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1.
Sea-spawned saury eggs collected 20 km off the west coast of the Cape Peninsula were hatched in laboratory tanks and the larvae reared. The larvae were fed initially on nauplii of cultured copepods, Tisbe holothuriae Humes and Pseudodiaptomus hessei (Mrázek). Growth rate during the first 47 days post-hatch averaged 0,62 mm·day?1 (at 18—19°C) and between the 47th and 120th day averaged 0,45 mm·day?1 (at 14,8—15,5°C). Some observations on feeding behaviour are included.  相似文献   

2.
Although the size distribution of larvae and early juveniles of the saury Scomberesox saurus scombroides in continental shelf waters off the Cape Province, South Africa, is consistent with a south-north passive dispersal by known currents, the size of late juveniles and adults increases from north-west to south-east. Occurrence of these stages is highly seasonal: they are found in summer off the Western Cape and mainly from late summer to winter in Algoa Bay in the Eastern Cape, possibly reflecting longitudinal migration. Large numbers of late juveniles and adults are often found downstream of upwelling plumes off the Western Cape when warmer waters lie close inshore. They are sometimes taken in purse-seines in association with adult round herring Etrumeus whiteheadi and pilchard Sardinops ocellatus. Important predators of late juvenile and adult saury are fast-moving, surface-feeding species: yellowfin tuna Thunnus albacares, Cape gannet Morus capensis and Cory's shearwater Calonectris diomedea. Cape gannets consume an estimated 2 277–6 044 tons of saury annually in South African waters. Predator diets provide important time-series of occurrence, abundance and length-frequency distributions of late juvenile and adult saury.  相似文献   

3.
Roving creel surveys and aerial surveys of shore-angling were undertaken as part of a national investigation into linefishing in South Africa. Shore patrols utilized a random stratified sampling procedure to collect catch-and-effort data, and a questionnaire provided information on fishing effort, angler demographics, economics and attitudes towards current regulations. A total of 1 677 patrols, covering 19 616 km, was conducted between April 1994 and February 1996, during which period 9 523 anglers had their catches checked and 4 490 were interviewed. A further 16 497 km were covered by aerial surveys, when 22 609 anglers were counted. From the aerial surveys, angler densities were highest on the KwaZulu-Natal coast (4.65 anglers·km?1), followed by the Southern Cape coast (2.29 anglers·km?1), the Eastern Cape coast (0.36 anglers·km?1) and the West Coast (0.12 anglers·km?1). Catch rates varied from 1.5 kg·angler?1·day?1 on the Southern Cape coast to 0.45 kg·angler?1·day?1 on the KwaZulu-Natal coast. Total effort was estimated at 3.2×106 angler days·year?1 and the total catch was estimated at 4.5×106 fish·year?1 or 3 000 tons·year?1. Targeted species varied regionally, with elf Pomatomus saltatrix (29%) being the most sought after species on the KwaZulu-Natal coast, kob Argyrosomus japonicus (18%) on the Eastern Cape coast and galjoen Dichistius capensis on the Southern Cape coast (30%) and along the West Coast (50%). The catch composition by mass was dominated by P. saltatrix on the KwaZulu-Natal coast (29%), the Eastern Cape coast (26%), and on the Southern Cape coast (56%) and by white stumpnose Rhabdosargus globiceps (40%) on the West Coast. Although anglers generally supported the regulations currently governing the linefishery, the questionnaire results showed that knowledge and compliance of them was poor. A low level of law enforcement was found, except for in KwaZulu-Natal. Management of the linefishery is discussed in relation to the findings of this study.  相似文献   

4.
The results of ichthyoplankton surveys carried out by the Instituto Nacional de Pesca (INAPE) in the Argentine–Uruguayan Common Fishing Zone (AUCFZ) in summer 1980 and the winters of 1980–1982 are presented. In addition, the results of joint research with INIDEP, the Argentine and Japan Fisheries Agency, on larvae, juveniles and adults of the short-finned squid Illex argentinus carried out in winter 1989 are given, as are data obtained during the joint sardine and anchovy recruitment project carried out by R.V. Meteor in November/December 1989. The short-finned squid Illex argentinus is the most important cephalopod resource of the area, and an extended fishery is carried out on the Patagonian shelf and in the proximity of the Falkland Islands. The fishing season in the AUCFZ, for pre-spawning and spawning animals, extends from early autumn to winter (March–August). Abundance of rhynchoteuthion larvae (417–485 larvae·10 m?2) was greatest in winter in surface temperatures of 12,1–16,9°C and surface salinities of 34,8 – 35,2 × 10?3. The distribution of the larvae is related to the western boundary of the Brazil Current and the convergence front.  相似文献   

5.
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   

6.
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   

7.
An integrated telephone and on-site questionnaire survey was used to estimate total shark fishing effort and specific catch of the ragged-tooth shark Carcharias taurus by coastal club-affiliated shore-anglers, primarily along the east coast of South Africa. Mean total shark fishing effort was estimated to be 37 820 fisher-days year?1 (95% CI = 28 281–47 359 fisher-days year?1) with a mean cpue of 0.073 C. taurus fisher?1 day?1 (95% CI = 0.068–0.078 fisher?1 day?1). Cpue for C. taurus varied significantly along the coast and ranged from a high of 0.260 fisher?1 day?1 in the Eastern Cape to zero fisher?1 day?1 on the West Coast. The total number of C. taurus caught annually by coastal club anglers was estimated at 1 764 fish year?1 (95% CI = 321–3 207 fish year?1). The majority (92.1%) of young-of-the-year sharks (<1.2m total length, TL) were recorded between East London and Jeffreys Bay, suggesting that this may be the primary nursery area for C. taurus. Post-release mortality ranged from 3.8% for young-of-the-year sharks to 18.5% for adult sharks (>2.4m TL). The majority (76.2%) of anglers interviewed stated that they now fished less for sharks since the banning of vehicles on beaches in December 2001. As a result of this ban, almost half (49.2%) of interviewed anglers stated that they now fished more for non-cartilaginous species.  相似文献   

8.
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   

9.
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   

10.
Volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in Western Australia. The filtered volumes were large, 19 m3 m?1 day?1 and 73 m3 m?1 day?1 on two ‘clean’ beaches but only 0·4 m3 m?1 per tidal cycle on a beach covered in kelp and seagrass wrack. The mean residence times of this water in the interstitial system and its percolation paths were both short, 1–7 h and 2–5 m respectively. Water input was greater across a beach cusp horn than across a cusp embayment. Most input occurred in the upper swash zone where the water table was less than 20 cm deep. Tidal variations in input volumes were evident even with tide ranges of only 20 cm. The inshore zone off these beaches filters on average 0·07 m3 m?2 day?1 at an average depth of 5·5 m under 0·4 m waves of 6·5 s duration. The importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore ‘lagoon ecosystem’ is estimated and discused.  相似文献   

11.
Tautog, Tautoga onitis, is an abundant species of fish in estuaries of the northeastern United States. Planktonic tautog larvae are abundant in summer in these estuaries, but there is little information on rates of growth of tautog larvae feeding on natural assemblages of food in the plankton. We examined abundance and growth of larval tautog and environmental factors during weekly sampling at three sites along a nearshore‐to‐offshore transect in Buzzards Bay, Massachusetts, USA during summer 1994. This is the first study of a robust sample size (336 larvae) to estimate growth rates of field‐caught planktonic tautog larvae feeding on natural diets, using the otolith daily‐growth‐increment method. The study was over the entire summer period when tautog larvae were in the plankton. The sampling sites contrasted in several environmental variables including temperature, dissolved oxygen (DO), and chlorophyll a concentration. There was a temporal progression in the abundance of tautog larvae over the summer, in relation to location and temperature. Tautog larvae were first present nearshore, with a pronounced peak in abundance occurring at the nearshore sites during the last 2 weeks in June. Larvae were absent at this time further offshore. From late June through August, larval abundance progressively decreased nearshore, but increased offshore although never approaching the abundance levels observed at the nearshore sites. The distribution and abundance of tautog larvae appeared to be related to a nearshore‐to‐offshore seasonal warming trend and a nearshore decrease in DO. Otoliths from 336 larvae ranging from 2.3 to 7.7 mm standard length had otolith increment counts ranging from 0 to 19 increments. Growth of larval tautog was estimated at 0.23 mm·day?1, and length of larvae prior to first increment formation was estimated at 2.8 mm indicating that first increment formation occurs 3–4 days after hatching at 2.2 mm. Despite spatial and temporal differences in environmental factors, there were no significant differences in growth rates at any of three given sites over time, or between sites. Because larval presence only occurred at a narrow range of temperature (17–23.5 °C) and DO (6.5–9.3 mg·l?1), in situ differences in growth did not appear to be because of differences in larval distribution and abundance patterns relative to these parameters.  相似文献   

12.
Information is presented on the distribution of chlorophyll a between the Cunene River (18°S), on the border of South West Africa (Namibia) and Angola, and East London (28°E) on the east coast of South Africa. Spectrophotometric measurements of samples collected during various research cruises and estimates from satellite measurements were used. The coast was divided into a number of oceanographic regions. Spatial and temporal variation of chlorophyll a in the waters off central-northern South West Africa, the Lüderitz region, the South-Western Cape and the Algoa region are discussed in some detail. There was a narrow coastal band of moderate to high chlorophyll a (3 to in excess of 10 mg·m?3) at the surface between Cape Cross (22°S) and Möwe Point (c. 19°S) throughout most of the year, whereas in much of the area between 23 and 33°S concentrations reached maximum values in autumn. Along the South-Western Cape coast, high concentrations of chlorophyll a were observed in the St Helena Bay area up to 90 km off shore throughout the year, evenly distributed in the upper 30 m. A narrower band of high concentrations of chlorophyll a extended southwards to Cape Agulhas during summer when upwelling was most active. During late summer and autumn a subsurface maximum developed on the Agulhas Bank associated with the thermocline. Low to moderate concentrations were widespread over the entire coastal zone during winter, with strong mixing in the upper 50 — 100 m. A fairly consistent feature of the Algoa region was the presence of moderate concentrations of chlorophyll associated with a wedge-shaped zone of coastal and dynamic upwelling. The implications of the distribution of chlorophyll in time and space are discussed with respect to the distribution and migration of pelagic fish species, particularly anchovy.  相似文献   

13.
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   

14.
Surveys of the distribution, abundance and size of the ctenophore Mnemiopsis leidyi were carried out in Narragansett Bay, R.I. over a 5-year period, 1975–1979. Yearly variations were observed in time of initiation of the ctenophore increase and maximum abundance. Biomass maxima ranged from 0·2 to 3 g dry weight m?3 at Station 2 in lower Narragansett Bay while maximum abundance varied from 20 to 100 animals m?3. Ctenophores less than 1 cm in length generally composed up to 50% of the biomass and 95% of the numerical abundance during the peak of the M. leidyi pulse. During the 1978 maxima and the declining stages of the pulse each year, 100% of the population was composed of small animals. M. leidyi populations increased earlier, reached greater maximum abundances, and were more highly dominated by small animals in the upper bay than toward the mouth of the bay. The averageclearance rate of M. leidyi larvae feeding on A. tonsa at 22°C was 0·36 l mg?1 dry weight day?1, with apparent selection for nauplii relative to copepodites. Predation and excretion rates applied to ctenophore biomass estimated for Narragansett Bay indicated that M. leidyi excretion is minor but predation removed a bay-wide mean of 20% of the zooplankton standing stock daily during August of 1975 and 1976. Variation in M. leidyi predation at Station 2 was inversely related to mean zooplankton biomass during August and September, which increased 4-fold during the 5-year period.  相似文献   

15.
A particle-size spectrum model is used to estimate standing stocks of some pelagic fish from measurements of phytoplankton chlorophyll in two exploited regions in southern Africa (southern Benguela and off South West Africa/Namibia) and in two unexploited regions (the Agulhas Bank and off the eastern Cape Province). The model is based on the assumption that equal biomasses occur in logarithmically equal size classes in the pelagic marine environment. Phytoplankton, with an equivalent spherical diameter ranging from 1 to 128 μm, occupy 21 size classes on the logarithmic scale. Two different size ranges are assumed for some commercial, pelagic fish species, equivalent to exploitation with two different purse-seine mesh sizes. A mesh of 12,7 mm would catch 8 size classes of pilchard, horse mackerel and anchovy whereas a mesh of 32 mm would catch only 3,3 size classes of pilchard and horse mackerel. From the model, the potential biomass of these commercial pelagic fish is estimated, after allowing for the presence of other commercial and non-commercial fish and other taxa in the exploited size range. Total pelagic fish production is estimated by assuming constant turnover rates of 1·y?1 and 1,5·y?1 when exploited with 32 and 12,7 mm mesh nets respectively. Consideration of the maximum and mean reported catches in the exploited areas indicates that only some 25 per cent of pelagic fish production is exploitable by man. On this basis, the unexploited Agulhas Bank region may yield some 400 000 metric tons (wet) of pelagic fish of the species considered, and the East Coast region some 90 000 tons. Exploitation in these regions cannot be recommended, because the Agulhas Bank is an important spawning ground for many pelagic species, and the fish in both regions probably act as a reserve buffer for the heavily exploited pelagic resource of the Western Cape.  相似文献   

16.
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   

17.
In January 1982, sediment microbial N transformations and inorganic N fluxes across the sediment/water interface were studied at nine sites off the South Island West Coast, New Zealand. The sediments showed a great variety in physical, chemical and biological properties. The sediment organic matter had a molar CN ratio of 5.9–10.9, and the total NP ratio was 1.2–4.0. The denitrification capacity in the top 7.5 cm of sediment was 0.1–77.2 mmol N m?2 day?1 and generally declined with increasing sediment depth. The in situ denitrification rate was 0.02–1.84 mmol N m?2 day?1 and highest activities were generally found in surface sediments and at 6–7.5 cm depth. Denitrification accounted for 82–100% of total nitrate reduction. Net N mineralization was indirectly estimated at 0.6–2.4 mmol N m?2 day?1, and the experimental determination of this N transformation gave 0.6–3.2 mmol N m?2 day?1. Denitrification accounted for 3–75% of net N mineralization. The diffusive flux of ammonium and nitrate across the sediment/water interface was 0.1–0.7 and 0.1–0.6 mmol N m?2 day?1, respectively.  相似文献   

18.
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   

19.
An in situ chamber of volume 3881 and bottom area 0·64 m2 was used to determine the flux of oxygen and inorganic nutrients across an estuarine sediment-water interface over a 65-day period. Over the first 7 days, oxygen uptake was 378 mg m?2 day?1 and the rates of ammonium and phosphate release were 2·22 and 0·34 mg at. m?2 day?1, respectively. The water became anoxic in 14 days.The rates of flux in a similar chamber containing only detritus recently settled from the water column were 371 mg m?2 day?1 (oxygen), 1·66 mg at. m?2 day?1 (ammonium) and 0 12 mg at. m?2 day?1 (phosphate), demonstrating that detritus contributes substantially to exchange across the sediment-water interface.The evolution of the two chambers was similar over the latter part of the experimental period. A third chamber containing only water exhibited very minor changes.The role of detritus in nutrient recycling at the sediment-water interface is discussed in relation to the productivity of shallow water bodies such as the estuary in which the experiment was conducted, which itself undergoes periodic deoxygenation during prolonged stratification. The measured flux of nitrogen across the interface was found to represent approximately 31% of the mean daily phytoplankton requirement.  相似文献   

20.
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   

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