Rotifer Abundance Research Articles

Nutrient addition increases rotifer abundance and diversity in a temperate bog

Rotifers are among the smallest metazoan animals living in lakes, ponds, rivers and in interstitial water within Sphagnum mats. When in sufficient numbers they are capable of regenerating large amounts of nitrogen (N) as NO3 and NH4 and phosphorus (P) as PO4; all of these nutrients are immediately available to bog plants. The ecological role of rotifers in bog ecosystems has been recognized at both local and global scales, but the effect of N and P addition on rotifers in bogs remains unknown. Here we present data on the influence of N and P addition on rotifers at a temperate Canadian bog dominated by Sphagnum mosses. We found that rotifer species abundance and diversity were significantly higher in surficial pore water after long-term exposure to increased N and P addition than in the control. A change in plant species distribution and increased rotifer abundance may partly explain the faster decomposition rates, jeopardizing the carbon sink capacity of bogs.

Species composition and abundance of rotifers (Rotifera: Eurotatoria) in Thrissur Kole wetland, Kerala, India.

Species composition and abundance of rotifers (Rotifera: Eurotatoria) in Thrissur Kole wetland, Kerala, India.

Ice-on and ice-off dynamics of ciliates and metazooplankton in the \u0141ucza\u0144ski Canal (Poland)

The ciliate–metazooplankton trophic coupling is well documented from both laboratory and field experiments. The knowledge about these relationships during winter ice-covered periods is very scarce. The abundance and composition of planktonic ciliates, rotifers and crustaceans were studied during the ice-covered and ice-free periods in the Łuczański Canal (Masurian Lakeland, Poland). We hypothesised that in winter, rotifers play a major role in the top-down control of ciliates and that ciliate–metazooplankton relationships differ not only between the ice-covered and ice-free periods, but also between ice-covered months. Our study showed that ciliates formed a significant part of zooplankton biomass during the winter ice-covered period when crustaceans occurred in very low abundances. Despite cold water temperature and the presence of ice cover, time was probably a cue that initiates zooplankton development. The ciliate, rotifer and crustacean numbers and biomass, as well as chlorophyll a concentrations, were lower in February than in ice-free periods. In the winter month with ice cover, bottom-up control by resources was more important than top-down control by zooplankton grazing in regulating ciliates. In the spring month with ice cover, crustaceans and rotifers may include ciliates as an important part of their diets. In April, the studied groups of organisms were not related to each other in contrast to the summer, when zooplankton communities were closely related to each other. In autumn, rotifers may play an important role in controlling ciliates. The abundance, composition and ciliate–metazoan relationships can vary considerably not only across seasons, but also across ice-covered months.

Use of rotifer trophic state indices to show the effect of hydrobionts and nutrients on water trophic status in mesocosms

Abstract We have determined how Crustacea, zebra mussels (Dreissena polymorpha), fish and nutrients affect the trophic state in mesocosms filled with water collected from the pelagic zone of a eutrophic lake. We hypothesized that the pool of nutrients would increase both directly due to the input of phosphorus and nitrogen and/or indirectly due to the introduction of animal biomass. We used trophic state indices based on the abundance and species structure of rotifers to assess changes in the trophic state in mesocosms. The role of small detritophages in rotifer communities increased as a result of treatments. Our results clearly demonstrated that D. polymorpha was able to reduce the trophic status of mesocosm waters as indicated by reduced rotifer trophic state indices regardless of interactions with other treatment factors. Contrary to our expectations, neither the nutrients added at the beginning of the experiment nor the introduction of crustaceans or fish affected the rotifer trophic indices.

Interactive effects of fish predation and sublethal insecticide concentrations on freshwater zooplankton communities.

Stresses imposed by insecticides and predators are possibly the most rigorous filters to which aquatic organisms are exposed in rivers and lakes associated with agricultural lands. However, their interactive effects on zooplankton communities are still unclear. This study elucidated the zooplankton community response to fish predation, the insecticide chlorpyrifos (CLP), and a combination of both factors, using a 30-day mesocosm experiment. The zooplankton assemblage was influenced by fish presence prior to CLP toxicity. Fish predation reduced microcrustacean density leading to a community dominated by microzooplankton (i.e.: rotifers and copepod nauplii). CLP decreased the species richness in treatments with and without fish, yielding an increase in the abundance of bdelloid rotifers, in the genera Lepadella and Trichocerca. The zooplankton:phytoplankton (<20μm) ratio decreased substantially when the two stressors, fish predation and insecticide toxicity, were combined. Although CLP dissipated relatively rapidly in the aqueous phase and accumulated in sediment and fish tissue, zooplankton richness was unable to recover. A possible explanation for this could be the inhibitory effect of CLP on resting stage hatchings in the sediment. Therefore, the combined effects of fish predation and CLP might influence zooplankton richness, leading to an assemblage dominated by rotifers that appeared to be resistant to both factors, with a limited capability to control phytoplankton growth. Thus, the effects of natural and anthropogenic stressors should be considered together when assessing community dynamics in aquatic ecosystems.

Long-term Variation Characteristics of Zooplankton Community Structure in Meiliang Bay, Lake Taihu

Zooplankton, as an important part of the water food chain, plays an important role in lake ecosystems. It is an important monitoring indicator for water bodies. However, due to the lack of long-term monitoring data of zooplankton community structure, there is a lack of understanding about its long-term characteristics. Based on monthly monitoring data from 1997 to 2017 of Meiliang Bay in Lake Taihu, the long-term trends of zooplankton community structure and its relation to the environment were examined. The results showed that the abundance and biomass of zooplankton in Meiliang Bay significantly decreased from 1997 to 2017 (P<0.05). In particular, the abundance and biomass of rotifer and copepod slowly declined, and the abundance of cladocerans fluctuated but its biomass presented a significant decreasing trend (P<0.05). The cladocerous biomass contributed the most to the zooplankton biomass in Meiliang Bay. The dominance of smaller cladocerans and copepods increased with decreasing rotifer density, significantly decreasing the average body size of zooplankton (P<0.05). This study indicated that zooplankton were becoming smaller, potentially weakening the top-down control on phytoplankton. In addition, zooplankton abundance and biomass showed an upward trend in spring and decreased in autumn and winter, and reached maximum values of 1406.70 ind.·L-1 and 25.64 mg·L-1, respectively, in September. In the summer, their changes were the opposite. Pearson correlation analysis showed that zooplankton community structure was significantly related to water physical characteristics (alkalinity, electrical conductivity, water depth, suspended substance, and water temperature), chlorophyll a, and nitrogen (P<0.05). This indicated that the eutrophication of Meiliang Bay in Lake Taihu had a significant impact on the community structure of zooplankton.

Biological indicators of ecological quality in typical urban river-lake ecosystems: The planktonic rotifer community and its response to environmental factors

Abstract River-lake system is the framework of the “sponge city”, tackling urban water problems of flooding. Rotifers, an essential zooplankton component of water ecosystems, are sensitive to environmental changes. However, the utility of rotifers as indicators of water quality in urban river-lake ecosystems is still unclear. We investigated the response of rotifer community to environmental factors and evaluated the availability of traditional taxonomic indicators and individual rotifer indicators in the river-lake ecosystem of Changde, south central China. A total of 95 rotifer species were identified in 15 sampling sites during a year survey. Rotifer abundance ranged from 1 (the Yuan River) to 2628 ind.·L−1 (Lake Liuye). Temperature, water depth and trophic state were the key factors for spatial-temporal variation of rotifer community in the urban river-lake ecosystems. Individual rotifer indicators, biodiversity indices, the Brachionus: Trichocerca ratio and the Keratella-index were less useful in evaluating the trophic status in this study. However, we founded that the rotifer trophic state index (TSIROT) values and total rotifer abundance were most consistent with values of the comprehensive trophic level index (TLIc). Furthermore, TSIROT values showed stability and resistance to changes when the time horizon increased. This study suggests that the TSIROT index is a reliable indicator of water quality in river-lake ecosystems with high water depth variation. This is a pilot study for evaluating of reliable bioindicators for sponge city design. Long-term studies in more sponge cities should be taken to validate our findings.

INVERTEBRATE COMMUNITIES IN HYDROGEN SULFIDE SPRINGS IN THE HIGH NORTH (USA RIVER CATCHMENT, RUSSIA)

In late July 2018, we studied the chemical composition of the water and benthic communities in two hydrogen sulfide springs in the catchment of the Iska-Shor Creek (lefthand tributary of the Usa River), as well as zoobenthos and plankton in the Usa River around the creek’s mouth. Compared to the reference site, water in the springs contained manyfold higher concentrations of chlorine, sodium, calcium, sulfate ions, and differed in the content of organic matter, heavy metals, and several micro elements. Water temperature did not exceed +6 °С. Zoobenthos abundance and biomass was low, comprising 31 taxa of invertebrates. Chironomid larvae and harpacticoids prevailed. Chironomids were the most diverse group in the creek – 20 taxa, of which 17 were found directly in the springs. Tanytarsus verralli Goetghebuer, 1928 was the most numerous species. Apart from chironomids, we found nematodes, ostracods, cladocerans, first instar larvae of mayflies, stoneflies and caddisflies, and others Dipteran families. The diversity of planktic and benthic invertebrates, and the set of dominant species showed little variation among the sites surveyed in the Usa River. The dominants in terms of abundance in the river’s benthic fauna were chironomid species from the subfamily Chironomini: Tanytarsus verralli, Cladotanytarsus (Cladotanytarsus) mancus (Walker, 1856), and Polypedilum (Pentapedilum) exsectum (Kieffer 1916). The share of roundworms decreased and the share of cyclops and water mites increased in the zoobenthos of the river downstream from the mouth of the creek. Among zooplankton dominants, the abundance of Euchlanis dilatata Ehrenberg, 1832 decreased and the share of Cladocera from the genus Bosmina increased downstream the river. Inside the area directly affected by the mineral water springs, we found a high abundance of euplanktic rotifers Asplanchna priodonta Gosse, 1850 and copepods Mesocyclops leuckarti (Claus, 1857), as well as an increased abundance of juvenile Cyclopoida. The studies have expanded our knowledge of the adaptive capabilities of invertebrates, and the ecology of aquatic communities forming in this extreme environment.

Day time variations of zooplankton species composition: observations from the wetlands of Assam, India

Abstract: Aim An attempt to justify the variations in the species composition of zooplankton over the day time period was made using the freshwater lakes of Assam, India, as a model study area. Methods The water bodies were sampled using a conical plankton net five times between 6 am and 6 pm in a day during July 2014. Apart from diversity analysis (SHE analysis), discriminant function analysis and a regression tree were built to justify the variations in the zooplankton species composition in the different time periods in a day. Results Repeated sampling during day time indicated the presence of 34 zooplankton species with varied composition over the different time periods. The species richness and abundance of Copepoda, Cladocera and Rotifer differed significantly revealed through the ANOVA (for rotifers – F4, 170 = 28.792; for cladocerans – F4, 170 = 16.343; for copepods - F4, 170 = 9.027). Apparently, the rotifer and copepod abundance was prominent during the early (6am) and late time (6pm) periods of a day while the cladoceran abundance was significant during the middle time periods (12 noon to 3pm) of a day. Variations in the relative abundance of the zooplankton species within a day were sufficient to discriminate the time periods significantly. The regression tree indicated the rotifer abundance (node 1), followed by the cladoceran and the copepod abundances (node 2). The nodes representing cladocerans explained 30.86% of the data while the copepod explained 69.14% data as a split from the rotifer groups. Conclusions A correspondence of high and low abundances of rotifers and cladocerans was characteristic of the species composition of the zooplankton in the study area. The variations in the species composition suggests that the zooplankton exhibits movements either in horizontal or vertical directions induced by physical and/or biological factors. Further studies may be adopted to elucidate the effects of the predators and environmental variables that shape the community of the zooplankton in shallow tropical lakes.

Variation of the rotifer community structure and its responses to environmental factors in Lake Liuye and its adjacent waters in Changde City, Lake Dongting Basin

城市河-湖连通使不同水文特征的水体连通构成多样化水环境，环境异质性为提高浮游动物多样性提供了多样性生境条件.为了解湖南常德柳叶湖及其邻近水体轮虫群落结构变化对不同水体连通性和异质性的响应，于2018年对柳叶湖、穿紫河和沅江常德市区河段共15个站点进行了每季度1次的轮虫群落结构和环境特征调查分析.调查期间，不同水体的营养水平呈现：穿紫河 > 柳叶湖 > 沅江，穿紫河和柳叶湖呈富营养化状态，沅江呈中营养状态.本研究共检出轮虫88种（包括亚种8种和变种1种），其中，长肢多肢轮虫（Polyarthra dolichoptera）为水系第一优势种.轮虫最高丰度为2535 ind./L，全年平均丰度空间分布呈现：柳叶湖 > 穿紫河 > 沅江；季节分布呈现：6月 > 9月 > 3月 > 12月.轮虫群落对水体连通性的响应表现为：柳叶湖、穿紫河和沅江3个水体轮虫种类组成具有一定的相似性且第一优势种相同.对异质性的响应表现为：不同水体轮虫群落年平均丰度和多样性指数存在空间差异.典范对应分析表明水温是影响轮虫群落结构变化的主要环境因子.;Urban river-lake connections in different hydrological characteristics waters result in a diverse aquatic environment, which provides heterogeneous habitat conditions and contributes to increase zooplankton diversity. To understand the effects of connectivity and heterogeneity on the rotifer community structure of Lake Liuye and its adjacent waters in Changde city of Hunan, we conducted the survey quarterly on the rotifer community structure and environmental characteristics at 15 sampling sites in Lake Liuye, Chuanzi River and the Changde section of the Yuan River in 2018. During our investigation, the trophic status in different waters decreased in the order: Chuanzi River > Lake Liuye > Yuan River. The Chuanzi River and Lake Liuye were eutrophic, and the Yuan River was mesotrophic. A total of 88 rotifer species (including 8 subspecies and 1 varietas) were recorded. Polyarthra dolichoptera was the dominant species in this system. The highest abundance of rotifers reached 2535 ind./L, and the spatial distribution of annual average abundance decreased in the order: Lake Liuye > Chuanzi River > Yuan River. The temporal distribution of abundance decreased in the order: June > September > March > December. The composition of rotifer species was similar among the three waters with the same first dominant species, while the annual average abundance and diversity indices varied according to spatial heterogeneity. Canonical correspondence analysis indicated that water temperature was the key factor to the variation of rotifer community structure.

Influence of Hydrological Heterogeneity on Rotifer Community Structure in Three Different Water Bodies in Shantou Area, Guangdong (China).

Rotifers, small but essential invertebrates in aquatic ecosystems, are sensitive to environmental changes and are proposed to be indicators of trophic state. However, the effects of hydrological heterogeneity on the rotifer community and the ability of rotifer indices to reflect trophic state across different water bodies are still unclear. Here, we investigated rotifer community structure in different seasons in the three types of water bodies: Han river downstream (HD), Reservoir (RE) and Tidal creek (TC) in Shantou City, Guangdong, China. Our findings revealed that rotifer community structure differes significantly among the three water bodies, resulting from a dominance of Keratella cochlearis, Anuraeopsis fissa and Polyarthra vulgaris, who largely accounted for the differences in water bodies. Chlorophyll-a and transparency were the main environmental drivers in RE rotifer communities, while total nitrogen, total phosphorus and salinity were the main factors in HD and TC communities. Rotifer abundance and the rotifer trophic state index decreased in the order: RE > HD > TC. However, both the Sladecek's B/T quotient and the Keratella- index decreased in the order: HD > RE > TC, which was in accordance with the Carlson's trophic index. We conclude that it is efficient to use rotifer composition in water quality assessments when comparing different water bodies. Alpha diversity of rotifers was the highest in HD, which is consistent with the intermediate disturbance hypothesis. Hydrological heterogeneity is the micro-factor that regulates rotifer community structures in the Shantou area.

Effect of salinity and food concentration on competition between Brachionus plicatilis Müller, 1786 and Brachionus calyciflorus Pallas, 1776 (Rotifera)

Natural populations of planktonic rotifers are affected by salinity and food density, among other stressors. Moreover, competition among congeneric species limits the abundance of certain rotifers in ecosystems without spatial heterogeneity and environmental fluctuations. We isolated Brachionus plicatilis and Brachionus calyciflorus from Salado River basin waterbodies and studied the demographic characteristics and competition between them at three salinity levels (0.75, 1.75 and 2.75gL–1 NaCl) and at two food concentrations (0.1×106 and 0.5×106 cells mL–1 Chlorella vulgaris). The lowest salinity level proved to be unfavourable for the population growth of B. plicatilis, but at higher salinity levels the growth was similar to that of controls (without competition), even in the presence of the competitor and at either food concentration. By contrast, the competitor almost always decreased the density of B. calyciflorus. Salinity greatly affected the peak density of B. plicatilis, whereas the effects of salinity and competition on B. calyciflorus were similar. Biomass was inversely related to salinity for both species, and was significantly affected by competition in B. plicatilis. These results show that B. calyciflorus is more adversely affected than B. plicatilis by competition and high salinity, and explain why both species can coexist in eutrophic saline lowland rivers and pampean shallow lakes.

Species richness and abundance of monogonont rotifers in relation to environmental factors in the UNESCO Sakaerat Biosphere Reserve, Thailand

The UNESCO Sakaerat Biosphere Reserve plays an important role in nature conservation and environmental protection. Previous focus on terrestrial habitats and neglect of aquatic ecosystems has resulted in an incomplete picture of biodiversity of the area. Based on the first investigation of planktonic diversity, rotifers were collected seasonally at five localities from September 2013 to May 2014 using a Schindler-Patalas plankton trap and a plankton net. Fifteen families, 25 genera and 71 species of rotifers were identified. The most diverse families were Lecanidae, Brachionidae, Lepadellidae, and Trichocercidae, accounting for 80% of the total species count. The maximum species richness was reported at the reservoir, with 57 species (80% of the total), while the minimum species richness (34) was observed at the ponds. The rainy season had the highest density, followed by winter and summer, with 149.15 N/l from an intermittent stream, and 95.43 and 50.68 N/l from a pond, respectively. Most of the sampling sites at the three seasonal occasions were dominated by a planktonic species Polyarthra vulgaris. The results indicate that the seasonal variation of the rotifer assemblage is related to the seasonal variation of physicochemical parameters.

Short-term toxicity effects of Prymnesium parvum on zooplankton community composition

Harmful algal blooms (HABs) can disrupt aquatic communities through a variety of mechanisms, especially through toxin production. Herbivorous and omnivorous zooplankton may be particularly susceptible to HAB toxins, due to their close trophic relationship to algae as grazers. In this study, the acute toxigenic effects of the haptophyte Prymnesium parvum on a zooplankton community were investigated under laboratory conditions. Total zooplankton abundances decreased during 48-h exposure, although species responses to P. parvum densities varied. Changes in community composition were driven by declines in Daphnia mendotae and Keratella spp. abundances, which resulted in an average shift in copepod abundance from 47.1 to 72.4%, and rotifer abundance from 35.0 to 7.1%. Total cladocerans were relatively unchanged in relative abundance (11.1–10.4%), though the dominant cladoceran shifted from Daphnia mendotae (61.3% of cladocerans) to Bosmina longirostris (81.5% of cladocerans). Daphnia mendotae and Keratella spp. are known to be non-selective or generalist feeders and were likely harmed through a combination of ingestion of and contact by P. parvum. Proportional increases in copepod and Bosmina abundances in the presence of P. parvum likely reflect selective or discriminate feeding abilities in these taxa. This study corroborates previous field studies showing that P. parvum can negatively affect zooplankton, reflecting species-specific differences in zooplankton-P. parvum interactions. Such changes can alter zooplankton community composition, leading to substantial food-web consequences and potential long-term ecosystem-level impacts in lakes that experience blooms.

Can zooplankton grazing affect the functional features of phytoplankton in subtropical shallow lakes? - Experiment in situ in the south of Brazil

Herbivory in aquatic environments reflects the organization of trophic webs as a structuring factor in the communities of prima-ry producers. We experimentally evaluated the influence of grazing by zooplankton and by different predator groups on the abundance and biomass of phytoplankton and morphologically-based functional groups (MBFGs), in a subtropical floodplain shallow lake (Brazil). We tested if different grazing levels modify the structure of the phytoplankton, considering that higher zooplankton abundance reduces the abundance and biomass of phytoplankton and the MBFGs. We used five treatments (5 L) with different zooplankton abundance and five replicas to represent an increasing grazing gradient. Sampling of phytoplankton and zooplankton was carried out after 24 hours, in each treatment. The zooplankton abundance presented significant differences among treatments (F = 11.79; p < 0.01), showing the evident grazing gradient in the experiment. Rotifers dominated all the treatments, followed by copepods, although their abundance decreased at the end of the experiment. In contrast, cladoceran abundance increased. An inverse and significant relationship was observed between zooplankton and rotifer abundances and MBFG III abundance (β = -0.85, p < 0.01; r2 = 0.32; β = -0.54; p < 0.01; r2 = 0.29, respectively), showing an effective preda-tor-prey interaction. Many positive and significant relationships were also observed among the grazers and the prey. The increase of the abundance and biovolume of phytoplankton was related to the bottom-up mechanisms, the rapid population growth of prey, and the short time of the experiment. The change in the MBFGs’ contribution was related to the increase in the zooplankton and group abundance, grazer competition and exploitative competition among the MBFGs. The experiment contributes to the knowledge on an important part of the trophic dynamics among planktonic communities in subtropical floodplain shallow lakes

Long-term acidification of pH neutral grasslands affects soil biodiversity, fertility and function in a heathland restoration

In the wider context of heathland restoration, we investigated how field scale experimental acidification with sulphur (sulfur) affected soil biodiversity, fertility and function over a period of 17 years. A field experiment was conducted in the Isle of Purbeck, England, using ferrous sulphate and elemental sulphur as acidifying agents. We tested the effects of acidification on soil fertility, plant communities, litter decomposition, microbiology (including fungi bacteria and actinomycetes), arbuscular and ericoid mycorrhizal colonisation, and soil fauna (including earthworms, nematodes, rotifers and tardigrades). We found that elemental sulphur had a considerable and persistent effect on soil pH, lowering it to levels found in the surrounding reference acid grassland and heathland sites. A newly adapted heathland restoration index based on soil chemistry, found that elemental sulphur was by far the most successful treatment leading to soil conditions similar to the heathlands. Overall, acidification caused a loss of base cations and an increase in toxic aluminium compounds. Consequently the more mesotrophic components of soil biology were reduced by acidification during the course of the experiment. This transformed the soil biological system into one typical of acid grasslands and heathlands. Concomitant litter decomposition was similarly inhibited by acidification, with the microbiota more strongly hindered in acidified soil than the macroscopic fauna. Acidification resulted in a reduction in nematode and rotifer abundance and earthworm biomass. The vegetation community was also strongly modified by the elemental sulphur treatments and, where grazing was restricted, soil acidification allowed a restored heathland community to endure. Arbuscular mycorrhizal colonisation of grasses was reduced where heather plants were established, while ericoid mycorrhizas had developed sufficient populations in the acidified pastures to match the colonisation rate in the native heathlands.

Zooplankton changes during bottom-up and top-down control due to sustainable restoration in a shallow urban lake

Long-term cyanobacterial blooms and hypereutrophic state have been typical for the shallow, urban Swarzędzkie Lake for many years. Diversion of sewage did not change its trophic status, so restoration began in autumn 2011 using the sustainable approach based on three methods. The aim of the study was to analyse how sustainable restoration affects zooplankton. We hypothesised that bottom-up and top-down methods reconstructed zooplankton composition. Thus, the abundance of large-size cladocerans increased and controlled phytoplankton effectively. The elimination of cyanobacteria bloom, the decrease of rotifer abundance and the twofold increase of filter-feeder effectiveness were observed in summer 2012. However, high phosphorus concentration, lack of regular cyprinid removal and insufficient fish stocking together with high temperature prevented zooplankton from controlling cyanobacteria bloom in summer 2013. Rotifer domination with high trophy species was noted, as before restoration. The number of rotifers decreased in 2014, while crustaceans increased due to the significant decrease of nutrient concentrations and an intensification of biomanipulation treatments. Therefore, summer phytoplankton growth was low, without cyanobacteria dominance. The rebuilding of zooplankton in Swarzędzkie Lake was observed during sustainable restoration. However, the treatments should be intensified when adverse changes were observed to obtain better results for the improvement of water quality.

Rearing of the Pacific white shrimp Litopenaeus vannamei (Boone, 1931) in BFT system with different photoperiods: Effects on the microbial community, water quality and zootechnical performance

In Biofloc Technology (BFT) Systems, there are changes in microbial communities during a shrimp culture cycle; usually, heterotrophic bacteria are replaced by a photoautotrophic or chemoautotrophic community, depending on the management employed. When the water is exposed to sunlight, it can abruptly change from a heterotrophic system (dominated by bacteria and protozoa) to a predominantly photoautotrophic system, with a dominance of microalgae. However, there is little information on the characterization and quantification of the microbial community in the culture of the Pacific white shrimp Litopenaeus vannamei in a BFT system with light restriction, especially the contribution of these microrganisms to the zootechnical performance of shrimp. The aim of this study was to evaluate the microbial community in a rearing environment with light restriction. The study was conducted in 12 tanks (800 L) with a storage density of 500 shrimp m−3 and an initial shrimp weight of 0.053 g. The experiment was designed with three treatments and four replicates distributed into the following groups: i) natural photoperiod - 12 h light/12 h dark (NP); ii) 24 h light (24hLI); and iii) 24 h dark (24hDA). Significant differences were found in water quality parameters (lower values of ammonia and nitrite in the 24hDA treatment), and higher values of CO2, light (Ix) and chlorophyll were observed for the NP and 24hLI treatments than for the 24hDA treatment (p < .05). Zootechnical performance registered higher values in final weight, final biomass, weekly growth rate and survival in the NP and 24hLI treatments than in the 24hDA treatment (p < .05). Proximal analysis of the biofloc showed higher concentrations of proteins and lipids in the NP and 24hLI treatments than in the 24hDA treatment (p < .05), and there was a greater abundance of bacteria (attached coccoid, free filamentous, and attached filamentous bacteria, Vibrio and Bacillus) in NP and 24hLI than in 24hDA (p < .05). There was a greater abundance of photoautotrophic flagellates, heterotrophic flagellates, ciliates, dinoflagellates, rotifers and nematodes in NP and 24hLI than in 24hDA (p < .05). The results show that light restriction favored nitrification. However, light exposition promoted an increased abundance of microrganisms, providing an additional food source and reflecting a lower rate of feed conversion, higher survival and better growth performance for L. vannamei.

Long-term effects of nutrient changes on rotifer communities in a subtropical lake

External nutrient loading has a major influence on the abundance, composition and diversity of zooplankton communities. To clarify how the reduction of nutrient loading during lake restoration interacts with other abiotic and biotic factors and how the interactive factors affect long-term changes in rotifer communities, we analyzed the relationships between the rotifer communities and environmental factors using a 17-year dataset. After the reduction of nutrients, both the abundance and biomass of rotifers declined, and the dominant rotifers changed from eutrophic-tolerant species to less tolerant ones. The lower TN:TP ratio that was caused by the imbalanced decrease in TN and TP after restoration promoted cyanobacteria, which negatively related to the resource-use efficiency of rotifers. Moreover, seasonal differences in the Shannon–Wiener index–TN relationships and the decrease in the Pielou index with the increase in water temperature implied there were interactive effects of water temperature and nutrients on species diversity. The study concluded that changes in rotifer abundance and community composition were mainly related to TN, but the changes in species diversity were mainly related to the interactive effects of the TN:TP ratio, water temperature and food quality. Our findings highlighted the effects caused by imbalanced nutrient changes on species diversity.

Effect of water parameters on temporal distribution and abundance of zooplankton at Kaptai lake reservoir, Rangamati, Bangladesh

Seasonal abundance of zooplankton in relation to different physico-chemical conditions of Kaptai lake has been studied. A total of four major groups of zooplankton were identified from study area of Kaptai lake during three seasons observation at pre-monsoon, monsoon and Post-monsoon. These four groups were categorized into rotifers, copepods, cladocerans and others (fish larvae, shrimp larvae, insects, mosquito larvae etc.). The mean abundance of group rotifers, copepods, cladoceras and others were 103, 84.67, 38.33 and 41.83 ind. L-1 respectively. The highest group was rotifers in terms of abundance and composition where compositions were recorded 38 % at three season’s observation. The lowest group was cladoceras in term of abundance and composition where compositions were recorded 14 %. The air temperature, water temperature, transparency, water pH, DO, BOD5, PO4-P, NO2-N, SiO3-Si, TSS, TDS, Alkalinity ranged between 21 and 27.50C, 23.5 and 31.50C, 0.8 and 3 m, 7.1 and 7.5, 5.72 and 8.58 mg/l, 8.55 and 12.87 mg/l, 3.22 and 4.13 μg/l, 0.992 and 1.19 μg/l, 161.18 and 201.15 μg/l, 0.28 and 0.48 g/l, 0.18 and 0.68 g/l, 40 and 60 ppm, respectively. Margalef richness index (d), Pielou’s evenness index (J'), Shannon-Wiener diversity index (H'), Simpson dominance index (λ) are analyzed by Primer V6 software to quantify the collected species. Through same software SIMPER, Cluster analysis also done to compare similarity between season.&#x0D; Asian J. Med. Biol. Res. December 2018, 4(4): 389-399