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1.
The Cape rock lobster Jasus lalandii is a major predator in the inshore Benguela system. The mean density and biomass at Oudekraal is 0,48 individuals ·m?2 or 49,75 g dry mass ·m?2. The main component of its diet is Aulacomya ater, the ribbed mussel, which has a mean biomass of 1,15 kg dry mass ·m?2. Daily consumption of carbon and nitrogen from this source reaches a maximum in summer and, when J. lalandii feed on mussels, 14,1 per cent of the flesh is lost to the environment as a result of "messy feeding". The absorption efficiency of ingested nitrogen is 86,2 per cent. Ammonia and urea excreted in the first 12 h after feeding represent 6,7 and 1,6 per cent respectively of the nitrogen ingested. Endogenous nitrogen excretion has a mean rate of 1,9 μg N·g (dry mass)?1·h?1 The range of estimates for combined figures of kelp and phytoplankton nitrogen requirements are 76,4 – 86,7 g N·m?2·year?1 J. lalandii returns 6,3 g N·m?2·year?1 to the system, accounting for 7,2 – 8,2 per cent of annual kelp and phytoplankton requirements. This could be of particular importance during downwelling when the supply of new nitrogen is limited.  相似文献   

2.
We conducted a study that shows that light and dark conditions do not affect the uptake rates of ammonium and nitrate by the seagrass Zostera noltei. This is an important advantage over some seaweed species in which these rates are severely reduced at night. In the light, the ammonium uptake rates were initially higher (15 and 20 μmol·g?1·h?1) and stabilized at a rate of 5 μmol·g?1·h?1 after 1 h, whereas in the dark the rates remained constant at a rate of 10 μmol·g?1·h?1 over the first 180 min of incubation. The rates of nitrate uptake in the light were high within the first 120 min of incubation (7.2–11.1 μmol·g?1·h?1) and decreased afterwards to lower values (0.8–3.9 μmol·g?1·h?1), whereas in the dark the rates fluctuated around 0.0–11.1 μmol·g?1·h?1 throughout the whole incubation time (7 h). The soluble sugar content of Z. noltei leaves increased significantly with both ammonium and nitrate incubations in the light, indicating the metabolic outcome of photosynthesis. In the dark, there was no significant variation in either the soluble sugar or in the starch content of leaves, rhizomes or roots in either the ammonium or nitrate incubations. However, the total starch content of plants decreased at night whereas the total soluble sugars increased, suggesting a process of starch catabolism to generate energy with the consequent production of smaller monosaccharide products. The starch content of rhizomes decreased significantly during the light incubations with nitrate but not with ammonium. These results suggest that carbohydrate mobilization is necessary for Z. noltei to account for extra energetic costs needed for the uptake and assimilation of nitrate. Furthermore, our results suggest that nitrate uptake, at least during the day, requires the mobilization of starch whereas the uptake of ammonium does not.  相似文献   

3.
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   

4.
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   

5.
The tropical seagrass Halophila stipulacea is dominant in most regions of the Indo‐Pacific and the Red Sea and was introduced into the Mediterranean Sea after the opening of the Suez canal. The species is considered invasive in the Mediterranean Sea and has been progressively colonizing new areas westward. Growth and photosynthetic responses of H. stipulacea have been described but no information is yet available on the nitrogen nutrition of the species. Here we simultaneously investigated the uptake kinetics of ammonium and nitrate and the internal translocation of incorporated nitrogen in H. stipulacea using 15N‐labelled substrates across a range of Ni levels (5, 25, 50 and 100 μm ). The ammonium uptake rates exceeded the nitrate uptake rates 100‐fold, revealing a limited capacity of H. stipulacea to use nitrate as an alternative nitrogen source. The uptake rates of ammonium by leaves and roots were comparable up to 100 μm 15NH4Cl. At this concentration, the leaf uptake rate was 1.4‐fold higher (6.22 ± 0.70 μmol·g?1 DW h?1) than the root uptake rate (4.54 ± 0.28 μmol·g?1 DW h?1). The uptake of ammonium followed Michaelis–Menten kinetics, whereas nitrate uptake rates were relatively constant at all nutrient concentrations. The maximum ammonium uptake rate (Vmax) and the half‐saturation constant (Km) of leaves (9.79 μmol·g?1 DW h?1 and 57.95 μm , respectively) were slightly higher than that of roots (6.09 μmol·g?1DW h?1 and 30.85 μm , respectively), whereas the affinity coefficients (α = Vmax/Km) for ammonium of leaves (0.17) and roots (0.20) were comparable, a characteristic that is unique among seagrass species. No substantial translocation (<2.5%) of 15N incorporated as ammonium was detected between plant parts, whereas the translocation of 15N incorporated as nitrate was higher (40–100%). We conclude that the Ni acquisition strategy of H. stipulacea, characterized by a similar uptake capacity and efficiency of leaves and roots, favors the geographical expansion potential of the species into areas with variable water‐sediment N levels throughout the Mediterranean.  相似文献   

6.
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   

7.
Quantitative research on composition, biomass and production rates of zooplankton community is crucial to understand the trophic structure in coral reef pelagic ecosystems. In the present study, micro‐ (35–100 μm) and net‐ (>100 μm) metazooplankton were investigated in a fringing coral reef at Tioman Island of Malaysia. Sampling was done during the day and night in August and October 2004, and February and June 2005. The mean biomass of total metazooplankton (i.e. micro + net) was 3.42 ± 0.64 mg C·m?3, ranging from 2.32 ± 0.75 mg C·m?3 in October to 3.26 ± 1.77 mg C·m?3 in August. The net‐zooplankton biomass exhibited a nocturnal increase from daytime at 131–264% due to the addition of both pelagic and reef‐associated zooplankton into the water column. The estimated daily production rates of the total metazooplankton community were on average 1.80 ± 0.57 mg C·m?3·day?1, but this increased to 2.51 ± 1.06 mg C·m?3·day?1 if house production of larvaceans was taken into account. Of the total production rate, the secondary and tertiary production rates were 2.20 ± 1.03 and 0.30 ± 0.06 mg C·m?3·day?1, respectively. We estimated the food requirements of zooplankton in order to examine the trophic structure of the pelagic ecosystem. The secondary production may not be satisfied by phytoplankton alone in the study area and the shortfall may be supplied by other organic sources such as detritus.  相似文献   

8.
Phytoplankton productivity, community composition and biomass were determined over a nine-month period in brackish waters of the lower Gunpowder River, a tributary of Chesapeake Bay. Primary productivity followed expected seasonal magnitudes for temperate estuaries with rates exceeding 142·4 mg C m?3 h?1 in July through September 1979 and minimum rates of 1·6 mg C m?3 h?1 in February 1980. Annual primary production was estimated at 45·5 gC m?2. Cell numbers were highest in August, September and November with cyanophytes dominating the planktonic algae. Primary productivity, chlorophyll concentrations and cell densities were dominated by nanoplanktonic forms (< 10 μm) through-out the study. Phytoplankton carbon calculated from cells volumes exceeded nutritional requirements of the pelagic herbivores in all months suggesting a mean daily export (to the bay or sediments) of 1607 mg C m?3 d?1.  相似文献   

9.
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   

10.
Ichthyoplankton and microzooplankton were collected twice monthly for one year at a single station in Biscayne Bay, Florida. Based on approximate 10-m3, 333-μm mesh bongo net samples, the mean annual densities were 17·7 m?3 and 1·8 m?3 for fish eggs and larvae, respectively. Ichthyoplankton was most abundant in spring-summer. The most common fish larvae were bay anchovy (Anchoa mitchilli), spotted dragonet (Callionymus pauciradiatus), thread herring (Opisthonema oglinum) and gobies (Gobiidae), which comprised 50% of all larvae collected. A comparison of 35-μm and 333-μm mesh, bongo net collections revealed that mean densities of fish larvae were 8·5 times higher in the smaller mesh. The most abundant microzooplankton, based on 35-μm bongo net collections, were copepod nauplii, <100 μm in width, which averaged 90·41?1 and tintinnids which averaged 168·51?1. The mean density of microzooplankton <100 μm wide, potentially suitable food for first-feeding fish larvae, was 104·91?1, exclusive of tintinnids, and 273·41?1 including tintinninds. Excepting tintinnids, seasonal variability in microzooplankton abundance was low relative to that for ichthyoplankton. High microzooplankton densities, combined with low seasonal variability, indicated that feeding conditions for fish larvae were usually good in Biscayne Bay. Copepods, especially nauplii, were the predominant food of fish larvae (71% of all food items). Only mollusc veliger larvae (18% of all food items) were highly preferred prey but they were a small component of most larval fish diets. Average width of prey eaten by first-feeding larvae was 74 μm. Prey size increased in relation to larval length.  相似文献   

11.
Abstract. The secondary production and population dynamics of the mole crab Emerita brasiliensis Schmitt, 1935 (Decapoda: Hippidae) were studied by taking monthly samples from June 1993 to May 1995 at each of three intertidal transects at Prainha beach, Brazil. The lifespan was ca. 8 months for males and females, but females showed higher growth, mortality, secondary production, and turnover rate. The higher production in spring versus autumn and winter was related to intense recruitment during that period. The population production was estimated at between 39.86 and 46.88 g (AFDW) · m?2 · a?1 for the first year (June 93–May 94) and between 150.95 and 156.07 g (AFDW) · m?2 · a?1 for the second year (June 94–May 95); the mean annual biomass was 4.91 and 23.09 g (AFDW) · m?2, respectively. High P/B rates, between ca. 6 and 9 · a?1, reflected the fast growth, high mortality, and low lifespan of the population, characterized by a high percentage of recently recruited individuals.  相似文献   

12.
To test the effects of site and successional stage on nitrogen fixation rates in salt marshes of the Venice Lagoon, Italy, acetylene reduction assays were performed with Salicornia veneta‐ and Spartina townsendii‐vegetated sediments from three restored (6–14 years) and two natural marshes. Average nitrogen fixation (acetylene reduction) rates ranged from 31 to 343 μmol C2H4·m?2·h?1 among all marshes, with the greatest average rates being from one natural marsh (Tezze Fonde). These high rates are up to six times greater than those reported from Southern California Spartina marshes of similar Mediterranean climate, but substantially lower than those found in moister climates of the Atlantic US coast. Nitrogen fixation rates did not consistently vary between natural and restored marshes within a site (Fossei Est, Tezze Fonde, Cenesa) but were negatively related to assayed plant biomass within the acetylene reduction samples collected among all marshes. Highest nitrogen fixation rates were found at Tezze Fonde, the location closest to the city of Venice, in both natural and restored marshes, suggesting possible site‐specific impacts of anthropogenic stress on marsh succession.  相似文献   

13.
Three harmful algal bloom (HAB) species, Phaeocystis globosa, Thalassiosira rotula, and Proro-centrum donghaiense were isolated from the coast of China and cultured in batches at three light intensities (40, 70 and 150 μmol photons·m-2·s-1). The variation patterns of cell numbers and growth rates with light intensity during growth process were different among species. In P. globosa and T. rotula, maximum growth rates were found at 150 μmol photons·m-2·s-1 and ranged from 0.60 divisions per day in T. rotula, to 1.17 divisions per day in P. globosa. The highest growth rate of P. donghaiense, however, was found at 70 μmol photons·m-2·s-1 (0.36 divisions per day). In general, all the three HAB species showed adaptation to increasing light intensity by decreas-ing cellular concentrations of chlorophyll a (Chl a), but the variation patterns during the growth process were species-specific. The cellular concentrations of Chl a in P. donghaiense and T. rotula increased gradually with incubation time, but the opposite trend was found in P. globosa. Most of the pigment ratios and pigment indices of these three species were nearly constant during the growth process and showed small changes at different light intensities illustrating the applicability of chemotaxonomy during the initial and developing stages of HAB events, which is very important to study the ecological issues related to HAB species. Ratios of photoprotective carotenoids, such as diadinoxanthin, diatoxanthin and β,β-carotene to total chlorophylls a (Tchl a) showed the trend of increasing with the increase of light intensity during growth process. The species-specific and pigment-specific variations in pigment ratios/indices at different light intensities during growth pro-cess probably reflected the differences in the pigment composition as well as the adaption capabilities of different species to the changes of physical conditions.  相似文献   

14.
Porites panamensis is a hermatypic coral present in the eastern Pacific Ocean. Skeletal growth parameters have been reported, but studies of the relationship between annual calcification rates and environmental controls are scarce. In this study, we investigated three aspects of the annual calcification rates of P. panamensis: growth parameters among three P. panamensis populations; the sea surface temperature as a calcification rate control spanning a latitudinal gradient; and calcium carbonate production among three sites. Growth parameters varied among the sites due to the colony growth form. Massive colonies in the north showed a higher calcification rate than encrusting colonies in the south (mean: 1.22–0.49 g CaCO3 · cm?2 · yr?1), where variations in calcification rates were related to growth rate (0.91–0.38 cm · yr?1) rather than to skeletal density differences (overall mean ± SD, 1.31 ± 0.04 g CaCO3 · cm?3). Our results showed a positive linear relationship between annual calcification rates and sea surface temperatures within these P. panamensis populations. Differences were related to distinct oceanographic environments (within and at the entrance of the Gulf of California) with different sea surface temperature regimes and other chemical properties. Different populations calcified under different environmental conditions. Calcium carbonate production was dependent upon the calcification rate and coral cover and so carbonate production was higher in the north (coral cover 12%) than in the south (coral cover 3.5). Thus, the studied sites showed low calcium carbonate production (0.25–0.43 kg CaCO3 · m?2 · yr?1). Our results showed reduced calcification rates, regional temperature regime control over calcification rates, different growth forms, low coral cover and low calcium carbonate production rates in P. panamensis.  相似文献   

15.
Available data on phytoplankton and bacterial abundance and production off the coasts of southern Africa (to the 500 m depth contour) have been assembled and analysed for a network analysis of carbon flow in the Benguela ecosystem. Phytoplankton carbon biomass (from measurements of chlorophyll a) in the northern Benguela (2 558 300 tons) was considerably higher than in the southern Benguela (671 420 and 516 400 tons for the West and South coasts respectively). However, overall annual production (from C14-uptake measurements) was similar, 77 416 608, 76 399 973 and 78 988 020 tons C·year?1 respectively. Phytoplankton respiration and sedimentation losses were calculated as functions of primary production and therefore followed similar trends. From the most conservative estimates (mean bacterial biomass of 10 mg C·m?3 and average P:B of 0,2·day?1) bacterial biomass is 2–7 per cent of phytoplankton biomass in the northern and southern Benguela, and bacterial production is 3–5 per cent of primary production. Assuming a net growth yield of 30 per cent, bacteria would need to consume 9–15 per cent of the total primary production in order to meet their requirements for carbon consumption. Calculations based on a mean bacterial biomass of 40 mg C·m?3 and a mean growth rate of 0,5·day?1 in the upper 30 m of the water column show bacterial biomass to be 8–27 per cent of phytoplankton biomass and bacterial production to be 26–44 per cent of phytoplankton production. Bacterial carbon consumption requirements at these rates amount to 86–147 per cent of total primary production.  相似文献   

16.
With a view to utilize local algae as food organisms in mariculture, the green alga Chlamydomonas plethora and the diatom Nitzschia frustula were isolated and studied from the unique coastal waters arid zone off Kuwait. Batch cultures of C. plethora and N. frustula had maximum division rates (μmax) of 2.5 and 3.4 day?1, respectively. Cultures grown for 36 h yielded comparable growth rates. Photosynthesis‐irradiance relationships in cultures harvested at various phases of growth showed that cultures attained log phase after 1‐day growth and yielded the highest assimilation numbers (P: μg C [μg Chl a]?1 h?1): 22.8 for C. plethora and 18.1 for N. frustula. Their initial slopes (αB: ng C [μg Chl a]?1 h?1 [μmol m?2 s?1]?1 were also the highest observed so far: 79.5 for C. plethora and 39.6 for N. frustula. Photoinhibition was low. Compared with these, assimilation numbers in senescent cultures of 20‐day growth were <8% of the maximum for both species, and the initial slope decreased to 17 and 13% in C. plethora and N. frustula, respectively. Two polyunsaturated fatty acids (20:5n‐3 eicosapentaenoic acid and 22:6n‐3 docosahexaenoic acid) that are essential in many marine animal diets constituted up to 24% and 1.9% of the total fatty acids, respectively. Of the two algae, N. frustula contained higher levels of 16:1n‐7, 20:5n‐3 and comparatively low levels of 22:6n‐3 fatty acids. Due to its rapid growth, high photosynthetic rate and presence of the amino acids leucine, lysine, glutamic acid and arginine N. frustula has good potential as a feed organism in mariculture applications. The capacity of these algae to produce a wide range of size groups (nano and net plankton) is an additional bonus for mariculture operations.  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.
We present the results of the first study to highlight the demography, morphometry and growth rates of Spinimuricea klavereni, a rare Mediterranean endemic gorgonian exceptionally common in shallow depths of the Northeast Marmara Sea. In the study area, this species forms vast populations on rocks, boulders and attached to pebbles/stones/shells on soft substrates between 20 and 45 m depth, with a total average density of 0.3 colonies·m?2 but comprising patches up to 3 colonies·m?2. Colonies, which are on average 42.9 (±20.1) cm in height, can reach up to 110 cm. Unlike other Mediterranean gorgonians, the colonies studied here showed fast growth rates that decreased with increasing colony height, between 1.5–11.1 and 4.96 ± 3.01 cm·year?1 on average. The low necrosis and high growth rates displayed by this species in the Northeast Marmara Sea confirm the previously hypothesized opportunistic behaviour of the species. The unique community consisting of S. klavereni and other rare gorgonian/soft corals has limited distribution in this area and should be considered to be a vulnerable marine ecosystem. Therefore we recommend that some conservation measures are taken, including the prohibition of all fisheries and anchoring over these assemblages.  相似文献   

19.
Abstract

Nitrogen fixing potential was measured in summer 1975 by acetylene reduction in situ at 5 stations on the intertidal flats of the Waimea Inlet, Nelson, New Zealand, which receive nutrients from several sources. Highest values (644 μmol?m?2.d?1) were obtained on sediments near an apple cannery effluent discharge and were linear through at least two tidal cycles. The cannery waste had the highest carbon to nitrogen ratio (10.3 : 1.0) of all the effluents examined and exhibited the highest rate of acetylene reduction (14.0 μmol?‐l?1.d?1). Sizeable populations of the nitrogen fixing bacteria Klebsiella pneumoniae were isolated from the cannery effluent (2 × 104 per millilitre) and also from the mud adjacent to the discharge pipe (5 × 105 per millilitrc). The stimulatory effect of the cannery effluent on nitrogen fixation in the sediment was shown to be restricted to close to the discharge point. Sediments in areas affected by slaughterhouse and sewage effluents exhibited the second and third highest rates of acetylene reduction, (130 &; 28 μmol?m?2.d?1 respectively). In both places, the activities were not restricted to the immediate vicinity of the effluent channels. Nitrogen fixation was lowest in sediments fronting a catchment of grazed pasture. Fixation was low also in sediments affected by effluents from the hydraulic debarker of a woodchip mill.  相似文献   

20.
Diel feeding pattern and food consumption of whitemouth croaker (Micropogonias furnieri) were examined and related to seasonal variations in an estuarine environment. To determine diel feeding pattern whitemouth croaker were collected from the Patos Lagoon Estuary over 24 h (～3‐h intervals) and their stomach contents were examined. Food consumption of whitemouth croaker was determined from evacuation rates estimated experimentally and in the field. The results suggested that whitemouth croaker in the Patos Lagoon estuary feed all day long. However, whitemouth croaker showed higher feeding intensity and food consumption during daylight hours when the water transparency increased than in others when water transparency was low. Thus, whitemouth croaker seemed to intensify their feeding when they could see their prey. Daily food consumption was between 0.9 and 5.3% of body wet weight (these being the lowest and highest consumption rates during the winter and summer, respectively). The maximum predation impact of whitemouth croaker on their preferential prey, the tanaid Kalliapseudes schubartii, was 27indiv·m?2·day?1. The results suggested that the changes in water transparency seem to affect the diel feeding pattern and food consumption of whitemouth croaker. This could have important consequences for fish growth.  相似文献   

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