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1.
We examined the bioaccumulation and trophic transfer of mercury in two marine finfish species, striped bass (Morone saxatilis) and tautog (Tautoga onitis), collected from the Narragansett Bay (Rhode Island, USA). For each of these target fish, white muscle tissue was analyzed for total mercury (Hg) and results were evaluated relative to fish age, body size, and Hg content of preferred prey. Dietary and stable isotope analysis was also used to elucidate the effect of trophic processes on Hg concentrations in fish. The Hg content of muscle tissue was positively correlated with fish age and length for both species, although striped bass accumulated Hg faster than tautog. Accelerated Hg bioaccumulation in striped bass is consistent with its high trophic level (trophic level = 4.07) and Hg-enriched prey (forage fish and macrocrustaceans; mean Hg content = 0.03 mg Hg kg wet wt?1). In contrast, tautog maintain a lower trophic status (trophic level = 3.51) and consume prey with lower Hg levels (mussels and crabs; mean Hg content = 0.02 mg Hg kg wet wt?1). Despite differences in Hg bioaccumulation between target fish, the mean Hg concentration of tautog exceeded levels in striped bass (0.24 and 0.16 mg Hg kg wet wt?1, respectively) due to a disparity in age-at-catch between sampled groups (mean age of tautog and bass = 11.3 and 4.3 yr, respectively). Taking into account legal minimum catch lengths further revealed that 75.0% of legal-size striped bass (>70.2 cm TL; n = 4) and 44.8% of tautog (>40.6 cm TL; n = 29) had Hg levels beyond the US EPA regulatory threshold of 0.3 mg Hg kg wet wt?1. Moreover, Hg-length relationships suggest that each target fish meets this threshold near their minimum legal catch length. Our findings reiterate the value of species ecology to improve predictions of fish Hg and permit better management of human contamination by this important dietary source.  相似文献   

2.
Deep-seafloor communities, especially those from the ice-covered Arctic, are subject to severe food limitation as the amount of particulate organic matter (POM) from the surface is attenuated with increasing depth. Here, we use naturally occurring stable isotope tracers (δ15N) to broaden our rudimentary knowledge of food web structure and the response of benthic organisms to decreasing food supplies along the bathymetric transect (～1300–5600 m water depth) of the deep-sea observatory HAUSGARTEN. Encompassing five trophic levels, the HAUSGARTEN food web is among the longest indicating continuous recycling of organic material typical of food-limited deep-sea ecosystems. The δ15N signatures ranged from 3.0‰ for Foraminifera to 21.4‰ (±0.4) for starfish (Poraniomorpha tumida). The majority of organisms occupied the second and third trophic level. Demersal fish fed at the third trophic level, consistent with results from stomach contents analysis. There were significant differences in the δ15N signatures of different functional groups with highest δ15N values in predators/scavengers (13.2±0.2‰) followed by suspension feeders (11.2±0.2‰) and deposit feeders (10.2±0.3‰). Depth (=increasing food limitation) affected functional groups in different ways. While the isotopic signatures of predators/scavengers did not change, those of suspension feeders increased with depth, and the reverse was found for deposit feeders. In contrast to the results of other studies, the δ15N signatures in POM samples obtained below 800 m did not vary significantly with depth indicating that changes in δ15N values are unlikely to be responsible for the depth-related δ15N signature changes observed for benthic consumers. However, the δ15N signatures of sediments decreased with increasing depth, which also explains the decrease found for deposit feeders. Suspension feeders may rely increasingly on particles trickling down the HAUSGARTEN slope and carrying higher δ15N signatures than the decreasing POM supplies, which elevates the δ15N value of their tissues. Our results imply that a depth-stratified approach should be taken to avoid a misinterpretation of data obtained at different depths.  相似文献   

3.
Temperate rocky reefs may occur in two alternative states (coralline barrens and erect algal forests), whose formation and maintenance are often determined by sea urchin grazing. The two sea urchin species Paracentrotus lividus and Arbacia lixula are considered to play a similar ecological role despite their differing morphological traits and diets. The patchy mosaic areas of Ustica Island, Italy, offer an ideal environment in which to study differences in the performance of P. lividus and A. lixula in barren versus forest states. Results show that the two sea urchin species differ in diet, trophic position, grazing adaptation, movement ability and fitness in both barren and forest patches. We confirmed herbivory in P. lividus and omnivory with a strong tendency to carnivory in A. lixula. When the sea urchin escape response to a predator was triggered, P. lividus responded faster in barren and forest patches. Forest patch restricted movement, especially in A. lixula (velocity in barren ≈ 10-fold greater than in forest). A large Aristotle's lantern, indicative of durophagy, confirmed adaptation of A. lixula to barren state.  相似文献   

4.
The trophic relationships of decapod crustaceans on Le Danois bank (NE of Iberian Peninsula, NE Atlantic Ocean) were studied within the framework of the multidisciplinary project ECOMARG during two surveys, one in October 2003 and the other in April 2004. The diets of eleven species of decapods were analyzed and, within a rather continuous gradient of food source exploitation, 3 trophic groups were identified: (1) plankton feeders, comprising the shrimps Acanthephyra pelagica, Sergia robusta, and Pasiphaea tarda, which preyed on meso-bathypelagic taxa such as euphausiids and calanoids; (2) benthos feeders, comprising the crangonids Pontophilus norvegicus and Pontophilus spinosus, the crab Geryon trispinosus and the shrimp Aristeus antennatus; and (3) an intermediate group, including the rest of species, with mixed diets that included detritus. Among the third group, anomurans (Munida tenuimana, Pagurus alatus, and Parapagurus pilosimanus) consumed phytoplanktonic detritus in April, suggesting a link with peaks of surface Chl a occurring between March and April in the study area. Gut pigment and isotopic (δ13C/δ15N correlations) analyses revealed that assemblages inhabiting the top of the bank (455–612 m) and the inner basin (642–1048 m, close to the Lastres canyon head) had different food sources, with species inhabiting the deepest region exhibiting a stronger dependence on marine snow derivatives. These results are consistent with the higher proportion of mud and sediment organic matter (OM) content in the inner basin (82.2% pellites; 6.3% OM at 1028 m) compared to the top of the Le Danois bank (only 13.9% pellites; 2.8% OM at 485 m), which is a hydrodynamically more active zone. Exploitation of different food sources is also consistent with differences in the trophic level of species, inferred from stable δ15N isotope analyses, which yield values ranging from 6.88‰ for the hermit crab P. alatus to 13.52‰ for the crangonid shrimp P. norvegicus. Stomach fullness was higher in April 2004 than in October 2003, both between and within species of the dominant decapods, including detritus feeders (M. tenuimana) and benthos feeders (e.g. G. trispinosus, P. norvegicus). Most species exhibited a parallel increase in their density in April 2004, with a significant positive correlation between density and stomach fullness. This increase coincides with a peak of surface Chl a concentration occurring in March–April.  相似文献   

5.
The life-histories and the secondary production of four dominant peracarid crustaceans (the mysids Boreomysis arctica and Parapseudomma calloplura, the amphipod Rhachotropis caeca, and the isopod Ilyarachna longicornis) in bathyal depths of the Bay of Biscay (NE Atlantic; between 383 and 420 m) and the Catalan Sea (Northwestern Mediterranean; between 389 and 1355 m) were established. Both the Atlantic and the Mediterranean populations of the major part of the target-species had two generations/year with mean cohort-production intervals (CPI) ranging from 5.5 mo for Ilyarachna longicornis to 6.3 mo for Parapseudomma calloplura. The Hynes method showed secondary production to vary in the Bay of Biscay between 0.113 mg DW m−2 yr−1 for I. longirostris and 3.069 mg DW m−2 yr−1 for P. calloplura, with P/B ratios between 4.57 (I. longirostris) and 7.93 (Boreomysis arctica). In the Catalan Sea, production varied between 0.286 mg DW m−2 yr−1 for I. longirostris and 1.096 mg DW m−2 yr−1 for P. calloplura, with P/B between 5.72 (I. longirostris) and 6.66 (P. calloplura). Application of two different empiric models to the whole peracarid assemblage gave similar levels of secondary production in both study areas (between 29.26 and 32.14 mgDWm−2 yr−1 in the Bay of Biscay; between 26.23 and 26.54 mg DW m−2 yr−1 in the Catalan Sea). From the analysis of gut contents of 22 species the dominant species in each study area were assigned to two basic trophic levels, detritus feeders and predators. Also, cumulative curves of dominance showed high diversity (low dominance) for peracarid assemblages distributed at mid-bathyal depths (524–693 m) both in the Bay of Biscay off Arcachon and in the Catalan Sea off Barcelona. We also discuss and compare, both within and between areas, how environmental features may explain the observed diversity patterns, the trophic structure, and the production results obtained for the suprabenthos assemblages.  相似文献   

6.
《Journal of Sea Research》2009,61(4):264-275
The food web structure and functioning of two north-western Mediterranean lagoons exhibiting contrasting degrees of eutrophication and marine influences were compared through δ13C and δ15N analysis of major potential food sources and consumers. The Lapalme Lagoon is well preserved and has kept a natural and temporary connection with the open sea. Conversely, the Canet Lagoon is heavily eutrophicated and its water exchange with the open sea has been artificially reduced. In Lapalme, all potential food sources and consumers exhibited δ15N values indicative of pristine coastal areas. Suspended particulate organic matter (POM) and sediment organic matter (SOM) pools seemed to constitute the main food sources of most primary consumers. Both primary producers and all consumers were much more 15N-enriched (by ∼ 10‰) and more 13C-depleted in Canet than in Lapalme. This reflected: (1) the assimilation of important amounts of anthropogenic nitrogen in the food web, and (2) a marked and uniform influence of 13C-depleted allochtonous sources of carbon. Based on the mean δ15N of primary consumers, we found rather similar food web lengths in both lagoons with top consumers at trophic levels 3.6 and 4.0 in Canet and Lapalme, respectively. However, the eutrophication of the Canet Lagoon resulted in a simplification of the food web structure (i.e., a single trophic pathway from a 15N-enriched fraction of the SOM pool to top predators) compared to what was observed in Lapalme Lagoon where additional 13C-enriched food sources played a significant trophic role. Moreover, some consumers of Canet tended to exploit primary producers to a larger extent (and thus to exhibit lower trophic levels) than in Lapalme.  相似文献   

7.
The stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of the muscle, ctenidia and viscera of the Sydney rock oyster, Saccostrea glomerata, showed the dilution and assimilation of tertiary treated sewage along an estuarine gradient. The enriched 15N values of oyster ctenidia and viscera from within 50 m of the sewage outfall indicated the use of 15N-enriched tertiary treated sewage effluent (16 ± 2.3‰) as a nutrient source. The effect of sewage nitrogen on oyster δ15N was localised, with oysters 5 km upstream and downstream of the outfall not significantly enriched. Viscera δ15N was most sensitive to sewage nutrients and δ13C significantly defined an ocean-to-estuarine gradient. High variance in isotope ratios of viscera compromised its use as an indicator of anthropogenic nutrients, and this also reduced the utility of whole-body stable isotope ratios. Ctenidia was the most useful indicator tissue of sewage discharge at the scale of this study, being consistently and significantly enriched in δ15N close to the sewage outfall and δ13C clearly defined an estuarine gradient with less internal variability than viscera. Muscle δ15N was least sensitive to sewage effluent and showed the least variability, making it more suited to investigations of anthropogenic nutrient enrichment over larger spatio-temporal scales.  相似文献   

8.
The aim of this study was to assess the changes in the elemental and stable isotope composition of Zostera noltii leaves during the early phases of decay. The litter biomass, the C, N and S elemental contents, the C:N ratios and the δ13C, δ15N and δ34S values were monitored in a litterbag experiment for 60 days at Ria Formosa lagoon, southern Portugal in two different field conditions, permanently submerged in a salt marsh pond and at high intertidal. The elemental and stable isotope composition of both attached leaves and leaf wrack of Z. noltii was also determined. The overall decay rate of Z. noltii leaf material throughout the whole experimental period was k = 0.016 ± 0.001 d−1. Even though the biomass loss of the Z. noltii leaves after 30 days was about 25% higher within the pond than at the high intertidal, at the end of the experiment there were no significant differences between sites. The decay of the C and N content was of the same magnitude and thus the C:N molar ratio did not vary significantly in the experiment. The elemental content of the leaf wrack was in the range of the element content of leaf litter after 30–60 days of incubation. Contrary to other vascular plants rich in lignin, which degrades slowly, and thus forces the decrease of the δ13C values during decay, the δ13C values of Z. noltii leaves did not vary significantly over time or between incubation sites. The δ15N values of leaves did not increase as has been reported for vascular plants with high C:N ratio. This suggests that during the early phase of the Z. noltii decomposition the community of decomposers relied mostly on the endogenous nitrogen of the plants, not needing to immobilize exogenous N. Stable isotope studies to assess the contribution of this species to the food web can rely on the natural δ13C and δ15N abundances of living tissues without any correction to account for decomposition. The analysis of the δ34S values of Z. noltii detritus was not useful probably due to the contamination of the samples with pyrite, which has a depleted δ34S signal.  相似文献   

9.
The hypothesis that benthic foraminifera are useful proxies of local methane emissions from the seafloor has been verified on sediment core KS16 from the headwall of the Ana submarine landslide in the Eivissa Channel, Western Mediterranean Sea. The core MS312 from a nearby location with no known methane emissions is utilised as control. The core was analysed for biostratigraphy, benthic foraminiferal assemblages, Hyalinea balthica and Uvigerina peregrina carbon and oxygen stable isotope composition, and sedimentary structures. The upper part of the core records post-landslide deglacial and Holocene normal marine hemipelagic sediments with highly abundant benthic foraminifera species that are typical of outer neritic to upper bathyal environment. In this interval, the δ13C composition of benthic foraminifera indicates normal marine environment analogous to those found in the control core. Below the sedimentary hiatus caused by the emplacement of the slide, the foraminiferal assemblages are characterised by lower density and higher Shannon Index. Markedly negative δ13C shifts in benthic foraminifera are attributed to the release of methane through the seabed. The mean values of the 13C anomaly in U. peregrina are ? 0.951 ± 0.208 in the pre-landslide sediments, and ? 0.269 ± 0.152 in post-slide reworked sediments deposited immediately above the hiatus. The δ13C anomaly in Hyalinea balthica is ? 2.497 ± 0.080 and ? 2.153 ± 0.087, respectively. To discard the diagenetic effects on the δ13C anomaly, which could have been induced by Ca–Mg replacement and authigenic carbonate overgrowth on foraminifera tests, a benthic foraminifera subsample has been treated following an oxidative and reductive cleaning protocol. The cleaning has resulted, only in some cases, in a slight reduction of the anomaly by 0.95% for δ13C and < 0.80% for δ18O. Therefore, the first conclusion is that the diagenetic alteration is minor and it does not alter significantly the overall carbon isotopic anomaly in the core. Consequently, the pre-landslide sediments have been subject to pervasive methane emissions during a time interval of several thousand years. Methane emissions continued during and immediately after the occurrence of Ana Slide at about 61.5 ka. Subsequently, methane emissions decreased and definitely ceased during the last deglaciation and the Holocene.  相似文献   

10.
We examine seasonal variations in the stable carbon and oxygen isotopic composition of individual shells of the pteropods Limacina inflata and Styliola subula, collected from Oceanic Flux Program sediment traps (at 500 m depth) near Bermuda in the western Sargasso Sea. Calcification depths estimated from L. inflata δ18O vary between 200 and 650 m in late winter and spring, and between 50 and 250 m in late summer and fall. S. subula shows similar seasonal variability with calcification depths between 250 and 600 m in late winter and spring and 50–400 m in late summer and fall. These results suggest that both species calcify across a greater range of depths than indicated by previous geochemical studies. Furthermore, the data indicate that these species change their calcification depth in conjunction with changes in thermal stratification of the water column. Pteropod shell δ13C values vary inversely with δ13CDIC but show a positive correlation with seawater [CO32−] and temperature after depth differences in δ13CDIC are accounted for. We hypothesize that either the influence of temperature on metabolic CO2 incorporation during shell growth and/or the influence of ambient [CO32−] on shell geochemistry can explain these relationships. Taken together, the individual shell δ18O and δ13C data suggest that shell calcification, and by inference the life cycle, of these pteropods is several months or less. Individual pteropod shell analyses have potential for contributing to our understanding of the environmental parameters that play a role in seasonal calcification depth shifts, as well as to our knowledge of past upper ocean thermal structure.  相似文献   

11.
Authigenic carbonates were collected from methane seeps at Hydrate Hole at 3113 m water depth and Diapir Field at 2417 m water depth on the northern Congo deep-sea fan during RV Meteor cruise M56. The carbonate samples analyzed here are nodules, mainly composed of aragonite and high-Mg calcite. Abundant putative microbial carbonate rods and associated pyrite framboids were recognized within the carbonate matrix. The δ13C values of the Hydrate Hole carbonates range from ?62.5‰ to ?46.3‰ PDB, while the δ13C values of the Diapir Field carbonate are somewhat higher, ranging from ?40.7‰ to ?30.7‰ PDB, indicating that methane is the predominant carbon source at both locations. Relative enrichment of 18O (δ18O values as high as 5.2‰ PDB) are probably related to localized destabilization of gas hydrate. The total content of rare earth elements (REE) of 5% HNO3-treated solutions derived from carbonate samples varies from 1.6 ppm to 42.5 ppm. The shale-normalized REE patterns all display positive Ce anomalies (Ce/Ce* > 1.3), revealing that the carbonates precipitated under anoxic conditions. A sample from Hydrate Hole shows a concentric lamination, corresponding to fluctuations in δ13C values as well as trace elements contents. These fluctuations are presumed to reflect changes of seepage flux.  相似文献   

12.
Generally, estuarine intertidal mudflats constitute important nurseries for fish and foraging grounds for coastal birds by providing a plenitude of mollusks, worms, and crustaceans as prey, which in turn mostly feed on suspended and benthic microalgae, bacteria, and detritus. Despite the high productivity of such habitats, pronounced variability in both salinity and temperature results typically in low diversity. The only sea anemone reported from estuarine mud is the edwardsiid Nematostella vectensis Stephenson, 1935. It occurs widely in the northern hemisphere, and occasionally in extremely high density. Here we document another sea anemone from estuarine mud and muddy sand found in Southern Chile which has similar ecological attributes. Taxonomic confusion has impeded the reporting on this small but prominent member in a macrozoobenthic assemblage, the brooding Anthopleura hermaphroditica (Carlgren, 1899; Anthozoa: Actiniidae). It differs from N. vectensis by the presence of symbiotic algae. Average density under poly- to euhaline conditions in mud and muddy sand at around mid tide level was about 3 actinians per cm2. An average abundance of 11,000 m? 2, a biovolume of 487 cm3 m? 2, and a biomass of 35.5 g dry organic weight m? 2 were found in mud and muddy sand in two surveys 20 years apart. The mean fishing area of fully expanded individuals covers 42 ± 25 mm2, corresponding to a circular area with a diameter of 7.3 ± 5.7 mm. Preliminary experiments indicate that associated benthos may be relegated to life below surface by the net of tentacles above the sediment. As no predators on A. hermaphroditica could be found on the mudflat, the success of this mixotrophic sea anemone may entail a trophic dead end.  相似文献   

13.
Using bifrequency sonar (38 kHz, 120 kHz) directed towards the open sea from the inside of a submarine cave, two species of Mysidacea (Crustacea), similar in shape but not in size, and with different patterns of behaviour, were observed simultaneously and discriminated, and their biomass was estimated during their migration. The first species, Hemimysis speluncola (<1 cm length), lives in the submarine cave, forming a distinct community that migrates horizontally. The second species, Siriella jaltensis (>1 cm length), lives in the open sea and migrates vertically. These species are both detected clearly at 120 kHz, but only the larger one, Siriella jaltensis, is detected at 38 kHz. This distinction allows one to determine the size limits of planktonic objects detected at these frequencies, i.e. 3 mm at 120 kHz and 10 mm at 38 kHz, corresponding to one quarter of the wavelength. The target strength (TS) of each species was calculated from the field data and compared to results calculated from three models. As the volume of the cave occupied by the Hemimysis population is about 300 m3, and the density of the swarm is 36,000 individuals/m3, the number of individuals in the cave is estimated to be around 10 million (or 24 kg). The density of the open-water population of Siriella is estimated to be 13 individuals/m3.  相似文献   

14.
Nutrient inputs associated with coastal population growth threaten the integrity of coastal ecosystems around the globe. In order to assess the threat posed by rapid growth in tourism, we analyzed the nutrient concentrations as well as the δ15N of NO3− and macrophytes to detect wastewater nitrogen (N) at 6 locations along a groundwater-dominated coastal seagrass bed on the Caribbean coast of Mexico. We predicted that locations with greater coastal development would have higher concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (P), as well as δ15N of NO3−, reflecting wastewater sources of N. However, concentrations of NO3− were not significantly different between developed (3.3 ± 5.3 μM NO3−) and undeveloped (1.1 ± 0.7 μM) marine embayments. The most important control on DIN concentration appeared to be mixing of fresh and salt water, with DIN concentrations negatively correlated with salinity. The δ15N of NO3− was elevated at an inland pond (7.0 ± 0.42‰) and a hydrologically-connected tide pool (7.6 ± 0.57‰) approximately 1 km downstream of the pond. The elevated δ15N of NO3− at the pond was paralleled by high δ15N values of Cladophora sp., a ubiquitous green alga (10 ± 1‰). We hypothesize that inputs of nitrogen rich (NO3− > 30 μM) groundwater, characterized by 15N enriched signatures, flow through localized submarine groundwater discharges (SGD) and contribute to the elevated δ15N signatures observed in many benthic macrophytes. However, changes in nitrogen concentrations and isotope values over the salinity gradient suggest that other processes (e.g. denitrification) could also be contributing to the 15N enrichments observed in primary producers. More measurements are needed to determine the relative importance of nitrogen transformation processes as a source of 15N to groundwaters; however, it is clear that continued inputs of anthropogenic N via SGD have the potential to severely impact ecologically and economically valuable seagrass meadows and coral reefs along the Caribbean coast of Mexico.  相似文献   

15.
Thicklip grey mullet, Chelon labrosus, is an important commercial fish species and has been studied worldwide. However, no recent studies have been made regarding polychlorinated biphenyls (PCBs) in wild C. labrosus. Due to that, the concentration of 13 PCBs congeners was measured in muscles and livers, of males and females, of C. labrosus of different ages, allowing the estimation of PCB bioaccumulation throughout the species lifespan, in the Mondego estuary, a southern European temperate estuary. Male muscle sample concentrations ranged from 32 to 96 ng g− 1 (lipid wt.) and in females from 32 to 62 ng g− 1 (lipid wt.). In male liver sample concentrations ranged from 106 to 158 ng g− 1 (lipid wt.), while female concentrations ranged from 88 to 129 ng g− 1 (lipid wt.). The most abundant congeners presenting higher percentages in all samples were CB 138, 153 and 180. No significant differences were found between the concentrations in both sexes, but muscle and liver PCB concentrations in males tended to increase with age whereas in females concentrations remained stable throughout the species lifespan. Significant differences were found between concentrations in muscle and liver.  相似文献   

16.
The distribution of the sea urchin Heliocidaris erythrogramma coincides with the southeast Australia global change hot spot where marine ecosystems are warming significantly due to changes in ocean circulation. To address questions on future vulnerabilities, the thermotolerance of the planktonic life phase of H. erythrogramma was investigated in the climate and regionally relevant setting of projected near-future (2100) ocean warming. Experimental treatments ranged from 18 to 26 °C, with 26 °C representing +3-4 °C above recent ambient sea-surface temperatures. Developmental success across all stages (gastrula, 24 h; larva, 72 h; juvenile, 120 h) decreased with increasing temperature. Development was tolerant to a +1-2 °C increase above ambient, but significant deleterious effects were evident at +3-4 °C. However, larvae that developed through the early bottleneck of normal development at 26 °C metamorphosed successfully. The inverse relationship between temperature and planktonic larval duration (PLD) was seen in a 25% decrease in the PLD of H. erythrogramma at 24 and 26oC. Ocean warming may be advantageous to a subset of larvae through early settlement and reduction of the vulnerable planktonic period. This positive effect of temperature may help buffer the negative effects of ocean warming. In parallel studies with progeny derived from northern (Coffs Harbour) and southern (Sydney) H. erythrogramma, northern embryos had significantly higher thermotolerance. This provides the possibility that H. erythrogramma populations might keep up with a warming world through poleward migration of thermotolerant propagules, facilitated by the strong southward flow of the East Australian Current. It is uncertain whether H. erythrogramma populations at the northern range of this species, with no source of immigrants, will have the capacity to persist in a warm ocean. Due to its extensive latitudinal distribution, its potential developmental thermotolerance and independence of its lecithotrophic larvae from exogenous food and the need to make a functional skeleton, H. erythrogramma may be particularly robust to ocean change.  相似文献   

17.
Seasonal depth stratified plankton tows, sediment traps and core tops taken from the same stations along a transect at 29°N off NW Africa are used to describe the seasonal succession, the depth habitats and the oxygen isotope ratios (δ18Oshell) of five planktic foraminiferal species. Both the δ18Oshell and shell concentration profiles show variations in seasonal depth habitats of individual species. None of the species maintain a specific habitat depth exclusively within the surface mixed layer (SML), within the thermocline, or beneath the thermocline. Globigerinoides ruber (white) and (pink) occur with moderate abundance throughout the year along the transect, with highest abundances in the winter and summer/fall season, respectively. The average δ18Oshell of G. ruber (w) from surface sediments is similar to the δ18Oshell values measured from the sediment-trap samples during winter. However, the δ18Oshell of G. ruber (w) underestimates sea surface temperature (SST) by 2 °C in winter and by 4 °C during summer/fall indicating an extension of the calcification/depth habitat into colder thermocline waters. Globigerinoides ruber (p) continues to calcify below the SML as well, particularly in summer/fall when the chlorophyll maximum is found within the thermocline. Its vertical distribution results in δ18Oshell values that underestimate SST by 2 °C. Shell fluxes of Globigerina bulloides are highest in summer/fall, where it lives and calcifies in association with the deep chlorophyll maximum found within the thermocline. Pulleniatina obliquiloculata and Globorotalia truncatulinoides, dwelling and calcifying a part of their lives in the winter SML, record winter thermocline (～180 m) and deep surface water (～350 m) temperatures, respectively. Our observations define the seasonal and vertical distribution of multiple species of foraminifera and the acquisition of their δ18Oshell.  相似文献   

18.
The Lophelia pertusa community at Viosca Knoll (VK826) is the most extensive found to date in the Gulf of Mexico. As part of a multi-disciplinary study, the physical setting of this area was described using benthic landers, CTD transects and remotely operated vehicle observations. The site was broadly characterised into three main habitats: (1) dense coral cover that resembles biogenic reef complexes, (2) areas of sediment, and (3) authigenic carbonate blocks with sparse coral and chemosynthetic communities. The coral communities were dominated by L. pertusa but also contained numerous solitary coral species. Over areas that contained L. pertusa, the environmental conditions recorded were similar to those associated with communities in the north-eastern Atlantic, with temperature (8.5–10.6 °C) and salinity (～35) falling within the known species niche for L. pertusa. However, dissolved oxygen concentrations (2.7–2.8 ml l?1) and density (σΘ, 27.1–27.2 kg m?3) were lower and mass fluxes from sediment trap data appeared much higher (4002–4192 mg m?2 d?1). Yet, this species still appears to thrive in this region, suggesting that L. pertusa may not be as limited by lower dissolved oxygen concentrations as previously thought. The VK826 site experienced sustained eastward water flow of 10–30 cm s?1 over the 5-day measurement period but was also subjected to significant short-term variability in current velocity and direction. In addition, two processes were observed that caused variability in salinity and temperature; the first was consistent with internal waves that caused temperature variations of 0.8 °C over 5–11 h periods. The second was high-frequency variability (20–30 min periods) in temperature recorded only at the ALBEX site. A further pattern observed over the coral habitat was the presence of a 24 h diel vertical migration of zooplankton that may form part of a food chain that eventually reaches the corals. The majority of detailed studies concerning local environmental conditions in L. pertusa habitats have been conducted within the north-eastern Atlantic, limiting most knowledge of the niche of this species to a single part of an ocean basin. Data presented here show that the corals at VK826 are subjected to similar conditions in temperature, salinity, and flow velocity as their counterparts in the north-east Atlantic, although values for dissolved oxygen and density (sigma-theta: σΘ) are different. Our data also highlight novel observations of short-term environmental variability in cold-water coral habitat.  相似文献   

19.
Previous work has shown that methane anomalies frequently occur within the rift valley of the Mid-Atlantic Ridge (MAR). The plumes appear confined within the high, steep walls of the valley, and it is not known whether methane may escape to the open ocean outside. In order to investigate this question, the concentration and 13C/12C ratio of methane together with CCl3F concentration were measured in the northeastern Atlantic including the rift valley near 50°N. This segment contained methane plumes centered several 100 m above the valley floor with δ13C values mostly between –15‰ and –10‰. A limited number of helium isotope measurements showed that δ3He increased to 17% at the bottom of the valley, which suggests the helium and methane sources may be spatially separated. In the eastern Atlantic away from the ridge (48°N, 20°W), the methane concentration decreased monotonically from the surface to the bottom, but the methane δ13C exhibited a mid-water maximum of about –25‰. The bottom water methane contained a significantly lower δ13C of about –36‰. Thus, it appears that isotopically heavy methane escapes from the MAR into North Atlantic Deep Water (NADW) that contacts the ridge crest while circulating to the east. The formation of NADW supplies isotopically light methane that dilutes the input of heavy carbon from the ridge. We employed a time-dependent box model to calculate the extent of isotope dilution and thereby the flux of MAR methane into the NADW circulation. The degree of methane oxidation, which affects the 13C/12C of methane through kinetic isotope fractionation, was estimated by comparing methane and CFC-11 model results with observations. The model calculations indicate a MAR methane source of about 0.06×10−9 mol L−1 yr−1 to waters at the depth of the ridge crest. Assuming this extends to a 500 m thick layer over half of the entire Atlantic, the amount of methane escaping from the MAR to the open ocean is estimated to be about 1×109 mol yr−1. The total production of methane within the rift valley is likely much greater than the flux from the valley to the outside because of local oxidation. This implies that serpentinization of ultramafic rocks supports much of methane production in the rift valley because the amount expected from basalt degassing in association with mantle helium (<0.6×109 mol CH4 yr−1) is less than even the net amount escaping from the valley. The model results also indicate the methane specific oxidation rate is about 0.05 yr−1 in open waters of the northern Atlantic.  相似文献   

20.
The trophic ecology, energy and reproductive states of the deep-water shrimp Aristaeomorpha foliacea, widely distributed along the slopes of the Mediterranean Sea Basins, were analysed in eight areas spread along ca. 3000 km in order to identify patterns in the habitat conditions supporting the species. From W to E the areas were situated between the north side of Eivissa (39°12′N, 1°20′E, in the Balearic Basin) and off Mersin, Turkey (36°15′N, 34°19′E, in the Levantine Sea). Trends identified mainly as a function of longitude from west to east were: (i) higher δ15N, parallel to δ15N shifts in the top 200 m of the water column for particulate organic N (Pantoja et al., 2002). The δ15N trend indicates that the deep trophic web, i.e. A. foliacea at 400–600 m, reflects the δ15N signal of the photic zone; (ii) a similar significant trend of δ13C, related with exploitation of pelagic versus benthic resources by A. foliacea in each area (i.e. by local variability of terrigenous inputs via submarine canyons). More depleted δ13C was found at mid-longitudes (Tyrrhenian Sea and Sicily Channel) linked to higher consumption of macroplankton prey (Pasiphaea spp., euphausiids and mesopelagic fishes). The feeding intensity (gut fullness, F) and prey diversity (J) of A. foliacea were related, according to generalized linear models, with the temperature and salinity of intermediate waters, variables in turn associated with latitude and longitude. Both F and J were higher in areas with greater shrimp density. The optimal ecological habitat of A. foliacea appears to be located in the Tyrrhenian Sea and the Sicily Channel, where we found the highest F, the greatest trophic diversity and A. foliacea in the best biological condition (i.e. with higher hepato-somatic index, HSI). These are also the areas with the highest densities of A. foliacea. In contrast, in the western Mediterranean Sea (Balearic Basin and the southern Balearic Islands), where A. foliacea has low densities, the shrimp showed generally lower values of trophic indicators and biological condition.  相似文献   

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