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1.
Hydration, ion-water interactions, and water structure effects in seawater were studied by determining differences (Δβ) between the compressibilities of test salt solutions and the compressibilities of reference solutions. The reference solutions were distilled water and seawater (35%0), and the test salt solutions were either 0.13 m or 0.26m with respect to one of the following test salts: LiCl, NaCl, KCl, CsCl, NaF, NaI, MgCl2, CaCl2, BaCl2, Na2SO4, K2SO4, and MgSO4. The compressibility measurements (to 900 bars) were carried out at 2°C and also at 15°C using a differential method in which a pressure increase or a temperature increase causes Δβ to become less negative. At 1 bar and 15°C, the Δβ (0.26 m, distilled water reference) values ranged from ?1.14 × 10?6 bar? for NaI to ?3.84 × 10?6 bar?1 for Na2SO4, and the Δβ (0.26 m, seawater reference) values ranged from ?1.30 × 10?6 bar?1 for NaCl to ?3.04 × 10?6 bar?1 for Na2SO4. The Δβ values were used to calculate hydration numbers. Entropy of transfer, excess hydrogen bond breaking (determined by NMR), and effective radii of ions are properties which can be used to describe the influence of ions on water structure. The extent to which these properties correlate with Δβ values depends upon whether the ion is an anion or a cation, and this correlation forms the thesis that anions alter water structure in a different way than do cations.  相似文献   

2.
Chemical extraction techniques show that the majority of the arsenic in North Atlantic deep-sea sediments is associated with an iron phase compositionally similar to that found in deep-sea ferromanganese nodules (As/Fe ～ 11 · 10?4) and is probably of seawater origin. Some sediments also contain As associated with Fe oxides produced by continental weathering. A minority (～8%) of the arsenic is of detrital origin but is not associated with Fe or Mn oxides; it has a content (1.7 ppm) similar to the average crustal abundance. In the Eastern Mediterranean Sea, near-shore sediments contain As associated with land-derived Fe oxides (As/Fe ～ 2 · 10?4), but As/Fe ratios increase to ～ 13 · 10?4 in deep-sea sediments as the contribution of seawater derived arsenic becomes dominant. Arsenic is enriched in metalliferous sediments (As/Fe ～ 20?50 · 10?4) but As/P ratios of metalliferous sediments, deep-sea ferromanganese nodules and deep-ocean water are all similar. Although a hydrothermal contribution cannot be discounted, it is likely that the arsenic is also of seawater origin, suggesting that hydrothermal iron oxyhydroxides remove As more efficiently from seawater than do iron phases (goethite) in deep-sea sediments and nodules. Arsenic accumulates in deep-sea sediments (～ 6 μg cm?2 10?3 yr?1) at sediments (～ 120 μg cm?2 10?3 yr?1) at rate sufficient to balance river input input (～3 · 1010 g yr?1). These estimates give an oceanic residence time for arsenic of 1–2 · 105 yr.  相似文献   

3.
From July 1981 to July 1982 Umbonium vestiarium (L.) on a north Penang sand shore numbered 573–11 077 m?2 (mean 4126 or 53·1 g dry tissue) near MLWN and 2164–12 414 m?2 (mean 6500 or 59·8 g dry tissue) further downshore. Heavy recruitment of young became evident in June and July 1982 and a closely corresponding cohort of young was present in July 1981. Progression of this cohort indicated that young settling in May–June grew to full size (11–13 mm diameter) by January–March the following year and that virtually all died during their second year, presumably having spawned in March–May. Recruitment of young was chiefly on the lower shore but adults came to be more abundant and predominant on the upper shore. There is some evidence of migration upshore during growth.Production is estimated at 105·4 g dry tissue m?2 y?1 (2118 kj) at the lower shore level and this is almost double the 58·8 g m?2 y?1 (1176·6 kj) at the higher level. These values represent almost the entire secondary production across much of the sand flats.Possible causes of such a marked annual cycle in the very weakly seasonal tropics of the Malacca Strait are considered and it is suggested that monsoonal changes in wind, wave action and salinity might be involved.  相似文献   

4.
A method for the determination of barium in sea water was investigated using inductively coupled plasma emission spectrometry, and sea water samples from the Japan Sea and the Pacific Ocean were directly analyzed by this method. Artificial sea water was used to prepare matrix matched standard solutions to overcome the problem of physical interference. The detection limit (signal/noise ratio=2) for barium in deionized and distilled water was 0.08µg l?1 and in sea water, 0.12µg l?1. The reproducibilities in the purified water and in the sea water at the 10µg l?1 level were 0.7% a#FFFFFFnd 0.5%, respectively. The barium concentration in both the Japan Sea and the Pacific Ocean increased with depth and ranged between 5.5–10.0µg l?1 and 4.1–18.4µg l?1, respectively.  相似文献   

5.
In order to characterize our study area and to provide reference values to be used in the future to measure the changes produced by an increase in contamination, the concentrations of chlorinated hydrocarbons have been investigated in fifty-one samples of seawater, taken at four different depths: air-sea interface, surface, one metre and bottom waters, and in twenty-three samples of surface sediments from Blanca Bay, Argentina. Of eleven organochlorine compounds we were looking for (α BHC, lindane, heptachlor, δ BHC. aldrin, heptachlor epoxide, dieldrin, o-p′DDD, p-p′DDD, o-p′DDT and p-p′DDT), seven could be detected in seawater and three in surface sediments with the following mean concentrations: α-BHC=48·2 ng l?1; lindane=54·2 ng l?1; heptachlor=45·0 ng l?1; δ BHC=12·5 ng l?1; aldrin=61·8 ng l?1 and ΣDDT=67·0 ng l?1; and δ BHC=3·2 ng g?1; lindane=4·2 ng g?1 and heptachlor=1·0 ng g?1 for seawater, regarding the surface waters, and sediment samples, respectively.Concentration factors among the different water layers were also studied to see if there was any correlation between chlorinated hydrocarbon contents and the water depths from which the samples were taken. As a mean value, the air-sea interface water contains 18 times more of these compounds than that of the water near the bottom. A comparison of the values corresponding to seawater and surface sediments from our study area with those levels measured in samples from other geographic locations is also presented.With the purpose to detect a relationship between chlorinated hydrocarbon concentrations and the contents of particulate matter (PM) on the one hand, and particulate organic material (POM) on the other hand, four groups of samples containing different amounts of PM and POM, respectively were formed. From a comparison of the results obtained, lindane, heptachlor and δ BHC showed a tendency to lower concentrations in those samples containing little PM whereas α BHC and aldrin remained without important changes. No significant correlation was found between organochlorine levels and contents of POM.  相似文献   

6.
Application of a simple model describing regional variations in the contents of manganese and associated minor metals in deep-sea sediments suggests that solid manganese phases are being removed from the <0.5 μm fraction of seawater at ～1–7 · 1012g yr?1 in excess of the rate of stream-supplied manganese. This flux is consistent with: (1) the relative rates of sediment accumulation in the Atlantic and Pacific Oceans; (2) the contrast between the oceanic residence time of manganese calculated from stream-supply data (14 · 103 yr) and from the flux of manganese precipitating in marine sediments or as manganese nodules (0.38–2.4 · 103 yr); (3) the surplus mass of manganese revealed by geochemical balance calculations (22.9 · 102g). On this basis excess manganese is accumulating in deep-sea sediments at 0.2–2.0 · 10?6 g cm?2yr?1. Manganese supplied to the upper layers of marine sediments by diagenesis has been evaluated with the aid of vertical advection—diffusion—reaction models. The calculated diagenetic flux of manganese at the sediment surface in a near-shore environment is in agreement with the known accretion rate of manganese deposits (1.7 · 10?2 g cm?2 10?3 yr?1) and the regionally variable flux over the area assessed is consistent with the presence or absence of manganese nodules at or near the water-sediment interface. The diagenetic flux at the surface of deep-sea sediments has been calculated at 0.7 · 10?4 g cm?2 10?3 yr?1 when the upper, oxic, zone of the sediment is ～20 cm thick. A limiting factor on the in situ production flux of dissolved manganese in deep-sea sediments appears to be the availability of reducing agents for manganese dissolution rather than the rate of downward transport of manganese-rich sediment to a reaction boundary where dissolution takes place. Various estimates of the rate of upward-migrating manganese suggest that manganese precipitates in the oxic zone with a rate constant of ～10?7 sec?1 with the result that diagenetic processes cannot supply the flux of excess manganese through more than ～0.25 m of oxic sediment. However, estimates of the flux of manganese to the oceans by submarine volcanic processes (0.79–1.1 · 1012g yr?1) are similar to the surplus mass of manganese detected by geochemical balance calculations (0.7 · 1012g yr?1). If submarine hydrothermal solutions provide only 10% of this excess then their computed discharge rate (39 g cm?2 yr?1) and residence time in the upper layer of oceanic crust (130,000 yr) agree well with these parameters for continental thermal springs.  相似文献   

7.
The flux of ammonia, phosphate, silica and radon-222 from Potomac tidal river and estuary sediments is controlled by processes occurring at the sediment-water interface and within surficial sediment. Calculated diffusive fluxes range between 0·6 and 6·5 mmol m?2 day?1 for ammonia, 0·020 and 0·30 mmol m?2 day?1 for phosphate, and 1·3 and 3·8 mmol m?2 day?1 for silica. Measured in situ fluxes range between 1 and 21 mmol m?2 day?1 for ammonia, 0·1 and 2·0 mmol m?2 day?1 for phosphate, and 2 and 19 mmol m?2 day?1 for silica. The ratio of in situ fluxes to diffusive fluxes (flux enhancement) varied between 1·6 and 5·2 in the tidal river, between 2·0 and 20 in the transition zone, and from 1·3 to 5·1 in the lower estuary. The large flux enhancements from transition zone sediments are attributed to macrofaunal irrigation. Nutrient flux enhancements are correlated with radon flux enhancements, suggesting that fluxes may originate from a common region and that nutrients are regenerated within the upper 10–20 cm of the sediment column.The low fluxes of phosphate from tidal viver sediments reflect the control benthic sediment exerts on phosphorus through sorption by sedimentary iron oxyhydroxides. In the tidal river, benthic fluxes of ammonia and phosphate equal one-half and one-third of the nutrient input of the Blue Plains sewage treatment plant. In the tidal Potomac River, benthic sediment regeneration supplies a significant fraction of the nutrients utilized by primary producers in the water column during the summer months.  相似文献   

8.
Oxy-anionic species of V, As, Se, Mo, Sb, Te and W were measured in solution and suspension in samples obtained during several cruises in the Dutch Wadden Sea, the offshore region of the Southern Bight (North Sea) and in the estuaries of the Rhine and Scheldt. Dissolved concentrations at salinities above 34·5 × 10?3 ( = 34·5%. S) agreed generally well with published open ocean values. It is suggested that Se speciation differs from the open ocean.In the Wadden Sea, concentrations of V, Se, Mo and Sb were linearly related to salinity (10–35 × 10?3). The good agreement between measured and extrapolated values at a salinity of 0·5 × 10?3 suggests conservative behaviour in the Rhine estuary (with residence time of freshwater in the order of a few days).Dissolved concentration vs. salinity plots in the Scheldt estuary (residence time 2–3 months) showed pronounced minima and maxima. These occurred in the low or medium salinity range for V, As and Sb. Linear behaviour was observed for Se and Mo (in some cases, relatively large differences between cruises were detected). Deviations from linearity in the plots are interpreted in terms of thermodynamic equilibrium conditions involving species with different solubilities (V), local input from land (As, Se, Sb, Te) and removal from solution (As), probably through coprecipitation with Fe(OH)3.In the offshore samples, the contributions of particulate forms to the total element concentrations were small (<15%). At higher SPM concentrations (about 30 mg dm?3), this percentage remained small for Se, Mo and Sb (<15%); it was substantial for V and As (25–50%).  相似文献   

9.
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   

10.
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   

11.
The ocypodid crab, Dotilla myctiroides, was studied on the south-west coast of peninsular Malaysia. The mean numbers and biomass over a year along a transect from high to low water ranged from 37·5 to 579 crabs m?2 and from 2·22 to 50·79 g m?2 (wet weight) respectively. Berried females were found in all months of the year but two peaks of activity were apparent, from November to February and May to July. It is suggested that this may be related to changes in food abundance associated with the effects of monsoon winds on sea currents. Laboratory growth studies indicated that maximum life span was approximately 13 months (from first crab stage) for males and 10 months for females. Growth rate decreased with increasing size of crab. Egg number increased with size of female.  相似文献   

12.
The concentrations of the trace metals Cd, Cu, Fe, Ni, Pb and Zn in the Göta River estuary have been investigated. The following metal fractions have been determined: acid-leachable, dissolved, labile and particulate.The estuary represents a salt wedge type estuary and is situated in a densely populated region of Sweden. The metal concentrations found for the dissolved fraction is in the range of what can be considered as background levels for freshwater. It is difficult to evaluate any estuarine processes other than conservative mixing for Cd, Cu, Ni and Zn. The dissolved levels in the freshwater end member are Cd, 9–25 ngl?1; Cu, 1·1–1·4 μgl?1; Fe, 20–75 μg l?1: Ni, 0·7–0·9 μg l?1: Pb 0·09–0·2 μg l?1; and Zn, 6–7 μg l?1:The results from the acid-leachable fraction show that at high suspended load the particles sediment in the river mouth. The trace metal levels in this fraction are subject to large variations.  相似文献   

13.
Concentrations of mercury were determined for the waters, suspended matter and sediments of the Tagus and of major French estuaries.The Tagus estuary is one of the most contaminated by mercury derived from the outfalls of a chloralkali plant and from other industrial sources. In deposited sediments the median level, 1·0 μg Hg g?1, is twenty times higher than the natural background and Hg contents depend on the sediment grain-size, age and the distance from waste-outfalls. Suspended matter is more regularly and highly contaminated (median value: 4·5 μg Hg g?1). In the French estuaries Hg levels in the suspended material decrease with salinity due to dilution and/or remobilization processes. In June 1982, in the Loire estuary, high values of Hg are observed in the middle estuary and attributed to urban and industrial sources.In the Tagus estuary, the general distribution of total dissolved Hg confirms the contamination: it increases seaward from 10 ng 1?1 in the river to 80 ng 1?1 in the estuary outlet. The dissolved Hg is almost totally organic in the river, inorganic in the middle estuary due to inorganic Hg effluents and again organic in the lower estuary. This variation is related to the dissolved organic carbon values. The dissolved Hg levels in the Loire Estuary (5–300 ng 1?1) are much higher than in the Gironde estuary (3–6 ng 1?1) and of the same order as those observed in the Tagus estuary.  相似文献   

14.
Particulate nitrogen (PN) and chlorophyll a (Chla) were measured in the northern reach of San Francisco Bay throughout 1980. The PN values were calculated as the differences between unfiltered and filtered (0·4 μm) samples analyzed using the UV-catalyzed peroxide digestion method. The Chla values were measured spectrophotometrically, with corrections made for phaeopigments. The plot of all PNChla data was found to be non-linear, and the concentration of suspended particulate matter (SPM) was found to be the best selector for linear subsets of the data. The best-fit slopes of PNChla plots, as determined by linear regression (model II), were interpreted to be the N: Chla ratios of phytoplankton. The Y-intercepts of the regression lines were considered to represent easily-oxidizable detrital nitrogen (EDN). In clear water ( < 10 mg l?1 SPM), the N: Chla ratio was 1·07 μg-at N per μg Chla. It decreased to 0·60 in the 10–18 mg l?1 range and averaged 0·31 in the remaining four ranges (18–35, 35–65, 65–155, and 155–470 mg l?1). The EDN values were less than 1 μg-at N l?1 in the clear water and increased monotonically to almost 12 μg-at N l?1 in the highest SPM range. The N: Chla ratios for the four highest SPM ranges agree well with data for phytoplankton in light-limited cultures. In these ranges, phytoplankton-N averaged only 20% of the PN, while EDN averaged 39% and refractory-N 41%.  相似文献   

15.
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   

16.
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   

17.
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   

18.
By simulating an upwelling event in a laboratory microcosm, it was possible to promote the development of a natural and diverse planktonic community. An initial bacterioplankton community which developed in response to phytoplankton growth was dominated by small coccoid forms (0,14–0,2 μm3) of the genera Vibrio and Pseudomonas. This group was heavily exploited by the heterotrophic microflagellate Pseudobodo sp. (30 μm3). Later, the bacterioplankton community was dominated by large rods (0,7 μm3) which the flagellates seemed unable to exploit. A Lotka-Volterra predator-prey model fitted to the observed data indicated that the flagellates consumed 2,4 times their carbon body mass per day or 19 bacteria·flagellate?1·h?1 when prey were not limiting. Clearance rates were inversely proportional to prey density and ingestion rate, ranging from 2 × 10?3 to 20 × 10?3) μ?·flagellate?1·h?1. At typical field densities of bacteria and heterotrophic flagellates in the southern Benguela region, between 5 and 30 percent of the water column could be cleared per day. Specific growth rates of the flagellates were positively related to prey density, the maximal rate being 0,84 · d?1. Their initially faster growth rates allowed bacteria to increase in numbers despite predation. The growth yield of the flagellates (34–36 per cent) was also positively related to food density. Such low values suggest inefficient transfer of carbon to higher trophic orders but considerable nitrogen regeneration. Nitrogen excretion rates were approximately 6–7 μg N·mg dry weight?1·h?1, comparable to other flagellates but faster than ciliates. These rates are comparable with in situ measurements of NH+4-N excretion in pycnoclinal regions based on 15N isotope studies but are only about 20 per cent of measured rates in surface waters. This is interpreted to mean that, in pycnoclinal regions where the relative input of "new" nitrogen is high, there are few regenerative steps and the model describes them satisfactorily. In surface waters, observed rates of excretion can only be accounted for by many regenerative steps in a highly complex food chain in which the cumulative total of nitrogen excretion at each step amounts to that based on 15N labelling studies.  相似文献   

19.
The nitrogen relations of Enteromorpha spp. growing on intertidal mud flats have been examined over a twelve-month period. Nitrogen assimilation rates using 15N have been used to calculate the production of the alga and were between 0·046 and 0·217 mg NH4+N (g dry wt alga)?1 h?1 A considerable quantity of the alga was buried beneath the sediment over the growth season and was calculated to be equivalent to an input of up to 9·52 g N m?2 per month and 32 g N m?2 over one complete growth season. Based on carbon, this latter value represented an input of approximately 320 g C m?2 annually. Low rates of nitrogenase activity (acetylene reduction) were found to be associated with the Enteromorpha. The organisms responsible for the nitrogenase activity were probably heterotrophic bacteria but they did not contribute significant quantities of nitrogen to the alga.  相似文献   

20.
Anchovy biomass and copepod standing stocks and growth rates on the Agulhas Bank were compared during the peak spawning period (November) in 1988 and 1989. In 1988, copepod biomass over the western Agulhas Bank was low (1,0 g dry mass·m?2) relative to anchovy biomass there (14,7 g dry mass·m?2). In November 1989 in the same area, fish biomass was much lower (5,7 g dry mass·m?2), following a recruitment failure, and copepod biomass was higher (2,4 g dry mass·m?2), possibly as a result of lesser predation by anchovy. By contrast, the eastern Agulhas Bank had a larger biomass of copepods (4–6 g dry mass·?2) and a lower biomass of anchovy during both years. Knowing, from laboratory studies, that a prey biomass of 0,78 g·m?2 is required for fish to obtain their daily maintenance ration, it is suggested that spawning on the western Agulhas Bank was food-limited in 1988. Copepods on the western Bank may be replaced by local growth or transport from the eastern Bank. Growth rates of copepods on the western Bank were 10–50 per cent of maximum in 1988, but total production (c. 100 mg dry mass·m?2·day?1) was low, primarily because biomass was low and less than the rate of consumption by anchovy (243 mg copepod dry mass·m?2·day?1). On the eastern Bank, copepod production exceeded anchovy consumption and it is concluded that the flux of copepod biomass onto the western Bank may be as important as local growth in replenishing copepod stocks there. Feeding conditions for anchovy on the western Agulhas Bank are often marginal compared to the situation on the eastern Bank, and it is suggested that the selection of the western Bank as the major spawning area is related more to the success of transport and survival of eggs and larvae on the West Coast recruiting grounds than to feeding conditions per se.  相似文献   

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