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1.
The plankton was examined as an indicator of water quality in 14 shrimp Litopenaeus vannamei farms in Brazil in 2003. The ponds were categorized by high stocking density (>30 PL m−2) of phytoplankton, consisting of 51 species with concentrations ranging from 365,218 ± 416,615 cells mL−1 to 1,961,675 ± 3,160,172 cells mL−1. Diatoms contributed to almost 70% of the species number and high densities resulted from Cyanophyta blooms, mainly Pseudanabaena cf limnetica. Forty zooplankton taxa were registered and were essentially composed of typical marine euryhaline species and suspension-feeders. Copepoda dominated (45%) the make-up, followed by Protozoa (18%), Rotifera (12%), and Mollusca (12%) larvae. Zooplankton varied from 972 ± 209 ind m−3 to 4235 ± 2877 ind m−3. Enhanced nutrient input affected plankton density and composition. Diatom and Copepoda dominance was replaced by cyanobacteria, protozoan, and rotifers as nutrient concentrations increased with the cultured period, indicating that plankton structure is affected by eutrophic conditions.  相似文献   

2.
The zooplankton of oligotrophic lakes in North Patagonia is often dominated by mixotrophic ciliates, particularly Stentor amethystinus and Stentor araucanus. Therefore, we tested whether Stentor spp. (i) is an important food for juvenile endemic (Cheirodon australe, Galaxias maculatus, Odontesthes mauleanum, Percichthys trucha) and introduced (Oncorhynchus mykiss) fish species, and (ii) represents a remarkable grazer of bacteria. Ingestion rates of fish estimated by disappearance of Stentor in feeding experiments ranged between 8 (G. maculatus) and 53 (C. australe) ciliates per fish and day, and assimilation rates measured by using radioactively labelled Stentor ranged between 3 (P. trucha) and 52 (C. australe) ciliates per fish and day. However, although we detected the consumption of Stentor by fish, the daily consumption amounted to at most 0.2% of the fish biomass which can not cover the energy requirement of the fish. Furthermore, the daily consumption was equivalent to a maximum of 1.6% of the Stentor standing stock so that fish predation does not seem to be an important mortality factor for the ciliates. The clearance rate of Stentor sp. on natural bacteria was on average 3.8 μl cil−1 h−1. The daily ingestion (mean 3.9 ng C cil−1 d−1) was about 3.5% of the individual biomass of Stentor sp. Therefore, bacteria ingestion might explain a ciliate growth rate of appr. 1% d−1, which was about 17% of the photosynthesis of endosymbiotic algae. The maximum density of Stentor sp. in the lake could ingest about 1 μg C L−1 d−1 bacteria which is only 3% of average bacterial production. Thus, grazing by Stentor sp. does not seem to be a main loss factor for the bacteria.  相似文献   

3.
Distribution, abundance and life history characteristics of Mysis relicta were studied in the Feldberg Lake District (Lake Breiter Luzin, Lake Schmaler Luzin, Lake Zansen) located in northeastern Germany. Between July 2001 and November 2002 mysids were collected by vertical net hauls. In order to determine the impact of the current trophic conditions on the distribution of mysids in these lakes, oxygen concentration, total phosphorus, chlorophyll a and water transparency were also measured. All investigated lakes are mesotrophic at present. Lake Breiter Luzin exhibited great seasonal and spatial variations in mysid abundance. Density of adults and juveniles had a mean of 44.9 ± 57.1 and 68.7 ± 99.6 m−2, respectively. Highest abundance of adults was 110.4 ± 76.5 m−2 in summer, lowest abundances of 2.0 ± 4.0 m−2 occurred in spring. For juveniles, highest density of 218.4 ± 174.6 m−2 was detected in summer and lowest of 0.8 ± 1.8 m−2 in winter. No mysids were caught in any of the daytime hauls, but they were widely distributed throughout the water column at night. Size frequency distribution of mysids suggested that reproduction occurred year-round, the most consistent influx of juveniles occurred in early summer and a smaller second cohort in autumn. Highest mysid abundance was 189.2 ± 318.6 adults and 127.0 ± 66.3 juveniles m−2 in Lake Schmaler Luzin, and 59.6 ± 5.6 adults and 79.4 ± 11.2 juveniles m−2 in Lake Zansen. There were great spatial differences in abundance in both lakes.  相似文献   

4.
The effect of monsoon, coastal current and temperature on the distribution and seasonal variations of Calanus sinicus abundance were studied. The samples from the northwest continental shelf of South China Sea were collected with 505 μm planktonic nets from July 2006 to October 2007. The abundance of C. sinicus made up 34.28% and 12.34% of all copepods in spring and summer, respectively. The distribution of C. sinicus varied seasonally and regionally. The distribution of C. sinicus ranged between east inshore and offshore waters from the Leizhou Peninsula to Hainan Island, with a mean of 23.00 (±77.78) ind. m−3 in spring. In summer it had a mean of 13.74 (±45.10) ind. m−3 occurring only in the east inshore waters from Leizhou Peninsula to Hainan Island. C. sinicus was not abundant during autumn and winter seasons. The surveyed area was divided into three sub-regions based on topographical analysis and water mass, region I (included the east inshore waters of Leizhou Peninsula), region II (included the east inshore waters of Hainan Island) and region III (included the offshore waters from Leizhou Peninsula to Hainan Island). The average abundance of C. sinicus within region I was determined to be 115.63 (±145.93) and 68.12 (±84.00) ind. m−3 in spring and summer, respectively, values higher than those of regions II and III. Our findings suggested that C. sinicus was transported from the East China Sea to the northwest continental shelf of South China Sea by the Guangdong Coastal Current, which was driven by the northeast monsoon in spring. The presence of a cold eddy, in addition to coastal upwelling driven by the southwest monsoon, provided suitable survival conditions for C. sinicus in summer. This species disappeared in autumn due to high temperatures (>27 °C) and did not begin to enter into the northwest continental shelf of South China Sea from the East China Sea during the period of investigation in winter. The frequency of C. sinicus was low in region III during the year as a result of the South China Sea Warm Current and pelagic waters with high temperature during the spring and summer months.  相似文献   

5.
The aim of this study was to present quantitative data on the population dynamics of Chlorella-bearing ciliates (Stentor, Ophrydium) compared to the total zooplankton community in a deep, oligotrophic North Patagonian lake. Mixotrophic and heterotrophic ciliates, rotifers and microcrustaceans, and important ecological parameters were sampled during a 1-year study. The results showed a low biodiversity with only a few dominant species in every zooplankton group. Three mixotrophic ciliates - Stentor araucanus, S. amethystinus and Ophrydium naumanni - were found. They peaked in summer and autumn with maximum values of 152-313 Ind L−1 (Stentor) and 1880 Ind L−1 (Ophrydium). Their contribution to the total ciliate abundance was 16±17% (annual average). Both Stentor species displayed a distinct vertical zonation during the stratification period with peak depth between 10 and 15 m (metalimnion). The contribution to total zooplankton biomass was 59.4% on an annual average (Stentor: 41%, O. naumanni: 18.4%) and 83% during the stratification period. Both abundance and biomass of mixotrophic ciliates correlated strongly with temperature and to a lesser degree with copepods, rotifers and small cladocerans. According to this study mixotrophic ciliates were by far the dominant zooplankton group in Lake Caburgua. We report for the first time the importance of O. naumanni in a deep Chilean North Patagonian lake.  相似文献   

6.
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7.
《Marine pollution bulletin》2012,64(5-12):230-236
The effects of hypoxia on the larvae of two sub-tidal nassariid gastropods, Nassarius siquijorensis and N. conoidalis were compared so as to understand how the species-specific tolerance to hypoxia might have resulted in changes in the abundance and distribution of these two species in the hypoxic Tolo Harbour, Hong Kong, since the 1980s. Respiration rates of N. siquijorensis and N. conoidalis larvae were reduced at 4.5 mg O2 l−1, or below, as compared with the normoxic control. Significant reduction in swimming velocity was also observed for 10-day old larvae which were exposed to <2.0 mg O2 l−1 for N. siquijorensis and <1.0 mg O2 l−1 for N. conoidalis. The 48 h LC50 values of N. siquijorensis and N. conoidalis larvae were 0.7 and 1.7 mg O2 l−1, respectively. The results suggested that N. siquijorensis are more tolerant to hypoxia than N. conoidalis.  相似文献   

8.
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9.
Hypoxia associated with eutrophication is a potential threat to the Chinese horseshoe crab Tachypleus tridentatus which inhabits intertidal sand flats in Asia. This study investigated the effect of dissolved oxygen level (DO) (6, 4 and 2 mg O2 l−1) on the physiological energetics in the juvenile T. tridentatus. They were exposed to various oxygen levels for three days and then transferred to normoxia for three days to examine the recovery from low oxygen stress. Feeding rate, respiration rate and scope for growth were reduced at lower DO levels while absorption efficiency and excretion rate were independent of DO levels. Although full recovery of the physiological responses and scope for growth from hypoxis stress was observed when normoxia resumed, their long term survival in suboptimal habitats with frequent occurrence of hypoxia deserves a close monitoring as hypoxia may be even more common in future in a warming world.  相似文献   

10.
Stratification (throughout the year) and low solar radiation (during monsoon periods) have caused low chlorophyll a and primary production (seasonal average 13–18 mg m−2 and 242–265 mg C m−2 d−1, respectively) in the western Bay of Bengal (BoB). The microzooplankton (MZP) community of BoB was numerically dominated by heterotrophic dinoflagellates (HDS) followed by ciliates (CTS). The highest MZP abundance (average 665±226×104 m−2), biomass (average 260±145 mg C m−2) and species diversity (Shannon weaver index 2.8±0.42 for CTS and 2.6±0.35 for HDS) have occurred during the spring intermonsoon (SIM). This might be due to high abundance of smaller phytoplankton in the western BoB during SIM as a consequence of intense stratification and nitrate limitation (nitracline at 60 m depth). The strong stratification during SIM was biologically evidenced by intense blooms of Trichodesmium erythraeum and frequent Synechococcus–HDS associations. The high abundance of smaller phytoplankton favors microbial food webs where photosynthetic carbon is channeled to higher trophic levels through MZP. This causes less efficient transfer of primary organic carbon to higher trophic levels than through the traditional food web. The microbial food web dominant in the western BoB during SIM might be responsible for the lowest mesozooplankton biomass observed (average 223 mg C m−2). The long residence time of the organic carbon in the surface waters due to the active herbivorous pathways of the microbial food web could be a causative factor for the low vertical flux of biogenic carbon during SIM.  相似文献   

11.
Annual litter production in alien (Sonneratia apetala) and native (Kandelia obovata) mangrove forests in Shenzhen, China were compared from 1999 to 2010. S. apetala had significantly higher litter production than K. obovata, with mean annual total litter of 18.1 t ha−1 yr−1 and 15.2 t ha−1 yr−1, respectively. The higher litter production in S. apetala forest indicates higher productivity and consequently more nutrient supply to the estuarine ecosystems but may be more invasive due to positive plant-soil feedbacks and nutrient availability to this alien species. Two peaks were recorded in S. apetala (May and October), while only one peak was observed in K. obovata, in early spring (March and April). Leaf and reproductive materials were the main contributors to litter production (>80%) in both forests. These results suggest that the ecological function of S. apetala and its invasive potential can be better understood based on a long-term litter fall analysis.  相似文献   

12.
Synechococci are small (<1 μm) coccoid prokaryotes that play a significant ecological role in microbial food webs and are important contributors to carbon and nitrogen biogeochemical cycles. Under funding from NOAA and NASA, we developed a time series observatory to understand the seasonal variability of Synechococcus and other phytoplankton. Our goal is to understand the distribution and relative contribution of Synechococcus to the carbon cycle and how they relate to nutrients and temperature. Synechococcus in the southern Mid-Atlantic Bight exhibited a clear seasonal abundance pattern in both inshore and offshore waters—peaking in abundance (11×104 cells ml−1) during warm periods of summer. Synechococci were numerically important during periods of stratification when waters were warm and macronutrients were low. Using a simple algorithm to convert cellular volume to cellular carbon using image analysis, we estimated that Synechococcus cellular carbon ranged from 0.1 to 1.5 pg C per cell and was most significant compared to total particulate carbon in the summer peaking at ∼25% of the total carbon available. No direct correlations were found between Synechococcus abundance and nitrate, nitrite, ammonium, phosphate, and silicate. However, inshore Synechococcus abundance peaked at 104 cells ml−1 when nitrogen concentrations were lowest. Our results suggest that Synechococcus is adapted to warm temperatures and are capable of demonstrating rapid growth during summer when macronutrients are limiting. The ability of Synechococcus to take advantage of high summer temperatures, low nutrient concentrations and low light levels allows them to maintain a picoplankton community during periods of low detritus and nanophytoplankton is nutrient limited. Temperature-dependence is important in altering the size spectrum of the phytoplankton community and affects the carbon cycle on the Mid Atlantic Bight.  相似文献   

13.
A spatial and temporal study on data collected along the longitudinal gradient of the Principal Channel of Bahía Blanca estuary, Argentina, was carried out during 1992–1993. At nine stations, phytoplankton abundance, chlorophyll a (Chl-a) concentration, inorganic nutrient levels, Secchi disk depth, euphotic depth:mixing depth ratio (Zeu:Zm), salinity and temperature were recorded. Phytoplankton abundance, Chl-a concentration and nutrient levels decreased towards the outer zone of the estuary. The inner zone (stations 1 and 2), which was characterized by high turbidity, high nutrient concentrations and high Zeu:Zm (>0.16, [critical mixing ratio]), registered the highest phytoplankton abundance and Chl-a concentrations. Temporal variability of data was also noteworthy in this zone. The highest biomass values thus corresponded to June, July, August and the beginning of spring (18 μg Chl-a L−1 and 9×106 cells L−1) concomitantly with a diatom bloom. In the middle zone (stations 3–6), a strong phytoplankton biomass decrease was observed and it coincided with both deep-mixed depths and low Zeu:Zm (<0.16). The outer zone (stations 7–9), which was characterized by low phytoplankton biomass values and low nutrient levels all along the year, was the area mostly influenced by waters from the adjacent continental shelf. In view of the above, it can be concluded that the most important primary production in the Bahía Blanca would be produced in the shallow inner zone during winter, being the spatial reach of the phytoplankton biomass principally limited to estuarine waters. Presumably, less than 5% of such biomass may reach the coastal area of the estuary.  相似文献   

14.
From September 2000 to December 2006, surface plankton samples were collected on a monthly basis, from a station located in the southern Bay of Biscay (43°37N; 1°43W France), near the deep Capbreton canyon. In this paper, the results for the ichthyoplankton assemblage are presented. Among the 62 taxa recorded, only 35 were present in the larval stage whilst only 10 were represented by their eggs. Taxa represented by both stages (eggs+larvae; N=17) had the highest abundance. The presence in the surface plankton assemblage of species, at either or both stage, is interpreted within the context of the bathymetric distribution of species. The maxima in abundance and diversity occurred in February–March, for eggs, and May–June, for larvae. This 3-month time-lag between the stages is proposed to be related to the timing of egg spawning and larval recruitment to the pelagic environment. Mean egg abundances (82.4±29.8 eggs/10 m2) were 10-fold higher than the larval abundances (7.1±1.8 larvae/10 m2). Despite pronounced monthly variability, no statistically significant decrease in either egg or larvae abundance was observed during this 6-year study period. Compared with previous published studies, this study shows that the peak in ichthyoplankton diversity occurred two months earlier. In addition, the spawning period occurred over the whole year, even during autumn and winter. Using ordination techniques, the annual sequence appearance of taxa are described at the study site: Gadiforms, Ammodytidae and Pleuronectiforms were present during the winter whilst Sparidae, Blennidae, Labridae and Gobiidae, formed the summer group. Only three species, European anchovy Engraulis encrasicolus, European pilchard Sardina pilchardus and Atlantic horse mackerel Trachurus trachurus were recorded throughout the year.  相似文献   

15.
Mussels (Mytilus edulis) were continuously exposed to dispersed crude oil (0.015-0.25 mg/l) for 7 months covering the whole gamete development cycle. After 1 month exposure to 0.25 mg oil/l, the level of alkali-labile phosphates (ALP) and the volume density of atretic oocytes in female gonads were higher than those in the gonads of control females, indicating that oil affected the level of vitellogenin-like proteins and gamete development. Spawning of mussels was induced after 7 months oil exposure. Parental oil exposure did not affect subsequent fertilization success in clean seawater but this was reduced in 0.25 mg oil/l. Parental exposure to 0.25 mg oil/l caused both slow development and a higher percentage of abnormalities in D-shell larvae 2 days post-fertilization; reduced growth 7 days post-fertilization. These effects were greatly enhanced when larval stages were maintained at 0.25 mg oil/l. Similar studies are warranted for risk assessment prognosis.  相似文献   

16.
As marine debris levels continue to grow worldwide, defining sources, composition, and distribution of debris, as well as potential effects, becomes increasingly important. We investigated composition and abundance of man-made, benthic marine debris at 1347 randomly selected stations along the US West Coast during Groundfish Bottom Trawl Surveys in 2007 and 2008. Anthropogenic debris was observed in 469 tows at depths of 55-1280 m. Plastic and metallic debris occurred in the greatest number of hauls followed by fabric and glass. Mean density was 67.1 items km−2 throughout the study area but was significantly higher south of 36°00′N latitude. Mean density significantly increased with depth, ranging from 30 items km−2 in shallow (55-183 m) water to 128 items km−2 in the deepest depth stratum (550-1280 m). Debris densities observed along the US West Coast were comparable to those seen elsewhere and provide a valuable backdrop for future comparisons.  相似文献   

17.
Estrogenic contaminants in the aquatic environment are associated with endocrine disruption and feminization in fish. The effects of endocrine disrupting chemicals (EDCs) on fish have been well documented. However, very few studies have focused on 17 β-estradiol (E2) and its effects on endocrine system and biotransformation in a single prolonged exposure. This study investigated changes in the levels of serotonin (5-hydroxytryptamine) and acetyl choline esterase (AchE) in brain, cortisol in plasma and Ethoxyresorufin-O-deethylase (EROD) activity in gill of two different size groups (fingerlings and juveniles) of Japanese sea bass (Lateolabrax japonicus) upon exposure to two sub-lethal concentrations (200 and 2000 ng L−1) of E2 for 30 d. The results indicate that cortisol level and EROD activity significantly increased in both groups, whereas serotonin level increased in juveniles and decreased in fingerlings due to E2 exposure. The correlation analysis revealed that E2 significantly affected the endocrine and biotransformation systems in both age groups.  相似文献   

18.
《Marine pollution bulletin》2009,58(6-12):302-306
Coastal environments are threatened by the increasing frequency, extent and severity of hypoxic events. Hypoxia affects vast areas around the world and often causes fish kills, reduced abundance, altered distribution, low benthic biomass and declines in fisheries. In Australia, many fisheries are based on sparid fishes and in the southern states black bream (Acanthopagrus butcheri) is important to both the recreational and commercial sectors. This species completes its entire life cycle in estuaries and annual recruitment is highly variable and very likely influenced by environmental conditions during the spawning season.In a laboratory-based experiment, fertilised black bream eggs (embryos) were exposed to five different levels of dissolved oxygen (DO). The DO levels were maintained in small test wells using nitrogen gas in a novel chamber design. Embryo development was assessed over a 2-day period and hatched larvae were observed until Day 2 post-hatch. Significant differences (p < 0.05) were observed in embryonic development and survival as a function of DO level. In severely hypoxic conditions (30% saturation) survival to 1 day was reduced and no hatching occurred. In moderately hypoxic conditions (45–55%S), both precocious and delayed hatching was observed and hatch rates were reduced, whilst the number of hatched larvae with deformities increased, resulting in reduced larval lengths. No larvae survived to Day 2 post-hatch when held in hypoxic conditions (<55%S). This study demonstrates the detrimental effect that severe hypoxia can have on the early development of black bream which could result in reduced recruitment and lowered abundance. Other species that share similar early life histories may also be at risk.  相似文献   

19.
The State of São Paulo is the most developed area in Brazil and was impacted by persistent organic pollutants for several decades. This study investigated organochlorines in five species of small cetaceans (Pontoporia blainvillei, Stenella frontalis, Sotalia guianensis, Tursiops truncatus and Steno bredanensis) found dead along the coast of São Paulo between 1997 and 2003. DDTs (15.9 μg g−1 lipid; mean for all pooled individuals) and PCBs (8.08 μg g−1) exhibited the highest concentrations in the animals, reflecting large amounts formerly used in Brazil. Lower levels of mirex (0.149 μg g−1), HCB (0.051 μg g−1), CHLs (0.008 μg g−1) and HCHs (0.007 μg g−1) were detected in all species. Residual pattern of DDTs in dolphins suggests that o,p′-DDT is more recalcitrant than p,p′-DDT in the body of the animals and/or the environment. In contrast to p,p′-DDT, residues of o,p′-DDT seem to be preferentially converted into o,p′-DDD rather than o,p′-DDE.  相似文献   

20.
While many surface foraging seabirds ingest plastic, the spatial overlap of these far-ranging predators with debris aggregations at-sea is poorly understood. We surveyed concurrent distributions of marine birds and debris along a 4400 km cruise track within a debris accumulation area in the North East Pacific Ocean using line and strip transect methods. Analysis of debris and bird distributions revealed associations with oceanographic and weather variables at two spatial scales: daily surveys and hourly transects. Hourly bird abundance (densities; 0-9 birds km−2) was higher in lower wind and shallower water. Hourly debris abundance (densities; 0-15,222 pieces km−2) was higher in lower wind, higher sea-level atmospheric pressure and deeper water. These results suggest that debris and seabird abundance and community structure are influenced by similar environmental processes, but in opposing ways, with only three far-ranging seabird species (Black-footed Albatross, Cook’s Petrel and Red-tailed Tropicbird) overlapping with high debris concentrations over meso-scales.  相似文献   

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