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1.
Feeding periodicity, consumption rate, absorption efficiency, respiration rate and ammonia excretion were measured as functions of wet body mass in abalone collected from the western and southern Cape coasts. A well developed diel feeding rhythm was evident, consumption being restricted to the period 16h00–08h00. Food intake averaged 8,1 per cent of wet flesh mass·d?1 at 14°C and 11,4 percent at 19°C. The daily consumption rate was related to body mass by the relationships C(g) = 0,54 W(g)0,67 at 14°C and C(g) = 0,35 W(g)0,77 at 19°C. Absorption efficiency averaged 37 per cent and was independent of body size. Equations relating respiration rate to wet body mass were R(m? O2·h?1) = 0,03 W(g)0,83 at 14°C and R = 0,03 W(g)0,94 at 19°C. No significant differences were detected between day and night rates or between fed and starved individuals. The rate of ammonia excretion (μmole·h?1) was related to wet body mass (g) by the equations U = 0,22 W0,43 at 14°C and U = 0,03 W0,85 at 19°C.  相似文献   

2.
Excess 210Pb in a core from a Mexican Coastal Lagoon, which has no connection with the sea shows a small but measurable decay over the length of the core, when different approaches were compared (excess and corrected 210Pb activity with depth, total and inorganic cumulative weights) significant differences in the values for the sedimentation rate are obtained. The best coefficient correlation was calculated when corrected 210Pb activity for the uneven distribution of organic matter and cumulative inorganic weight is considered (ω = 0·93 cm yr?1, R = ?0·86; ω = 0·51 cm yr?1 for the top 13 cm, R = ?0·90 and 1·52 cm yr?1 for the interval 14–46 with R = ?0·96).Time frames in the sedimentary column were in agreement between the 210Pb calculated time and the appearance of shells fragments probably associated with the disturbances caused by the 1961 hurricane Tara.The surface accumulation rate is equivalent to a mean deposition of 262·5 g m?2 yr?1 or organic matter which is minor but comparable to some salt marshes of United States.  相似文献   

3.
The number and size of bacteria at four depths (0–1, 5–6, 10–11 and 20–21 cm) in a North Carolina salt marsh were minotored by direct counts for 13 months. The number of bacteria reached a maximum of about 1·4 × 1010 cells cm?3 at the sediment surface in October, corresponding to the period of Spartina alterniflora die-back. Cell numbers were lowest and most consistent throughout the year at the 20 cm depth of sediment. Cell volumes averaged 0·2 μm3 at the marsh surface and decreased with depth. Mean standing crop of bacteria to a depth of 20 cm of sediment was about 14 g bacterial carbon m?2. In surface sediments bacteria contribute up to 15% and algae up to 10% of total living microbial biomass as estimated by adenosine triphosphate (ATP). Bacteria were the major biomass component at sediment depths of 5, 10 and 20 cm. At all depths the microbial community contributes < 4% total organic carbon and < 8% of total nitrogen.  相似文献   

4.
Multiple biotic and abiotic drivers regulate the balance between CO2 assimilation and release in surface waters. In the present study, we compared in situ measurements of plankton carbon metabolism (primary production and respiration) to calculated air–water CO2 fluxes (based on abiotic parameters) during 1 year (2008) in a hypereutrophic tropical estuary (Recife Harbor, NE Brazil – 08°03′S, 34°52′W) to test the hypothesis that high productivity leads to a net CO2 flux from the atmosphere. The calculated CO2 fluxes through the air–water interface (FCO2) were negative throughout the year (FCO2: –2 to –9 mmol C·m?2·day?1), indicating that Recife Harbor is an atmospheric CO2 sink. Respiration rates of the plankton community ranged from 2 to 45 mmol C·m?2·hr?1. Gross primary production ranged from 0.2 to 281 mmol C·m?2·hr?1, exceeding respiration during most of the year (net autotrophy), except for the end of the wet season, when the water column was net heterotrophic. The present results highlight the importance of including eutrophic tropical shallow estuaries in global air–water CO2 flux studies, in order to better understand their role as a sink of atmospheric CO2.  相似文献   

5.
The variability in dissolved and particulate organic matter, plankton biomass, community structure and metabolism, and vertical carbon fluxes were studied at four stations (D1–D4), placed along a coastal-offshore gradient of an upwelling filament developed near Cape Juby (NW Africa). The filament was revealed as a complex and variable system in terms of its hydrological structure and distribution of biological properties. An offshore shift from large to small phytoplankton cells, as well as from higher to lower autotrophic biomass, was not paralleled by a similar gradient in particulate (POC) or dissolved (DOC) organic carbon. Rather, stations in the central part of the filament (D2 and D3) presented the highest organic matter concentrations. Autotrophic carbon (POCChl) accounted for 53% (onshore station, D1) to 27% (offshore station, D4) of total POC (assuming a carbon to chlorophyll ratio of 50), from which nano- and pico-phytoplankton biomasses (POCA < 10 μm) represented 14% (D1) to 79% (D4) of POCChl. The biomass of small hetrotrophs (POCH < 10 μm) was equivalent to POCA < 10 μm, except at D1, where small autotrophs were less abundant. Dark community respiration (Rd) in the euphotic zone was in general high, almost equivalent to gross production (Pg), but decreasing offshore (D1–D4, from 108 to 41 mmol C m−2 d−1). POC sedimentation rates (POCsed) below the euphotic zone ranged from 17 to 6 mmol C m−2 d−1. Only at D4 was a positive carbon balance observed: Pg−(Rd + POCsed) = 42 mmol C m−2 d−1. Compared to other filament studies from the NE Atlantic coast, the Cape Juby filament presented lower sedimentation rates and higher respiration rates with respect to gross production. We suggest that this is caused by the recirculation of the filament water, induced by the presence of an associated cyclonic eddy, acting as a trapping mechanism for organic matter. The export capacity of the Cape Juby filament therefore would be constrained to the frequency of the interactions of the filament with island-induced eddies.  相似文献   

6.
Water flows, concentrations of total (TOC), dissolved (DOC), and particulate (POC) organic carbon and seston were monitored for 52 diel periods in the single creek draining a 270-ha Spartina patens-Distichlis spicata marsh on the upper Texas coast. Rainfall, creek water flows, and water levels in the creek and on the marsh were measured by recording instruments.Rainfall accounted for most marsh flooding, and water outflow was significantly correlated with both rainfall and marsh water level. Creek flows were predominantly outward because microtopographic features and dense vegetation restricted overmarsh water flows and thereby reduced tidal flooding while extending the time of precipitation runoff. Concentrations of organic carbon in water leaving the marsh were highest in spring and summer and averaged 25·62, 21·41 and 3·35 mg l?1 of TOC, DOC and POC, respectively. These were 9·34, 9·93 and 0·04 mg l?1, respectively, higher than bay water. Most POC was 0·3–28 μm in diameter. Seston > 28μ leaving the marsh was 95% amorphous material; the rest was plankton, grass particles and fecal pellets. Loss of organic carbon was directly correlated with net water flux, and thus rainfall accounted for most carbon loss. Net carbon loss averaged 196 kg TOC, 150 kg DOC and 32 kg POC per day. Net annual loss was 2·4–5·5% of net aerial primary productivity (NAPP), or 21·55-30·09 g TOC m?2 year?1.Export from this marsh falls within the range found for other marshes and the data collectively indicate that coastal marshes are not losing as much organic carbon as has been suggested by indirect measurements. The discrepancy between potential and realized export is explained by the fact that export is not a simple removal of excess detritus by tidal action but is a more complicated process mediated by the interaction of additional factors such as rainfall, vegetation structure, microtopographic variation and decomposition, which can serve to reduce the amount and quality of NAPP exported.  相似文献   

7.
Determinations of the activity of the respiratory electron transport system (ETS), during the FRAM III expedition permit us to estimate oxygen utilization rates (RO2) from the surface to 2000 m under the polar pack ice in the Nansen Basin just north of Svalbard (83°N, 7°E) during April 1981. We found RO2 at in situ temperatures ranging from 20 pM O2 min−1 just below the ice to 0.2 pM O2 min−1 at 2000 m. These rates are low compared to most other ocean regions, but they could decrease particulate organic carbon and nitrogen by 76% and 74%, respectively, over a period of ∼6 months. The RO2 calculations based on measurements made at 0 °C yielded a power function of RO2 vs. depth (Z) of RO2=67Z−0.5534. When this RO2 profile was superimposed on a more recent oxygen utilization rate profile made using the 3He–3H–AOU method (OUR), in the same vicinity of the Nansen Basin during 1987 (OUR=52Z–0.4058, [Zheng, Y., Schlosser, P., Swift, J.W., Jones, E.P., 1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]), the agreement of the two profiles was close. On one hand, this was to be expected because RO2 is the biological basis of OUR, on the other hand, it was a surprise because the methodologies are so different. Nitrate mineralization obtained from ETS activities also compared favorably with calculations based on the data of Zheng et al. [1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]. Chlorophyll ranged from 6 ng L−1 at 5 m to 0.06 ng L−1 at 2000 m. Particulate organic carbon (POC) decreased from 0.93 μM C just below the ice to less than 0.4 μM C at 500 m. Particulate organic nitrogen (PON) was not detectable below 70 m, however in the upper 70 m it ranged from 0.16 to 0.04 μM N. The C/N mass ratio over these depths ranged from 5.8 to 11.3. Annual carbon productivity as calculated to balance the total water column respiration was 27 g C m−2 y−1. The integrated respiration rate between 50 and 4000 m suggests that exported production and carbon flux from the 50 m level was 24 g C m−2 y−1. These are minimal estimates for the southern Nansen Basin because they are based on measurements made at the end of the Arctic winter.  相似文献   

8.
There is a well-defined succession of micro-organisms which colonize powdered leaf debris from Spartina alterniflora and Juncus roemerianus, and aged natural detrital material when these were incubated in estuarine water at temperatures near to those recorded in the habitat at the time of collection. The natural assemblage of free-living bacteria in estuarine water rapidly enters logarithmic growth, subsequently declining with the increase in numbers of bactivorous microflagellates. These are then replaced by a mixed population of ciliates, choanoflagellates, amoeboid forms and attached bacteria which form part of a complex microbial community associated with particulate debris. The rate of increase of bacterial cells (μ), in both spring and summer experiments ranged from 0·010–0·108 h?1 whilst estimates of bacterial carbon production ranged from 1·5 to 10·1 μg C 1?1 h?1, values which conform well with estimates obtained from natural assemblages of marine bacteria in coastal and estuarine waters elsewhere. Although both the ease of degradation of the detrital substrate and incubation temperature are of importance, enrichment of both powdered Spartina leaf debris and aged natural detritus with inorganic nutrients evidently enhances bacterial production under experimental conditions. In addition, the amount of carbon utilized to sustain bacterial carbon production shows a significant reduction following enrichment with NH4, NO3 or combinations of NO3 + PO4. The bacterial carbon conversion efficiency (μg C incorporated into bacterial production per μg C consumed) × 100, based on powdered Spartina leaves, and aged natural detritus, is thus increased from 9–14%, to as much as 38% in nutrient enriched media. Since NH4, NO3 and PO4 values are generally low in the water column, it seems likely that bacteria achieve a carbon conversion of only 9–14% on natural suspended detrital material, with the possibility of an enhanced conversion of up to 38% occurring at the sediment-water interface where ammonia regeration occurs. This suggests that suspended bacteria which characterize estuarine waters of salt marsh areas may be responsible for the oxidation of 86–91% of the carbon which enters water column microheterotroph food chains, and are probably implicated in the large CO2 fluxes recently recorded from coastal wetland habitats.  相似文献   

9.
Total, chemical and biological oxygen demand of intertidal sediment cores from 12 stations in a mangrove swamp in southern Africa were measured under mean temperature and salinity conditions. In addition to measuring oxygen removed from water overlying cores, the uptake of oxygen from air overlying sealed cores was also determined. Total oxygen consumption ranged from 2·9 to 37·0 ml O2 m?2 h?1 in water and from 22·1 to 81·6 ml O2 m?2 h?1 in air. Chemical oxygen demand usually equalled or exceeded the total, underlining problems in the measurement of this parameter. Since oxygen is not present below a few millimeters in the sediment, it is concluded that oxygen diffusing from the overlying water or air is rapidly utilized at the surface and its uptake rate does not give any measure of metabolic activity deeper down. The oxygen content of the overlying water present during high tide may drop to relatively low levels due to this demand.  相似文献   

10.
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11.
Different processes erode the plane and ramp, the two morphological elements of the shore platform. On the plane, desiccation of the shale causes contraction of the clay lattices in intertidal periods but wetting by the flood tides produces expansion. These movements crack the shale bedding laminae into polygons about 2 cm in diameter which are removed by waves. Desiccation is enhanced in well-drained areas and there is a positive correlation between altitude and erosion rate producing the smooth-sub-horizontal plane. Erosion is highest during summer. It averages 0.1 cm year?1 but ranges from 0.0 to 0.9 cm year?1.Corrasion is the main erosive process on the ramp. It is most active during winter, the stormy season, but is influenced by beach depth and possibly grain size. A shallow sand and pebble beach less than 5 cm deep allows erosion at all times. Beach depth is the most important influence on corrasion if it brings the ramp within 5 cm of the surface at some times and buries it more than 13.5 cm deep at others. Wave energy is the most important variable if the beach is usually more than 13.5 cm deep. Erosion rates for the zones of 0–5 cm depth, 5–13.5 cm depth, and greater than 13.5 cm depth were respectively 3.94 · 10?3 cm tide?1, 3.26 · 10?3 cm tide?1 and 1.13 · 10?3 cm tide?1.  相似文献   

12.
The biomass and productivity of phytoplankton populations inshore on the west coast of South Africa were investigated towards the end of the upwelling season, a period when high-biomass dinoflagellate blooms are common. Productivity was estimated from natural fluorescence measurements (PNF ), using photosynthesis (P) v. irradiance (E) relationships (PE ) and by means of the in situ 14C-method (PC ) A linear regression of PNF productivity against PC and PE productivities yielded a slope of 0.911 and an r 2 of 0.83 (n = 41). Physical and biological variability was high inshore, reflecting alternating periods of upwelling and quiescence. Mean chlorophyll inshore (within a 12 m water column) ranged from 0.7 to 57.8 (mean = 8.9) mg·m&minus3, mean PNF productivity ranged from 8.4 to 51.0 (mean = 24.6) mgC·m?3·h?1 and daily integral PNF productivity from 0.8 to 4.8 (mean = 2.3) gC·m?2·day?l. Transects sampled during active and relaxation phases of upwelling had different chlorophyll distributions. High chlorophyll concentrations (sometimes >50 mg·m?3) were associated with surface blooms within the region of the upwelling front. Estimates of daily water-column PNF productivity within these frontal blooms ranged from 4.0 to 5.6 gC·m?2·day?1. With relaxation of wind stress, blooms dominated by dinoflagellates flooded shorewards and often formed red tides. Chlorophyll concentrations of > 175 mg·m?3 and productivity rates > 500 mgC·m?3·h?1 and 12 gC·m?2·day?1 were measured during a particularly intense red tide. Offshore, the water column was highly stratified with a well-defined subsurface chlorophyll maximum layer within the pycnocline region. Estimates of daily water-column PNF productivity ranged from 2.4 to 4.0 gC·m?2·day?1 offshore. The high productivity of shelf waters on the West Coast in late summer can be ascribed largely to dinoflagellate populations and their success in both upwelling systems and stratified conditions.  相似文献   

13.
张正斌  刘莲生  王强 《海洋学报》1981,3(3):410-422
关于海水中铀(Ⅵ)与水合氧化钛的作用、国内外已有许多报导,内容包括水合氧化钛制备方法的不同对交换铀量的影响,水合氧化钛和海水中铀的基本物理—化学性质的研究及它们在反应过程中物理—化学性质变化规律的研究,海水中铀与水合氧化钛作用机理的研究等等。但对这一反应的动力学研究文献上报导极少,除了在本研究Ⅰ、Ⅱ和Ⅲ中报导的反应机理的研究[1,2]证明反应过程的速率由液膜扩散所控制之外,关于这一离子交换过程的反应级数和活化能的研究却至今未见有文献报导。  相似文献   

14.
The studied area is a 130 km long fast spreading graben in Central Greece. Its complex geodynamical setting includes both the presence of a subduction slab at depth responsible for the recent (Quaternary) volcanic activity in the area and the western termination of a tectonic lineament of regional importance (the North-Anatolian fault). A high geothermal gradient is made evident by the presence of many thermal springs with temperatures from 19 to 82 °C, that discharge along the normal faults bordering the graben.In the period 2004–2012, 58 gas and 69 water samples were collected and their chemical and isotopic analysis revealed a wide range of compositions.Two main groups of thermal waters can be distinguished on the basis of their chemical composition. The first, represented by dilute waters (E.C. <0.6 mS/cm) of the westernmost sites, is characterised by the presence of CH4-rich and mixed N2–CH4 gases. The second displays higher salinities (E.C. from 12 to 56 mS/cm) due to mixing with a modified marine component. Reservoir temperatures of 150–160 °C were estimated with cationic geothermometers at the easternmost sites.Along the graben, from west to east, the gas composition changes from CH4- to CO2-dominated through mixed N2–CH4 and N2–CO2 compositions, while at the same time the He isotopic composition goes from typical crustal values (<0.1 R/RA) up to 0.87 R/RA, showing in the easternmost sites a small (3–11%) but significant mantle input. The δ13C values of the CO2-rich samples suggest a mixed origin (mantle and marine carbonates).  相似文献   

15.
Understanding biogenic silica (bSi) dissolution kinetics in margin environments is important in assessing the global silicon cycle, a cycle closely linked to the global carbon cycle. This understanding is also essential to answer the question of whether bSi content in marine sediment is a valid indicator of productivity in the overlying surface ocean. In this study, plankton tow, sediment trap, and sediment samples were collected at sites in three Southern California borderland basins. Batch dissolution experiments with plankton tow and sediment trap materials (conducted in the laboratory at 22 °C) showed linear dissolution kinetics, from which mean dissolution rate constants of 0.05 d? 1 for plankton tow samples and 0.07 d? 1 for sediment trap samples could be calculated. The dissolution rate constants for both types of samples showed seasonal variability but not the same seasonal patterns. Faster dissolution was observed with sediment trap samples collected at 800 m than at 550 m. With sediment multi-core samples, non-linear dissolution kinetics was observed, which complicates the direct comparison of dissolution rates. Nonetheless, dissolution appeared to be slower for the sediments samples than for samples collected from the water column and to decrease with depth in the sediments. Rate constants for surface sediment (0–0.5 cm) were at least 3–5 times less, and sediments at depths > 2 cm had rate constants at least 6–13 times less than those for material sinking to the sediment surface at these sites. Dissolution experiments conducted with Santa Barbara Basin surface sediment samples amended with dissolved aluminum (Al) and San Pedro Basin trap samples amended with enriched detrital materials (obtained by leaching bSi from sediment samples) suggested that dissolution was inhibited by Al and that the sediments from the different basins varied in the extent of Al release.  相似文献   

16.
Euphotic zone plankton production (P) and respiration (R) were determined from the in vitro flux of dissolved oxygen during six latitudinal transects of the Atlantic Ocean, as part of the Atlantic Meridional Transect (AMT) programme. The transects traversed the North and South Atlantic Subtropical Gyres (N gyre, 18–38°N; S gyre, 11–35°S) in April–June and September–November 2003–2005. The route and timing of the cruises enabled the assessment of the seasonal variability of P, R and P/R in the N and S gyres, and the comparison of the previously unsampled N gyre centre with the more frequently sampled eastern edge of the gyre. Mean euphotic zone integrated rates (±SE) were P=63±23 (n=31), R=69±22 (n=30) mmol O2 m−2 d−1 in the N gyre; and P=58±26 (n=30), R=62±24 (n=30) mmol O2 m−2 d−1 in the S gyre. Overall, the N gyre was heterotrophic (R>P) and it was more heterotrophic than the S gyre, but the metabolic balance of both gyres changed with season. Both gyres were net heterotrophic in autumn, and balanced in spring. This seasonal contrast was most pronounced for the S gyre, because it was more autotrophic than the N gyre during spring. This may have arisen from differences in nitrate availability, because spring sampling in the S gyre coincided with periods of deep mixing to the nitracline, more frequently than spring sampling within the N gyre. Our results indicate that the N gyre is less heterotrophic than previous estimates suggested, and that there is an apparent decrease in R from the eastern edge to the centre of the N gyre, possibly indicative of an allochthonous organic carbon source to the east of the gyre.  相似文献   

17.
The total organic carbon (TOC) and total inorganic carbon (CT) exchange between the Atlantic Ocean and the Mediterranean Sea was studied in the Strait of Gibraltar in September 1997. Samples were taken at eight stations from western and eastern entrances of the Strait and at the middle of the Strait (Tarifa Narrows). TOC was analyzed by a high-temperature catalytic oxidation method, and CT was calculated from alkalinity–pHT pairs and appropriate thermodynamic relationships. The results are used in a two-layer model of water mass exchange through the Strait, which includes the Atlantic inflow, the Mediterranean outflow and the interface layer in between. Our observations show a decrease of TOC and an increase of CT concentrations from the surface to the bottom: 71–132 μM C and 2068–2150 μmol kg−1 in the Surface Atlantic Water, 74–95 μM C and 2119–2148 μmol kg−1 in the North Atlantic Central Water, 63–116 μM C and 2123–2312 μmol kg−1 in the interface layer, and 61–78 μM C and 2307–2325 μmol kg−1 in the Mediterranean waters. However, within the Mediterranean outflow, we found that the concentrations of carbon were higher at the western side of the Strait (75–78 μM C, 2068–2318 μmol kg−1) than at the eastern side (61–69 μM C, 2082–2324 μmol kg−1). This difference is due to the mixing between the Atlantic inflow and the Mediterranean outflow on the west of the Strait, which results in a flux of organic carbon from the inflow to the outflow and an opposite flux of inorganic carbon. We estimate that the TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from (0.97±0.8)104 to (1.81±0.90)104 mol C s−1 (0.3×1012 to 0.56×1012 mol C yr−1), while outflow of inorganic carbon ranges from (12.5±0.4)104 to (15.6±0.4)104 mol C s−1 (3.99–4.90×1012 mol C yr−1). The high variability of carbon exchange within the Strait is due to the variability of vertical mixing between inflow and outflow along the Strait. The prevalence of organic carbon inflow and inorganic carbon outflow shows the Mediterranean Sea to be a basin of active remineralization of organic material.  相似文献   

18.
Use of the quadratic shear-stress law for estimating boundary drag requires specific knowledge of the magnitude of a drag coefficient, CD, and sectional mean velocity, u?. In previous attempts to adapt the relationship for use in studies of marine-sediment transport, the flow measurement has been standardized at a level 100 cm above the bed. The particularized value of the drag coefficient has been designated as C100.In the entrance area to Chesapeake Bay, Virginia, C100 has been found to range through unacceptably wide limits. Two-thirds of the values obtained are between 3.5 · 10?3 and 5.4 · 10?2. Mean C100 for the area is 1.3 · 10?2 as compared to 3 · 10?3 for tidal channels within Puget Sound, Washington.Present data suggest that, given a moveable bed, a size hierarchy of mobile bed forms, time-varying flow, and a lack of equilibrium between flow and bed, C100 changes continuously with boundary shear stress.Accurate evaluation of boundary shear stress in tidal entrances with high flow rates and mobile beds presently requires measurement of velocity profiles.  相似文献   

19.
Nematodes are the most abundant metazoans of deep-sea benthic communities, but knowledge of their distribution is limited relative to larger organisms. Whilst some aspects of nematode processing techniques, such as extraction, have been extensively studied, other key elements have attracted little attention. We compared the effect of (1) mesh size (63, 45, and 32 μm) on estimates of nematode abundance, biomass, and body size, and (2) microscope magnification (50× and 100×) on estimates of nematode abundance at bathyal sites (250–3100 m water depth) on the Challenger Plateau and Chatham Rise, south-west Pacific Ocean. Variation in the effectiveness of these techniques was assessed in relation to nematode body size and environmental parameters (water depth, sediment organic matter content, %silt/clay, and chloroplastic pigments). The 63-μm mesh retained a relatively low proportion of total nematode abundance (mean±SD=55±9%), but most of nematode biomass (90±4%). The proportion of nematode abundance retained on the 45-μm mesh in surface (0–1 cm) and subsurface (1–5 cm) sediment was significantly correlated (P<0.01) with %silt/clay (R2=0.39) and chloroplastic pigments (R2=0.29), respectively. Variation in median nematode body weight showed similar trends, but relationships between mean nematode body weight and environmental parameters were either relatively weak (subsurface sediment) or not significant (surface sediment). Using a low magnification led to significantly lower (on average by 43%) nematode abundance estimates relative to high magnification (P<0.001), and the magnitude of this difference was significantly correlated (P<0.05) with total nematode abundance (R2p=0.53) and the number of small (≤250 μm length) individuals (R2p=0.05). Our results suggest that organic matter input and sediment characteristics influence the abundance of small nematodes in bathyal communities. The abundance of small individuals can, in turn, influence abundance estimates obtained using different mesh sizes and microscope magnifications.  相似文献   

20.
A total of 639 pink dentex Dentex gibbosus was collected in Canary Islands waters between April 1991 and September 1993. Total lengths ranged from 14,2 to 95,2 cm. Females dominated smaller size-classes and males the larger ones. The species was characterized by protogynous hermaphroditism. The overall ratio of males to females was 1 : 1,45. The reproductive period extended from April to September, spawning peaking in June/July. The total lengths at 50% maturity were 34,7 cm for females and 38,6 cm for males. The length-mass relationship for the whole sample can be described by the parameters a = 0,01014 and b = 3,0812. Fish aged 0–16 years were present in the samples. The parameters of the Von Bertalanffy growth equation were: L ∞ = 101,2 cm, k = 0,149·year?1, and t 0 = ?0,111 years. The rates of total mortality Z and natural mortality M were 0,57 and 0,28·year?1 respectively. Rates of fishing mortality F and exploitation E were 0,29 and 0,51·year?1 respectively. The estimated length at first capture (LC 50) was 17,8 cm total length.  相似文献   

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