海洋浮游纤毛虫包囊的研究进展*

作为微型浮游动物的重要组成部分,海洋浮游纤毛虫是连接微食物环和经典食物链的重要中介。有些浮游纤毛虫在生活周期中会形成包囊,条件适宜时包囊会萌发,这对纤毛虫种群动态有重要的意义。目前国际上对于浮游纤毛虫生态学的研究主要集中在其营养期细胞,浮游纤毛虫包囊的研究尚少,中国还没有这方面的研究。本文对浮游纤毛虫包囊研究进展进行概述,包括包囊的形态、沉积物中包囊的丰度、包囊形成的环境因素、包囊萌发过程及环境因素对包囊萌发的影响等方面,希望对国内开展浮游纤毛虫包囊的研究有所裨益。     

Rotifers as predators on components of the microbial web (bacteria,heterotrophic flagellates,ciliates) — a review

Recent investigations have shown that processes within the planktonic microbial web are of great significance for the functioning of limnetic ecosystems. However, the general importance of protozoans and bacteria as food sources for rotifers, a major component of planktonic habitats, has seldom been evaluated. Results of feeding experiments and the analysis of the food size spectrum of rotifers suggest that larger bacteria, heterotrophic flagellates and small ciliates should be a common part of the food of most rotifer species. About 10–40 per cent of rotifers' food can consist of heterotrophic organisms of the microbial web. Field experiments have indicated that rotifer grazing should generally play a minor role in bacteria consumption compared to feeding by coexisting protozoans. However, according to recent experiments regarding food selection, rotifers should be efficient predators on protozoans. Laboratory experiments have revealed that even nanophagous rotifers can feed on ciliates. Preliminary microcosm and chemostat experiments have indicated that rotifers, due to their relatively low community grazing rates compared to the growth rates of bacteria and protozoans, should generally not be able (in contrast to some cladocerans) to suppress the microbial web via grazing, though they may structure it. Filter-feeding nanophagous rotifers (e.g. brachionids) seem to be significant feeders on the smaller organisms of the microbial web (bacteria, flagellates, small ciliates), whereas grasping species (e.g. synchaetids and asplanchnids) seem to be efficient predators on larger organisms (esp. ciliates). Another important role of rotifers is their feedback effect on the microbial web. Rotifers provide degraded algae, bacteria and protozoans to the microbial web and may promote microbial activity. Additional experimental work is necessary for a better understanding of the function of rotifers in aquatic ecosystems.     

Predation by Acartia tonsa Dana on planktonic ciliates and rotifers

In laboratory experiments, adults and nauplii of the calanoid copepod Acartia tonsa Dana feed on planktonic ciliates and rotifers. Adults have a higher clearing rate for planktonic ciliates and rotifers than for phytoplankton. Adult copepods have a maximum clearing rate of ≈200 ml copepod⁻¹ · d⁻¹ for large ciliates, with lower clearing rates for small ciliates. Nauplii have higher clearance for small than for large ciliates. Addition of ciliates or rotifers to the diet of A. tonsa enhances egg production; this effect is due to improved food quality. Microzooplankton may be an important component of the diet of A. tonsa even when phytoplankton are plentiful. Selective predation by copepods probably influences the population dynamics of planktonic ciliates and rotifers in coastal waters.     

Trophic coupling within the microbial food web: a study with fine temporal resolution in a eutrophic freshwater ecosystem

• 1 The major components of the microbial food web (dissolved organic carbon, bacteria, protozoa, rotifers and algae) of Priest Pot, a small freshwater pond, were investigated over a period of 5 months. Water samples were collected from the epilimnion every 1–3 days.
• 2 Time series analysis helped identify the trophic relationships within the planktonic community. There were strong predator—prey relationships between both ciliates and large rotifers and the total nanoplankton, between rotifers and small ciliates and between the total microzooplankton community and phytoplankton. Small rotifers and small ciliates probably share the same food resources. The major bacterivores in the system could not be identified with our methods. However, our previous results point to a dominating role of nanoplanktonic (2–20 μm) heterotrophic protists as the main grazers of bacteria.
• 3 Rotifers are the major type of metazoan zooplankton in Priest Pot; crustacean zooplankton are absent from the community. Bacterial production probably reaches rotifers via a variety of pathways: there may be a three-step link from bacteria to bacterivorous nanoplankton, to ciliates and then to rotifers. Furthermore, a strong correlation between the nanoplankton and rotifers suggests a direct link between these components, implying a much shorter pathway. Some of the rotifers in the pond can graze directly on bacteria, and many of the larger planktonic organisms (large ciliates and rotifers) are algivores. The latter two predator—prey relationships suggest an efficient transfer of bacterial and primary production to higher trophic levels.

     

Live labeling technique reveals contrasting role of crustacean predation on microbial loop in two large shallow lakes

We tested the hypotheses that the ciliate assemblages in moderately eutrophic lake are controlled by the effective crustacean predation, and the high abundances of planktonic ciliates in highly eutrophic and turbid lake are due to insufficient regulation by crustacean zooplankton. A food tracer method coupled with natural assemblage of microciliates labeled with fluorescent microparticles was used to measure the cladoceran and copepod predation rates on planktonic ciliates and to estimate the carbon flow between the ciliate–crustacean trophic links. The results revealed that the microciliates (15–40 μm) were consumed by all dominant cladoceran and copepod species in both the lakes studied, mainly by Chydorus sphaericus and cyclopoid copepods in Lake Võrtsjärv, and by Daphnia spp. and Bosmina spp. in Lake Peipsi. The grazing loss in moderately eutrophic Peipsi indicated strong top-down control of ciliates mainly by cladocerans. The extraordinary abundant population of planktonic ciliates having a predominant role in the food web in highly eutrophic and turbid Võrtsjärv is explained by the measured low crustacean predation rates on ciliates. The estimated carbon flow from the ciliates to crustaceans suggest that in eutrophic lakes majority of the organic matter channeled via metazooplankton to higher trophic levels may originate from the microbial loop.     

Planktonic Food Web Structure along the Sau Reservoir (Spain) in Summer 1997

We studied the planktonic food web in eutrophic Sau Reservoir (Catalonia, NE Spain). Along the longitudinal axis from the Ter River downstream to the dam, we characterized a microbial succession of food web dominance of bacteria‐HNF‐ciliates. The Ter River transports a large load of organic material into the reservoir, with a bacterial density of ∼9 · 10⁶ large cells per ml. While at the first lacustrine station of the Reservoir HNF were the dominant bacterial consumers, at the others, an oligotrich ciliate, Halteria grandinella, was the main protozoan bacterivore. Most of the bacterial production in the reservoir epilimnion was consumed by grazing. The spatial succession of the reservoir microbial food webs was followed downstream by maximum densities of their potential predators among zoo‐plankters – rotifers, and early developmental stages of copepods.     

Trophic coupling of the microbial and the classical food web in Lake Baikal,Siberia

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Unimodal patterns of microbial communities with eutrophication in Mediterranean shallow lakes

The role of the microbial communities in the classical planktonic food web and its response to eutrophication in shallow lakes is still contradictory. Mediterranean shallow lakes with different eutrophication levels were sampled to study the influence of eutrophication on the microbial food web (MFW) and their contribution to the planktonic food web. Percentage of ciliate biomass in the metazooplankton (MZP) showed a U-shaped trend with eutrophication, with maximum at both ends of the chlorophyll-a (Chla) gradient. The MZP to phytoplankton ratio demonstrated a unimodal pattern with minimum values at the two ends of the Chla gradient and maximum values in the Chla range 5-10 μg l^?1. In contrast, the MFW to phytoplankton ratio reached its minimum in the central part of the Chla gradient and maximum values at the extremes of the gradient. These patterns support the hypothesis that the relative importance of bacteria and ciliates is lowest in mesotrophic shallow lakes, and highest in oligotrophic and hypereutrophic systems. These results stress the importance of protozoan in the trophic web, and indicate it is essential to include this group, especially ciliates, when quantifying zooplankton in warm shallow lakes.     

Seasonal and vertical distribution of the ciliated protozoa and micrometazoa in Kaštela Bay (central Adriatic)

Seasonal and vertical distribution of tintinnids, non-loricate ciliates and micrometazoa were studied in Kaštela Bay (central Adriatic Sea) throughout 1995. The species composition of tintinnids and copepods were studied as well. This is the first estimation of non-loricate ciliate biomass in the coastal area of the central Adriatic. Non-loricate ciliates were quantitatively the best represented ciliated protozoa, whereas nauplii were the most numerous micrometazoan organisms. Temperature affected the distribution of most micrometazoan components of the zooplankton and that of non-loricate ciliates. The temperature-dependent presence of individual size categories of non-loricate ciliates was also established. Apart from the interaction between microzooplankton groups, the influence of biotic factors, such as phytoplankton, bacteria, non-pigmented nanoflagellates (NNF) and mesozooplankton, was also discussed. The abundance of ciliates was controlled by both food supply (phytoplankton and NNF) and micrometazoan grazing. The results point to very complex trophic relationships within the planktonic community, suggesting that microzooplankton could be an important link between the microbial food web and higher trophic levels. Received in revised form: 8 November 2000 Electronic Publication     

The influence of humic substances on lacustrine planktonic food chains

Humic substances (HS) might influence planktonic food chains in lakes in two ways: 1) by altering the physical or chemical environment and thus modifying autotrophic primary production and the dependent food chains; 2) by acting as a direct carbon/energy source for food chains. HS compete with phytoplankton for available quanta underwater and this effect is seen in the reduced euphotic zone depth in lakes with high concentrations of HS. Thus potential photosynthetic production is lower in the presence of HS. However, this effect can be offset in small lakes in which the depth of mixing is also reduced when HS concentrations are high. Complexation by HS of important nutrients such as iron and phosphorus may also restrict primary production. Evidence is accumulating that photosynthetic primary production is insufficient to support measured metabolic activity in humic lakes, which implies that metabolism of allochthonous HS underpins much of the observed activity. Studies of bacterial abundance and growth in the presence of HS support the view that bacteria are the most significant utilisers of HS. This use is apparently facilitated by photolysis of HS, particularly by short wavelength radiation. Bacteria are grazed by both micro-zooplankton (heterotrophic and mixotrophic flagellates and ciliates) and macrozooplankton. It is within this microbial community that the food chains derived from autotrophic and allotrophic sources interact. These effects of HS on food chains are discussed in relation to possible implications for the response of different lake types to eutrophication.     

Microbial Food Webs in an Artificially Divided Acidic Bog Lake

The microbial loop of a naturally acidic bog lake, Große Fuchskuhle (Northeastern Germany), that had been artificially divided into 4 basins, was investigated. In the northeast (NE) and southwest (SW) basins, which differ strongly in chemistry and primary production, we conducted intensive studies of the main carbon fluxes through microbial food webs. In the less acidic, NE basin, much higher phytoplankton as well as bacterial biomass and production were found in parallel with negligible numbers of larger zooplankters. Weakly top-down controlled populations of protists were characterized by an exceptionally low numerical proportion of heterotrophic nanoflagellates (HNF) to ciliates (-1.5-3.5). The ciliate community was dominated by a scuticociliate, Cyclidium sp. (>95% of total ciliates), with an estimated grazing rate equal to 46–80% of heterotrophic bacterial production. In contrast, in the more humic, SW basin, both phyto- and bacterioplankton dynamics seemed to be top-down controlled by abundant populations of small fine-filter feeding cladocerans, Ceriodaphnia quadrangula and Diaphanosoma brachyurum. Consequently, ciliates disappeared from the food web structure of the SW basin, HNF dropped to negligible numbers and bacteria showed very uniform morphology, dominated by small cocci or short rods. Our investigations have shown that the division of the lake into separate compartments can lead to very different microbial food web structures with extreme species compositions.     

Production of lower-trophic organisms during incubation of unaltered deep-sea water

Incubation of unaltered deep-sea water and grazing experiment of nano- and micro- protozooplankton during incubation of deep-sea water were carried out to quantitatively characterize the planktonic structures of lower-trophic organisms and clarify the trophic pathways and controlling mechanisms involved. Phytoplankton biomass increased to 637 mg as carbon weight in a 500-l tank on Day 7 and was dominant in the planktonic structure of lower-trophic organisms. Nitrates in the incubation water was depleted after Day 7 and phytoplankton biomass decreased rapidly. On the other hand, bacteria, heterotrophic nano-flagellates and ciliates increased toward the end of incubation and were dominant in the later days of incubation. In grazing experiments on microbial organisms, bacterivory is more important for the carbon pathway in microbial food webs than herbivory when phytoplankton biomass is less than that of bacteria (low P/B conditions), while herbivory is more important than bacterivory when phytoplankton biomass is more than that of bacteria (high P/B conditions). Deep-sea water exhibited high phytoplankton productivity due to inherent high nutrients values. After depletion of nutrients, phytoplankton decreased (due also to enhanced nano- and micro-zooplankton grazing) and microbial organisms dominated. Thus, nutrients in the incubation water control the planktonic structure of lower-trophic organisms.     

Structure of planktonic microbial food web in a brackish stratified Siberian lake

The distribution of primary components of the microbial community (autotrophic pico- and nanoplankton, phototrophic bacteria, heterotrophic bacteria, microscopic fungi, heterotrophic flagellates, ciliates and heliozoa) in the water column of Lake Shira, a steppe brackish-water, stratified lake in Khakasia, Siberia (Russia), were assessed in midsummer. Bacterioplankton was the main component of the planktonic microbial community, accounting for 65.3 to 75.7% of the total microbial biomass. The maximum concentration of heterotrophic bacteria were recorded in the monimolimnion of the lake. Autotrophic microorganisms contributed more significantly to the total microbial biomass in the pelagic zone (20.2–26.5%) than in the littoral zone of the lake (8.7–14.9%). First of all, it is caused by development of phototrophic sulphur bacteria at the oxic-anoxic boundary. The concentrations of most aerobic phototrophic and heterotrophic microorganisms were maximal in the upper mixolimnion. Heterotrophic flagellates dominated the protozoan populations. Ciliates were minor component of the planktonic microbial community of the lake. Heterotrophic flagellates were the most diverse group of planktonic eucaryotes in the lake, which represented by 36 species. Facultative and obligate anaerobic flagellates were revealed in the monimolimnion. There were four species of Heliozoa and only three of ciliates in the lake.     

Structure and functioning of the microbial loop in a boreal reservoir

The abundance and biomass of the main components of the microbial plankton food web (“microbial loop”)—heterotrophic bacteria, phototrophic picoplankton and nanoplankton, heterotrophic nanoflagellates, ciliates and viruses, production of phytoplankton and bacterioplankton, bacterivory of nanoflagellates, bacterial lysis by viruses, and the species composition of protists—have been determined in summer time in the Sheksna Reservoir (the Upper Volga basin). A total of 34 species of heterotrophic nanoflagellates from 15 taxa and 15 species of ciliates from 4 classes are identified. In different parts of the reservoir, the biomass of the microbial community varies from 26.2 to 64.3% (on average 45.5%) of the total plankton biomass. Heterotrophic bacteria are the main component of the microbial community, averaging 63.9% of the total microbial biomass. They are the second (after the phytoplankton) component of the plankton and contribute on average 28.6% to the plankton biomass. The high ratio of the production of heterotrophic bacteria to the production of phytoplankton indicates the important role of bacteria, which transfer carbon of allochthonous dissolved organic substances to a food web of the reservoir.     

The toxic effects of rubber contaminants on microbial food webs and zooplankton of two lakes of different trophic status

Rubber is commonly used in recreational equipment and devicesforsampling in lakes, but there have been few studies of theeffectsof rubber on planktonic organisms. We investigated the toxiceffects of rubber on the microbial food webs of a mesotrophiclakeand a eutrophic lake. Lake water was collected by pumping via,(i) a polyvinylchloride hose and, (ii) a rubber hose. Samplesoflake water collected by each method were incubated insitu in4.25 l enclosures for four days. The lake water was sampledbeforeand after incubation to determine the concentrations ofinorganicnutrients, chlorophyll a, microorganisms (bacteria,picophytoplankton, flagellates, ciliates) and zooplankton.In the mesotrophic lake, momentary exposure (ten seconds) oflakewater to the rubber hose significantly lowered theconcentrationsof chlorophyll a, bacteria, picophytoplankton and somespecies of zooplankton (Boeckella hamata, Bosmina,androtifers), relative to those in water exposed to the plastichose;flagellates, ciliates and Ceriodaphnia dubia were notsignificantly affected. In the eutrophic lake, the effects oftherubber hose on components of the microbial food web were muchlesssevere, and were consistent with the lake's high levels ofdissolved organic carbon (DOC), which is known to chelatetoxicmetals in water.     

Parasitic Life Styles of Marine Dinoflagellates1

Several genera of marine dinoflagellates contain species that have evolved parasitic life styles. Dinoflagellate infections have been reported for a wide range of host organisms including sarcodines. ciliates, free-living dinoflagellates, various invertebrates, and a few vertebrates. Some dinoflagellates even parasitize other parasitic dinoflagellates. Most species are obligately parasitic and rely on heterotrophy as their sole means of nutrition; however, some are mixotrophic, as they possess chloroplasts during part or all of their life cycle. Many are ectoparasites that use highly specialized structures to attach to their host and feed, while others are intracellular parasites that feed by osmotrophy. Parasitic dinoflagellates often have adverse effects on their host that can lead to reproductive castration or death. The ecological importance of parasitic dinoflagellates is particularly evident during epidemic outbreaks that cause mass mortality of host organisms. Species that infect fish can pose threats to aquaculture. while other species can make commercially important crustacea unpalatable. In the planktonic realm, parasitic dinoflagellates influence the structure and function of the microbial food web. They compete with copepods and other grazers by utilizing ciliates as hosts and can stimulate rapid recycling of nutrients by causing the decline of toxic and non-toxic red tides.     

Does metazooplankton regulate the ciliate community in a shallow eutrophic lake?

1. As grazers on picoplankton and nanoplankton, planktonic ciliates form an important link in pelagic food webs. Ciliate communities may be controlled by predation by metazooplankton. In eutrophic systems, however, where the number of large crustaceans is often low, the mechanisms that regulate ciliate dynamics have rarely been described. 2. We conducted an enclosure experiment with natural and screened (145 μm) summer plankton communities to investigate the effect of the small‐sized crustacean zooplankton on ciliate community structure and the microbial loop in a shallow eutrophic lake. 3. The removal of the larger fraction of crustaceans initiated a decrease in total ciliate abundance. At the community level, we observed a substantial increase in large‐sized predacious ciliates (>100 μm) and a simultaneous decrease in the abundance of smaller ciliates (<20–40 μm) that were mostly bacterivores and bacterio‐herbivores. The compositional shift in the ciliate community, however, did not cascade down to the level of bacteria and edible phytoplankton.     

Changes in the pelagic microbial food web due to artificial eutrophication

The effect of nutrient enrichment on the structure and carbon flow in the pelagic microbial food web was studied in mesocosm experiments using seawater from the northern Baltic Sea. The experiments included food webs of at least four trophic levels; (1) phytoplankton–bacteria, (2) flagellates, (3) ciliates and (4) mesozooplankton. In the enriched treatments high autotrophic growth rates were observed, followed by increased heterotrophic production. The largest growth increase was due to heterotrophic bacteria, indicating that the heterotrophic microbial food web was promoted. This was further supported by increased growth of heterotrophic flagellates and ciliates in the high nutrient treatments. The phytoplankton peak in the middle of the experiments was mainly due to an autotrophic nanoflagellate, Pyramimonas sp. At the end of the experiment, the proportion of heterotrophic organisms was higher in the nutrient enriched than in the nutrient-poor treatment, indicating increased predation control of primary producers. The proportion of potentially mixotrophic plankton, prymnesiophyceans, chrysophyceans and dinophyceans, were significantly higher in the nutrient-poor treatment. Furthermore, the results indicated that the food web efficiency, defined as mesozooplankton production per basal production (primary production + bacterial production − sedimentation), decreased with increasing nutrient status, possibly due to increasing loss processes in the food web. This could be explained by promotion of the heterotrophic microbial food web, causing more trophic levels and respiration steps in the food web.     

A comparison of zooplankton densities and biomass in Lakes Peipsi and Võrtsjärv (Estonia): rotifers and crustaceans versus ciliates

The abundance and biomass of ciliates, rotifers, cladocerans and copepods were studied in Lake Peipsi and Lake Võrtsjärv, both of which are shallow, turbid and large. Our hypothesis was that in a large shallow eutrophic lake, the ciliates could be the most important zooplankton group. The mean metazooplankton biomass was higher in Peipsi than in Võrtsjärv (mean values and SD, 1.8 ± 0.7 and 1.3 ± 0.6 mg WM l^?1). In Peipsi, the metazooplankton biomass was dominated by filtrators that feed on large-sized phytoplankton and are characteristic of oligo-mesotrophic waters. In Võrtsjärv, the metazooplankton was dominated by species characteristic of eutrophic waters. The planktonic ciliates in both lakes were dominated by oligotrichs. The biomass of ciliates was much greater in Võrtsjärv (mean 2.3 ± 1.4 mg WM l^?1) than in Peipsi (0.1 ± 0.08 mg WM l^?1). Ciliates formed about 60% of the total zooplankton biomass in Võrtsjärv but only 6% in Peipsi. Thus, the food chains in the two lakes differ: a grazing food chain in Peipsi and a detrital food-chain in Võrtsjärv. Consequently, top-down control of phytoplankton can be assumed to be much more important in Peipsi than in Võrtsjärv. When the detrital food chain prevails, the planktonic ciliates become the most important zooplankton group in shallow, eutrophic and large lake. Neglecting protozooplankton can result in serious underestimates of total zooplankton biomass since two-thirds of the zooplankton biomass in Võrtsjärv comprises ciliates.     

The importance of herbivory by protists in lakes of a tropical floodplain system

Inland aquatic ecosystems play a critical role in the global carbon cycle, processing a great fraction of the organic matter coming from terrestrial ecosystems, and the microbial food web is crucial in this process. Thus, we aimed to evaluate whether the food resource of planktonic protozoa comes mainly from small primary producers or heterotrophic bacteria in tropical shallows lakes, assuming the hypothesis that, in general, picocyanobacteria would be the main food resource for protists. We also expected that the autotrophic fraction would be mainly related to protists at the surface of the environments, while the heterotrophic fraction would be more important at the lower strata of the water column. We performed size-fractionation experiments to evaluate the effects of predation of protists on heterotrophic bacteria and picocyanobacteria. We also sampled planktonic organisms at the subsurface and bottom of 20 lakes in a Neotropical floodplain. We found an herbivory preference of heterotrophic flagellates, while ciliates seem to exert a stronger impact on heterotrophic bacteria. We also found no relationship between heterotrophic bacteria and protists in the field data, whereas positive relationships between picocyanobacteria and protists were observed in environments where there was sunlight. Thus, both heterotrophic bacteria and picocyanobacteria were important components in the food webs of tropical shallow lakes. Moreover, the trophic cascade caused by zooplankton predation suggests that protists are efficient in transferring the energy from the base of microbial food webs to higher trophic levels.