Bacterial communities of the marine sponges Hymeniacidon heliophila and Polymastia janeirensis and their environment in Rio de Janeiro, Brazil

In this study we performed a survey of the bacterial communities associated with the Western Atlantic demosponges Hymeniacidon heliophila and Polymastia janeirensis, based on 16S rRNA sequencing and transmission electron microscopy (TEM). We compared diversity and composition of the sponge-associated bacteria to those of environmental bacteria, represented by free-living bacterioplankton and by bacteria attached to organic particulate matter in superficial sediments. Partial bacterial 16S rRNA sequences from seawater, sediment, and sponges were retrieved by PCR, cloning, and sequencing. Sequences were subjected to rarefaction analyses, phylogenetic tree construction, and LIBSHUFF quantitative statistics to verify coverage and similarity between libraries. Community structure of the free-living bacterioplankton was phylogenetically different from that of the sponge-associated bacterial assemblages. On the other hand, some sediment-attached bacteria were also found in the sponge bacterial community, indicating that sponges may incorporate bacteria together with sediment particles. Rare and few prokaryotic morphotypes were found in TEM analyses of sponge mesohyl matrix of both species. Molecular data indicate that bacterial richness and diversity decreases from bacterioplankton, to particulate organic sediment, and to H. heliophila and P. janeirensis. Sponges from Rio de Janeiro harbor a pool of novel and exclusive sponge-associated bacterial taxa. Sponge-associated bacterial communities are composed of both taxons shared by many sponge groups and by species-specific bacteria.     

Drinking water biotic safety of particles and bacteria attached to fines in activated carbon process

In this paper, the drinking water biotic safety of particles and bacteria attached to fines in activated carbon process was investigated by actual treatment process and advanced treatment pilot trial with granular activated carbon. In the experiment, the particles were detected by IBR particle calculating instrument, the activated carbon fines were counted on the basis of the most probable number (MPN) with a microscope, the total number of bacteria was analyzed between the conventional agar culture medium and the one with R2A, and the bacteria attached to activated carbon fines was resolved by the homogenization technique. The experimental results showed that the average total number of particles was 205 CNT/mL in the activated carbon effluent during a filter cycle, of which the number of particles with sizes > 2 μm was 77 CNT/mL more than the present particle control criterion of the American drinking water product standard (50 CNT/mL). The backwash of low density and long duration lowered particle number in the effluent. The MPN of activated carbon fines in the effluent was between 400 and 600 CNT/L, which accounted for less than 5‰ of the total particles from activated carbon filtration for a poor relative level (R ² = 0.34). The microorganisms in activated carbon effluent consisted mostly of heterotrophic bacillus and the total bacteria number was five times as high as that of the inflow, i.e. the effluent from sand filter. The actual bacteria number may be truly indicated by the detection technique with R2A culture medium compared with the traditional agar cultivation. The inactivation efficiency of bacteria attached to activated carbon fines was less than 40% under 1.1 mg/L of chlorine contacting for 40 min. Results showed that the particles and bacteria attached to activated carbon fines may influence drinking water biotic safety, and that the effective control measures need to be further investigated.     

太湖梅梁湾附生细菌和游离细菌群落结构分析

细菌是浮游藻类群落结构重要的生物调节因子之一.采用PCR-DGGE技术研究太湖梅梁湾水域的菌群结构,主要分析水华发展阶段和暴发阶段该水域附生细菌和游离细菌的群落结构,以获得富营养化水体更丰富的微生态信息,探讨附生细菌和游离细菌在水华过程中可能具有的重要生态功能.结果表明,附生菌群结构简单,具有较高的时空稳定性,是水华发展阶段的优势菌群,其优势种群主要为α-proteobacteria和γ-proteobacteria;比较而言,游离菌群具有明显的时间差异性,水华发展阶段的种群多样性非常低,水华暴发阶段的则相当高,从而成为这一时期的优势菌群,以Actinobacteria和α-proteobacteria为主.此外,在水华发展与暴发阶段均发现淡水水体中较为罕见的SAR11种群,且这类细菌在附生菌群和游离菌群中均可检测到.     

Biomass of suspended bacteria over coral reefs

The biomass of bacteria suspended in water flowing over coral reefs at Lizard Island and Yonge Reef (Northern Great Barrier Reef) was estimated by measurement of muramic acid. Values ranged from 20 mg C m^-3 in the open water up to about 60 mg C m^-3 over the reef flat. Direct counts of total numbers of free bacteria were made for comparison. Values of around 2.0x10⁹ cells g^-1 muramic acid showed that there was a good agreement between direct counts and muramic acid content of free bacteria in the open water. In samples containing suspended particulate matter, ratios of direct counts to muramic acid concentration were lower, because bacteria on particles could not be counted. Thus, these ratios were used to indicate the proportions of bacteria attached to particles. Changes in the biomass and numbers of bacteria were determined in water masses identified either by a drogue or fluorescein, as they moved across the reefs. In the zone on the outside of the reef, the number of free bacteria decreased compared to open sea water, but total biomass increased, showing that particulate matter containing bacteria was thrown up into suspension. About 50% of bacteria were attached to particles. Water flowing over the reef flats contained much particulate material with bacteria attached. Bacteria constituted between about 5 and 20% of particulate organic carbon.     

Kinetics of glucose and amino acid uptake by attached and free-living marine bacteria in oligotrophic waters

Kinetics of glucose and amino acid uptake by attached and free-living bacteria were compared in the upper 70 m of the oligotrophic north-western Mediterranean Sea. Potential uptake rates of amino acids were higher than those of glucose in all the samples analysed. Cell-specific potential uptake rates of attached bacteria were up to two orders of magnitude higher than those of total bacteria, both for amino acids and glucose (0.72–153 amol amino acids cell⁻¹ h⁻¹ and 0.05–58.42 amol glucose cell⁻¹ h⁻¹ for attached bacteria and 0.34–1.37 amol amino acids cell⁻¹ h⁻¹ and 0.07–0.22 amol glucose cell⁻¹ h⁻¹ for total bacteria). The apparent K _m values were also higher in attached bacteria than in total bacteria, both for amino acids and glucose. These results would reflect the presence of different uptake systems in attached and free-living bacteria, which is in accordance with the different nutrient characteristics of their microenvironments, ambient water and particles. Attached bacteria show transport systems with low affinity, which characterise a bacterial community adapted to high concentration of substrates. Received: 13 June 2000 / Accepted: 6 December 2000     

Carbon substrate usage by zooplankton-associated bacteria,phytoplankton-associated bacteria,and free-living bacteria under aerobic and anaerobic conditions

Mesozooplankton provide oxic and anoxic microhabitats for associated bacteria, whose carbon substrate usage activities complement those of the ambient bacteria. The metabolic profiles of bacterial communities associated with the calanoid copepod Acartia tonsa under aerobic and anaerobic conditions were examined in comparison with phytoplankton-associated bacteria. Carbon substrate usage by phytoplankton-associated bacteria was significantly different than that of copepod-associated bacteria in both aerobic and anaerobic conditions. Substrate utilization by copepod-associated bacteria was more dependent upon oxygen condition than whether the bacteria were located on the copepod exoskeleton or within the gut. Results suggest that gut bacteria were responsible for a large portion of anaerobic substrate usage by copepod-associated bacteria. The metabolic profiles of bacteria associated with six common zooplankton groups and free-living bacteria collected in July 2012 from the York River estuary, Virginia, (37°14′50.36″N, 76°29′58.03W) were also compared, and there were significant differences in their substrate utilization patterns between aerobic and anaerobic incubations, and among the different zooplankton groups. Through trophic interactions, phytoplankton-associated or free-living bacteria may be introduced to the anoxic zooplankton gut and its associated bacterial community. Inclusion of these anaerobic microenvironments and their microbial inhabitants increased the total number of substrates used by 57 % over what was used by aerobic phytoplankton-associated bacteria alone, and by 50 % over what was used by aerobic free-living bacteria in the York River. Therefore, the presence of zooplankton-associated microhabitats and their bacteria expanded the functionality of aquatic microbial communities and led to a more comprehensive substrate usage.     

Selection of unicellular algae by the littoral amphipods Gammarus oceanicus and Calliopius laeviusculus (Crustacea)

The effect of microalgal strength of adhesion to surfaces was examined with regard to their susceptibility to grazing by Gammarus oceanicus Segerstråle and Calliopius laeviusculus (Krøyer). Observations of the feeding behaviour and two feeding experiments were carried out under laboratory conditions. Naturally attached periphyton (strongly attached cells), homogenized periphyton (loosely attached cells), filtered phytoplankton (unattached cells) and bare surfaces (controls) were randomly located in a grid and offered for grazing to a fixed number of amphipods of each species separately. The number of individuals visiting each type of food presented in the grid was recorded for 24-h periods. The feeding habit of each species, their effect on food distribution and their efficiency at collecting small particles were also recorded. G. oceanicus has a low efficiency at collecting particles and does not select a particular type of food, owing to its feeding habit of indiscriminately resuspending loosely attached particles. C. laeviusculus is a highly efficient and selective grazer, preferring homogenized periphyton and phytoplankton to naturally attached periphyton. For epibenthic diatoms, strong adhesion to surfaces is advantageous to avoid grazers.     

Impact of conditions of cultivation and adsorption on antimicrobial activity of marine bacteria

The potency of free-living and animal-associated marine bacteria to produce antimicrobial substances has been studied in 491 strains isolated from northern and southern parts of the Pacific Ocean. A total of 26% (126 out of 491) of the strains examined produced antimicrobial compounds against 11 test bacterial strains (TBS) including the fish pathogens Aeromonas hydrophila and Vibrio anquillarum. Antimicrobial substances (AS) produced by marine bacteria were especially active against Staphylococcus epidermidis, Proteus vulgaris, Enterococcus faecalis, and Candida albicans. Twelve strains, isolated from different sources, were chosen as promising candidates, producing a number of AS. Production of AS varied within 24 to 72 h, increasing in a culture medium based on natural sea water with Br-ions, and after attachment to polymeric surfaces. In order to study the influence of adsorption, selected strains with a high potential for antimicrobial production were cultivated on polymeric surfaces with different hydrophobicities and chemical functionalities. These parameters of the surface hydrophobicity (measured by means of water contact angles) and chemical functionality of the surfaces were manipulated using the photo- and thermochemistry of a polymeric system (diazo-naphto-quinone/novolak) commonly used as a photoresistant material in semiconducto-manufacturing. The highest antimicrobial activities occurred on hydrophilic surfaces (standard exposed photoresistant films), whereas the number of attached cells was greater on hydrophobic surfaces, characterized as unexposed resistant films. These results suggest that the chemical nature of induced hydrophilicity may also be a major factor in controlling antimicrobial activity of adsorbed bacteria. Received: 5 March 1997 / Accepted: 24 August 1997     

Microbial activities in the emitted hydrothermal waters of the Galápagos rift vents

In-situ measurement of chemolithotrophic and some heterotrophic microbial activities were made in the immediate vicinity of actively discharging hydrothermal vents of the Galápagos Rift region at depths of 2 500 to 2 600 m. The CO₂-assimilation or chemosynthesis productivity in the emitted vent waters, freshly mixed with oxygenated ambient seawater of 2°C, was minor compared to the bacterial biomass produced within the subsurface vent system prior to emission. Uptake of acetate and glucose indicated the presence of mixotrophic or facultatively chemolithotrophic bacteria in the emitted vent waters in agreement with isolations. Demonstration of ribulose bisphosphate carboxylase and phosphoenol pyruvate carboxylase in cultures of thiobacilli isolated from these vent water supports the notion that chemoautotrophic sulfur-oxidizing bacteria are one of the sources of primary production in the form of particulate organic carbon for filtering organisms in the deep sea hydrothermal environment. The rates of bacterial metabolic activities in emitted vent water are too low for the amount of invertebrate biomass and the rate of its growth and maintenance. Therefore, the larger portion of chemosynthetic sustenance of deep sea vent ecosystems appears to be based on symbiotic associations between bacteria and invertebrates and on surface attached bacteria.     

Role of bacteria in decomposition of faecal pellets egested by the epiphyte-grazing gastropod Gibbula umbilicaris

The significance of the microheterotrophic utilization of faecal pellets derived from Gibbula umbilicaris — one of the most important gastropod species in the Posidonia oceanica ecosystem around the Isle of Ischia (Italy) — was investigated by means of microcosm-experiments. Initial total organic carbon (TOC) content of faecal pellets was 32 gC (mg faeces dry wt)^-1 and declined continuously over a 2-month incubation period. The low values of TOC coincided with SEM observations of pellets which were found to consist mainly of diatom frustules and other slowly utilizable material. In a long-term experiment freshly egested faecal pellets were rapidly colonized by bacteria, which reached densities of up to 14x10⁵ cells (mg faeces dry wt)^-1 within 12 h. Thereafter bacterial numbers declined and fluctuated in a very narrow range between 2 and 3.5x10⁵ cells (mg faeces dry wt)^-1 during the two months of the investigation period. In short-term experiments (over 5 d) similar trends were observed. Peak densities of attached bacteria were followed by a decline of this population. Concurrently the number of free-living bacteria increased. This observation was confirmed by O₂ consumption measurements of freshly egested faecal pellets over 24 h, where the highest O₂ consumption rates were obtained after 12 h, followed by a rapid decline, thus supporting the view that detachment of bacteria may occur. Moreover, the respiration data indicate that about 4% of faecal TOC are remineralized within the first day.     

Substrate-dependent bacterivory by intertidal benthic copepods

The trophic importance of bacteria to harpacticoid copepods in intertidal areas remains poorly understood, and so do the mechanisms of bacterial feeding. It is, for instance, unclear whether harpacticoids directly target bacterial cells or merely co-ingest them with substrates to which bacterial cells may be attached. Here, we investigate bacterial uptake and substrate requirement for four mud intertidal species (Microarthridion littorale, Platychelipus littoralis, Delavalia palustris and Nannopus palustris) by means of ¹³C-labeled bacteria and biomarker fatty acids (FA). Bacterial uptake strongly depended on grazing on a primary food source but bacterial ingestion rates were low, and no clear indication of copepods directly targeting bacteria was found. Delavalia was the only species that accumulated bacteria-derived FA and gained in polyunsaturated FA (PUFA) probably through bioconversion of bacteria-derived FA. In general, however, our results suggest that bacteria represent a relatively minor and low-quality food for intertidal harpacticoid copepods.     

Bacterial diversity of the sediments transiting through the gut of Holothuria scabra (Holothuroidea; Echinodermata)

This work analyzes bacterial diversity of sediments transiting through the gut of Holothuria scabra which is an important bioturbator in tropical shallow waters. This edible holothurian species has a social and economic importance for coastal populations in many developing countries. Bacterial biodiversity was analyzed by sequencing the 16S rRNA of bacterial cultures and clones. DAPI and FISH methods were used to determine and compare the number of bacteria found in the various gut compartments. A total of 116 phylotypes belonging to the γ-Proteobacteria (60.5 %), α-Proteobacteria (24.5 %), Bacteroidetes (6 %), Actinobacteria (2.75 %), Fusobacteria (1.75 %), Firmicutes (1.75 %), Cyanobacteria (1.75 %) and δ-Proteobacteria (1 %) were identified. The number of bacteria is significantly greater (1.5×) in the foregut than in the ambient sediments. The number of bacteria significantly decreases in the midgut and remains stable until defecation. Some γ-Proteobacteria, especially Vibrio, are less affected by digestion than other bacterial taxa. The season has an impact on the bacterial diversity found in the sediments transiting through the gut: in the dry season, γ-Proteobacteria are the most abundant taxon, while α-Proteobacteria dominate in the rainy season. Vibrio is the most frequent genus with some well-known opportunistic pathogens like V. harveyi, V. alginolyticus and V. proteolyticus. Findings show that sediment-associated microbial communities are significantly modified by H. scabra during their transit through the gut which supports the view that holothurians play a substantial role in the structuring of bacterial communities at the sediment–seawater interface.     

Extracellular enzymatic activity and secondary production in free-living and marine-snow-associated bacteria

Abundance, production (measured as thymidine incorporation) and extracellular enzymatic activity in free-living and marine-snow-associated bacteria were measured in the northern Adriatic Sea. Although bacterial density and production were similar in both free-living and marine-snow-associated bacteria, hydrolytic activity (- and -glucosidase and l-aminopeptidase) was significantly higher in marine-snow-associated bacteria, in terms of both absolute and per-cell rates. As concentrations of dissolved total and monomeric carbohydrates and free amino acids in marine snow were very close to those in the ambient water, we suggest that the observed differences between free-living and marine-snow-associated baycteria do not simply reflect catabolic repression of enzyme expression in one of the bacterial components. Whether substrate induction is responsible for the observed higher hydrolase activity in marine-snow bacteria and/or whether there are distinct bacterial species obligatorily associated with marine snow remains unknown.     

Comparative study of the carbon cycle in Venus verrucosa fed on bacteria and phytoplankton

The aim of this, the third part of our study, was to compare the quantities of food consumed and assimilated by Venus verrucosa L. fed on two different living suspensions: the bacterium Lactobacillus sp. and the alga Pavlova lutheri. The experimental results have been presented in parts I and II of our study. The present paper describes a model constructed for each series of experiments with bacteria and with phytoplankton. An analog-computer model was succesfully applied and revealed that bacterial food was more easily consumed and assimilated than algal food, the dissolved form more easily assimilated than the living particulate form.     

Benthic response to sedimentation events during autumn to spring at a shallow water station in the Western Kiel Bight

Seasonal variations in bacterial populations (total number, biomass, biomass-spectrum, number of dividing cells) as well as in concentrations and decomposition rates of particulate organic material were followed in a sandy mud sediment of the Western Kiel Bight (Baltic Sea; FRG). The strong seasonal variations observed could be traced back to the effect of certain ecological situations and events in the sediment from which the input of the phytoplankton blooms in autumn and spring, respectively, the accumulation of organic material during winter, and the spring development of the benthic fauna turned out to be the most important. Bacterial carbon net production following the breakdown of the phytoplankton blooms ranged between 9 g (autumn) and 16 g (spring) per g of dry weight sediment per day. The consequences of shifts in the size composition of the bacterial populations as well as the importance of the measurement of enzymatic decomposition rates of particulate organic material in sediments are demonstrated and discussed in relation to the events mentioned above.Publication No. 420 of the Joint Research Program at Kiel University (Sonderforschungsbereich 95 der Deutschen Forschungsgemeinschaft)     

The effect of conventional wastewater treatment on the levels of antimicrobial-resistant bacteria in effluent: a meta-analysis of current studies

Antimicrobial agents in the environment are a cause for concern. Antimicrobial drug residues and their metabolites reach the aquatic and terrestrial environment primarily through wastewater treatment plants (WWTP). In addition to the potential direct negative health and environmental effects, there is potential for the development of antimicrobial-resistant bacteria. Residue levels below the minimum inhibitory concentration for a bacterial species can be important in selection of resistance. There is uncertainty associated with resistance formation during WWTP processing. A meta-analysis study was carried out to analyse the effect of WWTP processing on the levels of antimicrobial-resistant bacteria within bacterial populations. An analysis of publications relating to multiple antimicrobial-resistant (MAR) bacteria (n?=?61), single antimicrobial-resistant (SAR) E. coli (n?=?81) and quinolone/fluoroquinolone-resistant (FR) bacteria (n?=?19) was carried out. The odds-ratio (OR) of MAR (OR?=?1.60, p?<?0.01), SAR (OR?=?1.33, p?<?0.01) and FR (OR?=?1.19, p?<?0.01) bacteria was determined. The results infer that WWTP processing results in an increase in the proportion of resistant bacteria in effluent, even though the overall bacterial population may have reduced (i.e. a reduction in total bacterial numbers but an increase in the percentage of resistant bacteria). The results support the need for further research into the development of antimicrobial-resistant strains and possible selective pressures operating in WWTPs.     

Uptake of dissolved organics by marine bacteria as a function of fluid motion

A mass transfer analysis predicts that fluid motion can increase the assimilation of dissolved organics by attached compared to free-living microorganisms under certain conditions. To test this we examined the effect of advective flow and fluid shear on the uptake of model compounds (leucine and glucose) by natural assemblages of heterotrophic bacteria, collected from Roosevelt Inlet, Delaware Bay (USA), in 1989. We found that [³H]leucine uptake by cells held in fluid moving at 20 to 70 m d^–1 was eight times larger than uptake by cells at a velocity of 3 m d^–1. This effect was only observed at low leucine concentrations (ca. 1 nM), when uptake was likely not saturated. When we added leucine at concentrations expected to saturate leucine uptake (ca. 11 nM), fluid motion past cells did not affect uptake. Fluid flow past bacteria did not increase [³H]glucose uptake, and laminar shear rates of 0.5 to 2.1 s^–1 did not increase either glucose or leucine uptake by suspended bacteria. These results indicate that fluid motion increases bacterial uptake of certain lowmolecular-weight dissolved organics only when the microorganism exists in an advective flow field. As predicted from a mass transfer model, fluid shear rates in natural systems are too low to affect bacterial uptake of such compounds.     

Lipid and fatty acids in naturally occurring particulate matter during spring and summer in a high arctic fjord (Kongsfjorden, Svalbard)

The total lipids and fatty acid composition of natural particulate matter and nutritional quality for zooplankton grazers was studied on a seasonal basis in the Arctic fjord Kongsfjorden (Svalbard) during the spring, summer of 2007 and during the early summer of 2006. Both years were abnormally warm, and the study attempted to evaluate the potential impact of the intrusion of North Atlantic waters. Samples were collected in surface layers and at deep chlorophyll maximum (DCM when present). Both years, chlorophyll concentrations were low (<2 μg L^?1) even during bloom periods. Species determination indicated Phaeocystis spp. as main constituent of the May bloom while ciliates and flagellates dominated the rest of the survey period. Total lipids showed similar changes at both depths with maximum values in mid-summer of 2007, while it showed reverse patterns between surface and DCM in 2006. Total fatty acid composition was dominated by saturates and monoenoic acids at both depths with significant percentages of pentaenoic acids and 22:6n-3 (DHA) recorded at all times. The 2007 fatty acid dynamics identified four main successions in term of particulate assemblage related mainly to the succession of living cells versus detrital material and to a lesser extent to phytoplankton community changes (diatoms versus non-diatoms). Redundancy analysis confirmed that live phytoplankton is one of the main drivers in the fatty acid changes. Temperature and density of the surface water are also influential in relation to water mass dynamics. Concentrations of fatty acids available to consumers showed n-3 PUFA ranging from 2 to 15 μg L^?1 and n-6 PUFA ranging from 0.3 to 2 μg L^?1. Concentration of EPA (20:5) and DHA are potentially limiting, suggesting a negative impact of Phaeocystis pouchetti-type phytoplankton linked to advection of Atlantic waters in relation to global warming of Arctic waters.     

Aspects of the ecology of a small estuarine embayment

A 1.8 ha brackish (5 to 15 S) embayment (Osborn Cove) on the Western Shore of Chesapeake Bay (USA) was studied during 1976 to examine some hydrologic and climatic influences on its phytoplankton, bacteria, intertidal benthos, a peripheral salt marsh (equivalent to 20% of the cove surface area), and the surrounding 48 ha forest watershed. Comparisons with 1975 and 1977 for temperature, salinity, rainfall and tidal extremes, show 1976 to have had normal rainfall but a cooler autumn. Sediment moves alongshore into the cove after rainfall, and erosion causes soil breakdowns from nearby cliffs. This movement, ice damage and predators appear to mediate distribution of the intertidal benthos. Phytoplankton density, chlorophyll and photosynthesis are compared with other portions of the Chesapeake Estuary sampled in parallel programs. Phytoplankton chlorophyll oscillations observed in the Bay and Potomac River were not seen in the cove. Cove gross and net photosynthesis averaged about the same as the bay, but the cove had higher rates in spring, a result of significantly higher net assimilation ratios rather than higher biomass. River-contributed nutrients may have produced this stimulation when used by tidally inoculated phytoplankton. Large numbers of small flagellates were not seen after heavy rainfall fluishing. Net phytoplankton production in the cove was estimated at 97.6 g C m^-2 yr^-1. A portion of the cove having restricted circulation apparently contributed 48% of this production in months when its phytoplankton was dominated by small flagellates. Total estimated net production by cove phytoplankton was 1.75x10³ kg C yr^-1, compared to 0.75x10³ kg C yr^-1 for a narrow peripheral zone of Spartina alterniflora growth occupying only 13% as much area. This ratio and circumstantial evidence suggests that leaf litter from the surrounding forest dominated particulate input to the cove. Bacterial plate counts showed increases in total numbers as a function of water temperature, with surface counts exceeding bottom counts. Indigenous bird and mammal waste are suggested as important bacterial inputs. Rainfall pulses resulted in rapid increases of fecal coliform and fecal streptococcus counts.     

Production of DMSP and DMS during a mesocosm study of an Emiliania huxleyi bloom: influence of bacteria and Calanus finmarchicus grazing

We investigated the influence of bacteria and metazooplankton on the production of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) during blooms of Emiliania huxleyi (Lohmann) Hay and Mohler in seawater mesocosms. The phytoplankton succession was marked by the rapid collapse of an initial Skeletonema costatum (Greville) Cleve bloom followed by a small E. huxleyi bloom. The collapse of the diatom bloom was accompanied by an increase in concentrations of dissolved DMSP (DMSP_d) and bacterial abundance and activity (as determined by the thymidine incorporation technique). The increase in bacterial activity was followed by a rapid decrease in DMSP_d concentrations which remained low for the rest of the experiment, even during the subsequent collapse of the E. huxleyi blooms. The absence of DMSP_d and DMS peaks during the declining phase of the E. huxleyi blooms was attributed to the high bacterial activity prevailing at that time. The influence of metazooplankton grazing on DMSP and DMS production was investigated by adding moderate (24 mg dry weight m^-3) and high (520 mg dry weight m^-3) concentrations of Copepodite Stage V and adults of Calanus finmarchicus to two of four filtered (200 m mesh net) enclosures during the E. huxleyi blooms. The addition of C. finmarchicus, even in high concentrations, had no apparent effect on the dynamics of E. huxleyi, suggesting that the copepods were not grazing significantly on nanophytoplankton. The addition of copepods in high concentrations favored an accumulation of chlorophyll a and particulate DMSP. These results suggest that copepods were preying on the herbivorous microzooplankton which, in turn, was controlling the biomass of nanophytoplankton. DMS production was also enhanced in the enclosure with maximum metazooplankton biomass, suggesting that the grazing of C. finmarchicus on microzooplankton containing DMSP may contribute to DMS production. These results provide strong support to the emerging idea that bacteria and metazooplankton grazing play a dominant role in determining the timing and magnitude of DMS pulses following phytoplankton blooms.