Behavioural responses of selected marine fishes to chlorinated seawater

Behavioural responses to chlorinated seawater were studied in the laboratory using eight species of fish (topsmelt, Atherinops affinis [Ayres]; pile perch, Rhacochilus vacca [Girard]; señorita, Oxyjulis californica [Günther]; blacksmith, Chromis punctipinnis [Cooper]; northern anchovy, Engraulis mordax [Girard]; opaleye, Girella nigricans [Ayres]; bluebanded goby, Lythrypnus dalli [Gilbert] and mussel blenny, Hypsoblennius jenkinsi Jordan and Evermann) which occur near the Units 7 and 8 discharge of Southern California Edison's Redondo Beach Steam Generating Plant in King Harbor, California, USA. All species except Engraulis demonstrated prolonged avoidance of chlorinated quadrants of the behaviour chamber. The avoidance thresholds were species-specific and species totally avoided estimated total residual oxidant (TRO) concentrations from 0·094 to 0·456 mg/litre. Calculated significant avoidance thresholds averaged 0·066 mg/litre TRO; young Atherinops significantly avoided TRO concentrations as low as 0·028 mg/litre (p < 0·001). The highest avoidance thresholds were exhibited by sedentary species and were modified by the presence of cover inside the behaviour chamber. The avoidance response protected against mortality in all species except Lythrypnus and Engraulis.     

Sulfide control of cadmium and copper concentrations in anaerobic estuarine sediments

Equilibrium concentrations of the toxic trace metals copper and cadmium were calculated for the physico-chemical conditions characterizing pore waters of anaerobic estuarine sediments using available thermodynamic data and assuming simple sulfide minerals control solubilities. Polysulfide complexes are responsible for the solubility of copper in the cuprous (Cu(I)) oxidation state. Predicated copper concentrations, assuming covellite (CuS) is the controlling solid phase, are in reasonable agreement with copper analyses in a wide range of sulfidic waters and sediment pore waters. In the absence of thermodynamic data, no account could be taken of possible polysulfide complexes of cadmium. However, bisulfide complexes appear to account satisfactorily for observed solubilities assuming the existence of greenockite (CdS) as the controlling solid phase. Anaerobic estuarine sediments may act as a sink for copper and cadmium in the common situation in which free sulfide concentrations are controlled by the coexistence of iron sulfide and iron oxide minerals. However, where free sulfides reach high concentrations of 10^?3 M or more, the concomitant increase in concentration of bisulfide and polysulfide complexes may result in the sediments acting as a source of copper and cadmium.     

低氧胁迫对菲律宾蛤仔抗氧化酶的影响

为了研究不同低氧水平对菲律宾蛤仔(Ruditapes philippinarum)的影响,在实验室条件下设置溶解氧为0.5 mg/L和2.0 mg/L的低氧海水环境,以溶氧水平为7.0 mg/L的天然海水为对照组,研究了低氧胁迫对菲律宾蛤仔抗氧化酶的影响。结果表明:在低氧胁迫的时间越长的条件下,乳酸脱氢LDH和琥珀酸脱氢酶SDH的活力逐渐降低,而碱性磷酸酶AKP活力逐渐增大;对于相同的酶,对照组的酶活力高于处理组的酶活力;在溶氧DO越低的情况下,菲律宾蛤仔的死亡率越高。     

Influence of estuarine hypoxia on feeding and sound production by two sympatric pipefish species (Syngnathidae)

This research utilizes the acoustic behavior of two sympatric pipefish species to assess the impact of hypoxia on feeding. We collected northern, Syngnathus fuscus, and dusky pipefishes, Syngnathus floridae, from the relatively pristine Chincoteague Bay, Virginia, USA and audiovisually recorded behavior in the laboratory of fish held in normoxic (>5 mg/L O(2)) and hypoxic (2 and 1 mg/L O(2)) conditions. Both species produced high frequency ( approximately 0.9-1.4 kHz), short duration (3-22 msec) clicks. Feeding strikes were significantly correlated with both wet weight of ingested food and click production. Thus, sound production serves as an accurate measure of feeding activity. In hypoxic conditions, reduced food intake corresponded with decreased sound production. Significant declines in both behaviors were evident after 1 day and continued as long as hypoxic conditions were maintained. Interspecific differences in sensitivity were detected. Specifically, S. floridae showed a tendency to perform head snaps at the surface. S. fuscus exhibited a breakdown in the coupling of sound production with food intake in 2 mg/L O(2) with clicks produced in other contexts, particularly choking and food expulsion. Reductions in feeding will ultimately impact growth, health, and eventually reproduction as resources are devoted to survival instead of gamete production and courtship. This work suggests acoustic monitoring of field sites with adverse environmental conditions may reflect changes in feeding behavior in addition to population dispersal.     

An evaluation of metal bioaccessibility in estuarine sediments using the commercially available protein, bovine serum albumin

The bioaccessibility of metals (Al, Ca, Fe, Mn, Ag, Cd, Co, Cu, Ni, Pb, Sn, Zn) in oxic estuarine sediments has been evaluated using solutions of a commercially available protein (bovine serum albumin; BSA) that mimic the chemical conditions encountered in the gut environment of many deposit-feeding organisms. Over a 20 h incubation period with 5 g L^− 1 BSA, metal mobilisation was generally biphasic in that a relatively short period of rapid release was succeeded by more gradual release or approach to equilibrium, although in some cases metal readsorption was evident during the time-courses. Availability to BSA, defined as metal released after 20 h relative to metal extracted by boiling aqua regia, was greatest for Cd, Ni, Ca and Zn and lowest for Fe and Mn, and correlated well with, but was an order of magnitude lower than, metal digested by acidified hydrogen peroxide. Time-courses conducted in the absence of the protein revealed that significant quantities of Ca and Mn were water-soluble, reflecting the partial dissolution of carbonates and hydrous Mn oxides, respectively. Additional experiments indicated a net increase in metal release with increasing BSA concentration and, with the exception of Ca and Mn, a substantial increase in metal mobilisation after sediment organic matter had been digested by peroxidation. These observations suggest that, apart from Ca and Mn, metal release proceeds via complexation with component amino acids of the protein, denudation of organic host phases, and exposure of inorganic, metal-bearing minerals. Accordingly, the bioaccessibility of a metal is predicted to be dependent on its (i) affinity for proteinaceous ligands, (ii) association with components of digestible sediment organic matter, and (iii) degree of binding at relatively weak sites on sediment phases that are exposed or modified by the action of proteins and other chemical constituents of the gut environment.     

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.     

Macrobenthic invertebrate responses to prolonged drought in South Africa's largest estuarine lake complex

St Lucia, the largest estuarine lake complex of its type in Africa, is characterised by natural physico-chemical spatial and temporal fluctuations. This estuary functions as an important nursery area making use of a number of different habitat types and associated environmental conditions. The system has been subject to a number of natural episodic events such as cyclonic flooding and cyclical droughts, the most current has persisted since 2001, resulting in almost permanent mouth closure. Furthermore, high levels of evaporation have reduced lake levels and resulted in compartmentalisation of the system for up to several years at a time. St Lucia is sensitive to evaporation and therefore to vast salinity fluctuations and hypersaline conditions. The upper reaches in North Lake are particularly sensitive to drying out and extended hypersaline events. The macrobenthos has been well studied, but no studies have concentrated on the entire system for such an extent of time. Macrobenthic samples were initially collected in 2004, again in 2005 and biannually from 2006 to 2008. This study was part of a larger multidisciplinary programme aimed at determining the effects of long term drought conditions on the ecology of the St Lucia system, and increasing current understanding of the system response to future catastrophic climatic events. Three areas were sampled (North and South Lake and Estuary) at five sites per area, over five years. Data were analysed by representing communities through time series depictions and discriminating sites and sampling periods to test multidimensional relationships. Linkages between biological distribution and selected environmental forcing variables were investigated. The system was found to be highly variable and supporting a large number of different habitats and co-occurring environmental conditions. This variability makes it difficult to discern spatial or temporal patterns in environmental conditions and macrobenthic ecology. However, some level of resilience to wide ranging environmental changes associated with drought is maintained. This study was able to determine that there exists a core of taxa able to persist even under shallow depth conditions and prolonged hypersalinity. These taxa clearly have a self recruiting strategy and are therefore not reliant on mouth opening to re-establish local populations. This finding alone has important bearing for future studies and management of the system under similar adverse conditions.     

Feeding preferences of estuarine mysids Neomysis integer and Rhopalophthalmus tartessicus in a temperate estuary (Guadalquivir Estuary,SW Spain)

Mysid shrimps are an important component of estuarine food webs because they play a key role in energy transfer as intermediate prey. We investigated the seasonal, tidal and depth specific variation in the diet of the estuarine mysids Neomysis integer and Rhopalophthalmus tartessicus and explored its implications for the planktonic community structure of a temperate estuary (Guadalquivir Estuary, SW Spain). Neomysis integer is an opportunistic omnivore feeding mainly on mesozooplankton and on members of the detrital–microbial loop, shifting prey seasonally according to availability. In contrast, R. tartessicus showed a more carnivorous diet and shifted its target prey during seasons of low resource availability. Despite statistically significant differences in diet composition, both species shared prey of similar size, particularly juvenile Mesopodopsis slabberi, the most abundant mysid species in this estuary, and copepods. Although these similarities imply inter-specific resource competition, their co-existence is achieved by niche partitioning and spatial segregation: the higher osmoregulatory capacity and foraging plasticity of N. integer confers a broader niche breadth for this species allowing N. integer to inhabit the more stressful oligohaline region of the estuary where R. tartessicus cannot survive. We propose that this mechanism relaxes the potential for competition between N. integer and R. tartessicus.     

Acclimation to cadmium by Fundulus heteroclitus as demonstrated by fin regeneration and cadmium accumulation

There is a body of literature indicating that pre-exposure to low levels of metals may increase tolerance during subsequent exposure.¹ We have previously demonstrated that exposure to cadmium at 100 to 500 μg/liter will retard the rate of fin regeneration in the killifish Fundulus heteroclitus.² These experiments were designed to investigate the effects of pre-exposure to cadmium, using fin regeneration as the parameter of effect. The results indicate that pretreatment allows this species to regenerate faster during cadmium treatment as compared to non-pretreated fish, and that the relationship between the pretreatment and treatment concentrations is relevant to pretreatment effects.     

Cellular responses of oysters, Crassostrea virginica, to metal-contaminated sediments

Elevation of metal concentrations in coastal environments associated with anthropogenic enrichment pose a significant threat to estuarine organisms. The purpose of this study was to evaluate the relationships between cellular responses that may be potentially valuable as indicators of chronic stress and metal-contaminated sediments. For these studies, hatchery-reared juvenile oysters were deployed in situ at 15 sites for approximately 1 month around Charleston Harbor, SC. The effects on lysosomal destabilization and glutathione concentrations were determined; and the relationships between the cellular responses and sediment metal concentrations were described. Both single metal and multiple metal parameters (based on total metal concentrations, aluminum normalizations, and summed sediment quality guidelines) were considered. Generally, significant correlations were observed for individual metal analytes and multiple metal parameters. Since many of the individual metal analytes covary, the responses may reflect overall contaminant loading rather than responses to individual metals. Methods for estimating overall contaminant loading based on multiple analytes provide a more realistic estimate of potential adverse effects.     

Behavioural responses to structures on the seafloor by the deep-sea fish Coryphaenoides armatus: Implications for the use of baited landers

Coryphaenoides armatus plays a fundamental role in the dispersal of organic matter on the deep-sea floor by consuming food-falls. The use of baited cameras to study population parameters (e.g. abundances and size frequencies) assumes that members of this species follow odour plumes directly to bait, appear immediately in the field of view, and depart as predicted by optimal foraging theory. Described here are behaviours to the contrary observed during the operation and development of more complex baited camera systems. Of the 247 C. armatus observed by a video lander, 72.5% of the fish explored the structure whilst only 6% fed, and 21.5% were indifferent. This exploratory behaviour increased individual staying time by 38.4% compared to those that just fed. Experiments with several models of in situ fish respirometry lander showed the importance of both equipment design, and an understanding of the behaviour of the target animals in maximising capture success. These results show how previously unexpected aspects of behaviour by C. armatus can greatly affect the chances of capturing members of this species and influence the results of baited camera experiments.     

Origins and temporal scales of hypoxia on the Louisiana shelf: Importance of benthic and sub-pycnocline water metabolism

Hypoxic-to-anoxic conditions (2–0 mg O₂ l^− 1) occur in the bottom waters of the northern Gulf of Mexico on the Louisiana shelf west of the Mississippi river delta during late spring and summer where the rate of oxygen consumption exceeds its rate of input from physical transport plus photosynthetic generation. Although consumption of oxygen in the water column primarily via oxic respiration is an important process, the loss of oxygen at and near the seafloor may also be an important sink contributing to seasonal low oxygen conditions in the relatively shallow overlying waters in this region. Associated with the flux of oxygen into the sediments is the flux of nutrients out of the sediments from the remineralization of sedimentary organic matter via a number of possible electron acceptors. The nutrients that are released from the sediment can potentially stimulate further primary production. This can lead to generation of oxygen in the water column and production of organic matter, much of which can be transported to the seafloor where it again becomes a sink for oxygen.A non-steady-state data driven numeric benthic–pelagic model was developed to investigate the role of sediment and water-column metabolism in the development of hypoxia on the Louisiana shelf. The model simulations bare out the importance of sediment oxygen demand as the primary sink for oxygen at the beginning and end of a hypoxic event on the shelf, but once hypoxia has developed, the sediments, now isolated from the oxygen-rich surface waters, are driven into a more anoxic mode, becoming more dependent on sulfate and metal reduction. As a result, the bottom water near the pycnocline becomes the major sink for oxygen.Model simulations also suggest that there is a delay of several weeks between metabolite production (especially ammonium) and its efflux from the sediments. Thus the maximum sediment ammonium export occurs in September and October in time to fuel autumnal phytoplankton production, thereby continuing a biogeochemical cycle that expands the temporal and spatial scales of hypoxia on the Louisiana shelf.     

Improving estuarine net flux estimates for dissolved cadmium export at the annual timescale: Application to the Gironde Estuary

Dissolved Cd (Cd_D) concentrations along the salinity gradient were measured in surface water of the Gironde Estuary during 15 cruises (2001–2007), covering a wide range of contrasting situations in terms of hydrology, turbidity and season. During all situations dissolved Cd concentrations displayed maximum values in the mid-salinity range, reflecting Cd addition by chloride-induced desorption and complexation. The daily net Cd_D fluxes from the Gironde Estuary to the coastal ocean were estimated using Boyle's method. Extrapolating Cd_D concentrations in the high salinity range to the freshwater end member using a theoretical dilution line produced 15 theoretical Cd concentrations (Cd_D⁰), each representative of one distinct situation. The obtained Cd_D⁰ concentrations were relatively similar (201 ± 28 ng L⁻¹) when freshwater discharge Q was >500 m³ s⁻¹ (508 ≤ Q ≤ 2600 m³ s⁻¹), but were highly variable (340 ± 80 ng L⁻¹; 247–490 ng L⁻¹) for low discharge situations (169 ≤ Q ≤ 368 m³ s⁻¹). The respective daily Cd_D net fluxes were 5–39 kg day⁻¹, mainly depending on freshwater discharge. As this observation invalidates the existing method of estimating annual Cd_D net fluxes, we proposed an empirical model, using representative Cd_D⁰ values and daily freshwater discharges for the 2001–2007 period. Subsequent integration produced reliable Cd_D net flux estimates for the Gironde Estuary at the annual timescale that ranged between 3.8–5.0 t a⁻¹ in 2005 and 6.0–7.2 t a⁻¹ in 2004, depending on freshwater discharge. Comparing Cd_D net fluxes with the incoming Cd_D fluxes suggested that the annual net Cd_D addition in the Gironde Estuary ranged from 3.5 to 6.7 t a⁻¹, without any clear temporal trend during the past seven years. The annual Cd_D net fluxes did not show a clearly decreasing trend in spite of an overall decrease by a factor 6 in Cd gross fluxes during the past decade. Furthermore, in six years out of seven (except 2003), the annual Cd_D net fluxes even exceeded river borne total (dissolved + particulate) gross Cd fluxes into the estuary. These observations were attributed to progressive Cd desorption from both suspended particles and bottom sediment during various sedimentation–resuspension cycles induced by tidal currents and/or continuous dredging (navigation channel) and diverse intra-estuarine sources (wet deposition, urban sources, and agriculture). Provided that gross fluxes remain stable over time, dissolved Cd exportation from the Gironde Estuary to the coastal ocean may remain at the present level for the coming decade and the estuarine sedimentary Cd stock is forecast to decrease slowly.     

Body and brood sizes of Tenagomysis spp. (Crustacea: Mysida) in southern estuaries in New Zealand

Mysids form a large biomass and mediate the benthic–pelagic coupling of numerous estuaries in southern New Zealand. An intra-annual (2011–2012) field survey in the breeding seasons (i.e. austral spring followed by summer) of mysids Tenagomysis chiltoni and Tenagomysis novaezealandiae, examining the body and brood sizes, was conducted. Samples were collected from six open and eight intermittently open/closed estuaries along the Otago coastline. Brood size of gravid females of T. chiltoni was not significantly related to their body size. Brood size of gravid females of T. novaezealandiae showed a significantly positive relationship with body size in spring but not in summer. It appears that brood size of gravid mysids do not always necessarily depend on body size, but may be influenced by breeding season (e.g. spring) and estuarine typology (e.g. intermittently open/closed).     

Sub-lethal effects of metal exposure: physiological and behavioural responses of the estuarine bivalve Macoma balthica

Variation in glycogen concentration, condition index (CI) and filtration activity were measured in the bivalve Macoma balthica buried in sediment and experimentally exposed to cadmium (Cd). The stress due to elevated but sub-lethal concentrations (300 ppb Cd) affected the overall fitness of the organism as all parameters monitored responded significantly. Lower concentrations tested (10, 30 and 100 ppb) only induced a significant decrease in filtration activity, which may play a protective role, enabling the organism to slow down its metabolic activity and preserving the integrity of its reserves (reflected by stable CI and glycogen levels). Hence, the various endpoints selected show different thresholds. Our results also demonstrate that under high exposure, small individuals loose proportionally more glycogen per unit of weight than larger ones, thus confirming the higher sensitivity of small individuals to metal contamination. Furthermore, exposure to intermediate concentration (30 ppb) seems to be beneficial to the small individuals as indicated by their high CI values compared to the control. These results showed thus that non-sigmoidal concentration-response relationship and sizes of individuals should be considered in monitoring programmes and risk assessment.     

经济海藻羊栖菜（Sargassum fusiforme）幼体对镉胁迫的响应特性

镉(Cd)是水生生态环境中常见的重金属污染物,通常会抑制植物的生长,减少生物量,对植物产生毒害作用。为了研究羊栖菜幼苗对海水中Cd胁迫的抗氧化响应特性,我们在天然海水和Cd加富(100 μmol·L^-1)海水两种不同的Cd浓度下培养羊栖菜幼体。实验结果表明:Cd加富胁迫显著抑制了羊栖菜幼苗生长,使藻体颜色变暗。此外,高Cd处理显著降低了羊栖菜中的色素含量,生长速率,过氧化物酶(POD)活性,脱氢抗坏血酸(DHA)含量和谷胱甘肽还原酶(GR)活性。相反,高Cd处理显著促进了藻体内的Cd元素积累、对Cd₂⁺吸收速率,并增加了其暗呼吸/净光合速率比值(R_d/P_n),抗坏血酸(Vc)含量,可溶性蛋白质(SP)含量,且还原型谷胱甘肽(GSH)以及羊栖菜的超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性均显著增加,但对丙二醛(MDA)的影响不显著。虽然羊栖菜幼苗增加了其抗氧化活性并促进AsA-GSH循环,以产生H₂O₂并维持健康的新陈代谢,但高Cd胁迫显著限制了幼苗的光合作用,降低了其光合色素,抑制了其生长,并使其藻体颜色发生变化。海水中高浓度的Cd对羊栖菜幼苗具有毒性作用,并且极大地增加了这种海藻的食用风险。