Experimental Bottles Research Articles

Sediment ballast accelerates sinking of Alaska North Slope crude oil measured ex situ with surface water from Cook Inlet

Oil spilled into the ocean interacts with suspended matter forming aggregates that transport oil into subsurface layers and towards the bottom. We conducted a series of laboratory experiments to explore aggregation of oil with natural phytoplankton assemblages from Cook Inlet, Alaska at three times during a spring bloom. Oil and phytoplankton formed marine oil snow (MOS) that remained positively buoyant with a small fraction of MOS sinking to the bottom of our experimental bottles. Seawater treatments amended with suspended sediments formed oil-mineral aggregates (OMAs) with an oil capacity similar to MOS (∼20% of aggregate area was covered with oil). OMAs accelerated oil sedimentation in our bottles relative to MOS sedimentation underlining the significance of suspended matter as ballast for sinking oil. Our results reveal potential transport mechanisms of oil in Cook Inlet which apply to other coastal systems with high productivity and sediment loads.

Escalating caffeine dose-dependently increases alcohol consumption in adult male, but not female, C57BL/6J mice

Although previous research has illustrated the effects of the consumption of alcohol and caffeine individually, less research has focused on the popular combination of the two drugs. The increase in alcohol consumption when combined with caffeine has led to the idea that the stimulant effects of caffeine may mask the depressant effects of alcohol, and this may contribute to increased binge drinking as the individual feels more awake and stimulated. Preclinical research has shown various effects of combined alcohol and caffeine where several studies show decreased alcohol consumption and others show increased alcohol consumption and even binge-like drinking. Results from a previous study in our lab indicate that intermittent access (IA) to steady levels of low (0.015 %) but not moderate (0.03 %) caffeine increased alcohol consumption in male C57BL/6J mice. The current studies further investigated the sex and dose differences in adult mice receiving varying concentrations of caffeine on combined alcohol intake. In Experiment 1, adult mice (n = 50, 25 males and 25 females) had IA to one of the following experimental bottles throughout the 4 week period: water, alcohol (10 % v/v), caffeine (0.015 % w/v), or 10 % alcohol +0.015 % caffeine. In Experiment 2, adult mice (n = 70, 35 males and 35 females) were given IA to one of the following experimental bottles: water, alcohol (10 % v/v; steady, maintained throughout the 4 weeks), caffeine (increasing 0.01 % to 0.015 % to 0.02 % to 0.03 % weekly), or 10 % alcohol+increasing caffeine (at the previously mentioned concentrations). When both caffeine and alcohol concentrations remained steady throughout the 4 weeks, there was no change in alcohol consumption. Chronic exposure to IA caffeine led to increased locomotor activity and decreased freezing episodes when tested in the open field test approximately 6 h after removal of the bottles. In Experiment 2, caffeine dose-dependently increased alcohol co-consumption in male mice whereas female mice consumed less alcohol when it was presented in conjunction with caffeine. The results in males are in line with clinical literature suggesting that the combination of alcohol and caffeine may lead to increased stimulation and alcohol drinking. Additionally, these studies provide evidence that the escalation of caffeine is crucial when investigating alcohol and caffeine co-consumption using the IA paradigm.

Impact of nutrient concentration and composition on shifting of phytoplankton community in the coastal waters of the Bay of Bengal

Nutrients from different sources with different concentrations can make significant changes in the phytoplankton community of coastal water. The experiment was conducted for ten days by adding nutrients from various sources such as a river, ground, sewage, aerosol, and bottom seawater to surface seawater of the Bay of Bengal to test this hypothesis. Higher nitrate, phosphate concentrations were observed in sewage water. Higher silicate was observed in groundwater during the study period. Upon spiking, dissolved inorganic nitrogen increased from 3.91 to 169.10μmol L−1, and the N:P ratio increased from 9.31 to 58.53. This enhanced phytoplankton biomass by four times in river water added bottles, five times in aerosol and Bottom seawater added bottles, 10 and 15 times in ground and sewage water added bottles. Initial days of the experiment in all experimental bottles, Fucoxanthin was the dominant pigment. Later in sewage and aerosol bottles, Peridinin was the dominant pigment and showed linear relation with N: P.In contrast, in all other experimental bottles still, Fucoxanthin was the dominant pigment and showed a linear connection with silicate. This indicates that silicate availability will alter the phytoplankton composition and community in the coastal waters of the Bay of Bengal. This experiment also revealed that sewage nutrients are the highest contributes to primary production (9%–35%), followed by groundwater (8%–23%), aerosol (9%–13%), river (2.5%–12%) and bottom seawater (3%–10%) in the coastal Bay of Bengal. This study suggests that the changes in the composition of nutrients from different sources enhance phytoplankton biomass in coastal waters of the Bay of Bengal and modify the phytoplankton community in coastal waters, supporting the hypothesis stated above.

The Influence of Various Growth Regulator of Growth Media on Biomass and Callus Induction in Elephantopus scaber Linn

Elephantopus scaber has the potential to be developed and isolated of secondary metabolites by tissue culture techniques. Secondary metabolites of E. scaber include scabertopin, scabertropinol, luteolin, flavonoids, deoxyelephantopin, phenols, saponins, tannins, elephantopins which can be isolated from the callus, so that various growth media are used to get the largest E. scaber callus. The aim of this study is to describe the biomass and induction of E. scaber callus in various growth media in vitro (tissue culture techniques), and to determine the proper media to produce E. scaber callus biomass optimally. E. scaber culture experiments were conducted descriptively, using 5 growth media, namely 1) MS + BAP media, 2) MS + Kinetin media, 3) MS + 2.4 D media, with concentrations of BAP, Kinetin and 2.4 D 0.5; 1; 1.5; and 2 mg/L respectively, 4) MS + BAP + 2.4 D and 5) MS + Kinetin + 2.4 D, with the ratio of BAP + 2.4 D and Kin + 2.4 D are 0.5 + 0.5; 1 + 0.5; 1 + 1; 1.5 + 1.5 mg/L. Each medium contained 25 experimental bottles, each bottle are containing 5 E. scaber explants. Stages of research method are include explant sterilization, manufacture and sterilization of media, and planting explants into growth media. The research parameters are callus induction and callus biomass. The data were analyzed by quantitative descriptive. The results showed that the use of MS + 0.5 mg/L BAP growth media gave the fastest callus induction periode, 14 days after planting, while MS + 1.5 mg/L BAP + 1.5 mg/L 2.4 D growth media gave the largest callus biomass that is 0.0797 grams with a friable callus texture.

BIO STIMULATORY INFLUENCE OF COMPOST AND INORGANIC FERTILIZER ON BACTERIAL DEGRADATION OF SPENT ENGINE OIL CONTAMINATED SOIL

The harmful effects of spent engine oil on aquatic and terrestrial ecosystems have been well established in literature. This study was conducted to assess the bio stimulatory influence of amendments; compost and inorganic fertilizer on bacterial degradation of spent engine oil contaminated soil. 500 g of unpolluted soil was collected and artificially contaminated with 5, 10 and 15% (v/w) spent engine oil. The experiment was laid out in a completely randomized design. Each amendment (50 g) was subsequently mixed thoroughly with the spent engine oil contaminated soil at varying levels except nine experimental bottles used as control. Incubation study was carried out and lasted for four weeks. Estimation of total petroleum hydrocarbon, pH, electrical conductivity, temperature and bacterial population density was done within two weeks interval during the incubation study. Results obtained indicate that compost significantly enhanced total petroleum hydrocarbon reduction by 87% while inorganic fertilizer facilitated 62% total petroleum hydrocarbon reduction on 5% spent engine oil contamination level respectively. Estimation of hydrocarbon utilizing bacteria on 5, 10 and 15% spent engine oil contaminated soil indicated that compost enhanced higher hydrocarbon utilizing bacteria thereby influencing bacterial degradation than those stimulated with inorganic fertilizer. pH remained in the range of alkalinity (7.8 and 8.06) for compost and 6.2 and 6.7 for inorganic fertilizer. The potential that compost recorded in influencing bacterial degradation of spent engine oil contaminated soil in this study has made it a good bio stimulant for the bioremediation of hydrocarbon polluted environments.

Coalescence in concentrated emulsions: theoretical predictions and comparison with experimental bottle test behaviour.

Fusion between emulsion drops, also called coalescence, may be undesirable for storage or sought after depending on the desired application. In this latter case, a complete separation of the two liquids composing the emulsion is required. The same objective may be applicable to foams. We have performed bottle test experiments on a model system of water in oil (w/o) emulsion stabilized by high amounts of hydrophobic surfactant Span 80. We observe two regimes for emulsion separation: the first regime, which is fast and includes sedimentation of the water droplets, and the second regime, which exhibits a very dense and stable emulsion zone. We predict the initial thickness of the dense zone as a simple function of surfactant concentration and mean droplet size. From the assumption that the coalescence rate depends only on the area of the thin film between two contacted droplets, we quantitatively model the separation kinetics of the dense emulsion zone. Our results give rise to a simple method that allows measuring the coalescence frequency per unit area, only by monitoring bottle test experiments.

BIOLARVACIDE ACTIVITY OF ETHANOL EXTRACT OF KEDONDONG STEM (Spondias pinnata) AGAINST Aedes aegypti

Aedes aegypti mosquito is a vector for Dengue Hemorrhagic Fever. One effort to prevent the spread of the disease is vector control. The use of insecticides is a form of vector control in an effort to control DHF. There are two broad categories of insecticides that are often used as household insecticides, namely insecticides that function to kill insects and insecticides that function to repel insects. Kedondong (Spondias pinnata) which is a family of anacardiaceae which generally grows well in tropical climates. Kedondong bark contains saponins, alkaloids, and flavonoids which are secondary metabolites involved in defense mechanisms against attack by many microorganisms. This study aims to determine the biolarvicidal activity of the ethanol extract of kedondong stem bark in killing Aedes aegypti mosquito larvae. This study used 5 treatments and 3 replications. Each treatment contained 20 Aedes aegypti mosquito larvae. Observations were made for 24 hours with observation times of 0 hours, 6 hours, 12 hours, 18 hours and 24 hours. The time calculation starts after the larvae are inserted into the experimental bottle. The results showed that kedondong bark extract was able to kill Aedes aegypti mosquito larvae. The effective dose of ethanol extract of kedondong stem bark in killing Aedes aegypti mosquito larvae is 20 mg/mL.

Exploiting scaling laws for designing polymeric bottle brushes: a theoretical coarse-graining for homopolymeric branched polymers.

Bottle brushes are polymeric macromolecules made of a linear polymeric backbone grafted with side chains. The choice of the grafting density σg, the length ns the grafted side chains and their chemical nature fully determines the properties of each macromolecule, such as its elasticity and its folding behaviour. Typically, experimental bottle brushes are systems made of tens of thousands of monomeric units, rendering a computational approach extremely expensive, especially in the case of bottle brush solutions. A proper coarse graining description of these macromolecules thus appears essential. We present here a theoretical approach able to develop a general, transferable and analytical multi-scale coarse graining of homopolymeric bottle brush polymers under good solvent conditions. Starting from scaling theories, each macromolecule is mapped onto a chain of tethered star polymers, whose effective potential is known from scaling predictions, computational and experimental validations and can be expressed as a function of the number of arms f, and the length na of each arm. Stars are then tethered to one another and the effective potential between them is shown to only depend on the key parameters of the original bottle brush polymer (σg, ns). The generalised form of the effective potential is then used to reproduce properties of the macromolecules obtained both with scaling theories and with simulations. The general form of the effective potentials derived in the current study allows a theoretical and computational description of the properties of homopolymeric bottle brush polymers for all grafting densities and all lengths of both backbone and grafted arms, opening the path for a manifold of applications.

Sensory and Chemical Quality of Bottle gourd Halwa Prepared Using Skim Milk Powder

The present investigation has been aimed to study the effect of replacing khoa with skim milk powder on sensory characteristics and chemical composition of fresh bottle gourd halwa. Control bottle gourd halwa from khoa (To) and four lots of experimental bottle gourd halwa samples were manufactured by incorporating skim milk powder (in the form of reconstituted skim milk) at 10 (T1), 20 (T2), 30 (T3) and 40 (T4) per cent (w/w) of shredded bottle gourd. The fresh bottle gourd halwa samples were analysed for sensory (colour and appearance, body and texture, flavour and overall acceptability) and chemical (moisture, fat, protein, total carbohydrate and ash) qualities. The product prepared using 20% SMP (w/w) of shredded bottle gourd was found most acceptable on the basis of overall acceptability among the experimental products and at par (Pandgt;0.05) with the control product. Proximate analysis indicated that on increasing the proportion of SMP; fat and moisture showed a decreasing trend and reverse in case of protein, total carbohydrate and ash contents. As the level of SMP increases the cost of bottle gourd halwa also increased.

Differential interactions between the nematocyst-bearing mixotrophic dinoflagellate Paragymnodinium shiwhaense and common heterotrophic protists and copepods: Killer or prey

To investigate interactions between the nematocyst-bearing mixotrophic dinoflagellate Paragymnodinium shiwhaense and different heterotrophic protist and copepod species, feeding by common heterotrophic dinoflagellates (Oxyrrhis marina and Gyrodinium dominans), naked ciliates (Strobilidium sp. approximately 35μm in cell length and Strombidinopsis sp. approximately 100μm in cell length), and calanoid copepods Acartia spp. (A. hongi and A. omorii) on P. shiwhaense was explored. In addition, the feeding activities of P. shiwhaense on these heterotrophic protists were investigated. Furthermore, the growth and ingestion rates of O. marina, G. dominans, Strobilidium sp., Strombidinopsis sp., and Acartia spp. as a function of P. shiwhaense concentration were measured. O. marina, G. dominans, and Strombidinopsis sp. were able to feed on P. shiwhaense, but Strobilidium sp. was not. However, the growth rates of O. marina, G. dominans, Strobilidium sp., and Strombidinopsis sp. feeding on P. shiwhaense were very low or negative at almost all concentrations of P. shiwhaense. P. shiwhaense frequently fed on O. marina and Strobilidium sp., but did not feed on Strombidinopsis sp. and G. dominans. G. dominans cells swelled and became dead when incubated with filtrate from the experimental bottles (G. dominans+P. shiwhaense) that had been incubated for one day. The ingestion rates of O. marina, G. dominans, and Strobilidium sp. on P. shiwhaense were almost zero at all P. shiwhaense concentrations, while those of Strombidinopsis sp. increased with prey concentration. The maximum ingestion rate of Strombidinopsis sp. on P. shiwhaense was 5.3ngC predator−1d−1 (41 cells predator−1d−1), which was much lower than ingestion rates reported in the literature for other mixotrophic dinoflagellate prey species. With increasing prey concentrations, the ingestion rates of Acartia spp. on P. shiwhaense increased up to 930ngCml−1 (7180cellsml−1) at the highest prey concentration. The highest ingestion rate of Acartia spp. on P. shiwhaense was 4240ngC predator−1d−1 (32,610 cells predator−1d−1), which is comparable to ingestion rates from previous studies on other dinoflagellate prey species calculated at similar prey concentrations. Thus, P. shiwhaense might play diverse ecological roles in marine planktonic communities by having an advantage over competing phytoplankton in anti-predation against potential protistan grazers.

Microbial food web connections and rates in a subtropical embayment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 590:19-34 (2018) - DOI: https://doi.org/10.3354/meps12432 Microbial food web connections and rates in a subtropical embayment K. E. Selph1,*, E. Goetze1, M. J. Jungbluth1,3, P. H. Lenz2, G. Kolker1 1Department of Oceanography, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822, USA 2Pacific Biosciences Research Center, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822, USA 3Present address: Romberg Tiburon Center for Environmental Sciences, San Francisco State University, Tiburon, California 94920, USA *Corresponding author: selph@hawaii.edu ABSTRACT: Kāne’ohe Bay, Hawai‘i, USA, an oligotrophic subtropical coastal embayment, is a stable ecosystem dominated by picophytoplankton through most of the year (dry state). After heavy rains, macronutrients from high stream flow result in elevated phytoplankton biomass and change the community to one dominated by diatoms (wet state). However, the effect of this perturbation on the overall productivity of the community, in particular linkages between lower trophic levels and planktonic metazoan consumers, is unknown. Given that microzooplankton are the main intermediaries between phytoplankton and higher trophic levels, this study examined phytoplankton growth and mortality rates using microscopy and flow cytometry, in conjunction with seawater dilution experiments during wet and dry system states. During low stream flow (dry state), Synechococcus dominated the phytoplankton, with growth rates of 1.1 ± 0.4 d-1, and pico- to nano-sized autotrophic eukaryotes were either growing slowly or dying. Growth increased rapidly in experimental bottles with macronutrient (ammonium and phosphorus) addition. Sixty percent of Synechococcus were consumed daily, whereas autotrophic eukaryote mortalities (0.5 d-1) greatly exceeded their growth rates. Microzooplankton were dominated by <30 µm oligotrich ciliates and gymnodinoid dinoflagellates. During the wet state, autotrophic biomass doubled, but microzooplankton biomass increased ~7-fold, including large increases in naupliar and larval stages of metazoans. During wet conditions, the path from primary producers to metazoan consumers had fewer trophic levels and episodically increased the overall productivity of the bay over the dry system state. KEY WORDS: Phytoplankton · Microzooplankton · Grazing rates · Growth rates · Subtropical coastal embayment Full text in pdf format PreviousNextCite this article as: Selph KE, Goetze E, Jungbluth MJ, Lenz PH, Kolker G (2018) Microbial food web connections and rates in a subtropical embayment. Mar Ecol Prog Ser 590:19-34. https://doi.org/10.3354/meps12432 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 590. Online publication date: March 12, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Daphnia magna fitness during low food supply under different water temperature and brownification scenarios

&lt;p class="BodyA"&gt;Much of our current knowledge about non-limiting dietary carbon supply for herbivorous zooplankton is based on experimental evidence and typically conducted at ~1 mg C L&lt;sup&gt;-1&lt;/sup&gt; and ~20°C. Here we ask how low supply of dietary carbon affects somatic growth, reproduction, and survival of &lt;em&gt;Daphnia magna&lt;/em&gt; and test effects of higher water temperature (+3 °C relative to ambient) and brownification (3X higher than natural water color; both predicted effects of climate change) during fall cooling. We predicted that even at very low carbon supply (~5µg C L&lt;sup&gt;-1&lt;/sup&gt;), higher water temperature and brownification will allow &lt;em&gt;D. magna&lt;/em&gt; to increase its fitness. Neonates (&amp;lt;24 h old) were incubated with lake seston for 4 weeks (October-November 2013) in experimental bottles submerged in outdoor mesocosms to explore effects of warmer and darker water. Higher temperature and brownification did not significantly affect food quality, as assessed by its fatty acid composition. &lt;em&gt;Daphnia&lt;/em&gt; exposed to both increased temperature and brownification had highest somatic growth and were the only that reproduced, and higher temperature caused the highest &lt;em&gt;Daphnia&lt;/em&gt; survival success. These results suggest that even under low temperature and thus lower physiological activity, low food quantity is more important than its quality for &lt;em&gt;D. magna&lt;/em&gt; fitness.&lt;/p&gt;

Instantaneous Growth Rate of Freshwater Nannochloropsis spp. at Different Salinity Levels

A study was conducted to determine the instantaneous growth rate of freshwater Nannochloropsis spp. at five different salinity levels (T1, 0 ppt - control; T2, 5 ppt; T3, 10 ppt; T 4, 15 ppt; and T5, 20 ppt) and were arranged in a Complete Randomized Design (CRD). Nannochloropsis spp. was cultured in fifteen 500 ml plastic experimental bottles based on the assigned treatment for eleven days. Initial sampling was done during the start of the experiment, and everyday thereafter. Cell density was counted using haemacytometer and viewed under the microscope. Results showed that the highest cell density and instantaneous growth rate of freshwater Nannochloropsis spp. was obtained in Treatment 3 with 18,510,000.00 cells/ml and16.00±0.36 cells/ml, respectively, while Treatment 5 had the lowest cell density and growth rate (10,040,833.33 cells/ml; 15.38±0.46 cells/ml).One-way ANOVA and Duncan’s Multiple Range Test revealed there was a significant difference (p&lt;0.05) on the days of culture (days 3, 7 and 8) among treatments. Results for both cell density (cells/ml) and instantaneous growth rate (K) proved that freshwater Nannochloropsis spp. can tolerate a wider range of salinity from 5 ppt to 15 ppt. However, further studies should be conducted at a wider range of salinity levels and other variables such as nitrogen levels and light intensity to have a complete picture of the reproductive biology of this species. Keywords - Aquatic Ecology, instantaneous growth rate, freshwater Nannochloropsis spp., salinity levels, experimental design, Philippines, Asia

Transformation of methyltin chlorides and stannic chloride under simulated landfill conditions

There is increasing concern regarding the fate of methyltins in the environment, particularly since large amounts of polyvinyl chloride (PVC) plastics are deposited in landfills. The potential transformation of methyltin chlorides and stannic chloride in landfills was investigated, by incubating the target substances at concentrations relevant to landfill conditions (100 and 500 µg Sn L(-1)). The amounts of methane formed in all treatment bottles, and controls, were measured to evaluate the general microbial activity of the inocula and possible effects of methyltins on the degradation of organic matter. The methyltins and stannic chloride were found to have no significant inhibitory effects on the activity of landfill micro-organisms, and the methanol used to disperse the tin compounds was completely degraded. In some experimental bottles, the methanol degradation gave rise to larger methane yields than expected, which was attributed to enhanced degradation of the waste material. Alkyltin analyses showed that monomethyltin trichloride at an initial concentration of 500 µg Sn L(-1) promoted methylation of inorganic tin present in the inoculum. No methylation activities were detected in the incubations with 100 µg Sn L(-1) methyltin chlorides (mono-, di- or tri-methyltin), but demethylation occurred instead. Levels of soluble inorganic tin increased during the incubation period, due partly to demethylation and partly to a release of tin from the waste inocula.

Abundance and nutrient limiting growth rate of heterotrophic bacterio‐plankton in Himalayan foot hill Lake Phewa, Nepal

We examined heterotrophic bacterial abundance, chlorophyll-a concentration and resources limiting bacterial growth from October 2004 to August 2005 in Lake Phewa. The lake has a large watershed that covers � 435 ha of water surface surrounded by � 23-time large catchment area that might receive up to 4850 mm annual precipitation. During the study, bacterial abundance ranged from 3.2 to 9.9 · 10 6 cells mL )1 , and chlorophyll-a varied from 2 to 32 l gL )1 . Bacterial abundance and chlorophyll-a weakly correlated (r = 0.40, n = 77, P < 0.1) in the lake. Experiments on resources, glucose (C), nitrogen (N), phosphorus (P) alone and in combination (CNP) limiting bacterial growth rate, were examined using dilution bioassays. Experimental bottles enriched with resources and controls without enrichment (in triplicate) were incubated in situ for 48 h at collection depth. Results showed that C, N and P in combination significantly (at 5% level) stimulated bacterial growth rate. Bioassays with single resource additions showed P as main nutrient limiting bacterial growth comparing with C and N, implying that rainfall received in the catchment might convey adequate resources causing increased P deficiency for bacterial growth in Himalayan foot hill Lake Phewa.

In vitro iron enrichment experiments in the Prydz Bay, the Southern Ocean: A test of the iron hypothesis

In “high nitrate, low chlorophyll” (HNLC) ocean regions, iron has been typically regarded as the limiting factor for phytoplankton production. This “iron hypothesis” needs to be tested in various oceanic environments to understand the role of iron in marine biological and biogeochemical processes. In this paper, three in vitro iron enrichment experiments were performed in Prydz Bay and at the Polar Front north of the Ross Sea, to study the role of iron on phytoplankton production. At the Polar Front of Ross Sea, iron addition significantly (P 0.05, Student’s t-test) as a consequence of iron addition was observed. These results confirmed the limiting role of iron in the Ross Sea and indicated that iron was not the primary factor limiting phytoplankton growth in Prydz Bay. Because the light environment for phytoplankton was enhanced in experimental bottles, light was assumed to be responsible for the rapid growth of phytoplankton in all treatments and to be the limiting factor controlling field phytoplankton growth in Prydz Bay. During the incubation experiments, nutrient consumption ratios also changed with the physiological status and the growth phases of phytoplankton cells. When phytoplankton growth was stimulated by iron addition, N was the first and Si was the last nutrient which absorption enhanced. The Si/N and Si/P consumption ratios of phytoplankton in the stationary and decay phases were significantly higher than those of rapidly growing phytoplankton. These findings were helpful for studies of the marine ecosystem and biogeochemistry in Prydz Bay, and were also valuable for biogeochemical studies of carbon and nutrients in various marine environments.

Zooplankton grazing in the Atlantic Ocean: A latitudinal study

Mesozooplankton and 63–200 ?m net-collected microzooplankton grazing on phytoplankton and protozoans was evaluated by 24-h incubations on a latitudinal transect in the Atlantic Ocean, from 35°N to 38°S (AMT-15; September–October 2004). The sampling area comprised contrasting ecosystems, including upwelling zones and oligotrophic subtropical gyres. Grazing impacts of mesozooplankton and 63–200 ?m microzooplankton on total chlorophyll a (Chl a), >5 ?m Chl a, ciliates, and dinoflagellates were low for both zooplankton size fractions, always removing<1.5% of the standing stocks of these groups. Grazing had a slightly greater impact upon primary production (up to 10% of primary production consumed daily), although on most occasions grazing removed<1% of primary production per day. To account for the reduction of micrograzers by predators in the experimental bottles and the consequent reduction of grazing pressure, the data were corrected with knowledge on the decrease of microzooplankton during incubations and global estimates of microzooplankton grazing. The corrected grazing rates for mesozooplankton ranged from 4% to 28% of the primary production consumed daily, and from 1% to 2% of the standing stock of Chl a removed every day. The 63–200 ?m microzooplankton corrected grazing impact was always<5% of the primary production and standing stock consumed per day. The corrected grazing activity of 63–200 ?m microzooplankton and mesozooplankton rendered daily rations ranging from 3% to 38% of the body carbon consumed daily, not sufficient for basal metabolism in most of the areas studied. Finally, the data on mesozooplankton grazing on primary production confirm the recent hypothesis of a decline of the relative importance of mesozooplankton grazing on primary producers with increasing primary production [Calbet, A., 2001. Mesozooplankton grazing effect on primary production: a global comparative analysis in marine ecosystems. Limnology and Oceanography 46, 1824–1830].

The effect of moisture content and alkalinity on the anaerobic biodegradation of pit latrine sludge

This study investigated the effect of additional moisture and/or alkalinity on the rate of anaerobic digestion in samples of material obtained from pit latrines. In modified serum bottle tests it was shown that poor gas production rates were observed from all experiments with material collected at the lower part of one pit. Using material from the top layer of a second pit it was shown that experimental bottles produced significant amounts of gas for all treatments. Analysis of data indicated that treatment with additional alkalinity had no discernible effect on anaerobic gas production rates, but that there was some correlation between moisture content and gas production rate. These results did not support the hypothesis that low pH buffering capacity was a limiting factor in the rate of digestion of pit latrine sludge, but confirmed that low moisture content could reduce the rate of stabilisation. This implies that increasing the moisture content in a pit latrine has the potential to increase biological stabilisation rates in the pit when the material is not already well-stabilised.

The effect of moisture content and alkalinity on the anaerobic biodegradation of VIP contents

This study investigated the effect of additional moisture and/or alkalinity on the rate of anaerobic digestion in samples of material obtained from pit latrines. In modified serum bottle tests it was shown that poor gas production rates were observed from all experiments with material collected at the lower part of one pit. Using material from the top layer of a second pit it was shown that experimental bottles produced significant amounts of gas with both the addition of water and the addition of alkalinity. The results supports the motivating hypotheses that moisture content and pH buffering capacity obtained in VIP material are low and may be limiting factors in the rate of stabilisation that may occur in these pits. This implies that increasing the moisture content and alkalinity in the pit has the potential to increase stabilisation rate in the pit when the material is not already well-stabilised.

Instantaneous salinity reductions affect the survival and feeding rates of the co-occurring copepods Acartia tonsa Dana and A. clausi Giesbrecht differently

Salinity variability at short time scales constitutes a severe restriction to marine life in coastal and estuarine ecosystems. In these environments zooplankters may experience rapid salinity variations due to diverse processes, yet lethal or sub-lethal responses to such changes have been scarcely studied. We assessed short-term (12 h) survival and time-integrated clearance (F; mL ind − 1 h − 1 ) and ingestion rates (I, µgC ind − 1 h − 1 ) after 1, 2, 4, 8 and 12 h of two widespread and abundant coastal copepods, Acartia tonsa and A. clausi, subjected to instant salinity changes from 32 PSU to 26, 20, 14, 8 and 4 PSU ( A. tonsa) and from 32 to 26, 20 and 14 PSU ( A. clausi). We expected that A. tonsa, which occur naturally in environments where sharp salinity gradients are common would tolerate wider salinity changes than A. clausi, which less frequently encounter sharp gradients in nature. For A. tonsa mortality for the extreme haline shock (change from 32 to 4 PSU) was 31%, whereas A. clausi reached 22% mortality already at a change from 32 to 14 PSU; in comparison, mortality for A. tonsa at the 32/14 PSU treatment was only 3%. F and I decreased significantly at extreme treatments, and the total clearance in experimental bottles with salinity shocked animals (F tot, mL h − 1 ) was only 5% of rates measured in non-shocked control bottles for A. tonsa (32/4 PSU change) and 20% for A. clausi (32/14 PSU change); corresponding total ingestion (I tot, µgC h − 1 ) represented 9.5% of that in control bottles for A. tonsa and 24% for A. clausi. In comparison, the 32/14 PSU treatment did not affect either clearance or ingestion rates in A. tonsa. Results suggest that in the field A. tonsa is not likely to suffer significant mortalities due to sudden salinity reductions in the surrounding medium — except under extreme circumstances— while A. clausi cannot tolerate changes > 18 PSU. However, in both species feeding activity could be severely compromised by salinity reductions. The decreased feeding rate may have direct implications for processes ranging from energy acquisition at individual level to organic matter transfers at ecosystem level and thus deserves more attention in experimental studies and population modelling.