Bishop, MJ, Kelaher, BP, Alquezar, R, York, PH, Ralph, PJ & Skilbeck, CG 2007, 'Trophic cul-de-sac, Pyrazus ebeninus, limits trophic transfer through an estuarine detritus-based food web', OIKOS, vol. 116, no. 3, pp. 427-438.
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The importance to food-webs of trophic cul-de-sacs, species that channel energy flow away from higher trophic levels, is seldom considered outside of the pelagic systems in which they were first identified. On intertidal mudflats, inputs of detritus from saltmarshes, macroalgae or microphytobenthos are generally regarded as a major structuring force underpinning food-webs and there has been no consideration of trophic cul-de-sacs to date. A fully orthogonal three-factor experiment manipulating the density of the abundant gastropod, Pyrazus ebeninus, detritus and macrobenthic predators on a Sydney mudflat revealed large deleterious effects of the gastropod, irrespective of detrital loading or the presence of predators. Two months after experimental manipulation, the standing-stock of microphytobenthos in plots with high (44 per m2) densities of P. ebeninus was 20% less than in plots with low (4 per m2) densities. Increasing densities of P. ebeninus from low to high halved the abundance of macroinvertebrates and the average number of species. In contrast, the addition of detritus had differing effects on microphytobenthos (positively affected) and macroinvertebrates (negatively affected). Over the two-months of our experiment, no predatory mortality of P. ebeninus was observed and high densities of P. ebeninus decreased impacts of predators on macroinvertebrate abundances. Given that the dynamics of southeast Australian mudflats are driven more by disturbance than seasonality in predators and their interactions with prey, it is likely that Pyrazus would be similarly resistant to predation and have negative effects on benthic assemblages at other times of the year, outside of our study period. Thus, in reducing microphytobenthos and the abundance and species richness of macrofauna, high abundances of the detritivore P. ebeninus may severely limit the flow of energy up the food chain to commercially-important species. This study therefore suggests that trop...
Collier, CJ, Lavery, PS, Masini, RJ & Ralph, PJ 2007, 'Morphological, growth and meadow characteristics of the seagrass Posidonia sinuosa along a depth-related gradient of light availability', MARINE ECOLOGY PROGRESS SERIES, vol. 337, pp. 103-115.
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Morphological and growth characteristics of the meadow-forming seagrass Posidonia sinuosa (Cambridge et Kuo), were measured along a depth-related gradient of light to infer its response to long-term differences in light availability. Morphometric measurements were carried out at 6 depths between 1.6 and 9.0 m in summer and winter at Cockburn Sound and summer only at Warnbro Sound in south-western Australia. The minimum light requirement for P. sinuosa of 8.5 % sub-surface light was among the lower range reported for seagrasses. Its slow growth rate (0.5-1.5 mgdry shoot-1 d -1), relative to similarly sized species, may contribute to the low light requirements of this species. Shoot density, leaf area index and biomass showed pronounced and consistent differences among depths (up to 88-fold reduction of above-ground biomass from shallow to deep sites). At the deeper sites, the reduced shoot density probably reduces respiratory demand and alleviates self-shading. Morphological differences (leaf length, width and thickness and number of leaves per shoot) did not follow a clear and consistent trend with depth. Despite a 70 % reduction in light availability at the canopy level between the shallowest and deepest sites, leaf growth rate was unaffected by depth during summer, and in winter differed between only a few depths. We propose that the reduction in shoot density partially alleviates the effects of self-shading and permits comparable leaf growth rates across the depth range. These results suggest that for interpreting long-term responses to light availability, shoot density is the most sensitive of the morphological characteristics measured here. © Inter-Research 2007.
Doblin, MA, Coyne, KJ, Rinta-Kanto, JM, Wilhelm, SW & Dobbs, FC 2007, 'Dynamics and short-term survival of toxic cyanobacteria species in ballast water from NOBOB vessels transiting the Great Lakes - implications for HAB invasions', HARMFUL ALGAE, vol. 6, no. 4, pp. 519-530.
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We measured the presence, viability and potential toxicity of cyanobacteria in ships' ballast tanks during three domestic voyages through the North American Great Lakes. Using molecular methods, the toxin-producing forms of Microcystis and Anabaena were monitored in ballast water after ships' ballast tanks were filled at their first port of call, and at subsequent ports as ships transited the Great Lakes. Microcystis weas detected in ballast water at intermidiate and final ports of call in all three experiemnts, but the presence of Anabaena was more variable, suggesting low abundance or patchy distribution in ballast tanks. Both species were detected in ballast water up to 11 days old. Detection of the mucrocystin synthetase gene, mcyE, in ballst tanks indicated entrained cells were capable of producing mycrocystin, and further analyses of RNA indicated the toxin was being expressed by Microcystis, even after 11 days in dark transit. These data demonstrate within-basin transport and delivery of planktonic harmful algal bllom (HAB) species to distant ports in the world's largest freshwater resevoir, with potential implications for drinking water quality. These implications are discussed with respect to management of microbial invasions and the fate of introduced phytoplankton in their receiving environment.
Drake, LA, Doblin, MA & Dobbs, FC 2007, 'Potential microbial bioinvasions via ships' ballast water, sediment, and biofilm', MARINE POLLUTION BULLETIN, vol. 55, no. 7-9, pp. 333-341.
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A prominent vector of aquatic invasive species to coastal regions is the discharge of water, sediments and biofilm from ships' ballast-water tanks. During eight years of studying ships arriving to the lower Chesapeake Bay, we developed an undertsnading of th mechanisms by which invasive microorganisms might arrive to the region via ships. Within a given ship, habitats included ballast water, unpumpable water and sediment (collectively known as residuals) and biofilms formed on internal surfaces of ballast-water tanks. We sampled 69 vessels arriving from foreign and domestic ports, largely from Western Europe and Mediterranean region and the US East and Gulf coasts. All habitats contained bacteria and viruses. By extrapolating the measured concentration of a microbial metric to the estimated volume of ballast water, biofilm or residual sediment and water within an average vessel, we calculated the potential total number of microorganisms contained by each habitat, thus creating a hierarchy of risk of delivery. The estimated concentration of microorganisms was greatest in ballast water >> sediment and water residuals >> biofilms. From these results, it is clear microorganisms may be transported within ships ina varierty of ways. Using temperature tolerence as a measure of survivability and the temperature difference between ballst-water samples and the water into which the ballast water was discharged, we estimated 56% of microorganisms could survive in the lower Bay. Extrapolated delivery and survival of microorganisms to thePort of Hampton Roads in lower Chesapeake Bay shows on the order of 10 20 microorganisms are discharged annually into the region.
Gloag, RS, Ritchie, RJ, Chen, M, Larkum, AWD & Quinnell, RG 2007, 'Chromatic photoacclimation, photosynthetic electron transport and oxygen evolution in the Chlorophyll d-containing oxyphotobacterium Acaryochloris marina', Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 1767, no. 2, pp. 127-135.
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Changes in photosynthetic pigment ratios showed that the Chlorophyll d-dominated oxyphotobacterium Acaryochloris marina was able to photoacclimate to different light regimes. Chl d per cell were higher in cultures grown under low irradiance and red or green light compared to those found when grown under high white light, but phycocyanin/Chl d and carotenoid/Chl d indices under the corresponding conditions were lower. Chl a, considered an accessory pigment in this organism, decreased respective to Chl d in low irradiance and low intensity non-white light sources. Blue diode PAM (Pulse Amplitude Modulation) fluorometry was able to be used to measure photosynthesis in Acaryochloris. Light response curves for Acaryochloris were created using both PAM and O2 electrode. A linear relationship was found between electron transport rate (ETR), measured using a PAM fluorometer, and oxygen evolution (net and gross photosynthesis). Gross photosynthesis and ETR were directly proportional to one another. The optimum light for white light (quartz halogen) was about 206 ± 51 μmol m- 2 s- 1 (PAR) (Photosynthetically Active Radiation), whereas for red light (red diodes) the optimum light was lower (109 ± 27 μmol m- 2 s- 1 (PAR)). The maximum mean gross photosynthetic rate of Acaryochloris was 73 ± 7 μmol mg Chl d- 1 h- 1. The gross photosynthesis/respiration ratio (Pg/R) of Acaryochloris under optimum conditions was about 4.02 ± 1.69. The implications of our findings will be discussed in relation to how photosynthesis is regulated in Acaryochloris. © 2007 Elsevier B.V. All rights reserved.
Hill, R & Ralph, PJ 2007, 'Post-bleaching viability of expelled zooxanthellae from the scleractinian coral Pocillopora damicornis', MARINE ECOLOGY PROGRESS SERIES, vol. 352, pp. 137-144.
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Coral bleaching events have been linked to elevated seawater temperatures in combination with intense light and can be characterised by the loss of symbionts (zooxanthellae, genus Symbiodinium) from the host tissue, as well as a reduction in photosynthetic pigments in these zooxanthellae. The long-term (days) viability of expelled zooxanthellae in the water column from the scleractinian coral Pocillopora damicornis was explored in this study through measurements of photosynthetic health and morphological condition. After initial expulsion, zooxanthellae were found to be photosynthetically competent and structurally intact. However, within 6 to 12 h following this time, photosystem II photochemical efficiency dramatically declined in these cells and photosynthetic damage was gradually manifested in the loss of structural integrity of the cell. The time of expulsion during bleaching exposure, as well as ambient water temperature, greatly influenced survivorship. Expelled zooxanthellae were collected at 4 different time intervals (0-6, 6-12, 12-24 and 24-36 h) following the onset of exposure to bleaching conditions (32°C and 400 μmol photons m-2 s-1) and then maintained at 28, 30 or 32°C and 100 μmol photons m-2 s-1 for up to 96 h. Those cells expelled within the first 6 h of bleaching and held at 28°C (lagoon temperature) had the greatest longevity, although even in this treatment, long-term photosynthetic viability was restricted to 5 d in the water column. This suggests that unless expelled zooxanthellae inhabit other environments of coral reefs (such as sediments) which may be more favourable for survival, their capacity for persistence in the environment is extremely limited. © Inter-Research 2007.
Larkum, A, Ip, C, Chen, M & Jermiin, L 2007, 'Phylogeny of Prochlorococcus marinus: how is this species related to the rest of the Cyanobacteria?', PHOTOSYNTHESIS RESEARCH, vol. 91, no. 2-3, pp. 272-273.
Larkum, A, Lockhart, P & Howe, C 2007, 'The origin of plastids: A shopping bag model', PHOTOSYNTHESIS RESEARCH, vol. 91, no. 2-3, pp. 272-272.
Larkum, A, Zhang, Y, Churdh, B & Jermiin, L 2007, 'Modelling the IsiA-PSI supermolecular complex of cyanobacteria', PHOTOSYNTHESIS RESEARCH, vol. 91, no. 2-3, pp. 172-172.
Larkum, AWD, Lockhart, PJ & Howe, CJ 2007, 'Shopping for plastids', Trends in Plant Science, vol. 12, no. 5, pp. 189-195.
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McMinn, A, Ryan, KG, Ralph, PJ & Pankowski, A 2007, 'Spring sea ice photosynthesis, primary productivity and biomass distribution in eastern Antarctica, 2002-2004', MARINE BIOLOGY, vol. 151, no. 3, pp. 985-995.
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While it is known that Antarctic sea ice biomass and productivity are highly variable over small spatial and temporal scales, there have been very few measurements from eastern Antarctic. Here we attempt to quantify the biomass and productivity and relate patterns of variability to sea ice latitude ice thickness and vertical distribution. Sea ice algal biomass in spring in 2002, 2003 and 2004 was low, in the range 0.01-8.41 mg Chl a m-2, with a mean and standard deviation of 2.08 ± 1.74 mg Chl a m-2 (n = 199). An increased concentration of algae at the bottom of the ice was most pronounced in thicker ice. There was little evidence to suggest that there was a gradient of biomass distribution with latitude. Maximum in situ production in 2002 was approximately 2.6 mg C m-2 h-1 with assimilation numbers of 0.73 mg C (mg Chl a)-1 h-1. Assimilation numbers determined by the 14C incubations in 2002 varied between 0.031 and 0.457 mg C (mg Chl a)-1 h-1. Maximum fluorescence quantum yields of the incubated ice samples in 2002 were 0.470 ± 0.041 with Ek indices between 19 and 44 μmol photons m-2 s-1. These findings are consistent with the shade-adapted character of ice algal communities. In 2004 maximum in situ production was 5.9 mg C m-2 h-1 with an assimilation number of 5.4 mg C (mg Chl a)-1 h-1. Sea ice biomass increased with ice thickness but showed no correlation with latitude or the time the ice was collected. Forty-four percent of the biomass was located in bottom communities and these were more commonly found in thicker ice. Surface communities were uncommon. © 2006 Springer-Verlag.
Nedbal, L, Červený, J, Rascher, U & Schmidt, H 2007, 'E-photosynthesis: a comprehensive modeling approach to understand chlorophyll fluorescence transients and other complex dynamic features of photosynthesis in fluctuating light', Photosynthesis Research, vol. 93, no. 1-3, pp. 223-234.
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Pernice, M, Destoumieux-Garzon, D, Peduzzi, J, Rebuffat, S & Boucher-Rodoni, R 2007, 'Identification of a Vibrio strain producing antimicrobial agents in the excretory organs of Nautilus pompilius (Cephalopoda : Nautiloidea)', REVIEWS IN FISH BIOLOGY AND FISHERIES, vol. 17, no. 2-3, pp. 197-205.
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Pernice, M, Pichon, D, Domart-Coulon, I, Favet, J & Boucher-Rodoni, R 2007, 'Primary co-culture as a complementary approach to explore the diversity of bacterial associations in marine invertebrates: the example of Nautilus macromphalus (Cephalopoda : Nautiloidea)', MARINE BIOLOGY, vol. 150, no. 5, pp. 749-757.
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Pernice, M, Wetzel, S, Gros, O, Boucher-Rodoni, R & Dubilier, N 2007, 'Enigmatic dual symbiosis in the excretory organ of Nautilus macromphalus (Cephalopoda : Nautiloidea)', PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, vol. 274, no. 1614, pp. 1143-1152.
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Prasil, O, Suggett, DJ, Cullen, JJ, Babin, M & Govindjee 2007, 'Aquafluo 2007: chlorophyll fluorescence in aquatic sciences, an international conference held in Nové Hrady', Photosynthesis Research, vol. 95, no. 1, pp. 111-115.
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Raghu, AV, Unnikrishn, KP, Hashim, KM, Balachandr, I & Mohanan, KV 2007, 'Studies on Morphological and Phytochemical Variability of Different Populations of Tribulus terrestris', International Journal of Plant Breeding and Genetics, vol. 1, no. 2, pp. 95-100.
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Ralph, PJ, Durako, MJ, Enriquez, S, Collier, CJ & Doblin, MA 2007, 'Impact of light limitation on seagrasses', JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY, vol. 350, no. 1-2, pp. 176-193.
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Seagrass distribution is controlled by light availability, especially at the deepest edge of the meadow. Light attenuation due to both natural and anthropogenically-driven processes leads to reduced photosynthesis. Adaptation allows seagrasses to exist under these sub-optimal conditions. Understanding the minimum quantum requirements for growth (MQR) is revealed when light conditions are insufficient to maintain a positive carbon balance, leading to a decline in seagrass growth and distribution. Respiratory demands of photosynthetic and non-photosynthetic tissues strongly influence the carbon balance, as do resource allocations between above- and below-ground biomass. Seagrass light acclimation occurs on varying temporal scales, as well as across spatial scales, from the position along a single leaf blade to within the canopy and finally across the meadow. Leaf absorptance is regulated by factors such as pigment content, morphology and physical properties. Chlorophyll content and morphological characteristics of leaves such as leaf thickness change at the deepest edge. We present a series of conceptual models describing the factors driving the light climate and seagrass responses under current and future conditions, with special attention on the deepest edge of the meadow. Crown Copyright © 2007.
Ralph, PJ, Larkum, AWD & Kuehl, M 2007, 'Photobiology of endolithic microorganisms in living coral skeletons: 1. Pigmentation, spectral reflectance and variable chlorophyll fluorescence analysis of endoliths in the massive corals Cyphastrea serailia, Porites lutea and Goniastrea australensis', MARINE BIOLOGY, vol. 152, no. 2, pp. 395-404.
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We used microscopy, reflectance spectroscopy, pigment analysis, and photosynthesis-irradiance curves measured with variable fluorescence techniques to characterise the endolithic communities of phototrophic microorganisms in the skeleton of three massive
Ralph, PJ, Ryan, KG, Martin, A & Fenton, G 2007, 'Melting out of sea ice causes greater photosynthetic stress in algae than freezing in', JOURNAL OF PHYCOLOGY, vol. 43, no. 5, pp. 948-956.
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Sea ice is the dominant feature of polar oceans and contains significant quantities of microalgae. When sea ice forms and melts, the microalgal cells within the ice matrix are exposed to altered salinity and irradiance conditions, and subsequently, their photosynthetic apparatuses become stressed. To simulate the effect of ice formation and melting, samples of sea-ice algae from Cape Hallett (Antarctica) were exposed to altered salinity conditions and incubated under different levels of irradiance. The physiological condition of their photosynthetic apparatuses was monitored using fast and slow fluorescence-induction kinetics. Sea-ice algae exhibited the least photosynthetic stress when maintained in 35‰ and 51‰ salinity, whereas 16, 21, and 65‰ treatments resulted in significant photosynthetic stress. The greatest photosynthetic impact appeared on PSII, resulting in substantial closure of PSII reaction centers when exposed to extreme salinity treatments. Salinity stress to sea-ice algae was light dependent, such that incubated samples only suffered photosynthetic damage when irradiance was applied. Analysis of fast-induction curves showed reductions in J, I, and P transients (or steps) associated with combined salinity and irradiance stress. This stress manifests itself in the limited capacity for the reduction of the primary electron receptor, QA, and the plastoquinone pool, which ultimately inhibited effective quantum yield of PSII and electron transport rate. These results suggest that sea-ice algae undergo greater photosynthetic stress during the process of melting into the hyposaline meltwater lens at the ice edge during summer than do microalgae cells during their incorporation into the ice matrix during the process of freezing. © 2007 Phycological Society of America.
Ralph, PJ, Smith, RA, Macinnis-Ng, CMO & Seery, CR 2007, 'Use of fluorescence-based ecotoxicological bioassays in monitoring toxicants and pollution in aquatic systems: Review', Toxicological & Environmental Chemistry, vol. 89, no. 4, pp. 589-607.
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Chlorophyll a fluorescence has the potential to become a valuable ecotoxicological endpoint, which could be used with a range of aquatic phototrophs. Chlorophyll a fluorescence bioassays have been applied in the assessment of heavy metals, herbicides, petrochemicals and nutrients. The strengths of this endpoint are that it is rapid, non-invasive and non-destructive, while the major weakness is the lack of clear ecological relevance. We provide an overview of chlorophyll a fluorescence applications in ecotoxicology. We reviewed test conditions, parameters and protocols used to date and found standardised protocols to be lacking. The most favoured fluorescence parameters were maximum quantum yield (Fv/Fm) and effective quantum yield (ΦPSII); microalgae were the most widely used tested organism, herbicides the most commonly tested toxicant, while most studies lacked a summary statistic (such as EC50). We recommend that future research in aquatic chlorophyll a fluorescence ecotoxicology focus on standardisation of test protocols and statistical techniques. © 2007 Taylor & Francis.
Raven, JA & Larkum, AWD 2007, 'Are there ecological implications for the proposed energetic restrictions on photosynthetic oxygen evolution at high oxygen concentrations?', PHOTOSYNTHESIS RESEARCH, vol. 94, no. 1, pp. 31-42.
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Santabarbara, S, Chen, M, Larkum, AWD & Evans, MCW 2007, 'An electron paramagnetic resonance investigation of the electron transfer reactions in the chlorophyll d containing photosystem I of Acaryochloris marina', FEBS Letters, vol. 581, no. 8, pp. 1567-1571.
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Electron paramagnetic resonance (EPR) spectroscopy reveals functional and structural similarities between the reaction centres of the chlorophyll d‐binding photosystem I (PS I) and chlorophyll a‐binding PS I. Continuous wave EPR spectrometry at 12 K identifies iron–sulphur centres as terminal electron acceptors of chlorophyll d‐binding PS I. A transient light‐induced electron spin echo (ESE) signal indicates the presence of a quinone as the secondary electron acceptor (Q) between and the iron–sulphur centres. The distance between and Q− was estimated within point‐dipole approximation as 25.23 ± 0.05 Å, by the analysis of the electron spin echo envelope modulation.
Seuront, L, Lacheze, C, Doubell, MJ, Seymour, JR, Van Dongen-Vogels, V, Newton, K, Alderkamp, AC & Mitchell, JG 2007, 'The influence of Phaeocystis globosa on microscale spatial patterns of chlorophyll a and bulk-phase seawater viscosity', BIOGEOCHEMISTRY, vol. 83, no. 1-3, pp. 173-188.
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A two-dimensional microscale (5 cm resolution) sampler was used over the course of a phytoplankton spring bloom dominated by Phaeocystis globosa to investigate the structural properties of chlorophyll a and seawater excess viscosity distributions. The microscale distribution patterns of chlorophyll a and excess viscosity were never uniform nor random. Instead they exhibited different types and levels of aggregated spatial patterns that were related to the dynamics of the bloom. The chlorophyll a and seawater viscosity correlation patterns were also controlled by the dynamics of the bloom with positive and negative correlations before and after the formation of foam in the turbulent surf zone. The ecological relevance and implications of the observed patchiness and biologically induced increase in seawater viscosity are discussed and the combination of the enlarged colonial form and mucus secretion is suggested as a competitive advantage of P. globosa in highly turbulent environments where this species flourishes.
Seymour, JR, Humphreys, WF & Mitchell, JG 2007, 'Stratification of the microbial community inhabiting an anchialine sinkhole', AQUATIC MICROBIAL ECOLOGY, vol. 50, no. 1, pp. 11-24.
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Bundera Sinkhole in northwestern Australia is an anchialine ecosystem characterised by a highly stratified water column comprising a complex polymodal profile of several physico-chemical parameters. We studied the microscale and finescale dynamics of the resident microbial community within the sinkhole. Sub-millimetre scale distributions of phytoplankton abundance were measured in the top 8 m of the water column using a free-falling high resolution fluorometer. Depth profiles were characterised by a strong, 10 to 20 cm layer of elevated fluorescence, occurring at approximately 1 m depth, which despite changes in magnitude and width was found to persist during a 24 h sampling period. Near surface distributions of microbial populations were measured using a syringe sampling profiler, which allowed for collection of water samples at 5 cm resolution, and flow cytometric analysis. These samples revealed a complex microbial assemblage, with multiple sub-populations of viruses, bacteria and picophytoplankton present throughout the water column. Within 3 m profiles, the bacterial and virus populations showed marked shifts in relative abundance, with changes of over 35-fold observed across as little as 20 cm. Samples collected from the surface to a depth of 30 m by divers also revealed distinct peaks and layers in the relative abundance of the different bacteria and virus sub-populations, which often corresponded to heterogeneities in chemical and nutrient parameters, and at some depths indicated the prevalence of chemolithotrophic populations. The complex patterns described here represent the first comprehensive observations of microbial spatiotemporal dynamics throughout an anchialine ecosystem and reveal a highly structured microbial habitat consisting of discrete niches, each dominated by heterotrophic, phototrophic or chemoautotrophic microorganisms.
Seymour, JR, Marcos & Stocker, R 2007, 'Chemotactic Response of Marine Micro-Organisms to Micro-Scale Nutrient Layers', Journal of Visualized Experiments, vol. 4, no. 4, pp. 1-3.
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The degree to which planktonic microbes can exploit microscale resource patches will have considerable implications for oceanic trophodynamics and biogeochemical flux. However, to take advantage of nutrient patches in the ocean, swimming microbes must overcome the influences of physical forces including molecular diffusion and turbulent shear, which will limit the availability of patches and the ability of bacteria to locate them. Until recently, methodological limitations have precluded direct examinations of microbial behaviour within patchy habitats and realistic small-scale flow conditions. Hence, much of our current knowledge regarding microbial behaviour in the ocean has been procured from theoretical predictions. To obtain new information on microbial foraging behaviour in the ocean we have applied soft lithographic fabrication techniques to develop 2 microfluidic devices, which we have used to create (i) microscale nutrient patches with dimensions and diffusive characteristics relevant to oceanic processes and (ii) microscale vortices, with shear rates corresponding to those expected in the ocean. These microfluidic devices have permitted a first direct examination of microbial swimming and chemotactic behaviour within a heterogeneous and dynamic seascape. The combined use of epifluorescence and phase contrast microscopy allow direct examinations of the physical dimensions and diffusive characteristics of nutrient patches, while observing the population-level aggregative response, in addition to the swimming behaviour of individual microbes. These experiments have revealed that some species of phytoplankton, heterotrophic bacteria and phagotrophic protists are adept at locating and exploiting diffusing microscale resource patches within very short time frames. We have also shown that up to moderate shear rates, marine bacteria are able to fight the flow and swim through their environment at their own accord. However, beyond a threshold high shea...
Seymour, JR, Seuront, L & Mitchell, JG 2007, 'Microscale gradients of planktonic microbial communities above the sediment surface in a mangrove estuary', ESTUARINE COASTAL AND SHELF SCIENCE, vol. 73, no. 3-4, pp. 651-666.
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The microscale (1 and 4 cm sampling resolution) distributions of chemical (O2, NH3, NO3-, NO2-, PO43-) and biological (Chl a, phytoplankton, bacterioplankton, viruses) parameters were measured in the 16 cm of water immediately overlaying the sediment-water interface (SWI) within a temperate mangrove estuary in South Australia during December 2003 and March 2004. Shear velocities (u*) during the time of sampling were very low (<0.1 cm s-1), and we consequently predict that resuspension of organisms and materials was negligible. In December 2003, profiles were often characterised by strong gradients in nutrients and organisms, with the highest concentrations often observed within 0.5 cm of the SWI. Microscale patterns in O2, NH3, NO3- and NO2- indicated that a variety of anaerobic and aerobic transformation processes probably occurred at the SWI and within profiles. Strong gradients in PO43- were indicative of nutrient flux across the SWI as a consequence of degradation processes in the sediments. Pico- and nanophytoplankton concentrations were strongly correlated (p < 0.01) to PO43-, and exhibited 12- and 68-fold changes in abundance, respectively, with highest concentrations observed nearest to the SWI. Several bacterial subpopulations were discriminated using flow cytometry and significant shifts in the `cytometric structure of the bacterial community were observed within microscale profiles.
Siboni, N, Lidor, M, Kramarsky-Winter, E & Kushmaro, A 2007, 'Conditioning film and initial biofilm formation on ceramics tiles in the marine environment', FEMS MICROBIOLOGY LETTERS, vol. 274, no. 1, pp. 24-29.
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Sudhakar R, S, Unnikrishn, KP, George, S, Remashree, AB, Udayan, PS, Tushar, KV & Balachandr, I 2007, 'Variation in Vasicine Content and Pharmacognostic Characters of Morphotypes of Adhatoda zeylanica Medic.', Journal of Plant Sciences, vol. 3, no. 1, pp. 61-68.
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As part of the gene bank activity of CMPR many collections of Adhatoda zeylanica Medic. were made from varying agroecological regions in South India. These collections could be grouped into four morphotypes based on growth habits and other morphological characters. These four morphotypes were evaluated for their chemical and pharmacognostical characters and significant differences among the morphotypes were noticed. Among quality characters vasicine content, fingerprint profiles, stomatal index, leaf architecture and venation pattern showed significant variation indicating the predominance of additive gene effects. A reverse phase HPLC method for the quantitative determination of vasicine in the morphotypes was developed based on which variation in the vasicine content was observed. Thin layer chromatographic analysis showed variation in the chemical composition of these morphotypes. These studies indicated variability in the chemical composition and pharmacognostic characters among the morphotypes of A. zeylanica. Two of the morphotypes containing significantly higher vasicine indicated the presence of chemical diversity, providing adequate scope for selection of superior chemotypes having high therapeutic value and economic benefit. © 2008 Academic Journals Inc.
Suggett, DJ, Le Floc’H, E, Harris, GN, Leonardos, N & Geider, RJ 2007, 'Different strategies of photoacclimation by two strains of Emiliania huxleyi (Haptophyta)1', Journal of Phycology, vol. 43, no. 6, pp. 1209-1222.
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Photoacclimation involves the modification of components of the light and dark reactions to optimize photosynthesis following changes in available light. All of the energy required for photosynthesis comes from linear electron transport through PSII and PSI and is dependent upon the amount of light harvested by PSII relative to PSI (a*PSII and a*PSI). The amount of light harvested is determined by the effective absorption cross‐sections (σPSII, σPSI) and cellular contents of the PSII and PSI reaction center complexes (RCII, RCI). Here, we examine the effective absorption cross‐sections and reaction center contents for calcifying (B11) and noncalcifying (B92) strains of the globally important coccolithophorid Emiliania huxleyi (Lohmann) W. H. Hay et H. Mohler when grown under various photon flux densities (PFDs). The two strains displayed different “strategies” of acclimation. As growth PFD increased, B11 preferentially changed σ and the cellular content of chl a per cell over PSU “size” (the total cellular chl a content associated with the reaction center complexes); strain B92 preferentially changed PSU size over the cellular content of reaction complexes. Neither strategy was specifically consistent with the majority of previous studies from other microalgal species. For both strains, cellular light absorption for PSII and PSI was maintained close to unity across the range of growth PFDs since changes of σPSII and σPSI were reciprocated by those of RCIIs and RCIs per cell. Our results demonstrate a significant adaptive flexibility of E. huxleyi to photoacclimate. Finally, we calculated the amount of chl a associated with either photos...
Ulstrup, KE, van Oppen, MJH, Kuehl, M & Ralph, PJ 2007, 'Inter-polyp genetic and physiological characterisation of Symbiodinium in an Acropora valida colony', MARINE BIOLOGY, vol. 153, no. 2, pp. 225-234.
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Corals harbouring genetically mixed communities of endosymbiotic algae (Symbiodinium) often show distribution patterns in accordance with differences in light climate across an individual colony. However, the physiology of these genetically characterised communities is not well understood. Single stranded conformation polymorphism (SSCP) and real time quantitative polymerase chain reaction (qPCR) analyses were used to examine the genetic diversity of the Symbiodinium community in hospite across an individual colony of Acropora valida at the spatial scale of single polyps. The physiological characteristics of the polyps were examined prior to sampling with a combined O2 microelectrode with a fibre-optic microprobe (combined sensor diameter 50-100 μm) enabling simultaneous measurements of O2 concentration, gross photosynthesis rate and photosystem II (PSII) quantum yield at the coral surface as a function of increasing irradiances. Both sun- and shade-adapted polyps were found to harbour either Symbiodinium clade C types alone or clades A and C simultaneously. Polyps were grouped in two categories according to (1) their orientation towardps light, or (2) their symbiont community composition. Physiological differences were not detected between sun- and shade-adapted polyps, but O2 concentration at 1,100 μmol photons m-2 s-1 was higher in polyps that harboured both clades A and C symbionts than in polyps that harboured clade C only. These results suggest that the acclimatisation of zooxanthellae of individual polyps of an A. valida colony to ambient light levels may not be the only determinant of the photosynthetic capacity of zooxanthellae. Here, we found that photosynthetic capacity is also likely to have a strong genetic basis and differs between genetically distinct Symbiodinium types.
Unnikrishn, KP, Fathima, A, Hashim, KM & Balachandr, I 2007, 'Antioxidant Studies and Determination of Wedelolactone in Eclipta alba', Journal of Plant Sciences, vol. 2, no. 4, pp. 459-464.
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The present research reports the results of the phytochemical studies carried out to identify the diagnostic features of the E. alba. A high performance thin layer chromatographic method was standardized to determine the wedelolactone content in whole plant of E. alba. Methanolic extracts of samples from three different sources were used for analysis. The mean assay of wedelolactone was of range 0.481-0.702 mg g-1 of drug powder. Radical scavenging activity of methanolic extract was evaluated by DPPH assay method superoxide radical scavenging activity in riboflavin/light/NBT system and nitric oxide radical scavenging activity in sodium nitroprusside/Griess reagent system. The assay results indicate that the DPPH, superoxide and nitric oxide scavenging activity were intense (19.25, 39.25 and 58.26 μg mL-1, respectively). The phytochemical features identified in the present study can be used as identification markers of this important analgesic agent. © 2007 Academic Journals Inc.
Zhang, Y, Chen, M, Zhou, BB, Jermiin, LS & Larkum, AWD 2007, 'Evolution of the Inner Light-Harvesting Antenna Protein Family of Cyanobacteria, Algae, and Plants', Journal of Molecular Evolution, vol. 64, no. 3, pp. 321-331.
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Two hypotheses account for the evolution of the inner antenna light-harvesting proteins of oxygenic photosynthesis in cyanobacteria, algae, and plants: one in which the CP43 protein of photosytem II gave rise to the extrinsic CP43-like antennas of cyanobacteria (i.e. IsiA and Pcb proteins), as a late development, and the other in which CP43 and CP43-like proteins derive from an ancestral protein. In order to determine which of these hypotheses is most likely, we analyzed the family of antenna proteins by a variety of phylogenetic techniques, using alignments of the six common membrane-spanning helices, constructed using information on the antenna proteins' three-dimensional structure, and surveyed for evidence of factors that might confound inference of a correct phylogeny. The first hypothesis was strongly supported. As a consequence, we conclude that the ancestral photosynthetic apparatus, with 11 membrane-spanning helices, split at an early stage during evolution to form, on the one hand, the reaction center of photosystem II and, on the other hand, the ancestor of inner antenna proteins, CP43 (PsbC) and CP47 (PsbB). Only much later in evolution did the CP43 lineage give rise to the CP43' proteins (IsiA and Pcb) of cyanobacteria. © 2007 Springer Science+Business Media, Inc.
