首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 234 毫秒
1.
Representative profiles of inorganic nitrogenous species dissolved in interstitial waters of coral reef sands are presented. Ammonium is the dominant nitrogenous species in these pore waters with concentrations of up to 40 μm. Nitrate is present but in lower concentrations. Nitrite is found only occasionally in trace amounts. Computations of diffusive fluxes and inferences concerning microbial activity are derived from the profile structures. Computed flux rates of nitrogenous species from the sediment to the water column range between 0.75 and 1.37 μM m−1 h−1. These inputs may represent a significant source of recycled nitrogen to the primary producers of the coral reef ecosystem.  相似文献   

2.
Cd, Cu, Fe, Ni, Pb and Zn were determined in 123 samples from the Baltic Sea proper. The trace metals were extracted directly on board the vessel, using a dithiocarbamate-Freon procedure. Final analyses of the extracts are performed onshore by atomic absorption spectrometry.Similar trace-metal concentrations are found in different areas of the Baltic proper. Most values fall in the following ranges: Cd, 30–60 ng 1?1; Cu, 0.6–1.0 μg 1?1; Fe, 0.3–0.9 μg 1?1; Ni, 0.6–0.9 μg 1?1; Pb, 0.05–0.2 μg 1?1; and Zn, 1.5–3.5 μg 1?1. The metal-concentrations are generally independent of depth. However, copper exhibits a small but significent decrease in concentration below 80 m.Filtration did not affect trace-metal concentrations, with the exception of iron in waters from lower layers. Similarly, storage under acid conditions was shown to affect only the concentration of iron. An electro-chemical technique was also used to determine Cu in some samples.  相似文献   

3.
A relatively precise and rapid method for the analysis of total dissolved monosaccharides at the concentrations that occur in seawater is described which uses 1-ml quantities for each analytical and control replicate. The alditols remain unchanged while the pentoses and hexoses are reduced to the alditol form by borohydride. The total alditols are then oxidized with periodate to form two moles of formaldehyde per mole of monosaccharide and the formaldehyde is determined spectrophotometrically with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH). Unlike other spectrophotometric methods, similar curves are obtained for equimolar concentrations of different carbohydrates while the differences on a weight basis are only due to the small difference in molecular weight between pentoses and hexoses. Winter—Spring samples from surface waters of lower Narragansett Bay ranged from 122 to 226 μg l?1 with a mean of 159 μg l?1.  相似文献   

4.
Recent studies suggest a future increase in sponge bioerosion as an outcome of coral reef decline around the world. However, the factors that shape boring sponge assemblages in coral reefs are not currently well understood. This work presents the results of a 17‐month assessment of the presence and species richness of boring sponges in fragments collected from living corals, dead coral reef matrix and coral rubble from Punta de Mita and Isabel Island, two coral reefs from the central coast of the Mexican Pacific Ocean. Both localities have a high cover of dead corals generated by past El Niño Southern Oscillation events, but Punta de Mita was also highly exposed to anthropogenic impacts. Additionally, environmental factors (water transparency, water movement, temperature, sediment deposition, SST, and chlorophyll concentration) were assessed to test the hypothesis that environmental conditions which are potentially harmful for corals can enhance sponge bioerosion. Isabel Island and Punta de Mita showed a similar species richness (13 and 11 species, respectively) but boring sponge presence in both live and dead corals was higher at Isabel Island (57.6%) than at Punta de Mita (35.7%). The same result was obtained when each type of substrate was analysed separately: dead coral reef matrix (81.3% versus 55.5%), coral rubble (47.7% versus 20.0%) and living corals (43.7% versus 31.7%). A principal components analysis showed a higher environmental heterogeneity at Punta de Mita, as well as important environmental differences between Punta de Mita and Isabel Island, due to sediment deposition (2.0 versus 0.2 kg·m?2·d?1) and water movement (24.5% versus 20.5% plaster dissolution day?1), that were also negatively correlated with boring sponge presence (r = ?0.7). By analysing the boring sponge assemblage, we found that environmental settings, together with habitat availability (i.e., dead coral substrate) differentiated assemblage structure at both localities. Major structural differences were largely due to species such as Cliona vermifera, Cliona tropicalis and Aka cryptica. In conclusion, factors such as habitat availability favored the presence of boring sponges but some environmental factors such as abrasion resulting from moving sediment acted restrictively, and exerted a major role in structuring boring sponge assemblages in the Mexican Pacific.  相似文献   

5.
珊瑚礁是全球生物多样性最高的海洋生态系统之一，底栖贝类是该生态系统的重要组成类群。为了解北部湾涠洲岛珊瑚礁底栖贝类的群落现状及特征，于2015年秋季(10月)与2018年春季(5月)采用水肺潜水截线样条定量调查法对涠洲岛珊瑚礁区6个断面的底栖贝类进行了调查，并分析了物种组成、丰度、生物多样性指数等群落特征。综合两次调查结果显示涠洲岛珊瑚礁区共有底栖贝类128种，分别属于多板纲1科1属3种，腹足纲25科46属68种，双壳纲22科31属57种。优势种为斑顶拟舌骨牡蛎、粗衣蛤、刺荔枝螺、马蹄螺、杂色牙螺、青蚶、旗江珧、甲虫螺、蕾丝蟹守螺、珠母爱尔螺。2018年春季定量断面采集到的样品为2纲14科43种，各断面的丰度、生物量、多样性指数、物种丰度指数和均匀度指数均值分别为3.39个/m2、86.94 g/m2、3.31、3.50、0.37。通过对两年的调查数据比较，发现2015?2018年涠洲岛珊瑚礁区的贝类生物群落呈现良好演替发育趋势。南海珊瑚礁区贝类群落结构可能受到了人为干扰强度和纬度的双重影响。本研究全面掌握了涠洲岛珊瑚礁底栖贝类的种类、分布区及群落的结构与变化，可为该地区海洋生物资源开发利用、珊瑚礁保护和生态修复等工作提供数据支持。  相似文献   

6.
A six-month-long study was conducted of the fate of turbid river plumes from the Enipein watershed in Pohnpei, Federated States of Micronesia. Pohnpei is one of the wettest places on earth, with a mean annual rainfall exceeding 4 m in the lowlands and 8 m in the highlands. The river waters were clear of sediment except after major storms with rainfall exceeding 5 cm day−1. Following a storm, the river plume spread in the mangrove fringed estuary and in the coral reef lagoon. The waters were highly stratified in temperature, salinity, and suspended sediment concentration. The brackish water was flushed out in four days, while the suspended sediment all settled out in the estuary, in the mangroves, and in the lagoon including on the coral reefs, in less than one day. The mean rate of sedimentation exceeded 35 mg cm−2 d−1 both over the mangroves and on the adjacent coral reefs. While this leads to no detrimental effects on the mangroves, sediment smothers corals and leads to substantial coral mortality in the lagoon. The mud is not flushed out from the lagoon because there are no strong currents from waves or tides. This high sedimentation rate is attributable to poor farming and land-use practices on the upland areas.  相似文献   

7.
A total of 150 samples were collected at a 10-days' anchor station in the Bornholm basin (55° 31.1′N, 15° 32.1′E) and analyzed for dissolved (< 0.4 μm) and particulate trace metals. For dissolved Mn, large gradients have been found in the vertical distribution with minimum concentrations (< 0.2 μgl?1) in the halocline zone and considerably higher values in the deep waters (up to 50 μgl?1). Ultrafiltration studies indicate that dissolved Mn is probably present as Mn2+ in the oxygenated bottom layer. The primary production process was not evident in the particulate Mn profile; the suspended particulate material (SPM), however, shows a considerable enrichment with depth, apparently due to Mn-oxide precipitation.The distribution of dissolved Fe was rather homogeneous, with average concentrations throughout the water column between 0.86 and 1.1 μgl?1, indicating that the oxidation of Fe2+ ions released from the sediments must already be complete in the very near oxidation boundary layer. Relatively high concentrations of particulate Fe were actually measured in the bottom layer, with the maximum mean of 11.2 μgl?1 at 72 m. Similarly to Mn, the profile of particulate Fe does not reflect the SPM curve of the eutrophic layer. On average, about 70% of the total Fe in surface waters was found to be particulate.The average concentrations of dissolved Zn, Cd and Cu were found to be rather homogeneous in the water column but showed a relatively high variability with time. A simplified model on trace-metal uptake by phytoplankton indicates no significant change in dissolved metal concentrations during the period of investigation. On average, only 1.7% Zn, 3.3% Cd and 9.8% Cu of the total metal concentrations were found in particulate form. SPM analyses showed significant correlations of Zn, Cd and Cu with Fe, indicating that particulate iron is an important carrier for particulate trace metals in Baltic waters.  相似文献   

8.
Microbioerosion rates and microbioeroder community structure were studied in four Kenyan protected coral-reef lagoons using shell fragments of Tridacna giant clams to determine their response to the influence of terrestrial run-off. Fourteen different microbioeroder traces from seven cyanobacteria, three green algae and four fungi species were identified. The river discharge-impacted reef and ‘pristine’ reef showed similar composition but higher microbioeroder abundance and total cyanobacteria- and chlorophyte-bioeroded areas when compared with the other study reefs. Cyanobacteria dominated during the north-east monsoon (NEM) relative to the south-east monsoon (SEM) season, with algae and cyanobacteria being major microbioeroders in the river-impacted and pristine reefs. The rate of microbioerosion varied between 4.3 g CaCO3 m?2 y?1 (SEM) and 134.7 g CaCO3 m?2 y?1 (NEM), and was highest in the river-impacted reef (127.6 g CaCO3 m?2 y?1), which was almost double that in the pristine reef (69.5 g CaCO3 m?2 y?1) and the mangrove-fringed reef (56.2 g CaCO3 m?2 y?1). The microbioerosion rates measured in this study may not be high enough to cause concern with regard to the health and net carbonate production of Kenya’s coral reefs. Nevertheless, predicted increases in the frequency and severity of stresses related to global climate change (e.g. increased sea surface temperature, acidification), as well as interactions with local disturbances and their influence on bioerosion, may be increasingly important in the future.  相似文献   

9.
The concentrations of suspended matter and particulate Cd, Cu, Pb and Zn were determined for 36 samples collected at 6 stations in the Antarctic Ocean during December, 1970 and January, 1971 using membrane filters. The concentration of suspended matter was determined gravimetrically and trace metal levels were determined using anodic stripping voltammetry. For waters deeper than 100 m the concentration of suspended matter was < 100 μg l?1. Concentrations up to 542 μg l?1 were recorded between surface and 100 m. Individual concentrations of the metals were scattered with depth. Average concentrations of particulate metals were: Cd, 3.5 ng l?1; Cu, 100 ng l?1; Pb, 35 ng l?1; and Zn, 230 ng ;l?1 These measurements represent non-steady state conditions of early Antarctic summer as the ice pack disintegrates and biological activity increases.  相似文献   

10.
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   

11.

Coral reef ecosystems worldwide are now being harmed by various stresses accompanying the degradation of fish habitats and thus knowledge of fish-habitat relationships is urgently required. Because conventional research methods were not practical for this purpose due to the lack of a geospatial perspective, we attempted to develop a research method integrating visual fish observation with a seabed habitat map and to expand knowledge to a two-dimensional scale. WorldView-2 satellite imagery of Spermonde Archipelago, Indonesia obtained in September 2012 was analyzed and classified into four typical substrates: live coral, dead coral, seagrass and sand. Overall classification accuracy of this map was 81.3% and considered precise enough for subsequent analyses. Three sub-areas (CC: continuous coral reef, BC: boundary of coral reef and FC: few live coral zone) around reef slopes were extracted from the map. Visual transect surveys for several fish species were conducted within each sub-area in June 2013. As a result, Mean density (Ind. / 300 m2) of Chaetodon octofasciatus, known as an obligate feeder of corals, was significantly higher at BC than at the others (p < 0.05), implying that this species’ density is strongly influenced by spatial configuration of its habitat, like the “edge effect.” This indicates that future conservation procedures for coral reef fishes should consider not only coral cover but also its spatial configuration. The present study also indicates that the introduction of a geospatial perspective derived from remote sensing has great potential to progress conventional ecological studies on coral reef fishes.

  相似文献   

12.
Phytoplankton productivity, community composition and biomass were determined over a nine-month period in brackish waters of the lower Gunpowder River, a tributary of Chesapeake Bay. Primary productivity followed expected seasonal magnitudes for temperate estuaries with rates exceeding 142·4 mg C m?3 h?1 in July through September 1979 and minimum rates of 1·6 mg C m?3 h?1 in February 1980. Annual primary production was estimated at 45·5 gC m?2. Cell numbers were highest in August, September and November with cyanophytes dominating the planktonic algae. Primary productivity, chlorophyll concentrations and cell densities were dominated by nanoplanktonic forms (< 10 μm) through-out the study. Phytoplankton carbon calculated from cells volumes exceeded nutritional requirements of the pelagic herbivores in all months suggesting a mean daily export (to the bay or sediments) of 1607 mg C m?3 d?1.  相似文献   

13.
The absorption of anthropogenic CO2 and atmospheric deposition of acidity can both contribute to the acidification of the global ocean. Rainfall pH measurements and chemical compositions monitored on the island of Bermuda since 1980, and a long-term seawater CO2 time-series (1983–2005) in the subtropical North Atlantic Ocean near Bermuda were used to evaluate the influence of acidic deposition on the acidification of oligotrophic waters of the North Atlantic Ocean and coastal waters of the coral reef ecosystem of Bermuda. Since the early 1980's, the average annual wet deposition of acidity at Bermuda was 15 ± 14 mmol m− 2 year− 1, while surface seawater pH decreased by 0.0017 ± 0.0001 pH units each year. The gradual acidification of subtropical gyre waters was primarily due to uptake of anthropogenic CO2. We estimate that direct atmospheric acid deposition contributed 2% to the acidification of surface waters in the subtropical North Atlantic Ocean, although this value likely represents an upper limit. Acidifying deposition had negligible influence on seawater CO2 chemistry of the Bermuda coral reef, with no evident impact on hard coral calcification.  相似文献   

14.
The results of determinations of cadmium, copper and lead in western Mediterranean waters collected during the PHYCEMED 81 cruise are discussed in this paper. The analyses were carried out according to two different methods: flameless atomic absorption and anodic stripping voltammetry. Very strict conditions of sampling and treatment were maintained in order to reduce the chance of contamination. The concentrations found are considerably lower than those usually reported for Mediterranean waters. The distributions are homogeneous, both vertically and from one station to another. The average concentrations are 8 ng 1?1 for Cd, 90 ng 1?1 for Cu and 30–40 ng?1 for Pb. This homogeneity, as well as the concentrations of cadmium and lead, may be explained by the hydrological conditions of the Mediterranean Sea.  相似文献   

15.
In the coastal and estuarine waters of Goa, particulate organic carbon (POC) varied from 0.52 to 2.51 mg l?1 and from 0.28 to 5.24 mg l?1 and particulate phosphorus (PP) varied from 0.71 to 5.18 μg l?1 and from 0.78 to 20.34 μg l?1, respectively. The mean values of chlorophyll and primary productivity were 1.94 mg m?3 and 938.1 mg C m?2 day?1 in the coastal waters and 4.3 mg m?3 and 636.5 mg C m?1 day?1 in the estuarine waters, respectively.POCchl ratios were low in June and October even when POC values were quite high. The POC in surface waters was linearly correlated with the chlorophyll content. Also PP increased when chlorophyll and primary productivity remained high. The results suggest that the phytoplankton was sharply increasing and contributed to POC and PP content. The percentage of detritus calculated from the intercept values of chlorophyll on POC varied from 46 to 76% depending on season. Results indicate that the major portion of POC and PP during postmonsoon (October–January) is derived from phytoplankton production while the allochthonous matter predominate during monsoon (June–September).  相似文献   

16.
The vertical distribution of dissolved aluminium in the Mediterranean Sea offshore of Corsica has been followed during a period of high biological activity (April–September). In May and August, the concentration of dissolved aluminium is at a relatively low (1.5 μg Al1?1) and rather constant value in the surface waters, while exhibiting minimum values of about 0.5 and 0.8 μg Al1?1 in April and September. It increases under the seasonal thermocline to a depth of 150–500 m. The bottom waters are characterized by a constant and relatively high value of 4 μg Al1?1.The observed concentrations of dissolved aluminium are not compatible with a precipitation-dissolution mechanism of clay minerals.The general distribution pattern and the seasonal changes of dissolved aluminium exhibit strong analogies with those of dissolved silica and nitrogen, suggesting a pre-dominant role of biological activity. It is not possible at this stage to attribute the aluminium uptake in the photic zone solely to the activity of diatoms, as suggested earlier.  相似文献   

17.
Quantitative research on composition, biomass and production rates of zooplankton community is crucial to understand the trophic structure in coral reef pelagic ecosystems. In the present study, micro‐ (35–100 μm) and net‐ (>100 μm) metazooplankton were investigated in a fringing coral reef at Tioman Island of Malaysia. Sampling was done during the day and night in August and October 2004, and February and June 2005. The mean biomass of total metazooplankton (i.e. micro + net) was 3.42 ± 0.64 mg C·m?3, ranging from 2.32 ± 0.75 mg C·m?3 in October to 3.26 ± 1.77 mg C·m?3 in August. The net‐zooplankton biomass exhibited a nocturnal increase from daytime at 131–264% due to the addition of both pelagic and reef‐associated zooplankton into the water column. The estimated daily production rates of the total metazooplankton community were on average 1.80 ± 0.57 mg C·m?3·day?1, but this increased to 2.51 ± 1.06 mg C·m?3·day?1 if house production of larvaceans was taken into account. Of the total production rate, the secondary and tertiary production rates were 2.20 ± 1.03 and 0.30 ± 0.06 mg C·m?3·day?1, respectively. We estimated the food requirements of zooplankton in order to examine the trophic structure of the pelagic ecosystem. The secondary production may not be satisfied by phytoplankton alone in the study area and the shortfall may be supplied by other organic sources such as detritus.  相似文献   

18.
Methods are described for routine analyses of individual pteridines and flavins from marine waters at picomolar concentrations. Samples were concentrated by adsorption on bonded-phase, C18 silica and Florisil Sep-Pak extraction columns connected in series. Sample extracts derived from Sep-Pak eluates were analysed by reverse-phase liquid chromatography with fluorometric detection. These methods proved sensitive for the quantitative identification of pterin, xanthopterin, isoxanthopterin, 6-biopterin, pterin-6-carboxylic acid, 6-hydroxymethylpterin, riboflavin, riboflavin-5′-phosphate, lumiflavin and lumichrome in reef waters at Davies Reef, Great Barrier Reef, Australia.Preliminary experiments were conducted to test the application of these methods to the measurement of pterin and flavin excretion from several reef-dwelling, benthic organisms. Results from these experiments suggest that the benthic community contributes these compounds to the coral reef environment.  相似文献   

19.
Lutjanus apodus (Schoolmaster) were collected from several mangroves and coral reefs at Turneffe Atoll, Belize, in order to investigate whether elemental concentrations from the otolith edge could be used as a means to identify the habitat (mangrove or coral reef) and site (9 mangrove sites and 6 reef sites) from which they were collected. Results of a two factor nested MANOVA (sites nested within habitat) indicated significant differences in elemental concentrations between habitats (i.e., mangrove versus reef) as well as among sites. When separate Linear Discriminant Function Analyses (LDFA) were used to assess whether the spatial variability in otolith chemistry was sufficient to differentiate individuals to their respective habitats or sites, the results indicated that fish were classified (jackknife procedure) with a moderate to poor degree of accuracy (i.e., on average, 67% and 40% of the individuals were correctly classified to the habitat and site from which they were collected, respectively). Using a partial Mantel test we did not find a significant correlation between the differences in otolith elemental concentrations between sites and the distance between sites, while controlling the effect of habitat type (mangrove or reef). This suggests that for mangrove and reef sites at Turneffe Atoll, Belize, the overlap in terms of L. apodus otolith elemental concentrations is too high for investigations of fish movement. Finally, by comparing previously published Haemulon flavolineatum otolith chemistry to that of L. apodus we assessed whether these species showed similar habitat and/or site specific patterns in their otolith chemistry. Although both species were collected from the same sites our results indicated little similarity in their elemental concentrations, thus suggesting that habitat and site elemental signatures are species specific.  相似文献   

20.
Pacific oyster, Crassostrea gigas Thunberg, embryos were exposed to copper and silver salts, alone and in combination, through the completion of embryogenesis and metal effects upon normal embryonic development were monitored. Copper concentrations throughout the test period ranged from 0·0 to 12·0 μg litre?1 while silver concentrations were between 0·0 and 18·0 μg litre?1.Administered individually, silver and copper yielded decreasing per cent normal embryonic development with increasing metal concentration. However, both metals exhibited ‘plateaus’ wherein per cent normal embryonic development did not decrease with increasing metal concentration until a particular concentration was attained. A rapid decrease in per cent normal embryonic development occurred with increasing metal concentrations greater than 6·0 μg litre?1 copper and 11·0 μg litre?1 silver.The dose-response patterns of copper and silver appear to be similar with copper exhibiting somewhat greater toxicity. At a copper concentration of 10 μg litre?1 only 50% of the embryos could be considered normally developed, whereas silver concentrations between 16·0 and 18·0 μg litre?1 yielded 50% normal embryonic development.Response surface methodology indicated that copper and silver interacted additively, with embryonic development affected to a much greater degree by copper than by silver. Optimum development of Crassostrea gigas embryos was greatly influenced by copper concentrations and occurred at all silver concentrations wherein the corresponding copper concentrations were 6·0 μg litre?1 or less. Above 6·0 μg litre?1 copper, per cent normal embryonic development was significantly reduced, even at the lowest tested silver concentrations.Abnormal embryos exhibited retarded shell growth, reduced size and extremely erratic swimming behaviour. These sublethal effects probably have a biochemical origin and would limit the organism's capacity to feed properly, escape predation and develop normally, thereby reducing the chances of successful metamorphosis and recruitment into the adult population.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号