Effects of exposure to sublethal concentrations of crude oil on the copepod Centropages hamatus

Female copepods of the species Centropages hamatus show decreased ingestion rates and decreased egg viability when exposed to crude oil/seawater dispersions having crude oil concentrations of 10–80 ppb. However, rates of egg production were not significantly affected by these exposure levels. In addition, we found no evidence for accumulation of petroleum hydrocarbons by copepods exposed to 200 ppb of South Louisiana crude oil. The results imply that biosynthetic pathways involved in oogenesis may be influenced by sublethal concentrations of crude oil or that petroleum hydrocarbons directly affect the viability of eggs. Recruitment into field populations of copepods could be severely reduced as a consequence of exposure to low levels of physically dispersed crude oil.     

Variation in cadmium uptake by estuarine phytoplankton and transfer to the copepod Eurytemora affinis

The pathways of cadmium (Cd) uptake and transfer within an estuarine planktonic community from the Patuxent River, Maryland, USA, were investigated using an assemblage of natural phytoplankton and the copepod Eurytemora affinis Poppe. The experiment was carried out in October 1992 in replicated 500-liter, flow-through, fiberglass tanks. Growth rate, species composition, and Cd loading affected the accumulation of Cd by the phytoplankton. Uptake of Cd by phytoplankton was proportional to the amount of Cd available in the water column. Partition coefficients (K _d) for phytoplankton uptake averaged 4.4 × 10⁴. As metal loading rates and phytoplankton species composition changed during the 12-d experiment, Cd partitioning declined. Transfer of Cd to E. affinis occurred from Cd-laden phytoplankton, with levels in the copepods being approximately the same as, or somewhat less, than in the phytoplankton. Some Cd uptake occurred in copepods exposed to dissolved Cd only; however, the uptake was considerably less than that seen from food. Thus, Cd content of higher trophic levels, such as copepods, can be affected by the degree of Cd incorporation in their food source, and by ecological factors regulating phytoplankton ingestion. Received: 13 September 1995 / Accepted: 29 October 1998     

Accumulation of cadmium by larvae and adults of an Hawaiian bivalve,Isognomon californicum,during chronic exposure

Larvae and adults of an Hawaiian bivalve, Isognomon californicum, were exposed to sublethal, environmentally realistic concentrations of cadmium (2 and 20 ppb) for 28 d, and the accumulation of cadmium was evaluated. The concentrations of cadmium were expressed in terms of total cadmium (tissue and shell concentrations combined) and tissue cadmium. The accumulation rates of larvae were one to two orders of magnitude greater than adult rates. This study suggests that the faster uptake rates of larvae may explain why larvae are more sensitive than adults. Furthermore, the magnitude of differences between larval and adult accumulation rates may be related to metabolic rate. When larvae and adults were exposed to cadmium for only 14 d, followed by a 14 d depuration period, a substantial loss of cadmium was observed during the depuration period. Possible accumulation mechanisms and their similarity between larvae and adults are discussed.     

Accumulation and elimination of cadmium and lead in juvenile milkfish during sublethal exposure

Pollution of aquatic environments by trace metals is a worldwide environmental problem. Metal pollutants are increasingly being released into the environment as a result of industrialization. In this study, the bioaccumulation of cadmium and lead in young juvenile milkfish liver (Chanos chanos) was investigated after exposure to three sublethal concentration of each pollutants (1/20, 1/10, and 1/5 LC₅₀ of 96-h LC₅₀) for acute time 12, 24, and 96 h and subchronically for 7, 14, and 21 days. Cadmium and lead accumulation in liver increased with the exposure period and concentrations of pollutant. Compared to controls, the uptake of cadmium is much higher than that of lead. Accumulation factors showed an increase with exposure time and for lead an inverse relationship between accumulation factor and exposure concentration. The elimination of the two pollutants during the 30 days depuration was investigated after 30 days depuration time. During this phase, cadmium and lead concentrations decreased.     

Bioenergetics and survival of the marine snail Thais lima during long-term oil exposure

The carnivorous snail Thais lima was fed Mytilus edulis during a 28-d exposure to the water soluble fraction (WSF) of Cook Inlet crude oil. The LC-50 of T. lima declined from >3000 ppb aromatic hydrocarbons on Day 7 to 818±118 ppb on Day 28. The LC-50 of M. edulis declined from >3 000 ppb aromatic hydrocarbons on Day 7 to 1 686±42 ppb on Day 28. Predation rate declined linearly with increasing aromatic hydrocarbon concentration up to 302 ppb; little predation occurred at 538 ppb and none at 1 160 or 1 761 ppb. Snail absorption efficiency averaged 93.5% and did not vary as a function of WSF dose. Total energy expenditure (R+U) increased at 44 ppb aromatics and declined at lethal WSF exposures. At sublethal WSF exposures, percentages of total energy expenditure were: respiration (87%), ammonia excretion (9%) and primary amine loss (4%). These percentages did not vary as a function of WSF dose or time. Oxygen:nitrogen ratios were not affected by WSF concentration or time and indicated that T. lima derived most of its energy from protein catabolism. The uptake of aromatic hydrocarbons into the soft tissues of snails and mussels was directly related to the WSF concentration. Naphthalenes accounted for 67 to 78% of the aromatic hydrocarbons in T. lima and 56 to 71% in M. edulis. The scope for growth was negative above 150 ppb WSF aromatic hydrocarbons and above 1 204 ppb soft-body aromatic hydrocarbons. These snails were physiologically stressed at an aromatic hydrocarbon concentration which was 19% of the 28-d WSF LC-50 (818±118 ppb) and/or 48% of the 28-d LC-50 of soft tissue aromatics (2 502 ppb).     

Biochemical fractionation of primary production by phytoplankton in Belgian coastal waters during short- and long-term incubations with 14C-bicarbonate

Short- and long-term time course studies of radiocarbon accumulation in the intracellular end-products of photosynthesis (proteins, polysaccharides, lipids, small metabolites) and extracellular monomers and polymers were conducted at natural light intensity during a 24-h period in Belgian coastal waters dominated by large diatoms species in September, 1983. It is shown that carbon losses observed during the long-term incubation are due to the catabolism of reserve products (polysaccharides and lipids), which occurs both during the light and dark periods and provides carbon and energy for pursuing protein synthesis during the dark. Catabolism rates, as calculated by means of a simple mathematical model, indicate reduced rates of lipid catabolism (1–2% h^-1, respectively for the light and dark periods), although polysaccharide catabolism proceeds at much higher rates, namely 20% h^-1 during the light and 8% h^-1 during the dark period. Assuming that protein synthesis proceeds at a constant rate during the 24-h period and that 1–3 glucan constitutes the main storage product of this diatom population, it is shown that at least 65% of the gross primary production is catabolized by the cells. From this, only 16% are mobilized for dark protein synthesis. The remaining is respired, especially during the light period.     

Hydrodynamic and chemical conditions during onset of a red-tide assemblage in an estuarine upwelling ecosystem

The hydrodynamics and nitrogen/silicon biogeochemistry accompanying the development of a red-tide assemblage were examined in the Ría de Vigo (northwest Spain), a coastal embayment affected by upwelling, during an in situ diel experiment in September 1991. Despite a low N:Si molar ratio (0.5) of nutrients entering the surface layer, which was favourable for diatom growth, the diatom population began to decline. Limited N-nutrient input, arising from moderate coastal upwelling in a stratified water column, restricted net community production (NCP = 630 mg C m⁻² d⁻¹). In addition, light-limitation of gross primary production (GPP = 1525 mg C m⁻² d⁻¹) was observed. The relatively high f-ratio (= NCP:GPP) recorded (0.41, characteristic of intense upwelling conditions) would have been as low as 0.15 had not GPP been limited by light intensity. Temporal separation of carbohydrate synthesis during the photoperiod from protein synthesis in the dark could be inferred from the time-course of the C:N ratio of particulate organic matter. Severe light-limitation would lead to diatom collapse were the diatoms not able to meet all their energy requirements during the hours of darkness. Under the hydrodynamic, nutrient and light conditions of the experiment, an assemblage of red-tide-forming species began to develop, aided by their ability to migrate vertically and to synthesize carbohydrates during the light in surface waters and protein during the dark at the 4 m-deep pycnocline. Thermal stratification, reduced turbulence, intense nutrient mineralization, and the limited nitrogen input through moderate upwelling were all favourable to the onset of a red-tide assemblage. Received: 15 February 1997 / Accepted: 26 September 1997     

Metabolic and molecular stress responses of the gilthead seabream Sparus aurata during long-term exposure to increasing temperatures

Tolerance to a changing climate regime and persistence in the natural environment depends on the limited capacity to acclimate to changing temperatures. The present study aimed to identify and characterize thermal limits of the Mediterranean fish Sparus aurata as well as the processes providing heat protection during exposure to high temperatures. Processes studied included heat shock protein expression, protein kinase activity and metabolic adjustments. Molecular responses were addressed through the expression of Hsp70 and Hsp90 and the phosphorylation of stress-activated protein kinases, p38 mitogen-activated protein kinase (p38 MAPK) and cJun-N-terminal kinases (JNKs). Thermal impacts on metabolic capacities were assessed by studying the maximum activities of citrate synthase (CS), malate dehydrogenase (MDH) and 3-hydroxyacyl CoA dehydrogenase (HOAD) as well as pyruvate kinase (PK) and lactate dehydrogenase (L-LDH). The expression of Hsp70 and hsp90 was activated when the fish were exposed to temperatures beyond 20°C. Increased phosphorylation of p38 MAPK and JNKs indicated the parallel activation of MAPK signaling cascades and the potential involvement of MAPKs in the induction of Hsp genes. Exposure to extreme temperatures beyond 24°C caused an increase in the enzymatic activity of PK and LDH indicating an enhanced glycolytic potential.     

Tolerance of estuarine benthic diatoms to high concentrations of ammonia,nitrite ion,nitrate ion and orthophosphate

A carbon-14 assimilation method was used to determine action spectra and photosynthesis versus irradiance (P versus I) curves of natural populations of phytoplankton and zooxanthellae from a coral reef fringing Lizard Island in the Australian Barrier Reef. The action spectra were related to the phytoplankton species composition. The curves showed shade adaptation in phytoplankton from deeper waters and in the zooxanthellae. Rates of photosynthesis of zooxanthellae were shown to be highly but variably dependent on their host organisms. Photosynthetic production by zooxanthellae was about 0.9 gC m^-2 day^-1, which is about three times higher than phytoplankton production in the waters close to the reef.     

Depression of feeding and growth rates of the seastar Evasterias troschelii during long-term exposure to the water-soluble fraction of crude oil

To test the effect of petroleum hydrocarbons on predation by the seastar Evasterias troschelii (Stimpson, 1862) on the mussel Mytilus edulis (L.), we exposed the predator with the prey to six concentrations of the water-soluble fraction (WSF) of Cook Inlet crude oil. Seastars and mussels were collected at Auke Bay, Alaska, in November 1980. During a 28 d exposure in a flow-through system, seastars were more sensitive to the WSF than mussels: the LC₅₀ for the seastars was 0.82 ppm at Day 19 and, although no mussels were exposed to WSF for more than 12 d, none died. Daily feeding rates (whether in terms of number of mussels seastar^-1 d^-1 or dry weight of mussels seastar^-1 d^-1) were significantly reduced at all concentrations above 0.12 ppm. At 0.20, 0.28 and 0.72 ppm WSF, daily feeding rates (in terms of dry weight of mussels) were, respectively, 53, 37, and 5% of the control rate; at the two highest concentrations (0.97 and 1.31 ppm WSF), the seastars did not feed. Seastars at concentrations greater than 0.12 ppm WSF grew slower than individuals from the control group and the 0.12 ppm-treatment group combined. These laboratory results show that E. troschelii is more sensitive to chronic low levels of the WSF of crude oil. The possibility that such oil pollution could reduce predation and permit M. edulis to monopolize the low intertidal zone of southern Alaska remains to be studied.     

Metabolism and model of an estuarine bay ecosystem affected by a coastal power plant

The effects of a coastal power plant on an outer estuarine bay ecosystem on the west coast of Florida were evaluated with measurements and an ecological model. Field measurements of community metabolism and biomass were taken from the thermally affected bay and from similar control bays. Model simulations were used to help understand these observations in terms of ecosystem structure and functioning.In the outer discharge bay the direct impact of the thermal plume was diluted and spread overlarge areas. The ecosystem developed structure and functions with lower biomass than in the control bays but with slightly faster rates of organic turnover. The productive turnover time of producer biomass during the summer was about 5 days in the discharge bay and about 6 days in the control bays. Power plant influence on total community metabolism was small with less than 10% difference in annual averages between the discharge and control bays (5.22 and 5.58 g O₂/m²/day). The selection for faster metabolic turnover rates in the discharge by was evidenced by a dominance of plankton metabolism over benthic metabolism. The annual average gross planktonic production was around 3 g O₂/m²/day in the discharge bay and around 2 g/m²/day in the control bays.In the model, temperature served as a stimulant to both productivity and respiration. When the isolated effects of increased temperature were simulated the model responded with lower producer biomass and faster rates of organic turnover, as was found in field measurements. These simulations also showed increased nutrient recycling and indicated patterns of temperature-induced migrations. Since power plant operation affected water exchange in the bays, several levels of total water exchange were simulated. These simulations indicated the importance of water exchange as a stabilizing factor, especially for sensitive compartments with rapid turnover rates (i.e. plankton and phosphorus stocks). Simulations of the effects of future power plant units on the bay ecosystem showed no large changes in total metabolism but indicated larger effects of plankton entrainment mortality and temperature-induced migrations of larger organisms.     

Experimental study on acute effects of the combined exposure to temperature increase and chlorination upon the marine copepod Acartia omorii

The acute effects of combined exposure to temperature increase and chlorination on a neritic marine copepod, Acartia omorii Bradford (collected offshore of Onjuku, Japan in 1982), were investigated in the laboratory. Continuous flow exposure and batch exposure modes were compared. Based on the results of continuous flow experiments, the 24-h median lethal concentration (24-h LC₅₀, in mg l^-1) of total residual chlorine was estimated using the multiple regression equation below, with a multiple correlation coefficient of 0.955: 24-h LC₅₀=2.988-0.034 dT-1.611 log₁₀ t where dT is temperature rise (°C) and t is exposure duration (min). In batch experiments, the predictive power of the multiple regression equation was reduced, probably due to variations in chlorine concentration during exposure duration.     

Mitochondrial dysfunction,impaired oxidative-reduction activity,degeneration, and death in human neuronal and fetal cells induced by low-level exposure to thimerosal and other metal compounds

Thimerosal (ethylmercurithiosalicylic acid), an ethylmercury (EtHg)-releasing compound (49.55% mercury (Hg)), was used in a range of medical products for more than 70 years. Of particular recent concern, routine administering of Thimerosal-containing biologics/childhood vaccines have become significant sources of Hg exposure for some fetuses/infants. This study was undertaken to investigate cellular damage among in vitro human neuronal (SH-SY-5Y neuroblastoma and 1321N1 astrocytoma) and fetal (nontransformed) model systems using cell vitality assays and microscope-based digital image capture techniques to assess potential damage induced by Thimerosal and other metal compounds (aluminum (Al) sulfate, lead (Pb)(II) acetate, methylmercury (MeHg) hydroxide, and mercury (Hg)(II) chloride) where the cation was reported to exert adverse effects on developing cells. Thimerosal-associated cellular damage was also evaluated for similarity to pathophysiological findings observed in patients diagnosed with autistic disorders (ADs). Thimerosal-induced cellular damage as evidenced by concentration- and time-dependent mitochondrial damage, reduced oxidative–reduction activity, cellular degeneration, and cell death in the in vitro human neuronal and fetal model systems studied. Thimerosal at low nanomolar (nM) concentrations induced significant cellular toxicity in human neuronal and fetal cells. Thimerosal-induced cytoxicity is similar to that observed in AD pathophysiologic studies. Thimerosal was found to be significantly more toxic than the other metal compounds examined. Future studies need to be conducted to evaluate additional mechanisms underlying Thimerosal-induced cellular damage and assess potential co-exposures to other compounds that may increase or decrease Thimerosal-mediated toxicity.     

低剂量Aroclor 1254和BDE-209单一和复合暴露的甲状腺干扰作用

本文旨在探讨低剂量PCBs和PBDEs单一暴露和复合暴露的甲状腺干扰作用.非洲爪蟾46期蝌蚪单独或共暴露于100 ng·L-1Aroclor 1254和BDE-209至62期.暴露结束后检测变态时间、甲状腺组织学结构、甲状腺相关基因表达水平等指标.结果发现,Aroclor 1254和BDE-209单独暴露使蝌蚪变态发育呈现一定的延迟趋势,而复合暴露却显著抑制蝌蚪变态发育;所有的暴露处理均导致蝌蚪甲状腺组织代偿性改变,表现为胶质面积减少,甲状腺滤泡上皮细胞高度显著增加;Aroclor 1254单独暴露显著抑制甲状腺激素受体(TRA)、Ⅱ和Ⅲ型脱碘酶(DI-2,DI-3)的表达,BDE-209单独暴露仅抑制DI-2的表达,但BDE-209协同促进Aroclor1254对肝脏内TRA表达的抑制作用.综上,低剂量Aroclor 1254和BDE-209单独暴露和复合暴露对非洲爪蟾变态发育具有一定的甲状腺抑制作用,复合暴露的抑制作用明显高于单一暴露的作用.鉴于甲状腺系统在脊椎动物生长发育过程中的重要作用,低剂量PCBs和PBDEs复合暴露的甲状腺干扰效应应该受到格外关注.     

Interactive effects of salinity,temperature and chronic exposure to oil on the survival and developmental rate of embryos of the estuarine killifishFundulus heteroclitus

The combined effect of salinity, temperature and chronic exposure to water-soluble fractions (WSF) of a No. 2 fuel oil on the survival and development rate of embryos ofFundulus heteroclitus Walbaum are described. The embryos were exposed at 3 salinities (10, 20, 30 S) and 3 temperatures (20°, 25°, 30°C) to 3 different oil concentrations (15, 20, 25% WSF, equivalent to approx 0.28, 0.38 and 0.47 ppm total naphthalenes) and to one control without oil. The results were analyzed by responsesurface methodology. The lowest oil concentration was only mildly toxic to embryos under optimal salinity/temperature conditions, while the highest was extremely toxic in all factor combinations. Under optimal conditions, only the highest oil concentration resulted in more than 50% mortality. Under suboptimal conditions, especially high and low temperatures, all 3 oil concentrations caused greater than 50% mortality. The interactive effect of salinity and temperature on survival was greatest at the lowest oil concentration. Temperature had a marked effect and salinity only a slight effect on the developmental rate of the embryos. Exposure to the low oil concentration tended to increase the temperature sensitivity of developmental duration slightly. Generally, exposure to oil decreased the time interval between fertilization and hatching.     

Food ingestion by the marine planktonic copepod Paracalanus in relation to abundance and size distribution of food

Juveniles and adult females were presented a food spectrum of three algae of different sizes (4.5, 12 and 20 m cell width). The increase in rate of ingestion of the medium-sized alga with an increase in copepod size was significantly greater than the increase in rate of ingestion of the small alga. It is hypothesized that the perception of chemical signals from the small alga by a copepod decreases as the copepod moults from stage to stage. The rate of ingestion of the large alga by copepod stage V (CV) and adult females was lower than the rate of ingestion of the medium-sized alga at mid- and high phytoplankton concentrations. The amount of nitrogen ingested when the medium-sized alga alone was offered was either higher than (stage C II) or not significantly different from that when the three algae were offered together (stage C IV). Ingestion rates are reduced when there is a multialgal food source. This implies that there is increased stability in the ocean because multiparticle food sources are more slowly depleted than unialgal foods. Weight-specific ingestion rates of copepods fed the three algae simultaneously increased from nauplius to stage C III and then decreased as adulthood approached. The contribution of the small alga to the total amount of nitrogen ingesied was greatest for naupliar stages while the contribution of the medium-sized cells was greater for later stages. The largest alga was readily ingested by stage C V and adult females but never contributed more than 25% of the nitrogen ingested. Eight to 12% of the nitrogen ingested by adult females was from the small alga. It is hypothesized that the algal cell size for maximum nitrogen ingestion in upwelled waters is relatively small, round or square and close to the size threshold below which adult females do not sense individual cells.     

Effects of fertilization and development of the common mussel Mytilus edulis after long-term exposure to a nonionic surfactant

Common mussels (Mytilus edulis L.) were exposed over a 5-month period to low-level concentrations (0.5 to 1.5 ppm) of a nonionic surfactant. Upon maturation at the end of this period, spawning ability was examined. Fertilization occurred at low-level concentrations (0.1 to 2.0 ppm) of the surfactant, and was most successful for gametes from the long-term controls and the highest long-term concentration (1.5 ppm). Inhibited or delayed larval development was observed, related to the concentration gradient of the short-term exposures. Gametes from mussels long-term exposed to the surfactant were more sensitive than those from the long-term control.     

Vegetation succession of low estuarine marshes is affected by distance to navigation channel and changes in water level

Climate change and engineering activities have modified the hydrology and morphology of estuaries. However, the potential effects of these modifications on vegetation succession in estuarine marshes are still poorly understood. Therefore, we studied temporal changes in tidal habitats of the Elbe estuary over a period of 30 years. We compared vegetation maps from 1980 to 2010 and calculated the change in area of habitats with respect to three salinity and three elevational zones. To analyze the direction of the temporal change, we differentiated between progressive and regressive succession. By using regression tree models (conditional inference trees), we identified the most influential factors determining progressive or regressive succession of low marshes. The total area of the estuarine tidal marshes at the Elbe increased by 2 % from 1980 to 2010, but changes were unequal among the salinity zones. In the salt and brackish zones, the area covered by high marshes increased substantially but decreased in the tidal freshwater zone, while that covered by low marshes decreased in all the salinity zones. Additionally, we determined high persistence of tidal flats and high marshes, whereas only 19 to 28 % of the low marshes found in 1980 remained in 2010. In salt and brackish marshes, more than two-thirds of the area that had been identified as low marshes in 1980 had progressively developed into high marshes. In contrast, 44 % of the area of low marshes in tidal freshwater marshes showed regressive succession back into tidal flats. The distance to the navigation channel was the main factor determining successional direction in salt and brackish marshes. Here, greater proximity to the channel was correlated with higher risk of regressive succession. In tidal freshwater marshes, we identified both the distance to the navigation channel and the situation on the river shore (i.e. inner bank, outer bank or straight bank) as the main factors for marsh succession. Here, considerable engineering activities in the channel had simultaneously decreased the mean low water level and increased the mean high water level between 1980 and 2010, which led to an increase in tidal amplitude. It is quite likely that these changes negatively modified marsh distribution, increased regressive succession and, thus, lowered the quality of tidal freshwater marshes.     

Modeling effects of toxin exposure in fish on long-term population size, with an application to selenium toxicity in bluegill (Lepomis macrochirus)

A primary goal in ecotoxicology is the prediction of population-level effects of contaminant exposure based on individual-level response. Assessment of toxicity at the population level has predominately focused on the population growth rate (PGR), but the PGR may not be a relevant toxicological endpoint for populations at equilibrium. Equilibrium population size may be a more meaningful endpoint than the PGR because a population with smaller equilibrium size is more susceptible to the negative effects of environmental variability. We address the individual-to-population extrapolation problem with modeling utilizing classical mathematical theory. We developed and analyzed a general model applicable to many freshwater fish species, that includes density-dependent juvenile survival and additional juvenile mortality due to toxicity exposure, and we quantified effect on equilibrium population size as a means of assessing toxicity. Individual-level effects are typically greater than population-level effects until the individual effect is large, due to compensatory density-dependent relationships. These effects are sensitive to the recruitment potential of a population, in particular the low-density first-year survival rate S_b. Assuming high S_b could result in underestimating effects of population-level toxicity. The equilibrium size depends directly on S_b, the reproductive potential, the toxin concentration at which mean mortality is 50% (LC₅₀), and the rate at which individual mortality increases with increasing toxin concentration. More experimental data are needed to decrease the uncertainty in estimating these parameters. We then used existing data for selenium toxicity in bluegill sunfish to parameterize a simulation version of the model as an example to assess the effects of environmental stochasticity on toxicity response. Effects of environmental variability resulted in simulated extinctions at much lower toxin concentrations than predicted deterministically.