Combined effects of heavy metal (Hg) concentration and algal (Chlorella vulgaris) food density on the population growth of Brachionus calyciflorus (Rotifera: Brachionidae)

The combined effects of two food levels (0.5 x 10(6) and 1.5 x 10(6) cells ml(-1) of Chlorella vulgaris) and five concentrations (0, 0.000625, 0.00125, 0.0025, 0.005 mg l(-1) of HgCl2) of mercury on the population growth of the rotifer Brachionus calyciflorus was evaluated. The growth experiments were conducted for 18 days at 23+/-1 degrees C under continuous fluorescent illumination. For each food level - heavy metal combination, we maintained 3 replicates. Our data showed that regardless of food level, increase in the heavy metal concentration in the medium resulted in decreased population growth of B. calyciflorus. At any given heavy metal concentration, B. calyciflorus grown under higher food levels had higher population abundance. The rate of population increase was significantly influenced by both the heavy metal concentration and the algal level. The highest population growth rate (0.435+/-0.003 per day) was observed in controls at 1.5 x 10(6) cells ml(-1). The results of this study were discussed in relation to the protective role of algal density against heavy metal toxicity.     

Review of recent ecotoxicological studies on cladocerans

Cladocerans have been widely used as the bioassay organisms in evaluating the impact of different toxic substances. Literature survey during the last 10 years revealed that cladoceran ecotoxicological research has been in an exponential phase constituting nearly 10% of publications on this group. Many studies have considered typically planktonic taxa such as Daphnia magna, D. pulex, Moina macrocopa, M. micrura and Ceriodaphania dubia. Experimental data on toxicity tests, to a lesser extent, are also available for littoral-benthic genera such as Simocephalus, Macrothrix and Alona. Most toxicity tests are limited to the derivation of median lethal concentrations of various durations but mostly at 24 or 48 h. Studies related to the evaluation of changes in the life history variables of cladocerans as a result of sublethal exposure to toxic substances are not many, but gaining importance. The common toxic substances used in the cladoceran toxicity tests appear to be heavy metals, pesticides and a few natural toxins such as cyanotoxins. We review here the effect of different toxic substances on cladocerans based on both the field and the laboratory studies from an ecotoxicology point of view. Suggestions for the future cladoceran ecotoxicology are also commented on.     

Elaphoidella grandidieri (Harpacticoida: Copepoda): demographic characteristics and possible use as live prey in aquaculture

In freshwater ecosystems, rotifers and cladocerans are ideal prey for fish larvae whereas copepods, due to their purported low growth rate and predatory tendency, are not. We recently isolated the parthenogenetic Elaphoidella grandidieri (Gueme et Richard, 1893) a benthic freshwater harpacticoid, from a fish farm in the State of Morelos, central Mexico and tested its potential as a live prey organism for larval vertebrates. Population growth and life table demography experiments were conducted, in 100 ml recipients with 50 ml of test medium on a diet of Scenedesmus acutus at a density of 1.0 X 10(6) cell ml(-1); the former on live algae alone while the latter on live algae as well as detritus. We also conducted experiments to document the prey preference for this copepod by the larval Ameca splendens (Pisces: Goodeidae) and Ambystoma mexicanum (Amphibia: Ambystomatidae), fed the rotifer Plationus patulus, the ostracod Heterocypris incongruens, and the cladocerans Moina macrocopa and Daphnia pulex. Elaphoidella grandidieri is relatively easy to maintain under laboratory conditions, reaching densities (copepodites and adults) of more than 10,000 l(-1). The generation time ranged between 30-45 days, depending on the diet. The net reproductive rate was as high as 60 nauplii female(-1) day (1). Population growth rates ranged between 0.03 and 0.11 d(-1), live algae being the superior diet compared to detritus. Both predators showed no preference for E. grandidieri, but in the absence of alternate prey they consumed 80% of the harpacticoids offered. The data have been discussed in relation to the potential of E. grandidierias live food for aquaculture.     

Solid waste management of temple floral offerings by vermicomposting using Eisenia fetida

Recycling of temple waste (TW) mainly comprising of floral offerings was done through vermitechnology using Eisenia fetida and its impact on seed germination and plant growth parameters was studied by comparing with kitchen waste (KW) and farmyard waste (FYW) vermicompost (VC). The worm biomass was found to be maximum in TW VC compared to KW and FYW VCs at both 40 and 120 days old VCs. Physico-chemical analysis of worm-worked substrates showed better results in TW VC especially in terms of electrical conductivity, C/N, C/P and TK. 10% TW VC–water extract (VCE) showed stimulatory effect on germination percentage of chickpea seeds while KW and FYW VCE proved effective at higher concentration. Variation in growth parameters was also observed with change in the VC–soil ratio and TW VC showed enhanced shoot length, root length, number of secondary roots and total biomass at 12.5% VC compared to KW and FYW VC.     

Discriminating zooplankton assemblages through multivariate methods: A case for a tropical polluted harbour and Bar-built estuary

A comparative study (June-July 2001) on zooplankton community structure amid polluted conditions in a stagnant harbour and relatively unaffected tidal estuary near Visakhapatnam, on the east coast of India, revealed a marked disparity in species composition and abundance. While the harbour supported a rich population of calanoids (46.4%), the estuary sustained mostly cyclopoids (55.2%). Univariate and multivariate techniques (species diversity, clustering, non-metric multi-dimensional scaling and one-way ANOSIM) revealed the existence of two differing zooplankton assemblages and associated water quality (similarity 50.6%). While the estuary is typified by high amounts of dissolved silica (67.4 ± 17.7 μmol l^-1) linked with monsoon influx, the harbour waters revealed abnormal levels of phosphate (40.9 ± 9.2 μmol l^-1) and nitrate (15.3 ± 5.41 μmol l^{- 1}) suggestive of intense eutrophication, caused by the discharge of fertilizer-factory waste and domestic sewage. On the basis of routines (e.g. BVSTEP, SIMPER) implemented in Plymouth Routines in Multivariate Ecological Research, it was possible to demonstrate that while species such as Oithona rigida, Oithona brevicornis, crustacean nauplii, gastropod veligers, Acartia spinicauda, and Acartia centrura played a key role in discriminating the zooplankton assemblage in the estuary, Acrocalanus spp. (mainly Acrocalanus gracilis) played a keyed role in harbour waters. Canonical Correspondence Analysis revealed species-environment relationships; for example, while the distribution of Oithona spp. and its associates in the estuary corresponded intimately with high silicate, temperature, and low salinity, it was high salinity, phosphate, and nitrate in the harbour channel that supported a different assemblage of copepods dominated by calanoids.     

Changes in life histories of cladocerans (Cladocera) from the rotifer-mediated allelochemicals

ABSTRACT

We hypothesised that at higher densities herbivorous rotifers through their allelochemicals affect the survival and reproduction of cladocerans. To test this, we separately cultured three rotifers (Brachionus calyciflorus, Brachionus havanaensis, and Plationus patulus) and three cladocerans (Ceriodaphnia dubia, Daphnia pulex, and Moina macrocopa). Chlorella vulgaris was used as food and reconstituted moderately hard water was used as medium. The conditioned-medium (CM) obtained from each of rotifer species was used to conduct cohort life table tests of cladocerans. SDS PAGE electrophoresis revealed the molecular weights of proteins present in the rotifer conditioned medium were 55–63?kDa. Compared to C. dubia and D. pulex, Moina was more resistant to rotifer-mediated chemicals. Gross reproductive rate of C. dubia was significantly stimulated by the rotifer-CM. However, gross and net reproductive rates of D. pulex were strongly reduced (72–85%) due to P. patulus-CM but not from the other two rotifer species. The rate of population increase of M. macrocopa was significantly reduced by the rotifer CM. Overall, about 46% (adverse effect: 24%; stimulatory impact: 22%) of the life history variables in controls significantly differed from rotifer-CM treatments, thus proving our hypothesis that rotifer-mediated allelochemicals had some effect on the cladoceran life history variables.     

Impact of crude oil pollution on species number and live standing herbaceous crop biomass

Summary The impact of crude oil spill on the number of plant species and the above-ground live standing crop biomass (AGLSCB) of a herbaceous plant community was assessed. The spillage had a devastating effect on the herbaceous community and especially on the component herbaceous annuals. At least 80–90% of the species were absent in the affected areas in comparison to nearby unaffected areas, most of these being annuals. Perennial species were generally less affected. The total herbaceous production for a period of 12 months in the polluted areas was 885.1 gm^–2 compared with 4860.7 gm^–2 for the unaffected areas. The average monthly production in the polluted areas was 73.8 gm^–2 compared with 405.0 gm^–2 for the unaffected areas.Dr Debojit Baruah is the senior author of this paper and he is a research scholar at Dibrugarh University. Dr Sarada K. Sarma is a Pofessor in the Botany Department of Guwahati University in Assam.     

The microcystins-induced DNA damage in the liver and the heart of zebrafish,Danio rerio

Microcystins (MCYST) are the freshwater cyanobacterial toxins, known to induce hepatocellular carcinoma, necrosis, intrahepatic bleeding, as well as human and livestock mortality. Within hepatocytes, MCYST selectively bind to protein phosphatases 1 and 2A, resulting in severe liver damage. The toxicology of MCYST in mice and rats has been well studied, but little is known regarding genotoxicity in aquatic animals. In this study, the zebrafish, Danio rerio was exposed to crude extract of Microcystis aeruginosa bloom. Liver and heart were examined for MCYST-induced toxicity. Light microscopy at 36?h revealed severe, widespread apoptotic necrosis of the majority of hepatocytes, and cytoskeletal deformation in myocardiocytes. Hepatocytes were dissociated with cell shrinkage and margination of nuclear chromatin. Laddering of genomic DNA from the liver and heart of the exposed fish in an increment of 180–200?bp was consistent with apoptosis. Fluorimetric analysis of DNA unwinding was carried out to determine the DNA strand breakage. After 36?h exposure, the % double-stranded DNA was significantly reduced in hepatocytes and myocardiocytes. In conclusion, the results obtained in this study indicate that, the extract of M. aeruginosa bloom is genotoxic to fish. The DNA damage observed in this study may be attributed to the activation of DNA endonucleases. This model of DNA damage may contribute for identifying novel molecular mechanisms of interest for therapeutic application.     

Life table demography of Ceriodaphnia dubia (Cladocera) exposed to copper at different levels and periods

We studied the demographic responses of Ceriodaphnia dubia exposed to copper at 3 different levels (0.1, 0.2 and 0.4 mg l(-1)) and at 4 exposure periods (3, 6, 12 and 24 hr) in addition to controls (without the heavy metal). The tested levels of Cu concentration and the chosen periods of exposure affected some demographic variables (average lifespan, gross and net reproductive rates and generation time). Depending on the heavy metal concentration and the period of exposure, the average lifespan of C. dubia varied from 18 to 24 day Net reproductive rates (NRR) ranged from 50 to 80 offspring per female per lifespan, while the rate of population increase (r) varied from 0.30 to 0.34 per day Though gross reproductive rates (especially at low and intermediate copper levels and shorter duration of exposure) showed significantly higher values than controls, both NRR and r were either unaffected or decreased. It is therefore necessary to regulate the release of untreated industrial effluents containing copper into freshwater ecosystems. Our study thus highlights the importance of including, not only toxicant concentrations but also exposure time, in ecotoxicological evaluations.