Influence of metazooplankton on interactions of bacteria and phytoplankton in an oligotrophic lake

Commensalism based on organic carbon supplied by phytoplanktonand competition for mineral nutrients are important interactionsbetween bacteria and phytoplankton in oligotrophic clear-watersystems. Both interactions are influenced by zooplankton activity.To examine the relation ship between algae and bacteria in LakeLa Caldera, we studied: the correlations among phyto plankton,bacteria and phosphorus (P) dynamics; the ratio of organic carbonsupplied by algae to organic carbon demand by bacteria; andthe importance of P remineralized by metazooplankton for bothcommunities. Phytoplankton and bacteria had a similar seasonaldynamics, and there was a sig nificant and positive relationshipbetween bacterial abundance and algal biomass (P<0.01). However,the release of organic carbon from phytoplankton was usuallyhigher than the bacterioplankton carbon requirement. P availablevia zooplankton remineralization satisfied between 74 and 316%of the minimum P demands of algae and bacteria. To elucidatewhether zooplankton operate similarly on algae and bacterialgrowth or indirectly influence bacterial growth through phytoplanktonmetab olism, we performed zooplankton manipulation experiments.High zooplankton biomass in these experiments stimulated bothprimary and bacterial production, but release of organic carbonfrom phytoplankton declined. These results suggest a directstimulus of bacterial growth, so algae and bac teria can balancegrazing losses by compensatory growth. Further, the algal decreaseof the organic carbon supply for bacteria could, over time,lead to a change in the algae-bacteria interaction from competitionto commensalism. This reduction in organic carbon excretioncould affect the balance of the competitive interaction.     

How important is the crustacean plankton for the maintenance of water clarity in shallow lakes with abundant submerged vegetation?

• 1 We measured the abundance and biomass of filter‐feeding microcrustacean zooplankton and calculated their grazing impact on phytoplankton biomass during summer in five shallow, mesotrophic to eutrophic lakes. For three of the lakes data exist both from years with dense submerged vegetation and low turbidity (the clearwater state), as well as from years characterised by sparse vegetation and high turbidity (the turbid state). In the other two lakes data are available only for clearwater conditions.
• 2 In all lakes conditions of dense vegetation and clear water coincided with a low abundance of crustacean plankton during summer. In the three lakes that shifted, the calculated biovolume ingested by crustacean plankton (filtering rate) was 3–11 times lower during clearwater conditions compared with turbid conditions. Because phytoplankton biomass was lower during clearwater conditions, however, daily grazing pressure from microcrustacea (expressed as percentage of phytoplankton biomass) did not differ between states. In three of the five lakes, grazers were estimated to take less than 10% of the phytoplankton biomass per day, indicating filtration by zooplankton was not the most important mechanism to maintain clearwater conditions.
• 3 High densities of Cladocera were found in three of the lakes within dense stands of Charophyta. However, these samples were dominated by plant‐associated taxa that even during the night were rarely found outside the vegetation. This indicates that plant‐associated zooplankton has no major influence on the maintenance of water clarity outside the vegetation.
• 4 Spring peak abundance of Cladocera was observed in three of the lakes. In two of these, where seasonal development was studied in both the clearwater and the turbid state, spring peaks were lower during the clearwater state.
• 5 Predation, low food availability or a combination of both may explain the low zooplankton densities. Phytoplankton may be limited by low phosphorus availability in the lakes dominated by Charophyta. Our results indicate that the importance of zooplankton grazing may have minor importance for the maintenance of the clearwater state in lakes with dense, well‐established submerged vegetation.

     

Seasonal dynamics of crustacean zooplankton, heterotrophic nanoflagellates and bacteria in a shallow, eutrophic lake

1. The seasonal development of crustacean zooplankton, heterotrophic nanoflagellates (HNF) and bacteria was examined in Grosser Binnensee, a shallow, eutrophic lake in northern Germany. The grazing impact of Daphnia on bacteria and nanoflagellates was estimated from field data on population abundances and from clearance rates obtained in laboratory experiments. 2. The seasonal succession of zooplankton showed distinct peaks of Daphnia magna, cyclopopid copepods, Bosmina longirostris and Daphnia galeata and D. hynlina. The population dynamics of Dapfinia had the strongest impact on all sestonic components. Daphnia maxima coincided with clearwater phases, and were negatively correlated with particulate organic carbon (POC), HNF and phytoplankton. Bacterial abundance was only slightly affected although daphnids were at times more important as bacterial consumers than HNF, as estimated from measured bacterial clearance rates. Other crustaceans (copepods, Bosmina) were probably of minor importance as grazers of bacteria and nanoplankton. 3. HNF abundance varied from 550 ml^?1 to more than 30000 ml^?1. HNF appeared to be suppressed by daphnids and reached highest densities when copepods dominated the metazooplankton. The variation in HNF abundance was not reflected in the concentration of heterotrophic bacteria, which fluctuated rather irregularly between 5 and 20 ± 10⁶ ml^?1. Long filamentous bacteria which were probably resistant to protozoan grazing, however, appeared parallel to the development of HNF. These bacterial cells, although small in number, could comprise more than 30% of the total bacterial biomass.     

Response of phytoplankton and bacteria to nutrients and zooplankton: a mesocosm experiment

Although both nutrient inputs and zooplankton grazing are importantto phytoplankton and bacteria in lakes, controversy surroundsthe relative importance of grazing pressure for these two groupsof organisms. For phytoplankton, the controversy revolves aroundwhether zooplankton grazers, especially large cladocerans likeDaphnia, can effectively reduce phytoplankton populations regardlessof nutrient conditions. For bacteria, little is known aboutthe balance between possible direct and indirect effects ofboth nutrients and zooplankton grazing. However, there is evidencethat bacteria may affect phytoplankton responses to nutrientsor zooplankton grazing through direct or apparent competition.We performed a mesocosm experiment to evaluate the relativeimportance of the effects of nutrients and zooplankton grazingfor phytoplankton and bacteria, and to determine whether bacteriamediate phytoplankton responses to these factors. The factorialdesign crossed two zooplankton treatments (unsieved and sieved)with four nutrient treatments (0, 0.5, 1.0 and 2.0 µgphosphorus (P) l^–1 day^–1 together with nitrogen(N) at a N:P ratio of 20:1 by weight). Weekly sieving with 300µm mesh reduced the average size of crustacean zooplanktonin the mesocosms, decreased the numbers and biomass of Daphnia,and increased the biomass of adult copepods. Nutrient enrichmentcaused significant increases in phytoplankton chlorophyll a(4–5x), bacterial abundance and production (1.3x and 1.6x,respectively), Daphnia (3x) and total zooplankton biomass (2x).Although both total phytoplankton chlorophyll a and chlorophylla in the <35 µm size fraction were significantly lowerin unsieved mesocosms than in sieved mesocosms, sieving hadno significant effect on bacterial abundance or production.There was no statistical interaction between nutrient and zooplanktontreatments for total phytoplankton biomass or bacterial abundance,although there were marginally significant interactions forphytoplankton biomass <35 µm and bacterial production.Our results do not support the hypothesis that large cladoceransbecome less effective grazers with enrichment; rather, the differencebetween phytoplankton biomass in sieved versus unsieved zooplanktontreatments increased across the gradient of nutrient additions.Furthermore, there was no evidence that bacteria buffered phytoplanktonresponses to enrichment by either sequestering P or affectingthe growth of zooplankton.     

Spatial patterns and relationships between phytoplankton, zooplankton and water quality in the Saimaa lake system, Finland

The interactions between phytoplankton and zooplankton were studied in two large lakes in the Saimaa lake system, Finland. Both are subjected to substantial waste water loading, and exhibit a clear trophic gradient between the loaded and unloaded areas. The phytoplankton and zooplankton were compared in terms of composition, abundance and biomass at 34–39 stations located in different parts of the lakes. At least four mechanisms were thought to affect the composition of plankton communities: (1) the amount of nutrients (trophic gradient), (2) grazing of algae by herbivores, (3) the effect of the algal species composition on feeding by zooplankters (large, colonial algae in the more loaded parts of the lakes) and (4) the regeneration and reorganization of nutrients.     

Bacterioplankton interactions with Daphnia and algae in experimental enclosures

Development of bacterioplankton was studied by manipulation of planktivorous fish and/or nutrients in experimental enclosures in a fish pond. Grazing pressure exerted by large zooplankton (Daphnia galeata and Daphnia pulicaria) strongly influenced the counts and size distribution of bacterial populations. Morphometric analyses by scanning electron microscope revealed a shift in size distribution from larger mainly rod-type bacteria under low grazing pressure towards smaller mainly coccus-type under strong grazing pressure. The metabolic activity of bacteria measured as glucose uptake was higher under strong grazing pressure. After removal of large daphnids, the increase in bacterial density was probably the result of two additive factors: low grazing pressure and high level of dissolved organic matter (DOM) due to photosynthetic activity of more abundant algae. Composition of bacterial populations shifted toward larger, rod-type bacteria, and their metabolic efficiency measured by uptake, was lowered. The basic dimensionality of the system and interactions between variables was describe by R-mode factor analysis. The manipulated enclosures were relate with factor score.     

Nutrient Utilization Strategies of Algae and Bacteria after the Termination of Nutrient Amendment with Different Phosphorus Dosage: A Mesocosm Case

The impacts of nutrient amendment termination on the growth strategies of algae and bacteria were conducted in experimentally designed mesocosm in which two different phosphorus (P) dosages were treated. The algal community composition did not change greatly in Group A (low phosphorus) and Group B (high phosphorus). In Group A, the secretion of bacterial alkaline phosphatase (AP) after nutrient termination stimulated bacterial phosphorus acquisition, which caused the decrease in algal phosphorus levels, in terms of the increase of bacterial abundance and bacterial production, as well as the decrease in chlorophyll a and particulate organic carbon. The algal collapse resulted in dissolved organic carbon secretion, further fuelling bacterial growth. In Group B, excess phosphorus input urged algae to store phosphorus as poly-phosphate. When phosphorus input ceased, in order to maintain their used high phosphorus demand, algae strengthened to gain phosphorus through the hydrolysis of dissolved organic phosphorus in water column and ploy-phosphate inside the cells by AP, evidenced by high algal alkaline phosphatase activity, algal growth continuation, and bacterial growth decline. These facts indicated that phosphorus content should reduce to a lower level than expected, so that algal bloom can be effectively controlled in eutrophic water bodies.     

Dissolved organic carbon released by zooplankton grazing activity-a high-quality substrate pool for bacteria

Experiments were designed to investigate whether processes relatedto zooplankton feeding have a positive effect on bacterial growth.Bacterial abundance and [³H]thymidine incorporation rates werefollowed in grazer-free batch cultures originally containingeither Scenedesmus quadricauda or Rhodomonas lacustris as foodsources, and Daphnia cucullata or Eudiaptomus graciloides asgrazers. Compared with controls lacking either animals or algae,a significantly higher bacterial abundance and productivityoccurred in cultures which contained both phyto- and zoo-plankton.The same experimental methodology was tested during the declineof a diatom spring bloom in a eutrophic, temperate lake. A significantincrease in bacterial biomass was observed due to the grazingactivity of in situ mesozooplankters during the clear-waterphase. Our results demonstrated that the dissolved carbon pathwayfrom mesozooplankton to bacteria averaged 57% (26–78%)of the algal carbon filtered from suspension.     

An artificial neural network approach for studying phytoplankton succession

Artificial neural networks are used to model phytoplankton succession and gain insight into the relative strengths of bottom-up and top-down forces shaping seasonal patterns in phytoplankton biomass and community composition. Model comparisons indicate that patterns in chlorophyll aconcentrations response instantaneously to patterns in nutrient concentrations (phosphorous (P), nitrite and nitrate (NO₂/NO₃–N) and ammonium (NH₄–H) concentrations) and zooplankton biomass (daphnid cladocera and copepoda biomass); whereas lagged responses in an index of algal community composition are evident. A randomization approach to neural networks is employed to reveal individual and interacting contributions of nutrient concentrations and zooplankton biomass to predictions of phytoplankton biomass and community composition. The results show that patterns in chlorophyll aconcentrations are directly associated with P, NO₂/NO₃–N and daphnid cladocera biomass, as well as related to interactions between daphnid cladocera biomass, and NO₂/NO₃–N and P. Similarly, patterns in phytoplankton community composition are associated with NO₂/NO₃–N and daphnid cladocera biomass; however show contrasting patterns in nutrient– zooplankton and zooplankton–zooplankton interactions. Together, the results provide correlative evidence for the importance of nutrient limitation, zooplankton grazing and nutrient regeneration in shaping phytoplankton community dynamics. This study shows that artificial neural networks can provide a powerful tool for studying phytoplankton succession by aiding in the quantification and interpretation of the individual and interacting contributions of nutrient limitation and zooplankton herbivory on phytoplankton biomass and community composition under natural conditions.     

Phytoplankton periodicity in a subtropical lake (Lake Kinneret,Israel)

Lake kinneret is a subtropical monomictic lake characterized by a Pyrrhophyta-Chlorophyta assemblage, supplemented by Cyanophyta in some years. Concerning their abundance and seasonal occurrence, the phytoplanktonic algae belong to two groups: algae appearing in quantity at a definite annual period and algae present throughout the year. Four stages of algal succession occur in the lake. There is a marked periodicity in the phytoplankton composition with a high standing stock in winter-spring, due to the dinoflagellate water-bloom, and a low one during the summer months, related to the high stability of summer stratification. The annual succession at the species level has been an almost constant event in the lake for many years.The increase in nutrient concentrations in 1973 and 1974 increased the diversity and abundance of algae (except Peridinium) but did not lead to significant changes in algal succession. Conversely, the decrease of the zooplankton grazing pressure in 1975 and 1976 facilitated the development of algal maxima during summer-fall. They were caused by nanoplanktonic forms, and they developed without additional enrichment of nutrients. The algal abundance and diversity decreased. The years 1981 and 1982 were characterized by both an increase in phosphorus and a decrease in zooplankton. These conditions favored the concomitant abundance of many species and an increase of non-Pyrrhophyta biomass.     

Top-down control of natural phyto- and bacterioplankton prey communities by Daphnia magna and by the natural zooplankton community of the hypertrophic Lake Blankaart

Biomanipulation, through the reduction of fish abundance resulting in an increase of large filter feeders and a stronger top-down control on algae, is commonly used as a lake restoration tool in eutrophic lakes. However, cyanobacteria, often found in eutrophic ponds, can influence the grazing capacity of filter feeding zooplankton. We performed grazing experiments in hypertrophic Lake Blankaart during two consecutive summers (1998, with and 1999, without cyanobacteria) to elucidate the influence of cyanobacteria on the grazing pressure of zooplankton communities. We compared the grazing pressure of the natural macrozooplankton community (mainly small to medium-sized cladocerans and copepods) with that of large Daphnia magna on the natural bacterioplankton and phytoplankton prey communities. Our results showed that in the absence of cyanobacteria, Daphnia magna grazing pressure on bacteria was higher compared to the grazing pressure of the natural zooplankton community. However, Daphnia grazing rates on phytoplankton were not significantly different compared to the grazing rates of the natural zooplankton community. When cyanobacteria were abundant, grazing pressure of Daphnia magnaseemed to be inhibited, and the grazing pressure on bacteria and phytoplankton was similar to that of the natural macrozooplankton community. Our results suggest that biomanipulation may not always result in a more effective top-down control of the algal biomass.     

Marine macroalgae affect abundance and community richness of bacterioplankton in close proximity1

Many macroalgae employ chemical means to suppress epibiosis by micro‐ and macroorganisms. Previous studies have focused on the effects of tissue extracts of entire algae on a few bacterial isolates, thereby missing not only ecologically relevant bacteria but also natural delivery mechanisms of algal antimicrobial agents. In this study, we investigated the potential antimicrobial effects of waterborne macroalgal metabolites utilizing a culture‐independent approach to compare the bacterial community richness in seawater in the presence and absence of macroalgae. The methodology comprised the collection of planktonic bacteria in algal culture water on membrane filters followed by filter PCR and denaturant gradient gel electrophoresis (DGGE) of 16S rRNA gene sequences of harvested bacteria with universal primers. Similarity analysis distinguished two groups of macroalgae under investigation, one of which showed >55% difference, and the other <50% difference in bacterial community composition in comparison to natural seawater. The bacterial abundance in algal culture water of different algae was reduced between 20% and 50%. Further experiments demonstrated that the observed effects were caused by waterborne algal compounds. However, some bacterial types were exclusively eliminated in the presence of algae, indicating causative modes of action other than direct exposure of bacteria to waterborne compounds, such as surface‐mediated antimicrobial effects.     

Short-term productivity responses of algae and bacteria to zooplankton grazing in two freshwater lakes

SUMMARY. 1. The specific productivities of algae and bacteria were measured in short-term (4 day) experiments consisting of enclosures with natural or reduced zooplankton biomass. Experiments were repeated five times over a season in each of two lakes that differed in the background concentration of dissolved organic carbon (DOC).
2. Algal biomass as estimated by chlorophyll a was suppressed in enclosures with ambient grazer levels in six of ten experiments and enhanced in one experiment. Distribution of chlorophyll among net and nanoplankton was not significantly affected by grazing.
3. Relative to enclosures with reduced zooplankton, normal grazer biomass (97–466μg 1⁻¹ dry weight) enhanced specific algal productivity in only one of five experiments in the low DOC take and had no effect in all five experiments in the high DOC lake. The main effects of grazers on algae was through removal of biomass rather than through indirect changes in turnover rate.
4. Between experiments, bacterial density was either unaffected, or mildly enhanced (4–87%) in enclosures with ambient macrozooplankton compared to those with reduced levels. Bacterial productivity and turnover estimated by incorporation of [³H]thymidine into DNA showed different responses across experiments; increasing, declining or remaining the same with grazer minipulation. This variability was not related to differences in dissolved primary production or to background DOC between lakes or experiments. Comparison of bacterial productivities based on thymidine incorporation rates with changes in cell densities indicated that control of bacterial loss processes by macrozooplankton is more important than control of growth rates.     

Interactions between the diatom Thallasiosira pseudonanna and an associated pseudomonad in a mariculture system

The marine diatom Thallasiosira pseudonanna (3H) and several bacteria associated with it were isolated from batch cultures at the University of Delaware mariculture facility. The interaction between the algae and each of the bacteria was investigated. One of the isolates, T827/2B (Pseudomonas sp.), was incapable of surviving in f/2 culture medium unless the algae were present. When the algae and T827/2B were grown together in the f/2 medium, the bacterial growth was stimulated and the algal growth was inhibited. Bacterial filtrate had a similar effect on the algae, indicating that the bacterial effect is an indirect one most likely resulting from the excretion of a harmful compound into the medium. Preliminary characterization of the material excreted by the bacteria indicates that it s proteinaceous in nature. The interactions observed does not fit into any single category of interactions but can be explained as a combination of competition and indirect parasitism.     

Interactions between the diatom Thallasiosira pseudonanna and an associated pseudomonad in a mariculture system.

The marine diatom Thallasiosira pseudonanna (3H) and several bacteria associated with it were isolated from batch cultures at the University of Delaware mariculture facility. The interaction between the algae and each of the bacteria was investigated. One of the isolates, T827/2B (Pseudomonas sp.), was incapable of surviving in f/2 culture medium unless the algae were present. When the algae and T827/2B were grown together in the f/2 medium, the bacterial growth was stimulated and the algal growth was inhibited. Bacterial filtrate had a similar effect on the algae, indicating that the bacterial effect is an indirect one most likely resulting from the excretion of a harmful compound into the medium. Preliminary characterization of the material excreted by the bacteria indicates that it s proteinaceous in nature. The interactions observed does not fit into any single category of interactions but can be explained as a combination of competition and indirect parasitism.     

Interactions between algae and the microbial loop in experimental microcosms

We conducted a short-term microcosm experiment to study the direct and indirect effects of a bacterivore on bacteria and the dynamics of two species of green algae. We introduced Scenedesmus , Chlorella and Colpidium , a bacterivorous ciliate, successively in a carbon-rich medium. Bacteria were introduced with Scenedesmus , Chlorella and Colpidium . The experiment lasted 40 days, preventing us from detecting whether the populations had reached equilibrium. The bacterivore had a positive effect on both species of algae by limiting the abundance of bacteria. In absence of the bacterivore, bacteria did not exclude the two algal species, despite the high carbon:nutrient ratio of the medium. Unexpectedly, by the end of the experiment the bacterivore declined in all microcosms. Also, Chlorella growth was impeded by the presence of Scenedesmus . These two observations might be explained by allelopathic interactions. Our experiment suggests that the functioning of such a simple community is far more complex than assumed in previous theoretical and experimental models. Studying the dynamics of the system, however, allowed us to disentangle species interactions.     

Can a community of small-bodied grazers control phytoplankton in rivers?

1. Phytoplankton, zooplankton and grazing were monitored throughout the growing season for three years (1994–96) in the Belgian section of the River Meuse.
2. A size structure analysis of the algal community shows that there was a summer shift toward larger algal units, following a decline in phytoplankton biomass. These changes occurred after an increase in zooplankton biomass and diversity.
3. Daily filtration rates of grazers ranged from 1 to 113% day^–1 and maxima were observed during the summer period. Higher rates tended to correspond with peaks of rotifer biomass. A decline in total phytoplankton biomass within two weeks followed the increase in zooplankton biomass and filtration rate. A rapid biomass recovery was then observed, along with a shift of the algal community toward larger units. When grazing activity was not sustained, due to zooplankton fluctuations, the change in phytoplankton size structure was less marked.
4. We suggest that the composition of the phytoplankton community of large rivers may at times be controlled by grazers. However, such biotic interactions can take place only when physical constraints are reduced, i.e. when discharge is low, and when increased transfer time, high temperature and availability of grazeable algae allow high zooplankton biomass.     

Trophic relationships in the pelagic zone of Mondsee,Austria

Data are presented on nutrient concentrations, phytoplankton biovolume development, zooplankton composition and population dynamics, and fish from a deep, stratifying, alpine lake (Mondsee, Austria) during a three-year period between 1982 and 1984. Development of the phytoplankton is closely related to structuring events of the physico-chemical environment. Dissolved silicate and phosphorus concentrations are critical for the summer situation. During summer algal abundance is largely affected by grazing of zooplankton, but no clear-water phase was observed at the end of the spring peak of phytoplankton.Temperature and food are factors responsible for the timing and growth of the zooplankton populations. Because of close overlap in the epilimnion, exploitative and mechanical interference competition and predation by invertebrate and vertebrate predators are the main structuring forces acting on the zooplankton community, and hence influence phytoplankton indirectly.     

浮游动物诱发藻类群体的形成

从研究蓝藻水华形成机理的需要出发,综述了浮游动物的牧食压力对藻类群体形成的诱发作用。指出诱发藻类群体形成的化合物来自牧食性浮游动物对藻类的有效牧食,是藻类群体形成的重要原因之一,而这些诱发性的化合物并不是有关生物体的组成成分,是种间相互作用的结果。藻类群体的形成方式有源于一个母细胞的分裂和业已存在的单细胞的聚合两种方式,栅藻的诱发性群体可能是来自一个母细胞的分裂,而在其它藻类的诱发性群体形成如铜绿微囊藻则可能是业已存在的单细胞的聚合。由于藻类形成群体后能显著降低浮游动物对其牧食速率,因此,这种诱发性群体形成的现象,可以解释为藻类对变化的牧食压力的一种有效的反牧食防御策略,也是两者协同进化的结果。浮游动物对藻类群体形成的重要作用,在研究模拟蓝藻群体及水华形成值得借鉴应用。作者还提出推测,水华蓝藻的群体形成,可能就是在富营养化条件下藻类快速生长,加上浮游动物的牧食压力共同作用下联合驱动的结果,而这种群体形成很可能在积累到一定程度后,结合特定的气象水文等理化因子,就会聚集于水表“爆发”出肉眼可见的水华。因此,开展浮游动物牧食作用对水华蓝藻早期群体形成诱发效应的研究不仅能加深对水华形成的全面认识,而且对于进一步认识藻类的诱发性反牧食防御适应机制、揭示生态系统中生物之间的复杂关系也具有重要的理论意义。     

沱江浮游生物群落时空分布及相关环境因子分析

为研究沱江浮游生物群落结构的时空特征,并探讨影响其形成的环境因子,于2013年对沱江10个采样断面按季节进行采样分析。研究期间共检出浮游甲壳动物13种,以中小型枝角类和剑水蚤为主; 尽管桡足类密度与枝角类接近,但由于体型原因桡足类生物量始终占据优势地位。检出浮游植物7门95种,优势属7个,全年均以硅藻为主。两类生物在上游资阳市区的断面中总生物量最高,中游农村断面最低; 其生物量季节变化也趋于一致,均在丰水季节8月取得最高值,枯水季节2月最低。与历史数据相比,呈现出浮游植物增多,浮游甲壳动物减少的趋势。根据结构方程模型(SEM)和冗余分析(RDA)的结果,浮游甲壳动物生物量在浮游植物生物量和溶氧高的环境中较大,桡足类对溶氧的要求比中小型枝角类高。浮游植物对高温、高营养和高pH较偏好,尤其是一些优势属。尽管受浮游植物生物量影响,浮游动物对浮游植物的控制力却极弱。在流速缓慢且污染较严重的城市江段浮游植物密度已高达2.7107 cells/L,浮游动物尽管能选择性地以部分浮游植物为食,对其控制力却极弱,如不加强污染控制,沱江可能有暴发水华的危险。