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 937 毫秒
1.
Nereis diversicolor is generally considered to be a predator and deposit feeder, but have also been found to graze on benthic algae in shallow coastal areas. In this study we investigated the grazing effects on the development and growth of green algae, Ulva spp. Algal growth was studied in an experiment including two levels of sediment thickness; 100 mm sediment including macrofauna and 5 mm sediment without macrofauna, and three treatments of varying algal biomass; sediment with propagules, sediment with low algal biomass (120 g dry weight (dwt) m− 2) and sediment with high algal biomass (240 g dwt m− 2). In the 100 mm sediment, with a natural population of macrofauna, N. diversicolor was the dominating (60% of total biomass) species. After three weeks of experimentation the result showed that N. diversicolor was able to prevent initial algal growth, affect growth capacity and also partly reduce full-grown algal mats. The weight of N. diversicolor was significantly higher for polychaetes in treatments with algae added compared to non-algal treatments. There were also indications that a rich nutrient supply per algae biomass counteracted the grazing capacity of N. diversicolor.  相似文献   

2.
An intertidal Zostera marina landscape in Torbay, Devon, UK, was sampled to investigate the relationship between patch size, diversity and infaunal assemblage composition with the intention of defining a minimum Zostera patch size where the infaunal seagrass assemblage becomes distinct from the bare sand assemblage. All Zostera patches were found to support a higher level of biodiversity than the surrounding bare sand. However, the size of the Zostera patch had no impact on the level of diversity; it was just the presence or absence of seagrass that made a difference. The sediment and seagrass variables were not significantly different across the range of Zostera patch sizes, indicating that the environment characteristics were homogeneous within the Zostera patches at the patch scale. Multivariate analysis revealed that assemblage composition did vary between the patch types, although the opportunistic polychaete Capitella capitata was present in all patch types and was the most abundant species overall. The presence of opportunistic species and the homogeneity of the Zostera patch variables may be due to the location of this intertidal seagrass bed, which is relatively exposed compared to the locations of other seagrass beds along the south coast of Devon, resulting in a more dynamic and disturbed environment. Nevertheless, our results demonstrate that even small patches of seagrass comprising a few plants support a higher abundance and diversity of infaunal invertebrates than bare sand, indicating that Zostera patches have conservation value whatever their size.  相似文献   

3.
Macrofauna, nutrient fluxes, porewater chemistry and sediment characteristics were measured at six intertidal mudflat sites in the Humber Estuary, U.K., during the different seasons. Nereis diversicolor , Macoma balthica and Corophium volutator were found to be the dominant macrofauna. Salinity was the baseline control on macrofauna distribution but this was overprinted by periodic impoverishment due to sediment mobilization. High resolution gel probe porewater samplers provided direct evidence for the impact of burrows on porewater chemistry. The macrofauna modified nutrient fluxes during periods of mud flat stability. Nereis caused a decrease in silicate and phosphate effluxes but enhanced ammonia release and nitrate uptake. Macoma enhanced ammonia and nitrite release. The impact of Corophium was not possible to discern. The Humber is a large, highly dynamic macrotidal estuary in which sediment resuspension has a large impact on porewater profiles, nutrient fluxes and macrofaunal communities. Simple patterns and inter-relationships which are seen in small sheltered estuaries are not observed in the Humber.  相似文献   

4.
Ulva species can grow rapidly in nutrient-rich habitats causing green tides and marine fouling. A more complete understanding of the reasons behind these outbreaks is urgently required. Accordingly, this study attempts to use microsatellite markers based expressed sequence tag（EST） to analyze the genetic variation of several Ulva prolifera populations in the South Yellow Sea of China. Two hundred and thirty-eight SSRs were identified from 8 179 unique ESTs（6 203 newly sequenced and 1 976 downloaded from NCBI database） and 37 primer pairs were successfully designed according to the ESTs; 11 pairs were selected to detect the genetic diversity and relationship of 69 attached U. prolifera samples and 13 free-floating samples collected from coastal and off-coast areas of the South Yellow Sea. The results of cross-species transferability showed that six of the 11 EST-SSR primers could give good amplification in other five Ulva species and the average allele number was 4.67. Genetic variation analysis indicated that all 82 U. prolifera samples were clearly divided and most samples collected from the same site clustered together as a group in the dendrogram tree produced by unweighted pair-group mean analysis（UPGMA） method and the cluster results showed some consistency with the geographical origins. In addition, 13 free-floating samples（except HT-001-2） were grouped as a single clade separated from the attached samples.  相似文献   

5.
The microscopic community of a microtidal sandy sediment on the Swedish west coast was studiedin situat two depths (0·5 and 4 m) on four occasions (January, April, August and October). Biomass of microalgae, bacteria, ciliates and meiofauna, as well as primary and bacterial productivity, were quantified. Meiofaunal grazing on algae and bacteria was measured simultaneously by radiolabelling intact sediment cores. Autotrophic biomass dominated the microbial community at both depths and on all sampling occasions, accounting for 47–87% of the microbial biomass. Meiofauna contributed 10–47%, while bacteria and ciliates together made up less than 6%. The microflora was dominated by attached (epipsammic) diatoms, but occasional ‘ blooms ’ of motile species occurred. Vital cells of planktonic diatoms contributed to benthic algal biomass in spring. Primary productivity exceeded bacterial productivity in April and August at both depths, while the balance was reversed in October and January. Meiofauna grazed between 2 and 12% of the algal biomass per day, and between 0·3 and 37% of the bacterial biomass. Almost an order of magnitude more algal (17–138 mg C m−2) than bacterial (0·1–33 mg C m−2) carbon was grazed daily. At the shallow site, primary productivity always exceeded grazing rates on algae, whereas at the deeper site, grazing exceeded primary productivity in October and January. Bacterial productivity exceeded grazing at both depths on all four occasions. Thus, meiofaunal grazing seasonally controlled microalgal, but not bacterial, biomass. These results suggest that, during summer, only a minor fraction (<10%) of the daily microbenthic primary production appears to enter the ‘ small food web ’ through meiofauna. During spring and autumn, however, a much larger fraction (≈30–60%) of primary production may pass through meiofauna. During winter, meiofaunal grazing is a less important link in the shallow zone, but at sublittoral depths, algal productivity may be limiting, and meiofauna depend on other food sources, such as bacteria and detritus.  相似文献   

6.
孔隙水是沉积物-海水界面链接沉积物颗粒和上覆水体的一个重要过渡相态,针对其研究可更好地了解痕量金属在固-液界面的早期成岩过程。近年来,针对孔隙水中痕量元素研究的方法较为匮乏,为此建立了一种分析测定海洋沉积物孔隙水中7种痕量金属元素(Mn、Cu、Zn、Ni、Cd、Co、Pb)的方法,该方法使用Nobias PA1树脂进行富集分离,再使用电感耦合等离子体质谱(ICP-MS)进行测试,可针对孔隙水中的痕量金属元素进行准确分析。通过实验结果发现该方法最优实验条件为: Nobias PA1树脂富集时的pH值为5.5~6.0,洗脱酸浓度为1.3 mol/L硝酸,体积为1 mL。同时,样品需进行紫外消解4 h以上以分解有机络合物,该消解步骤对Cu和Co这两种元素尤其重要。该方法通过加标回收获得Mn、Cu、Ni、Co和Pb的回收率在92%~100%, Zn和Cd的回收率分别为72%和82%; Mn、Cu、Zn、Ni的方法检出限范围为0.03~0.53 nmol/L, Cd、Co、Pb的方法检出限范围为2.66×10-3~8.60×10-3 nmol/L,满足孔隙水中痕量金属浓度的测试需求。同时,根据检出限计算的结果显示,孔隙水样品只需1 mL,即可应用该方法进行测试。应用该方法测试了一根采集于北黄海中部沉积物短柱的孔隙水样品,测试结果显示其垂相分布合理、较符合早期成岩过程规律。此研究为分析海洋沉积物孔隙水中痕量金属元素提供了一种准确而简便的方法。  相似文献   

7.
The influence of seagrass beds on intertidal infaunal communities has been widely studied, with vegetated areas typically having higher diversity and abundances than adjacent bare sand patches. Such “seagrass–sand” comparisons, however, do not reflect the gradient of seagrass cover that may exist across large landscapes. We studied the large-scale distribution of intertidal macrozoobenthos over approximately 10,000 ha of sandflat on Farewell Spit, New Zealand. The benthic fauna, sediment composition and surface cover of the seagrass Zostera muelleri were studied at 192 sites evenly spaced along 30 transects covering the length of the 30 km spit. Most sites had Zostera present, generally at low densities (1–25% surface cover). Overall, invertebrate taxon diversity increased with Zostera cover, from a median of 4 taxa at sites with no Zostera to 23 at sites with high Zostera cover. Multivariate analyses of 37 frequently occurring taxa (of the 91 recognised) indicated that there was a site gradient of taxon abundances that reflected seagrass cover, with 23 taxa increasing as Zostera cover increased. Only three taxa tended to be found more where Zostera was scarce. Seventeen taxa were identified as being significant indicators of Zostera cover; in all cases abundances peaked with high Zostera scores. Cluster analysis revealed a number of major groupings. One group was associated with low Zostera; two were strongly associated with high Zostera cover; a fourth was probably distinguished by low tidal elevation and proximity to channels. On the Farewell Spit tidal flats, large-scale patterns of abundance seem to be largely structured by the presence and density of Zostera.  相似文献   

8.
Seasonal monitoring of the levels of carbon, nitrogen and phosphorus in two green macroalgae (Ulva and Enteromorpha) was carried out at 22 sampling sites in four embayments (rías) on the northwest coast of Spain. Sediments were also analysed to determine the concentrations of these elements as well as organic matter, organic carbon, iron and texture. In addition, accumulations of Ulva were monitored. Nitrogen levels in algae were similar to those found in comparable studies, whereas carbon concentrations were generally higher and those of phosphorus were lower. As a result the macroalgae were relatively enriched by carbon and nitrogen compared with phosphorus. Seasonal variations in algal tissue nitrogen and phosphorus followed the usual pattern for temperate zones, with minimum levels in summer and maximum levels in winter. Variations in carbon concentrations were much less accentuated. The low levels of P in the algae appear to indicate limitation by this element, however, comparison of the monthly changes in nitrogen and phosphorus in Ulva with the critical concentrations of these elements suggests dual nutrient limitation in this alga in summer. By contrast, the sediments were more enriched by phosphorus; high retention of this element by the sediment may explain the low levels in algae. The highest accumulations of Ulva occurred in spring and summer; hydrodynamic factors appeared to be important in determining the extent of these accumulations.  相似文献   

9.
The grazing pressure of the macrofaunal invertebrates associated with the biomass of Ulva rigida in the Venice lagoon, their species composition and relationship with environmental variables have been studied. Fifteen sampling campaigns were carried out during different seasons both in the central basin of the lagoon, dominated by macroalgae (especially U. rigida C. Ag.) and in the southern basin, prevalently populated by seagrasses (especially Zostera marina L.). Replicate experiments were conducted in the field by exposing Ulva fronds in net cages of 10 and 1 mm (control) mesh-sizes to allow or prevent grazer entrance. The grazing pressure was determined as Ulva growth rate difference in the cages. In the absence of invertebrate herbivores, Ulva exhibited per cent relative growth rates (%RGRs) ranging from 1.5 to 9.5% day(-1), whereas in their presence the %RGRs were significantly lower (from -2.5 to 3.4% day(-1)) and frequently negative, especially in the station dominated by macroalgae. In this area, peak grazing rates and macrofauna biomasses of up to 8.6% day(-1) and 1,480 g m(-2) fwt (84.4 ash-free dry weight), respectively, were found. On the whole, during in field experiments in the Ulva-dominated station, herbivores removed an amount of biomass whose percentage ranged from 59 to 165% (mean: 103%) of the biomass yield (grazers excluded) found in the cages. These results suggest the possibility that grazers could act as an important factor affecting Ulva production in the Venice lagoon. Macrofauna populations were analysed by means of multivaliate techniques applied to biological variables only and biological and environmental variables together. Data of individual abundance, after a log(x + 1) transformation and the calculation of the Bray-Curtis matrix, were classified using the Cluster Analysis and ordinated by means of the Non-Metric Multidimensional Scaling (MDS) technique, in accordance with the strategies used in the study of multispecies distributions. Finally, biological and environmental variables were analysed together by means of correlation matrices and the Principal Component Analysis.  相似文献   

10.
The presences of the common macroalgae Ulva sp. and Jania rubens vary between seasons along the Israeli Mediterranean intertidal zone. To reveal some of the potential acclimation mechanisms of these algae, we examined their photosynthetic traits during the year using rapid light curves (RLC) derived from pulse amplitude modulated (PAM) fluorometry. In addition, the relationships between those photosynthetic traits and the relative abundances of the two algae were investigated. Ulva sp. showed high maximal electron transport rates (ETRmax) (49.7–68.8 μmol electrons m−2 s−1) and onsets of light saturation values (Ek) (75.8–85.6 μmol photons m−2 s−1) in the winter months of December–February, while low values were found in the summer months of June–July (5.2–20.6 μmol electrons m−2 s−1 and 6.0–23.7 μmol photons m−2 s−1, respectively). At noon time (during the highest irradiance of the day), the maximal effective quantum yield (Y0) did not vary significantly during the year. These results indicate that seasonal irradiance influences the number of reaction centres per thallus area. Both algae showed depressions in Y0 at noon (23.8% for Ulva sp. and 20.3% for Jania rubens), indicating an efficient non‐photochemical quenching mechanism. A positive correlation between the relative abundance and the photosynthetic parameter Y0 was found for Jania rubens when Y0 was sampled in the morning or noon, indicating that growth rate and primary production for this alga can be estimated from RLCs. No such correlation was found for Ulva sp., indicating that, in addition to photosynthetic traits, the relative seasonal abundance of this alga is influenced by other factors such as grazing and/or catastrophic events.  相似文献   

11.
Mytilus galloprovincialis digestive gland microsomes were prepared from (i) indigenous populations sampled from a clean reference (Lido) and an urban-contaminated site (Salute) and (ii) mussels transplanted for up to 3 weeks from Lido to an industrial-contaminated site (CVE) in Venice Lagoon, Italy. Western blot analysis was performed using antibodies to five mammalian or fish CYP forms (1A, 2B, 2E, 3A, 4A). Simultaneously run M. edulis digestive gland partially purified CYP aided identification of immunopositive bands. Levels of CYP1A, CYP2E, and CYP4A-immunopositive proteins were 50 to 300% higher in indigenous M. galloprovincialis from Salute compared to Lido (p < 0.05). Three weeks after transplantation to CVE, levels of only the CYP1A-immunopositive protein were determined to be higher (63%) than levels for Lido (p < 0.05), indicating that anti-CYP1A shows greater specificity for a contaminant-inducible CYP form than the other antibodies.  相似文献   

12.
The characteristics of Mn(II) removal from sediment porewater and the potential role of manganese-oxidizing bacteria in this process were examined in sediments from a 335-m deep station in the Laurentian Trough of the St. Lawrence estuary. Manganese-oxidizing bacteria were most abundant in the thin layer of oxidized surface sediment, where Mn(II) removal rates were also fastest. The first-order rate constants for Mn(II) removal decreased from 1·2 × 103 day−1 to 6·6 day−1 over the first 30-mm depth. In experimental slurries, sediments removed Mn(II) from reduced zone porewater by a two-step process: a rapid saturation of Mn(II) binding sites was followed by a slower O2-enhanced removal rate which paralleled the apparent rate of Mn(II) oxidation. Sodium azide and mercuric chloride were tested specifically for their usefulness as bacterial poisons in sediment slurry systems. Sodium azide interfered with Mn(II) removal at low concentrations and was not an effective poison. Mercuric chloride inhibited bacterial activity at concentrations far lower than those at which significant interference of Mn(II) removal occurred. The response of sediment slurries treated with mercuric chloride indicated that the initial oxidation of sorbed Mn(II) was not bacterially-mediated under the experimental conditions tested.  相似文献   

13.
We adapted the dilution technique to study microzooplankton grazing of algal dimethylsulfoniopropionate (DMSP) vs. Chl a, and to estimate the impact of microzooplankton grazing on dimethyl sulfide (DMS) production in the Labrador Sea. Phytoplankton numbers were dominated by autotrophic nanoflagellates in the Labrador basin, but diatoms and colonial Phaeocystis pouchetii contributed significantly to phytomass at several high chlorophyll stations and on the Newfoundland and Greenland shelfs. Throughout the region, growth of algal Chl a and DMSP was generally high (0.2–1 d−1), but grazing rates were lower and more variable, characteristic of the early spring bloom period. Production and consumption of Chl a vs. DMSP followed no clear pattern, and sometimes diverged greatly, likely because of their differing distributions among algal prey taxa and size class. In several experiments where Phaeocystis was abundant, we observed DMS production proportional to grazing rate, and we found clear evidence of DMS production by this haptophyte following physical stress such as sparging or filtration. It is possible that grazing-activated DMSP cleavage by Phaeocystis contributes to grazer deterrence: protozoa and copepods apparently avoided healthy colonies (as judged by relative growth and grazing rates of Chl a and DMSP), and grazing of Phaeocystis was significant only at one station where cells were in poor condition. Although we hoped to examine selective grazing on or against DMSP-containing algal prey, the dilution technique cannot differentiate selective ingestion and varying digestion rates of Chl a and DMSP. We also found that the dilution method alone was poorly suited for assessing the impact of grazing on dissolved sulfur pools, because of rapid microbial consumption and the artifactual release of DMSP and DMS during filtration. Measuring and understanding the many processes affecting organosulfur cycling by the microbial food web in natural populations remain a technical challenge that will likely require a combination of techniques to address.  相似文献   

14.
In this study we test the hypothesized negative relationship between seagrass status and porewater hydrogen sulfide (H2S) levels, through a comparative analysis within a range of seven Posidonia oceanica meadows growing over carbonate sediments in the NW Mediterranean Sea around Mallorca Island. The studied meadows range from meadows growing on sediments with very low sulfide porewater concentrations (4.6 μM) to those growing over higher sulfide conditions (33.5 μM). Organic matter content, sulfate reduction rates and sulfide porewater concentrations in the sediments were determined concurrently with the assessment of demographic plant dynamics (specific mortality and net population growth rates). Sulfide porewater concentration increased with increasing organic matter content in the sediment, while net population growth decreased significantly with low increases of sulfide concentrations. Our results confirm the previously suspected vulnerability of seagrass meadows growing on carbonate sediments to increased sulfide levels. An excess of 10 μmols H2S L−1 porewater is identified to already conduce P. oceanica meadows to decline, which this study identifies, particularly, as strongly sensitive to sulfides. The results reported here suggest that even moderate increases in organic carbon inputs may lead to enhancement of dissolved sulfides and may be an important factor for seagrass status in these iron-depleted carbonate sediments from the Mediterranean Sea.  相似文献   

15.
The structure and the trophic interactions of the planktonic food web were investigated during summer 2004 in a coastal lagoon of south-western Mediterranean Sea. Biomasses of planktonic components as well as bacterial and phytoplankton production and grazing by microzooplankton were quantified at four stations (MA, MB, MJ and R) inside the lagoon. Station MA was impacted by urban discharge, station MB was influenced by industrial activity, station MJ was located in a shellfish farming sector, while station R represented the lagoon central area. Biomasses and production rates of bacteria (7–33 mg C m−3; 17.5–35 mg C m−3 d−1) and phytoplankton (80–299 mg C m−3; 34–210 mg C m−3 d−1) showed high values at station MJ, where substantial concentrations of nutrients (NO3− and Si(OH)4) were found. Microphytoplankton, which dominated the total algal biomass and production (>82%), were characterized by the proliferation of several chain-forming diatoms. Microzooplankton was mainly composed of dinoflagellates (Torodinium, Protoperidinium and Dinophysis) and aloricate (Lohmaniellea and Strombidium) and tintinnid (Tintinnopsis, Tintinnus, Favella and Eutintinnus) ciliates. Higher biomass of these protozoa (359 mg C m−3) was observed at station MB, where large tintinnids were encountered. Mesozooplankton mainly represented by Calanoida (Acartia, Temora, Calanus, Eucalanus, Paracalanus and Centropages) and Cyclopoida (Oithona) copepods, exhibited higher and lower biomasses at stations MA/MJ and MB, respectively. Bacterivory represented only 35% of bacterial production at stations MB and R, but higher fractions (65–70%) were observed at stations MA and MJ. Small heterotrophic flagellates and aloricate ciliates seemed to be the main controllers of bacteria. Pico- and nanophytoplankton represented a significant alternative carbon pool for micrograzers, which grazing represented 67–90% of pico- and nano-algal production in all stations. Microzooplankton has, however, a relatively low impact on microphytoplankton, as ≤45% of microalgal production was consumed in all stations. This implies that an important fraction of diatom production would be channelled by herbivorous meso-grazers to higher consumers at stations MA and MJ where copepods were numerous. Most of the microalgal production would, however, sink particularly at station MB where copepods were scare. These different trophic interactions suggest different food web structures between stations. A multivorous food web seemed to prevail in stations MJ and MA, whereas microbial web was dominant in the other stations.  相似文献   

16.
Fluxes of dissolved forms of iron and manganese across the sediment–water interface were studied in situ in the Gulf of Finland and the Vistula Lagoon (Baltic Sea), and in the Golubaya Bay (Black Sea) from 2001 to 2005. Fluxes were measured using chamber incubations, and sediment cores were collected and sliced to assess the porewater and solid phase metal distribution at different depths. Measured and calculated benthic fluxes of manganese and iron were directed out of sediment for all sites and were found to vary between 70–4450 and 5–1000 µmole m− 2 day− 1 for manganese and iron, respectively. The behavior of the studied metals at various redox conditions in the near-bottom water and in the sediment was the main focus in this study. Our results show the importance of bottom water redox conditions for iron fluxes. We measured no fluxes at oxic conditions, intermediate fluxes at anoxic conditions (up to 200 μmole m− 2 day− 1) and high fluxes at suboxic conditions (up to 1000 μmole m− 2 day− 1). Total dissolved iron fluxes were generally dominated by iron(II). Contribution of iron(III) to the total iron flux did not exceed 20%. Obtained fluxes of manganese at all studied regions showed a linear correlation (r2 = 0.97) to its concentration in the porewater of the top sediment layer (0–5 mm) and did not depend on dissolved oxygen concentrations of bottom water. Organically complexed iron and manganese were in most cases not involved in the benthic exchange processes.  相似文献   

17.
Drifting sediment trap experiments were conducted during various seasons to elucidate the characteristics of particles sinking through the upper 200 m of the water column in the western Pacific at subarctic station K2 and subtropical station S1. The sinking particle flux increased when primary productivity was high at each station, during June–July at K2 and during February at S1. Biogenic opal (Opal) and CaCO3 were the major components of the fluxes at K2 and S1, respectively. Contrary to the expectation of a high flux at the eutrophic station K2 and low flux at the oligotrophic station S1, the annual average organic carbon fluxes at 100 m were comparable at both stations: 62.7 mg C m?2 day?1 at K2 and 56.1 mg C m?2 day?1 at S1. The similarity of the fluxes was perhaps a reflection of the unexpectedly high primary production at S1. At K2, the organic carbon export ratio (organic carbon flux/primary productivity) was significantly and negatively correlated with primary production and tended to decrease with depth. The magnitude of the rate of attenuation of the organic carbon flux with depth was larger at S1 than at K2. This rate of attenuation tended to decrease and increase with primary production at K2 and S1, respectively. The explanation for these patterns may be that the flux of labile organic carbon at relatively shallow depths decreased with increasing primary production at K2, and zooplankton grazing pressure increased with increasing primary productivity at S1.  相似文献   

18.
The trophic efficiency of the planktonic food web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major metabolic activities of auto- and heterotrophic planktonic communities (primary production, bacterial production, nanoproto-, micro- and mesozooplankton feeding activities) were determined in nine field assemblages collected during spring at reference station 330. In 1998, the phytoplankton spring flowering was characterised by a moderate diatom bloom followed by a massive Phaeocystis colony bloom. Phaeocystis colonies, contributing 70% to the net primary production, escaped the linear food chain while the early spring diatom production supplied 74% of the mesozooplankton carbon uptake. The rest of mesozooplankton food requirement was, at the time of the Phaeocystis colony bloom, partially fulfilled by microzooplankton. Only one-third of the microzooplankton production, however, was controlled by mesozooplankton grazing pressure. Ungrazed Phaeocystis colonies were stimulating the establishment of a very active microbial network. On the one hand, the release of free-living cells from ungrazed colonies has been shown to stimulate the growth of microzooplankton, which was controlling 97% of the nanophytoplankton production. On the other hand, the disruption of ungrazed Phaeocystis colonies supplied the water column with large amounts of dissolved organic matter available for planktonic bacteria. The budget calculation suggests that ungrazed colonies contributed up to 60% to the bacterial carbon demand, while alternative sources (exudation, zooplankton egestion and lysis of other organisms) provided some 30% of bacterial carbon requirements. This suggests that the spring carbon demand of planktonic bacteria was satisfied largely by autogenic production. The trophic efficiency was defined as the ratio between mesozooplankton grazing on a given source and food production. In spite of its major contribution to mesozooplankton feeding, the trophic efficiency of the linear food chain, restricted to the grazing on diatoms, represented only 5.6% of the available net primary production. The trophic efficiency of the microbial food chain, the ratio between mesozooplankton grazing on microzooplankton and the resource inflow (the bacterial carbon demand plus the nanophytoplankton production) amounted to only 1.6%. These low trophic efficiencies together with the potential contribution of ungrazed Phaeocystis-derived production to the bacterial carbon demand suggest that during spring 1998 most of the Phaeocystis-derived production in the Belgian coastal area was remineralised in the water column.  相似文献   

19.
The seasonal dynamics of molluscan assemblages inhabiting the algal fronds and the underlying sediment of photophilous algae were analyzed in NW Alboran Sea between July 2007 and April 2008. Molluscs were sampled using SCUBA in two different algal stands (7 km apart) dominated by the brown algae Stypocaulon scoparium, and following an inter-strata sampling protocol consisting in first sampling the algal fronds and then the underlying substratum. The studied algal stands harbored a highly biodiverse malacofauna, with 193 species identified. Assemblages on algal fronds and sediment displayed significant seasonal variations, being more apparent on the fronds, with maximum species richness, abundance and Shannon–Wiener diversity values in summer in both strata. The between-strata differences were also observed in the trophic structure of the assemblages: algal fronds were quantitatively dominated by microalgae or periphyton grazers and the sediment by detritivores and plankton and seston feeders. The high dominance of some species resulted in lower values of diversity and evenness in autumn in the sediment (e.g. Nodulus contortus and Bittium reticulatum) and in spring on the fronds (e.g. Rissoa guerinii and Musculus costulatus). The seasonal variability of the assemblages was mainly related to the population dynamics of dominant species (22 spp. displaying dominance values > 1%) (i.e. recruitment events, high mortality rates of juveniles and/or migrations among habitats). Other factors analyzed were (1) the vegetative cycle of algae, which played an important role in the abundance of some dominant epifaunal grazers, with high abundance and species richness values coinciding with high biomass of algae; and (2) the percentage of organic matter in the sediment, which was related to the abundance changes of some depositivores species. Further conservation strategies for macroalgal stands should be taken into consideration, as this type of photophilous habitat harbors rich associated faunistic communities and it is not generally considered in conservation lists of habitats to be protected.  相似文献   

20.
Blooms of drifting green algae often develop in shallow coastal zones that receive significant nutrient inputs. Each spring and summer, some fifty bays and coves in Brittany (France) are affected in this way. Until now, in this region, only the algae present in the surf zone or stranded ashore, constituting an intertidal stock, have been taken into account. Another stock of algae, which was subtidal and of the same species (Ulva spp.), was found in the Bay of Douarnenez, one of the ten areas most affected by these algal blooms. This subtidal Ulva stock was located beyond the surf zone, at depths reaching 15 m. It was about the same size as the intertidal stock, viz., a few thousand tons on average. Subtidal Ulva stocks were generally found lying on the sandy bottom in a distribution showing no particular pattern. Biomass ranged from almost zero to 1.547 kg m−2 of fresh and spun-dried algae. However, at depths from 3 to 7 m they were often arranged in strips a few dm wide, due to the swell's effect. The bottom conditions of temperature, salinity, irradiance and dissolved inorganic nitrogen measured during spring and summer are suitable for the growth of Ulva in the subtidal zone. Both intertidal and subtidal drifting Ulva stocks are mobile and capable of exchanging material. In spring, the intertidal stock's inoculum is likely to come from the subtidal. Later in the season, the subtidal stock could be supplied, at least partially, by the intertidal.  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