The food and feeding habits of greenback grey mullet, Liza subviridis (Valenciennes), from different habitats and at various stages of growth

An analysis of the stomach contents of Liza subviridis at various stages of growth and from different habitat types is given. Transitions in diet with respect to size were observed. Postlarval stages of less than 12 mm standard length fed only on zooplankton. The transition to bottom feeding occurred in specimens 16–20 mm, with food items consisting of zooplankton, diatoms, detrital material and inorganic sediment. The transition was complete on attaining a length of 24 mm whereby food items comprised diatoms, detrital material, filamentous algae and inorganic sediment. The relevance of this information in aquaculture is discussed. The stomach contents of adult Liza subviridis taken from different habitat types were consistent, comprising diatoms, detrital material and inorganic sediment. Filamentous algae was also consumed where available.     

Assimilation of Diazotrophic Nitrogen into Pelagic Food Webs

The fate of diazotrophic nitrogen (N_D) fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous zooplankton. Current theory suggests that N_D fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable N_D (exuded from viable cyanobacterial cells) by palatable phytoplankton or microbial consortia. Alternatively, N_D can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable N_D (e.g., nitrate, ammonium) by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom) would be the primary pathway by which N_D was incorporated into the planktonic food web. Instead, in situ stable isotope measurements and grazing experiments clearly documented that the assimilation of N_D by zooplankton outpaced assimilation by palatable phytoplankton during a bloom of toxic Nodularia spumigena Mertens. We identified two distinct temporal phases in the trophic transfer of N_D from N. spumigena to the plankton community. The first phase was a highly dynamic transfer of N_D to zooplankton with rates that covaried with bloom biomass while bypassing other phytoplankton taxa; a trophic transfer that we infer was routed through bloom-associated bacteria. The second phase was a slowly accelerating assimilation of the dissolved-N_D pool by phytoplankton that was decoupled from contemporaneous variability in N. spumigena concentrations. These findings provide empirical evidence that N_D can be assimilated and transferred rapidly throughout natural plankton communities and yield insights into the specific processes underlying the propagation of N_D through pelagic food webs.     

Field and laboratory studies of the feeding behaviour of the piper Hyporhamphus ihi with reference to the role of the lateral line in feeding

Piper school in large groups close to the water surface during daylight hours, whereas at night the schools break up and individual fish can be observed swimming slowly through the water. Analysis of gut contents indicates that during the day piper feed primarily on copepods, and terrestrial insects trapped on the water surface; after dark the demersal zooplankton which enter the water column form the major dietary component. Prey selectivity is evident in that certain groups present in the plankton are not found in the stomach contents of piper, and that the size of prey taken is biased towards the larger size classes of plankton. Laboratory experiments establish that piper are capable of locating prey in total darkness, and that under these conditions live prey are consumed in a higher proportion, and much more quickly than dead prey. These results strengthen the hypothesis that piper use their anterior lateral line to feed on zooplankton at night.     

轮虫培育池生态系统颗粒悬浮物的研究

对两种模式轮虫培育池的悬浮物结构及动态进行了比较研究．结果表明,颗粒悬浮物总量波动在6．76～65．39mg·L^-1之间．静水池塘14#颗粒悬浮物平均值为11．50mg·L^-1,其中颗粒有机物占66．8％,浮游植物占30．5％,浮游动物占5．3％。颗粒腐质和细菌占31％,颗粒无机物占33．2％．流水池塘82#池颗粒悬浮物平均值为41．83mg·L^-1,其中颗粒有机物占70．4％,浮游植物占30％,浮游动物占1．2％,颗粒腐质和细菌占39．2％,颗粒无机物占29．6％．颗粒悬浮物含量静水轮虫池小于流水轮虫池．轮虫培育池是一类特殊类型的生态系统,消费者以褶皱臂尾轮虫为主,群落结构简单,生境易变,这些都会影响水层颗粒悬浮物的动态,造成其含量的较大波动和构成的改变．轮虫培育池生态系统颗粒悬浮物中以颗粒有机物所占比例较大,颗粒腐质和细菌所占份额与浮游生物量相当．     

Predation on Protozoa: its importance to zooplankton

Protozoa are an important component of both the nano- and microplanktonin marine and freshwater environments and are preyed upon byzooplankton, including suspension-feeding cope pods, some gelatinouszoopiankters and some first-feeding fish larvae. The clearancerates of suspension-feeding zooplankton for ciliates, in particular,are higher than for most phytoplankton. For at least some suspension-feedingzooplankton, protozoans are calculated to be quantitativelyan important component of the diet during certain seasons. Inlaboratory studies, protozoan components in the diet appearto enhance growth and survival of certain life-history stagesor enhance fecundity. These data suggest that protozoans arequalitatively as well as quantitatively important in the dietsof marine zooplankton. Most studies of predation on Protozoahave focused on the euphotic zone in nearshore waters. Predationon Protozoa is expected, however, to be particularly importantboth quantitatively and qualitatively in marine environmentsand seasons in which primary production is dominated by cells<5 µm in size, such as nearshore environments afterthe spring phytoplankton bloom, in oligotrophic waters, andin environments dominated by detritus-dominated food webs, suchas the deep sea. In detritus-dominated food webs, Protozoa maybe a source of essential nutrients and may thus facilitate utilizationof bacterial and detrital carbon by metazoan plankton.     

Climate Change and Eutrophication Induced Shifts in Northern Summer Plankton Communities

Marine ecosystems are undergoing substantial changes due to human-induced pressures. Analysis of long-term data series is a valuable tool for understanding naturally and anthropogenically induced changes in plankton communities. In the present study, seasonal monitoring data were collected in three sub-basins of the northern Baltic Sea between 1979 and 2011 and statistically analysed for trends and interactions between surface water hydrography, inorganic nutrient concentrations and phyto- and zooplankton community composition. The most conspicuous hydrographic change was a significant increase in late summer surface water temperatures over the study period. In addition, salinity decreased and dissolved inorganic nutrient concentrations increased in some basins. Based on redundancy analysis (RDA), warming was the key environmental factor explaining the observed changes in plankton communities: the general increase in total phytoplankton biomass, Cyanophyceae, Prymnesiophyceae and Chrysophyceae, and decrease in Cryptophyceae throughout the study area, as well as increase in rotifers and decrease in total zooplankton, cladoceran and copepod abundances in some basins. We conclude that the plankton communities in the Baltic Sea have shifted towards a food web structure with smaller sized organisms, leading to decreased energy available for grazing zooplankton and planktivorous fish. The shift is most probably due to complex interactions between warming, eutrophication and increased top-down pressure due to overexploitation of resources, and the resulting trophic cascades.     

Emergence of Holling type III zooplankton functional response: Bringing together field evidence and mathematical modelling

Food-web population models are rather sensitive to parameterization of functional response in predation terms. Theoretical studies predict enhancing of ecosystems’ stability for a functional response of sigmoid type (Holling type III). The choice of a correct type of response is especially important for modelling outcome of grazing control of algal blooms by zooplankton in nutrient-rich ecosystems. Extensive experiments on zooplankton feeding in laboratories show non-sigmoid nature of response for most herbivorous zooplankton species. As a consequence, there is a strong opinion in literature that the implementation of Holling III type grazing in plankton models is biologically meaningless. I argue, however, that such an ‘evident’ claim might be wrong and sigmoid functional responses in real plankton communities would emerge more often than was suggested earlier. Especially, this concerns plankton models without vertical resolution, which ignore heterogeneity in vertical distribution of species. Having conducted extensive literature search of data on zooplankton feeding in situ, I show that vertical heterogeneity in food distribution as well as active food searching behaviour of zooplankton can modify the type of functional response. In particular, the rate of food intake by the whole zooplankton population in the column, as a function of total amount of food, often exhibits a sigmoid behaviour, instead of a non-sigmoid one postulated previously based on laboratory experiments. This conceptual discrepancy is due to the ability of zooplankton to feed mostly in layers with high algal density. I propose a generic model explaining the observed alteration of type between overall and local functional responses. I show that emergence of Holling type III in plankton systems is due to mechanisms different from those well known in the ecological literature (e.g. food search learning, existence of alternative food, refuge for prey).     

Modelling phosphorus fluxes in the hypertrophic Loosdrecht Lakes

A dynamic, deterministic model is presented to simulate the phosphorus cycle and plankton growth in the shallow, hypertrophic Loosdrecht Lakes (The Netherlands) before and after restoration measures. Besides inorganic phosphorus (SRP) in both the surface water and the interstitial water, the model comprises three algal groups, zooplankton, fish, detritus, zoobenthos and upper sediment (all modelled both in carbon and in phosphorus). Within the model system, the phosphorus cycle is completely closed. Carbon and phosphorus are described independently, so that the dynamics of the P/C ratios can be modelled. Sediment processes are described in a simplified form.Simulated values are largely within the range of observed ones. The detrital fraction of the seston (=phytoplankton+detritus) varies from 50–60% in summer to about 90% in winter. SRP in the surface water is very low during most of the year. Sensitivity for external phosphorus input is larger for algal and detrital P than for algal and detrital C and chlorophyll-a. So the P/C ratio of the seston decreases following restoration measures, as is observed in the lakes, while the much higher P/C ratios of zooplankton and fish remain constant. Phosphorus mobilisation from the sediment decreases with decreasing external input. Adaptation of the model system to the reduced loading takes place within about two years.Sources of uncertainty in the model include the limited knowledge on selective grazing as well as on mortality and mineralisation processes.     

Comparative studies on the feeding selectivity of silver carp Hypophthalmichthys molitrix and bighead carp Aristichthys nobilis

Silver carp and bighead carp exhibited size-selection for food particles in aquarium experiments, but did not select their preferred species of plankton actively when they were distributed evenly in the water. They also possessed the capacity of selection for feeding area. The removal rates (% g⁻¹ fish weight) of silver carp for smaller plankton (phytoplankton) were higher than those of bighead carp. The removal rates by the latter for bigger plankton (zooplankton) were higher than those of silver carp, but for plankton about 70 μm dia. the rates by the two species were almost equal.     

Feeding at different plankton densities alters invasive bighead carp (<Emphasis Type="Italic">Hypophthalmichthys nobilis</Emphasis>) growth and zooplankton species composition

Invasive Asian carps Hypophthalmichthys spp. are an ecological threat to non-native aquatic ecosystems throughout the world, and are poised to enter the Laurentian Great Lakes. Little is known about how these filter-feeding planktivores grow and impact zooplankton communities in mesotrophic to oligotrophic systems like the Great Lakes. Our purpose was to determine how different plankton densities affect bighead carp H. nobilis biomass and how bighead carp affect zooplankton species composition. We conducted a 37-day indoor mesocosm experiment (volume = 678 l) with high and low plankton treatments (zooplankton dry mass ≈ 1,900 and 700 μg l⁻¹; chlorophyll a = 25 and 14 μg l⁻¹, respectively) in the presence and absence of juvenile bighead carp (mean = 5.0 g, 8.5 cm). Carp lost weight in the low plankton treatment and gained weight in the high plankton treatment, suggesting that food availability may be a limiting factor to bighead carp growth in regions of low plankton densities. In the presence of carp, zooplankton shifted from Daphnia to copepod dominance, while in the absence of carp, Daphnia remained dominant. Chydorids and ostracods increased in the presence of carp, but only in the low plankton treatment, suggesting that the impact of bighead carp on zooplankton species composition may vary with zooplankton density. Chlorophyll was higher in the absence of carp than in the presence. Chlorophyll and zooplankton densities in many Great Lakes ecosystems are substantially lower than our low treatment conditions, and thus our results suggest that Asian carp establishment in these regions may be unlikely. Handling editor: S. Declerck     

Nitrogen subsidies to pelagic food webs through profundal methane-oxidising bacteria in oligotrophic fresh water

相似文献   

Comparison of Plankton-Water Chemistry Relationships in Three Acid Stressed Lakes in Nova Scotia,Canada

A field program was conducted in 1980 and 1981 on three lakes in Kejimkujik National Park, Nova Scotia, to study plankton-water chemistry relationships in a region of potential acid precipitation stress. Among lake and between year comparisons were made. The three study sites represent two different types of lakes. Kejimkujik Lake (pH 4.8) and Pebbleloggitch Lake (pH 4.5) are both high-colored, dystrophic acid lakes. Beaverskin Lake is a clear, oligotrophic lake which is not as acidic (pH 5.4). The phytoplankton of Kejimkujik Lake was dominated by diatoms, while Pebbleloggitch Lake was dominated by chlorophytes and chrysophytes, and Beaverskin Lake was dominated by cyanophytes. Kejimkujik Lake had the highest total algal cell volume per liter, and Pebbleloggitch Lake the lowest. Rotifer populations composed the majority of the zooplankton communities, while the crustacean zooplankton were dominated by the acid-tolerant copepod Diaptomus minutus. Kejimkujik Lake had the lowest zooplankton biomass and Pebbleloggitch Lake the highest zooplankton biomass per m³. A pattern of highest algal density in Beaverskin Lake, but highest zooplankton density in Pebbleloggitch Lake emerged in both years. This is likely an effect of abundant, but unsuitable food (blue-green algae) in Beaverskin Lake and important detrital food resources in Pebbleloggitch Lake in both years. Multiple regression analysis of water chemistry variables with plankton species produced many significant effects, but failed to show clear patterns. Cause and effect relationships in aquatic ecosystems are poorly delineated by such techniques.     

Modelling the Effects of Current on Prey Acquisition in Planktivorous Fishes

Many planktivorous fishes forage in currents, where they actively maintain position and visually strike at current-entrained zooplankton. In general, the zooplankton are wafted by the foraging fish at a rate equivalent to the current velocity. From a fish's viewpoint the plankton approach either head-on or offset at varied distances from the fish's position. We present a model that describes the relative motion of particles as they approach and pass a foraging fish at different offset distances, and the rate of change in apparent size as they close on a fish. In addition, a series of experiments of fish feeding on plankton in a flume at increasing current velocities revealed that two basic tactics are utilized. At low current velocities (<10-14 cm s m 1), the fish swims toward the prey, whereas at higher current velocities the fish tends to fall back with the current to capture a prey item. The model and experimental results are discussed in terms of the visual problems associated with the detection and tracking of items in motion.     

Environmental influences on long-term variability in marine plankton

The major patterns of geographical and seasonal variability of the plankton of the north-east Atlantic and the North Sea are described to provide the background to a presentation of the dominant patterns of year-to-year fluctuations in the abundance of the plankton of the area for the period 1948 to 1984. A feature of the variability is a marked similarity both between species and between areas. The main pattern of year-to-year change has the form of a quasi linear downward trend in abundance with, superimposed on this, an element of variability with a periodicity of about three years. There is a complex relationship between the plankton and an estimate of changes in the frequency of westerly weather which can be interpreted in terms of influences acting over limited periods of the seasonal cycle coupled with persistence in the stocks of zooplankton. Relationships between year-to-year variations in the abundance of phytoplankton and zooplankton can be interpreted in terms of a response by the zooplankton to variations in food supply coupled with feed-back to the phytoplankton involving in situ nutrient regeneration.     

The importance of zooplankton in the diets of three native fish species in floodplain waterholes of a dryland river,the Macintyre River,Australia

The zooplankton of freshwater systems has been recognized as an important energy resource for fish of small body size that, in turn, provide energy to piscivorous fish consumers higher up the food web. This study evaluates the importance of zooplankton to the diets of three species of fish living in floodplain waterholes of an Australian dryland river. The species selected for study represent different trophic categories in waterhole food webs: Ambassis agassizii is a microcarnivore, Leiopotherapon unicolor is an omnivore, and Nematalosa erebi is a detritivore. Dietary differences among size classes of each species were also evaluated to understand possible ontogenetic shifts in zooplankton consumption. Ambassis agassizii fed primarily on zooplankton (99.9%, made up mostly of 81.6% Calanoida and 17.4% Moinidae), regardless of the size of individual fish. Leiopotherapon unicolor fed on zooplankton (47%, mostly Daphniidae and Moinidae) and aquatic insects (46.7%). Smaller individuals of Leiopotherapon unicolor (30–49 mm TL—total length) were responsible for 36.1% of the plankton consumed by the species. Nematalosa erebi fed on detritus (84.6%) with zooplankton (Calanoida, Moinidae, and Cyclopoida) contributing only 13.7% of the mean diet. Smaller individuals (40–69 mm TL) were responsible for 98% of the plankton consumed by Nematalosa erebi, and individuals of 40–49 mm (TL) fed exclusively on zooplankton (53.8% Moinidae and 46.2% Calanoida). Although the three fish species had different diets, reflecting differences in species-specific and ontogenetic morphological and behavioral characteristics, zooplankton formed the basis of the diet of all species when young. These results confirm the importance of zooplankton as a major food resource for three fish species and smaller size classes of these species in floodplain waterholes of the Macintyre River, Australia. Guest editors: U. M. Azeiteiro, I. Jenkinson & M. J. Pereira Plankton Studies     

Effects of mineral turbidity on freshwater plankton communities: Three exploratory tank experiments of factorial design

We conducted three exploratory experiments of factorial design on the effects of mineral turbidity in 18 large (7 000 1) fiberglass tanks containing plankton communities derived from Lake Texoma (Oklahoma-Texas), a large reservoir often subject to turbid inflows. Replicate plankton communities developed for 30–45 d in response to 4–9 treatments of planktivorous fish, dead fish, nutrient additions and artificial removal of zooplankton with plankton netting (or combinations of these manipulations). In one experiment we then added three concentrations of kaolin and in the other two experiments we added bentonite or powdered silica to the replicate tank communities. We measured the responses of the diverse plankton communities to the addition of mineral turbidity for an additional period of 30–45 d.Effects of introduced minerals (quality or concentration effects) and food web treatments after mineral addition (fish, nutrients, etc.) were determined by analysis of covariance after observations were adjusted for the value of each response variable at the time of mineral addition. Covariance analysis resulted in a statistical model explaining > 80% of the variance for most response variables. The values of response variables at the time of mineral addition were often the most important source of variation, suggesting the importance of biotic community resiliency to the effects of mineral turbidity. There were few effects of mineral particles on physical or chemical (temperature, conductivity, oxygen, pH), nutrient (nitrate, phosphate, alkalinity) or biotic (algal or zooplankton populations) components of the tank communities. Mineral effects were found for several measures of water clarity (Secchi depth, turbidity, and the concentration of small sestonic particles).     

罗非鱼对盐碱池塘围隔浮游生物群落的影响

本文报道了单养尼罗罗非鱼 (Orecohromisniloticus)对施肥处理下盐碱池塘围隔生态系统浮游生物群落的影响。结果表明 ,罗非鱼的放养使浮游植物丰度、叶绿素a含量和初级生产力增大 ,浮游植物小型化 ,生物量以小型硅藻和绿藻占优势 ,裸藻占有相当比重 ;浮游动物生物量也增大 ,桡足类占优势 ,枝角类小型化 ,原生动物密度增大。施肥特别是施有机肥能显著地提高浮游植物生物量 ,使透明度降低 ,但施无机肥对初级生产力和浮游动物生物量影响不大。施有机肥围隔浮游植物和浮游动物密度、浮游动物生物量和浮游生物多样性指数高于其他有鱼围隔 ,罗非鱼的生长最好。文后讨论了罗非鱼滤食和施肥对浮游生物群落结构的影响 ,并与鲢鱼的实验结果 (赵文 ,1999)进行了比较     

Rising temperature and marine plankton community dynamics: Is warming bad?

Global warming is a major threat to the natural environment worldwide with potential adverse impact on plankton community. This will ultimately lead to a change in the dynamics of aquatic food webs. In this study we used seasonally forced multi-species version of the classic Rosenzweig–MacArthur predator–prey model to understand the role and stochastic influence of increasing temperature on marine plankton. First, stable coexistence of four phytoplankton and three zooplankton species was created in a system and then the level of temperature changed to achieve our research goal. We found that the stable coexistence of phytoplankton and zooplankton was related to periodic shifts in species biomass, variation in inter-specific competition and niche configuration. Warming significantly reduced total plankton biomass and changed turnover time of a species, with gradual warming breaking the stable coexistence of phytoplankton and zooplankton. In addition, we found that warming make specialist species more vulnerable than generalist species. After adding noise, a significant variation was observed in plankton biomass and amplification of noise was higher for phytoplankton compared to zooplankton. These results suggest that stochastic or unpredictable nature of temperature fluctuations may create a window of opportunity for the emergence of new species. Overall, warming would induce a shift in plankton dynamics and thereby exert pressure on plankton dependent communities such as fish in the long run.     

The biogeography of marine plankton traits

Changes in marine plankton communities driven by environmental variability impact the marine food web and global biogeochemical cycles of carbon and other elements. To predict and assess these community shifts and their consequences, ecologists are increasingly investigating how the functional traits of plankton determine their relative fitness along environmental and biological gradients. Laboratory, field and modelling studies are adopting this trait‐based approach to map the biogeography of plankton traits that underlies variations in plankton communities. Here, we review progress towards understanding the regulatory roles of several key plankton functional traits, including cell size, N₂‐fixation and mixotrophy among phytoplankton, and body size, ontogeny and feeding behaviour for zooplankton. The trait biogeographical approach sheds light on what structures plankton communities in the current ocean, as well as under climate change scenarios, and also allows for finer resolution of community function because community trait composition determines the rates of significant processes, including carbon export. Although understanding of trait biogeography is growing, uncertainties remain that stem, in part, from the paucity of observations describing plankton functional traits. Thus, in addition to recommending widespread adoption of the trait‐based approach, we advocate for enhanced collection, standardisation and dissemination of plankton functional trait data.     

汞在新建水库食物网中生物累积与风险评价研究进展

汞是唯一参与全球循环的液态重金属。1974年,自美国学者Smith首次报道水库中鱼类总汞含量高于邻近自然湖泊以来,水库中鱼类汞升高的风险成为新建水库环境影响评价中的重要内容之一。汞在水库生态系统生物组分和非生物组分中含量升高的现象先后在世界各国报道,包括加拿大、美国、芬兰、泰国和巴西等。通过对系列的野外研究进行回顾,表明了水库形成后生态系统中汞的甲基化过程发生了变化。水库形成对汞在食物网中的鱼类、底栖生物、浮游生物的累积产生影响。水库中汞的生物累积、迁移转化主要与被淹没土壤和植物腐解过程有着直接或间接的关系。水库形成后,总汞、甲基汞和甲基汞比例在生态系统食物网各组分中的变化并不一致。蓄水后,水体中总汞变化较小,甲基汞和甲基汞比例上升明显;浮游生物尤其是浮游动物中总汞升高,但甲基汞和甲基汞比例升高更为明显;与浮游动物类似,底栖水生昆虫中总汞升高,甲基汞和甲基汞比例升高也更为明显;鱼类作为食物网顶级消费者,甲基汞比例一般在80%以上,在水库形成后鱼类总汞和甲基汞均明显升高,但甲基汞比例变化已经不大。这些变化揭示了水库形成后甲基汞在食物网传递的两个主要可能途径,一是微型生物食物网。通过悬浮颗粒物、浮游植物、浮游动物这一环节,甲基汞和甲基汞比例有明显的增加。第二个途径是底层生物食物网。通过悬浮颗粒物、细菌、碎屑食性底栖水生昆虫、肉食型底栖水生昆虫环节,甲基汞和甲基汞比例明显增加。这两种途径均能导致以水生昆虫、小鱼、甲壳类等为食的肉食性鱼类汞含量增加。水库形成后,生态系统中汞的甲基化发生了明显的"加速"过程。这种"加速"过程最直接的因素是成库后大量土壤淹没使得汞的甲基化平衡被打破。这个过程主要有两方面的影响。一方面是直接影响,被淹没土壤和植被在腐解过程中主动或被动地将甲基汞释放到水库生态系统中;另一方面是间接影响,被淹没土壤和植被的腐解使水库底部形成厌氧环境,有利于无机汞从被淹没土壤和植被中溶出,为甲基化反应提供充裕的、可供甲基化的无机汞,同时腐解产生的大量营养物质为微生物提供丰富食物来源,使硫酸盐还原菌大量繁殖,促进无机汞的甲基化。在我国,有关汞在新建水库食物网中生物累积和风险评价的研究有待进一步加强。