of particles with differing biological and chemical characteristics. Total suspended sediment, organic carbon and nitrogen, chlorophyll a and phaeopigment concentrations were measured in each fraction, as well as rates of bacterial hydrolytic enzyme activity [β-1,4-glucosidase (βGase) and β-xylosidase (βXase)]. The majority of the suspended sediment (by weight) was in the truly suspended fraction; all measured parameters were largely associated with this fraction as well. When compared to the settleable material, the truly suspended material was significantly higher in % POC (5·7±0·6 vs. 3·9±1·8), % chlorophyll (0·07±0·02 vs. 0·03±0·01), % phaeopigment (0·030±0·006 vs. 0·018±0·012), and weight-specific maximal uptake rates (V_maxper mg suspended sediment) of both enzymes (1·8±0·4 vs. 0·7± 0·2 nmol mg⁻¹ h⁻¹βGase and 1·1±0·3vs . 0·3±0·2 nmol mg⁻¹ h⁻¹βXase), providing clear evidence for a qualitative distinction between the two fractions. These results are interpreted to mean that the more organic-rich, biologically active material associated with the suspended fraction is likely to have a different fate in this Estuary, as ‘ truly suspended ’ sediments will be readily transported whereas ‘ settleable ’ sediments will settle and be resuspended with each tide. These types of qualitative differences should be incorporated into models of particle dynamics in estuaries.     

Cadmium in Mytilus spp.: Worldwide survey and relationship between seawater and mussel content

A worldwide literature survey of data on cadmium concentration in the soft tissue of the mussel, Mytilus spp., from 591 stations is presented. These stations are from 13 regions. Geometric means for the regions vary from 0·6 to 3·3 μg g⁻¹ (dry weight) for the Barents Sea and the Northeastern Pacific coast, respectively.The averages of seven of these regions, for which reliable cadmium concentrations in seawater were available, were used to calculate a relationship between cadmium concentrations in seawater and mussel soft tissue. The relationship was highly significant: (Cd) mussel (μg g⁻¹, dry weight) = 0·074 (Cd) water (ng litre⁻¹) + 0·39 (P ≤ 0·0005).This model has been successfully applied in the context of the contamination of the Gironde estuary (France). It can also be used to define a water quality criterion for mussel maturing parks consistent with the quality criterion defined for shellfish for human consumption.     

Behavioural and siphonal tissue responses of Scrobicularia plana (bivalvia) to zinc

The effects of zinc being added to sea water, to final concentrations of 0·1–20 ppm, have been studied on the heart rate, valve movements, mortality of Scrobicularia and on both isolated and in situ inhalant siphon preparations.The acute toxicity threshold for added zinc was determined to be about 10 ppm at 10°C. The median lethal times for 10 and 20 ppm zinc were 143·5 and 116·1 h respectively.The responses of Scrobicularia to zinc concentrations in sea water of between 0·1 and 10 ppm were tested by exposure for 6 h. Above 1 ppm, valve closure and bradycardia occur within 10–15 min. Below 5 ppm the valves subsequently opened and heart rate increased over the 6 h period, but in 10 ppm closure and pronounced bradycardia were maintained throughout.Addition of zinc, to final concentrations of 1, 5 and 10 ppm, had no effect on the isolated inhalant siphon in contrast to copper at 0·25 and 0·5 ppm which caused very marked siphonal contractions. However, when zinc (1–10 ppm) was added to an in situ inhalant siphon preparation, contractions occurred which were lost on removal of zinc from the bathing medium. Cutting the cruciform muscles medially resulted in the loss or delay of the response to zinc. This suggests the possibility of the cruciform muscle complex (muscle strands and associated sense organs) responding to zinc. This contrasts with the direct action of copper on the neuromuscular system of an isolated siphon.     

Effects of alkaline aluminate waste dumping on seawater chemistry

The alkaline aluminate waste, of which 1000–2000 tonnes are dumped a few times a year off the Belgian coast in the Southern Bight of the North Sea, contains 5·4% NaCl, 1·8% dissolved Al and 7·4% NaOH, in addition to traces of heavy metals and some aniline- and phenol-derivatives. The pH rises locally to 8-5 and the total Al-concentration reaches 120niglitre⁻¹(corresponding to an initial waste dilution factor of only 150) in the 10-m wide track just beyond the discharging barge, but these decay quickly to pH 8·1 and 1 mg litre^-1 in the 30-m wide track, 500m behind the barge. The relation between the waste concentration and seawater pH was studied. The white precipitate that forms immediately in the sea was identified as Mg₆---Al₂---CO₃---(OH)₁₆---4H₂0 (hydrotalcite-manasseite like). No trace of it was found in the local sediments.     

Eddy Diffusion Coefficients of Suspended Particulate Matter: Effects of Wind Energy Transfer and Stratification

Gross sedimentation rates (GSR) have been measured using sediment traps placed at nine different levels above the bed (0·3, 0·5, 0·8, 1·0, 2·0, 4·0, 6·0, 8·0 and 10·0 m). The sediment traps were deployed for 1·25 years and recovered 28 times during the study period. Low average GSR values of 5·5 g m^-2 day^-1 were obtained at 10·0 m, and high average GSR values of 114·8 g m^-2 day^-1 were obtained at 0·3 m. An expression for the eddy diffusion coefficient of suspended particulate matter (K_s), based on the measured GSR is given. The expression has been used for modelling of K_s at the different trap levels above the bed. High values (≈42 cm² s^-1) of K_s were obtained at the upper traps, whereas low values (≈2 cm² s^-1) were obtained near the bed. Comparison between level of turbulent energy in terms of shear stress at the boundaries of the water column, i.e. from the wind and the bed flow, showed that wind energy exceeded that of the bed flow by a factor 16. At 5·0 m K_s was positively correlated (r=0·66) to the eddy diffusion coefficient of momentum (K_m) derived from the wind energy transfer to the water, giving an average β of 0·5 for K_s =βK_m. The density difference between surface and bottom waters has been designated a parameter of stratification, and is discussed in relation to variations of K_s and K_m .     

Carbon and nitrogen primary productivity in three North Carolina estuaries

Uptake of inorganic carbon and ammonium by the plankton community of three North Carolina estuaries was measured using ¹⁴C and ¹⁵N isotope methods. At 0% light, C appeared to be lost via respiration, and at increasing light levels uptake of inorganic carbon increased linearly, saturated (mean I_k = 358±30 μEin m⁻² s⁻¹), and frequently showed inhibition at the highest light intensities. At 0% light NH₄⁺ uptake was significantly greater than zero and was frequently equivalent to uptake in the light (light independent); at increasing light levels NH₄⁺ uptake saturated (mean I_k = 172±44 μEin m⁻² s⁻¹) and frequently indicated strong inhibition. Light-saturated uptake rates of inorganic carbon and NH₄⁺ were a function of chlorophyll a (r² = 0·7−0·9); average assimilation numbers were 625 nmol CO₂ (μg chl. a)⁻¹ h⁻¹ and 12·9 nmol NH₄⁺ (μg chl. a)⁻¹ h⁻¹ and were positively correlated with temperature (r² = 0·3−0·7). The ratio of dark to light-saturated NH₄⁺ uptake tended to be near 1·0 for large algal populations at low NH₄⁺ concentrations, indicating near light independence of uptake; whereas the ratio was lower for the opposite conditions. These data are interpreted as indicative of nitrogen stress, and it is suggested that uptake of NH₄⁺ deep in the euphotic zone and at night are mechanisms for balancing the C:N of cellular pools. A 24-h study using summed short-term incubations confirmed this; the cumulative C:N of CO₂ and NH₄⁺ uptake during the daylight period was 10–20, whereas over the 24-h period the ratio was 6 due to dark NH₄⁺ uptake. Annual carbon and nitrogen primary productivity were respectively estimated as 24 and 4·0 mol m⁻² year⁻¹ for the South River estuary, 42 and 7·3 mol m⁻² year⁻¹ for the Neuse River estuary, and 9·6 and 1·6 mol m⁻² year⁻¹ for the Newport River estuary.     

The effect of cadmium on some oxygen-binding properties of the blood pigment of the lugworm Arenicola marina (annelida, polychaeta)

The effect of cadmium was determined on some oxygen-binding characteristics (viz. oxygen affinity, subunit cooperativity, Bohr-effect and temperature effect) of the erythrocruorin of the lugworm, Arenicola marina.Oxygen affinity and subunit cooperativity were measured directly in the blood of Arenicola, both in blood collected from specimens kept under experimental conditions and from specimens obtained from their natural habitat.In the pH range of 7·3–7·8, which closely resembles in vivo blood pH values, cadmium does not affect the oxygen affinity at low concentrations (10⁻⁸-10⁻⁵ ), and decreases the O₂-affinity only slightly at higher concentrations (10⁻⁵-2·10⁻³ ). In the more alkaline pH range, the oxygen affinity increases considerably with increasing cadmium concentrations.Cadmium exerts a facilitating influence on the haem cooperativity at lowest concentrations (10⁻⁸-10⁻⁷ ) and a minor inhibiting influence at higher concentrations.The oxygen affinity, subunit cooperativity, the Bohr-effect and the temperature effect are pH dependent.The influence of cadmium on the magnitude of the Bohr-effect is pH-dependent.In vivo measurement of the oxygen affinity of Arenicola erythrocruorin gives evidence of a more pronounced inhibition of oxygen binding at increasing cadmium concentrations in the blood, compared with the effect on purified erythrocruorin solutions.     

Chronic sublethal effects of the water soluble fractions of no. 2 fuel oils on the marine isopod, Sphaeroma quadridentatum

Two series of experiments were carried out to assess the long-term effects of the water soluble fractions (WSF) of fuel oils on the marine isopod, Sphaeroma quadridentatum. In one experiment, juvenile isopods (one month old) were exposed to sublethal concentrations (0·1% to 15% WSF) of a fuel oil (Baytown, Exxon) at room temperatures of 24 ± 1–6°C for nine months. These isopods survived to maturity and reproduced. However, growth rate was adversely affected at concentration ≥ 3% WSF and fecundity was depressed at concentrations ≥ 1% WSF. Survival of offspring in clean seawater was dependent to a large extent on the history of the previous generation. Offspring from groups exposed to ≥ 1% WSF experienced high mortality (> 70% within five weeks) even in clean seawater. This may imply that a population of Sphaeroma exposed to WSF as low as 0·2 ppm may eventually disappear, although animals can grow to maturity and reproduce at concentrations < 3 ppm.In another experiment, adult Sphaeroma (three months old) were subjected to the WSFs of four fuel oils (Baton Rouge, Baytown, Montana and New Jersey) for one month. Fecundity was depressed at a concentration > 15% WSF, regardless of the kind of fuel oil. On the other hand, the number of young produced bythe surviving females varied with the type of fuel oil for the same level of WSF. This may be attributed to different relative amounts of toxic components present in the WSF.     

Nitrogen dynamics within a wind-driven eddy

Wind-driven cyclonic eddies are hypothesized to relieve nutrient stress and enhance primary production by the upward displacement of nutrient-rich deep waters into the euphotic zone. In this study, we measured nitrate (NO₃⁻), particulate carbon (PC), particulate nitrogen (PN), their stable isotope compositions (δ¹⁵N-NO₃⁻, δ¹³C-PC and δ¹⁵N-PN, respectively), and dissolved organic nitrogen (DON) within Cyclone Opal, a mature wind-driven eddy generated in the lee of the Hawaiian Islands. Sampling occurred in March 2005 as part of the multi-disciplinary E-Flux study, approximately 4–6 weeks after eddy formation. Integrated NO₃⁻ concentrations above 110 m were 4.8 times greater inside the eddy (85.8±6.4 mmol N m⁻²) compared to the surrounding water column (17.8±7.8 mmol N m⁻²). Using N-isotope derived estimates of NO₃⁻ assimilation, we estimated that 213±59 mmol m⁻² of NO₃⁻ was initially injected into the upper 110 m Cyclone Opal formation, implying that NO₃⁻ was assimilated at a rate of 3.75±0.5 mmol N m⁻² d⁻¹. This injected NO₃⁻ supported 68±19% and 66±9% of the phytoplankton N demand and export production, respectively. N isotope data suggest that 32±6% of the initial NO₃⁻ remained unassimilated. Self-shading, inefficiency in the transfer of N from dissolved to particulate export, or depletion of a specific nutrient other than N may have led to a lack of complete NO₃⁻ assimilation. Using a salt budget approach, we estimate that dissolved organic nitrogen (DON) concentrations increased from eddy formation (3.8±0.4 mmol N m⁻²) to the time of sampling (4.0±0.09 mmol N m⁻²), implying that DON accumulated at rate of 0.83±1.3 mmol N m⁻² d⁻¹, and accounted for 22±15% of the injected NO₃⁻. Interestingly, no significant increase in suspended PN and PC, or export production was observed inside Cyclone Opal relative to the surrounding water column. A simple N budget shows that if 22±15% of the injected NO₃⁻ was shunted into the DON pool, and 32±6% is unassimilated, then 46±16% of the injected NO₃⁻ remains undocumented. Alternative loss processes within the eddy include lateral exchange of injected NO₃⁻ along isopycnal surfaces, remineralization of PN at depth, as well as microzooplankton grazing. A 9-day time series within Cyclone Opal revealed a temporal depletion in δ¹⁵N-PN, implying a rapid change in the N source. A change in NO₃⁻ assimilation, or a shift from NO₃⁻ fueled growth to assimilation of a ¹⁵N-deplete N source, may be responsible for such observations.