Grazing effects of a freshwater bivalve (Corbicula leana Prime) and large zooplankton on phytoplankton communities in two Korean lakes

This study examined the effects of a freshwater filter feeding bivalve (Corbicula leana Prime) and large zooplankton (>200 μm, mostly cladocerans and copepods) on the phytoplankton communities in two lakes with contrasting trophic conditions. A controlled experiment was conducted with four treatments (control, zooplankton addition, mussel addition, and both zooplankton and mussel addition), and each established in duplicate 10-l chambers. In both lakes there were significant effects of mussel grazing on phytoplankton density and biomass. The effects were greater in mesotrophic Lake Soyang than in hypertrophic Lake Ilgam. Effects of zooplankton grazing did not differ between these lakes, and zooplankton effects on phytoplankton were much less than the effects of mussels. Although mussels exerted a varying effect on phytoplankton according to their size, mussels reduced densities of almost all phytoplankton taxa. Total mean filtering rate (FR) of mussels in Lake Soyang was significantly greater than that in Lake Ilgam (p=0.002, n=5). Carbon fluxes from phytoplankton to mussels (977–2,379 μgC l^?1d^?1) and to zooplankton (76–264 μgC l^?1 d^?1) were always greater in Lake Ilgam due to the greater phytoplankton biomass (p<0.01, n=6). Based on the C-flux to biomass ratios, the mussels consumed 170–754% (avg. 412%) of phytoplankton standing stock in Lake Soyang, and 38–164% (avg. 106%) in Lake Ilgam per day. The C-flux to biomass ratio for mussels within each lake was much greater than for large zooplankton. Mussels reduced total phosphorus concentration by 5–34%, while increasing phosphate by 30–55% relative to the control. Total nitrogen also was reduced (by 9–25%), but there was no noticeable change in nitrate among treatments. The high consumption rate of phytoplankton by Corbicula leana even in a very eutrophic lake suggests that this mussel could affect planktonic and benthic food web structure and function by preferential feeding on small seston and by nutrient recycling. Control of mussel biomass therefore might be an effective tool for management of water quality in shallow eutrophic lakes and reservoirs in Korea.     

Decreased Silica Land–sea Fluxes through Damming in the Baltic Sea Catchment – Significance of Particle Trapping and Hydrological Alterations

We tested the hypothesis that reservoirs with low water residence time and autochthonous production influence river biogeochemistry in eutrophied river systems draining cultivated watersheds. The effect of a single artificial water reservoir and consecutive reservoirs on silica (Si) river fluxes is exemplified by the moderately dammed Vistula River and the heavily regulated Daugava River that are compared with the practically undammed Oder River. The sum of the discharge weighted annual mean biogenic silica (BSi) and dissolved silicate (DSi) concentrations in the rivers Oder, Vistula and Daugava were about 160 μ M (40 + 120 μ M), 150 μ M (20 + 130 μ M) and 88 μ M (6 + 82 μ M), respectively. Assuming BSi and DSi concentrations as observed in the Oder River as typical for eutrophied but undammed rivers, complete trapping of this BSi could have lowered Si fluxes to the Baltic Sea from rivers with cultivated watersheds by 25%. The superimposed effect of hydrological alterations on reduced Si land–sea fluxes is demonstrated by studies in the boreal/subarctic and oligotrophic rivers Kalixälven and Lueälven. The DSi yield of the heavily dammed Luleälven (793 kg km^?2 yr^?1) constituted only 63% of that was found in the unregulated Kalixälven (1261 kg km^?2 yr^?1), despite the specific runoff of the Luleälven (672 mm m^?2 yr^?1) being 19% higher than that of theKalixälven (563 mm m^?2 yr^?1); runoff normalized DSi yield of the former, regulated watershed, was only half the DSi yield of the latter, unperturbed watershed. Based on these findings, it is hypothesized here that perturbed surface water–groundwater interactions are the major reasons for the reduced annual fluctuations in DSi concentrations as also seen in the heavily dammed and eutrophic river systems such as the Daugava and Danube.     

Influence of Potamogeton pectinatus and microphytobenthos on benthic metabolism,nutrient fluxes and denitrification in a freshwater littoral sediment in an agricultural landscape: N assimilation versus N removal

The influence of Potamogeton pectinatus colonisation on benthic nitrogen dynamics was studied in the littoral zone of a lowland pit lake with high nitrate concentration (~200 μM). Our hypothesis was that in aquatic environments where nitrogen availability is not limiting, colonisation by rooted macrophytes changes the dynamics of the benthic nitrogen cycle, stimulating N assimilation and denitrification and increasing the system capacity to take up external nitrogen loads. To test this hypothesis, we quantified and compared seasonal variations of light and dark benthic metabolism, dissolved inorganic nitrogen (DIN) fluxes, denitrification and N assimilation rates in an area colonised by P. pectinatus and a reference site colonised by microphytobenthos. In both areas, the benthic system was net autotrophic and a sink for DIN (2,241–2,644 mmol m^?2 y^?1). Plant colonisation increased nitrogen losses via denitrification by 30% compared to the unvegetated area. In contrast to what is generally observed in coastal marine systems, where the presence of rooted macrophytes limits denitrification rates, under the very high nitrate concentrations in the studied lake, both denitrification (1,237–1,570 mmol m^?2 y^?1) and N assimilation (1,039–1,095 mmol m^?2 y^?1) played important and comparable roles in the removal of DIN from the water column.     

Carbon Sequestration in a Large Hydroelectric Reservoir: An Integrative Seismic Approach

Artificial reservoirs likely accumulate more carbon than natural lakes due to their unusually high sedimentation rates. Nevertheless, the actual magnitude of carbon accumulating in reservoirs is poorly known due to a lack of whole-system studies of carbon burial. We determined the organic carbon (OC) burial rate and the total OC stock in the sediments of a tropical hydroelectric reservoir by combining a seismic survey with sediment core sampling. Our data suggest that no sediment accumulation occurs along the margins of the reservoir and that irregular bottom morphology leads to irregular sediment deposition. Such heterogeneous sedimentation resulted in high spatial variation in OC burial—from 0 to 209 g C m^?2 y^?1. Based on a regression between sediment accumulation and OC burial rates (R ² = 0.94), and on the mean reservoir sediment accumulation rate (0.51 cm y^?1, from the seismic survey), the whole-reservoir OC burial rate was estimated at 42.2 g C m^?2 y^?1. This rate was equivalent to 70% of the reported carbon emissions from the reservoir surface to the atmosphere and corresponded to a total sediment OC accumulation of 0.62 Tg C since the reservoir was created. The approach we propose here allows an inexpensive and integrative assessment of OC burial in reservoirs by taking into account the high degree of spatial variability and based on a single assessment. Because burial can be assessed shortly after the survey, the approach combining a seismic survey and coring could, if applied on a larger scale, contribute to a more complete estimate of carbon stocks in freshwater systems in a relatively short period of time.     

Predominance of phytoplankton-derived dissolved and particulate organic carbon in a highly eutrophic tropical coastal embayment (Guanabara Bay,Rio de Janeiro,Brazil)

We investigate the carbon dynamics in Guanabara Bay, an eutrophic tropical coastal embayment surrounded by the megacity of Rio de Janeiro (southeast coast of Brazil). Nine sampling campaigns were conducted for dissolved, particulate and total organic carbon (DOC, POC and TOC), dissolved inorganic carbon (DIC), partial pressure of CO₂ (pCO₂), chlorophyll a (Chl a), pheo-pigments and ancillary parameters. Highest DOC, POC and Chl a concentrations were found in confined-shallow regions of the bay during the summer period with strong pCO₂ undersaturation, and DOC reached 82 mg L^?1, POC 152 mg L^?1, and Chl a 800 μg L^?1. Spatially and temporally, POC and DOC concentrations varied positively with total pigments, and negatively with DIC. Strong linear correlations between these parameters indicate that the production of TOC translates to an equivalent uptake in DIC, with 85% of the POC and about 50% of the DOC being of phytoplanktonic origin. Despite the shallow depths of the bay, surface waters were enriched in POC and DOC relative to bottom waters in periods of high thermohaline stratification. The seasonal accumulation of phytoplankton-derived TOC in the surface waters reached about 105 g C m^?2 year^?1, representing between 8 and 40% of the net primary production. The calculated turnover time of organic carbon was 117 and 34 days during winter and summer, respectively. Our results indicate that eutrophication of coastal bays in the tropics can generate large stocks of planktonic biomass and detrital organic carbon which are permanently being produced and partially degraded and buried in sediments.     

Net sediment N2 fluxes in a southern New England estuary: variations in space and time

Over the past three decades, Narragansett Bay has undergone various ecological changes, including significant decreases in water column chlorophyll a concentrations, benthic oxygen uptake, and benthic nutrient regeneration rates. To add to this portrait of change, we measured the net flux of N₂ across the sediment–water interface over an annual cycle using the N₂/Ar technique at seven sites in the bay for comparison with measurements made decades ago. Net denitrification rates ranged from about 10–90 μmol N₂–N m^?2 h^?1 over the year. Denitrification rates were not significantly different among sites and had no clear correlation with temperature. Net nitrogen fixation (?5 to ?650 μmol N₂–N m^?2 h^?1) was measured at three sites and only observed in summer (June–August). Neither denitrification nor nitrogen fixation exhibited a consistent relationship with sediment oxygen demand or with fluxes of nitrite, nitrate, ammonium, total dissolved inorganic nitrogen, or dissolved inorganic phosphate across all stations. In contrast to the mid-bay historical site where denitrification rates have declined, denitrification rates in the Providence River Estuary have not changed significantly over the past 30 years.     

2-Methylisoborneol production characteristics of <Emphasis Type="Italic">Pseudanabaena</Emphasis> sp. FACHB 1277 isolated from Xionghe Reservoir,China

The cyanobacterium Pseudanabaena sp. FACHB 1277, a 2-methylisoborneol (2-MIB) producer isolated from Xionghe Reservoir, was identified by molecular biological methods based on the 16S rDNA sequence. Pseudanabaena sp. FACHB 1277 is a planktonic freshwater species with relatively high 2-MIB per cell density value (7.76?×?10^?6 ng cell^?1) and specific growth rate (0.25?±?0.01 d^?1). The effects of temperature and light intensity on 2-MIB production of Pseudanabaena sp. FACHB 1277 were investigated. Of the six temperatures tested, 10, 15, 20, 25, 30, and 35 °C, the maximum total 2-MIB per cell density and minimum cell density were observed at 10 °C, while the total 2-MIB and dissolved 2-MIB (including extracellular and dissolved intracellular 2-MIB) increased with increasing temperature. Among the six tested light intensities (10, 25, 40, 55, 70, and 85 μmol photons m^?2 s^?1), the minimum total 2-MIB per cell density and maximum cell density were observed at 25 μmol photons m^?2 s^?1. The total 2-MIB and extracellular 2-MIB increased with light intensity increasing from 10 to 40 μmol photons m^?2 s^?1, while no significant increase was observed when the light intensity was higher than 40 μmol photons m^?2 s^?1. The maximum intracellular 2-MIB (including dissolved and bound) occurred at 25 μmol photons m^?2 s^?1. The present study indicates that increasing temperature could favor the conversion of bound intracellular to dissolved 2-MIB, while increasing light intensity stimulates the release of dissolved intracellular 2-MIB into the environment.     

Long-term trends and causal factors associated with Microcystis abundance and toxicity in San Francisco Estuary and implications for climate change impacts

The impacts of climate change on Microcystis blooms in San Francisco Estuary are uncertain because factors associated with the abundance and distribution of Microcystis blooms since their inception in 1999 are poorly understood. Discrete and continuous data collected between 2004 and 2008 were used to assess what factors controlled bloom initiation and persistence, if there was an impact of the bloom on mesozooplankton abundance and toxicity or dissolved organic carbon concentration, and how these might vary with climate change. Microcystis abundance was greater in dry years than wet years and both total microcystins concentration and the microcystins content of mesozooplankton tissue increased with abundance. The bloom began in the upstream portions of the estuary and spread farther west during dry years. Bloom initiation required water temperature above 19°C and surface irradiance in the visible range above 100 W m^?2. The bloom persisted during a wide range of water quality conditions but was closely correlated with low turbidity. The intensity of Microcystis blooms will likely increase with climate change due to increased water temperature and low streamflow during droughts. Elevated water temperature earlier in the spring could also extend the duration of Microcystis blooms by up to 3 months.     

Role of Environmental Factors and Toxic Genotypes in the Regulation of Microcystins-Producing Cyanobacterial Blooms

The aim of this study was to understand: (1) how environmental conditions can contribute to formation of Microcystis-dominated blooms in lowland, dam reservoirs in temperate climate—with the use of quantitative molecular monitoring, and (2) what is the role of toxic Microcystis genotypes in the bloom functioning. Monitoring of the Sulejow Reservoir in 2009 and 2010 in two sites Tresta (TR) and Bronislawow BR), which have different morphometry, showed that physicochemical conditions were always favorable for cyanobacterial bloom formation. In 2009, the average biomass of cyanobacteria reached 13 mg L^?1 (TR) and 8 mg L^?1 (BR), and in the second year, it decreased to approximately 1 mg L^?1 (TR and BR). In turns, the mean number of toxic Microcystis genotypes in the total Microcystis reached 1 % in 2009, both in TR and BR, and in 2010, the number increased to 70 % in TR and 14 % in BR. Despite significant differences in the biomass of cyanobacteria in 2009 and 2010, the mean microcystins (MCs) concentration and toxicity stayed at a similar level of approximately 1 μg L^?1. Statistical analysis indicated that water retention time was a factor that provided a significant difference between the two monitoring seasons and was considered a driver of the changes occurring in the Sulejow Reservoir. Hydrologic differences, which occurred between two studied years due to heavy flooding in Poland in 2010, influenced the decrease in number of Microcystis biomass by causing water disturbances and by lowering water temperature. Statistical analysis showed that Microcystis aeruginosa biomass and 16S rRNA gene copy number representing Microcystis genotypes in both years of monitoring could be predicted on the basis of total and dissolved phosphorus concentrations and water temperature. In present study, the number of mcyA gene copies representing toxic Microcystis genotypes could be predicted based on the biomass of M. aeruginosa. Moreover, MCs toxicity and concentration could be predicted on the basic of mcyA gene copy number and M. aeruginosa (biomass, 16S rRNA), respectively. Present findings may indicate that Microcystis can regulate the number of toxic genotypes, and in this way adjust the whole bloom to be able to produce MCs at the level which is necessary for its maintenance in the Sulejow Reservoir under stressful hydrological conditions.     

Estimating stable carbon isotope values of microphytobenthos in the Arctic for application to food web studies

Most studies on Arctic food webs have neglected microphytobenthos as a potential food source because we currently lack robust measurements of δ¹³C values for microphytobenthos from this environment. As a result, the role of microphytobenthos in high latitude marine food webs is not well understood. We combined field measurements of the concentration of aqueous carbon dioxide and the stable carbon isotopic composition of dissolved inorganic carbon (δ¹³C_DIC) from bottom water in the Beaufort and Chukchi seas with a set of stable carbon isotopic fractionation factors reflecting differences in algal taxonomy and physiology to estimate the stable carbon isotope composition of microphytobenthos-derived total organic carbon (δ¹³C_p). The δ¹³C_p for Phaeodactylum tricornutum, a pennate diatom likely to be a dominant microphytobenthos taxon, was estimated to be ?23.9 ± 0.4 ‰ as compared to a centric diatom (Porosira glacialis, δ¹³C_p = ?20.0 ± 1.6 ‰) and a marine haptophyte (Emiliana huxleyi, δ¹³C_p = ?22.7 ± 0.5 ‰) at a growth rate (µ) of 0.1 divisions per day (d^?1). δ¹³C_p values increased by ~2.5 ‰ when µ increased from 0.1 to a maximum growth rate of 1.4 d^?1. We compared our estimates of δ¹³C_p values for microphytobenthos with published measurements for other carbon sources in the Arctic and sub-Arctic. We found that microphytobenthos values overlapped with pelagic sources, yet differed from riverine and ice-derived carbon sources. These model results provide valuable insight into the range of possible isotopic values for microphytobenthos from this region, but we remain cautious in regard to the conclusiveness of these findings given the paucity of field measurements currently available for model validation.     

Effects of an Experimental Water-level Drawdown on Methane Emissions from a Eutrophic Reservoir

Reservoirs are a globally significant source of methane (CH₄) to the atmosphere. However, emission rate estimates may be biased low due to inadequate monitoring during brief periods of elevated emission rates (that is, hot moments). Here we investigate CH₄ bubbling (that is, ebullition) during periods of falling water levels in a eutrophic reservoir in the Midwestern USA. We hypothesized that periods of water-level decline trigger the release of CH₄-rich bubbles from the sediments and that these emissions constitute a substantial fraction of the annual CH₄ flux. We explored this hypothesis by monitoring CH₄ ebullition in a eutrophic reservoir over a 7-month period, which included an experimental water-level drawdown. We found that the ebullitive CH₄ flux rate was among the highest ever reported for a reservoir (mean = 32.3 mg CH₄ m^?2 h^?1). The already high ebullitive flux rates increased by factors of 1.4–77 across the nine monitoring sites during the 24-h experimental water-level drawdown, but these emissions constituted only 3% of the CH₄ flux during the 7-month monitoring period due to the naturally high ebullitive CH₄ flux rates that persist throughout the warm weather season. Although drawdown emissions were found to be a minor component of annual CH₄ emissions in this reservoir, our findings demonstrate a link between water-level change and CH₄ ebullition, suggesting that CH₄ emissions may be mitigated through water-level management in some reservoirs.     

Evidence of elevated mercury levels in carnivorous and omnivorous fishes downstream from an Amazon reservoir

Hydroelectric reservoirs can stratify, producing favorable conditions for mercury methylation in the hypolimnion. The methylmercury (MeHg) can be exported downstream, increasing its bioavailability below the dam. Our objective was to assess the mercury levels in plankton, suspended particulate matter (SPM) and fish collected upstream (UP) and downstream (DW) from the Reservatório de Samuel dam, an Amazonian reservoir that stratifies during half of the year. Mercury concentrations in both SPM and plankton were similar between the two sites, which could indicate there are no conditions favoring methylation at the moment of sampling (absence of stratification). Almost all mercury found in the muscle of fishes was in organic form, and differences of mercury levels between sites were dependent on the fishes trophic level. Herbivores showed similar mean organic mercury levels (UP = 117 μg g^?1; DW = 120 μg g^?1; n = 12), whereas omnivores (UP = 142 μg g^?1; DW = 534 μg g^?1; n = 27) and carnivores (UP = 545 μg g^?1; DW = 1,366 μg g^?1; n = 69) showed significantly higher values below the dam. The absence of a reservoir effect in herbivores is expected, since they feed on grassy vegetation, near the riverbanks, which is not much influenced by mercury in aquatic systems. On the other hand, the higher mercury levels below the dam observed for omnivores and carnivores suggest a possible influence of the reservoir since they feed on items that could be contaminated by MeHg exported from upstream. The results highlight the necessity of assessing areas downstream of reservoirs.     

Cyanotoxin production and phylogeny of benthic cyanobacterial strains isolated from the northeast of Brazil

Most of the knowledge about cyanobacteria toxin production is traditionally associated with planktonic cyanobacterial blooms. However, some studies have been showing that benthic cyanobacteria can produce cyanotoxins. According to this, we aimed to evaluate the production of microcystins and saxitoxins in benthic cyanobacteria isolated from aquatic ecosystems in the Northeast of Brazil and to use a polyphasic approach for their identification. Forty-five clonal strains were isolated from rivers and water supply reservoirs, and identified using morphological and molecular phylogenetic characteristics. In order to evaluate the toxins production, the strains were screened for genes involved in the biosynthesis of microcystins and saxitoxins, positive results were confirmed and cyanotoxins quantified using HPLC. Eight species were identified belonging to the Phormidiaceae, Pseudanabaenaceae and Nostocaceae families. This is the first study in Brazil that shows that strains from the Geitlerinema genus correspond to at least three phylogenetic lineages, which possibly correspond to three distinct species to be subsequently reclassified. The strains that showed one of the genes involved in the cyanotoxins production were analyzed by HPLC and Geitlerinema amphibium, Geitlerinema lemmermannii, Cylindrospermum stagnale and Phormidium uncinatum were identified as producing one or more saxitoxins variants. Thus, this is the first report of saxitoxins production for those first three species and the first report in Brazil for P. uncinatum.     

Chemical and Microbial Composition of Sediments in Reservoirs with Different Trophic State

For the assessment of the metabolic potential of a sediment, the upper 5 cm layer should preferentially be regarded, since this is the horizon with the highest biochemical activity in the entire reservoir. Sediment cores from four different reservoirs were examined. These represent a broad range of trophic conditions (Neunzehnhain – oligotrophic; Muldenberg – oligotrophic, acidic, dystrophic; Saidenbach – mesotrophic; Quitzdorf – highly eutrophic). The vertical concentration gradients in the interstitial water of the examined sediments showed the tendencies characteristic of the trophic state of the reservoirs. The gradients increased with the trophic state, which affected the release of dissolved substances. The internal P load was substantial in all cases, in Quitzdorf it even exceeded the external P load. The total cell numbers of the bacteria in the sediment were only slightly influenced by the trophic state, all being in the same order of magnitude. The reservoir Quitzdorf displayed very high P release rates from the sediment and mass growths of Microcystis with a high content of intracellular polyphosphate granules in the summer months.     

Monitoring and assessment of water quality in the Haraz River of Iran,using benthic macroinvertebrates indices

The objective of this study was to assess the relationship between river water quality and the distribution of benthic macroinvertebrate communities in the Haraz River in Iran. Using a surber net sampler, benthic macroinvertebrate communities along the stream was sampled in wet and dry seasons of 2015 at nine stations with three replications. The physicochemical water quality parameters were measured in the field by water checker. Hilsenhoff biotic Indices, Shannon Wiener Diversity Indices, Average Score per Taxon (ASPT) Index and Pielou Evenness Index were applied to carry out a biological assessment of water quality. A total of 3781 (spring 769, summer 1092, autumn 1095 and winter 825) benthic macroinvertebrate specimens belonging to 4 orders, 11 classes and 16 families were identified. The lowest number of taxa was recorded in spring while the highest was recorded in autumn. Station 9 had the lowest number of taxa while the highest number of taxa was recorded at station 3. The average values (±SD) of the water quality parameters were temperature 14.75?±?4.38 °C, pH 7.93?±?0.62, water flow 14.11?±?9.04 m³ s^?1, electric conductivity 532.75?±?161.35 μmohs cm^?1, total dissolved solids 296.61?±?76.21 mg L^?1, salinity 0.28?±?0.07 mg L^?1, turbidity 580.77?±?149.92 NTU and dissolved oxygen 8.08?±?0.75 mg L^?1. The assessment of stations 1 to 6 indicated that water quality conditions were suitable. In addition, substantial level of organic pollution was observed in stations 7 and 8. In station 9 water quality was fairly poor, requiring a more favourable management based on the capacity of the self-purification of the Haraz River.     

Underwater sinkhole sediments sequester Lake Huron’s carbon

Lake Huron’s submerged sinkhole habitats are impacted by high-conductivity groundwater that allows photosynthetic cyanobacterial mats to form over thick, carbon-rich sediments. To better understand nutrient cycling in these habitats, we measured the stable isotopic content of carbon and nitrogen in organic and inorganic carbon pools in Middle Island sinkhole, a ~23 m deep feature influenced by both groundwater and overlying lake water. Two distinct sources of dissolved CO₂ (DIC) were available to primary producers. Lake water DIC (δ ¹³C = ?0.1 ‰) differed by +5.9 ‰ from groundwater DIC (δ ¹³C = ?6.0 ‰). Organic carbon fixed by primary producers reflected the two DIC sources. Phytoplankton utilizing lake water DIC were more enriched in ¹³C (δ ¹³C = ?22.2 to ?23.2 ‰) than mat cyanobacteria utilizing groundwater DIC (δ ¹³C = ?26.3 to ?30.0 ‰). Sinkhole sediments displayed an isotopic signature (δ ¹³C = ?23.1 ‰) more similar to sedimenting phytoplankton than the cyanobacterial mat. Corroborated by sediment C/N ratios, these data suggest that the carbon deposited in sinkhole sediments originates primarily from planktonic rather than benthic sources. ²¹⁰Pb/¹³⁷Cs radiodating suggests rapid sediment accumulation and sub-bottom imaging indicated a massive deposit of organic carbon beneath the sediment surface. We conclude that submerged sinkholes may therefore act as nutrient sinks within the larger lake ecosystem.     

Effect of photodynamic inactivation of <Emphasis Type="Italic">Escherichia coli</Emphasis> by hypericin

The present study has focused on the effects of hypericin (Hyp) based photodynamic inactivation (PDI) of Escherichia coli (E. coli). To evaluate the efficiency of Hyp based PDI of E. coli, single factor experiments and response surface optimization experiment were conducted to obtain the optimum parameter values (36 µM Hyp, 5.9 J cm^?2 light dose: 16.4 mW cm^?2, 60 W, 260 s, 590 nm and 68 min incubation time) and finally achieved a 4.1 log CFU mL^?1 decrease of E. coli. Cell-Hyp interaction and intracellular reactive oxygen species (ROS) level were detected by fluorescence spectrometric photometer. Data indicated that Hyp possessed a strong ability to bind with cells. In addition, a significant increase was observed in intracellular ROS level after Hyp-based photosensitization treatment. Therefore, Hyp-based photosensitization seems to be a promising method to efficiently inactivate E. coli. It is expected to be a safe, efficient, low cost and practical method which can be applied in the field of food safety.     

Accumulation of hydroxybenzoic acids and other biologically active phenolic acids in shoot and callus cultures of Aronia melanocarpa (Michx.) Elliott (black chokeberry)

Phenolic acids are plant metabolites important in phytotherapy and also in cosmetology. In this study, proliferating shoot and callus cultures of Aronia melanocarpa were established and maintained on Linsmaier and Skoog (L-S) medium containing different levels of α-naphthaleneacetic acid (NAA) and 6-benzyladenine (BA), ranging from 0.1 to 3.0 mg l^?1. Methanolic extracts from the biomass of these cultures and from the fruits of soil-grown plants were used to determine the amounts of free phenolic acids and cinnamic acid using the high-performance liquid chromatography (HPLC) method. Out of a total of twelve analyzed compounds, all of the extracts contained four of them: caffeic acid, p-hydroxybenzoic acid, syringic acid, and vanillic acid. Moreover, shoot extracts also contained salicylic acid (o-hydroxybenzoic acid), while callus extracts contained p-coumaric acid. On the other hand, fruit extracts also contained both salicylic acid and p-coumaric acid. The total amount of the analyzed compounds in extracts from both shoot and callus cultures depended on the L-S medium used, and varied between 103.05 and 150.95 mg 100 g^?1 dry weight (DW), and between 50.23 and 81.56 mg 100 g^?1 DW, respectively. Both types of culture contained higher levels of phenolic acids than the fruit extracts (32.43 mg 100 g^?1 DW). In shoot cultures, p-hydroxybenzoic acid and salicylic acid were the predominant metabolites (reaching 55.14 and 78.25 mg 100 g^?1 DW, respectively), while in callus cultures, p-hydroxybenzoic acid (25.60 mg 100 g^?1 DW) and syringic acid (41.20 mg 100 g^?1 DW) were the main compounds. In fruit extracts, salicylic acid (15.60 mg 100 g^?1 DW) and p-hydroxybenzoic acid (5.29 mg 100 g^?1 DW) were predominant.     

The trophic importance of algal turfs for coral reef fishes: the crustacean link

On coral reefs, the epilithic algal matrix (EAM) is widely recognised as an important resource for herbivorous and detritivorous fishes. In comparison, little is known of the interaction between benthic carnivores and the EAM, despite the abundance of Crustacea within the EAM. The trophic importance of the EAM to fishes was investigated in Pioneer Bay, Orpheus Island, Great Barrier Reef. Fish densities were quantified using visual and clove oil censuses, and gut content analyses conducted on abundant fish species. Crustaceans were found to be an important dietary category, contributing between 49.5 and 100 % of the gut contents, with harpacticoid copepods being the dominant component. Of the benthic carnivores, the goby Eviota zebrina was found to consume the most harpacticoids with a mean of 249 copepods m^?2 day^?1. This represents approximately 0.1 % of the available harpacticoid population in the EAM. In a striking comparison, herbivorous parrotfishes were estimated to consume over 12,000 harpacticoids m^?2 day^?1, over 27 times more than all benthic carnivores surveyed, representing approximately 5.3 % of the available harpacticoid copepod population each day. The high consumption of harpacticoid copepods by benthic carnivores and parrotfishes indicates that harpacticoids form an important trophic link between the EAM and higher trophic levels on coral reefs.