Global Change Abstracts The Swiss Contribution - SCNAT

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140 Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems 08.1-270 One-year survey of a single Micronesian reef reveals extraordinarily rich diversity of Symbiodinium types in soritid foraminifera Pochon X, Garcia Cuetos L, Baker A C, Castella E, Pawlowski J USA, Switzerland Marine & Freshwater Biology , Biodiversity , Ecology Recent molecular studies of symbiotic dinoflagellates (genus Symbiodinium) from a wide array of invertebrate hosts have revealed exceptional fine-scale symbiont diversity whose distribution among hosts, regions and environments exhibits significant biogeographic, ecological and evolutionary patterns. Here, similar molecular approaches using the internal transcribed spacer-2 (ITS-2) region were applied to investigate cryptic diversity in Symbiodinium inhabiting soritid foraminifera. Approximately 1,000 soritid specimens were collected and examined during a 12-month period over a 40 m depth gradient from a single reef in Guam, Micronesia. Out of 61 ITS-2 types distinguished, 46 were novel. Most types found are specific for soritid hosts, except for three types (Cl, C15 and C19) that are common in metazoan hosts. The distribution of these symbionts was compared with the phylotype of their foraminifera hosts, based on soritid small subunit ribosomal DNA sequences, and three new phylotypes of soritid hosts were identified based on these sequences. Phylogenetic analyses of 645 host-symbiont pairings revealed that most Symbiodinium types associated specifically with a particular foraminiferal host genus or species, and that the genetic diversity of these symbiont types was positively correlated with the genetic diversity found within each of the three host genera. Compared to previous molecular studies of Symbiodinium from other locations worldwide, the diversity reported here is exceptional and suggests that Micronesian coral reefs are home to a remarkably large Symbiodinium assemblage. Coral Reefs, 2007, V26, N4, DEC, pp 867-882. 08.1-271 Continuous measurement of sediment transport in the Erlenbach stream using piezoelectric bedload impact sensors Rickenmann D, Mcardell B W Switzerland Hydrology , Geomorphology We report on bedload transport observations using piezoelectric bedload impact sensors (PBIS), an indirect method of estimating the volume of bedload transport of coarse sediment. The PBIS device registers vibrations produced by bedload (particle diameter >similar to 20 mm) and records the signal as a sum of the number of impulses per time. Sediment transport at the Erlenbacb stream has been continuously monitored with a PBIS array starting in 1986. The sensor array spans the width of an entire cross-section and is mounted Hush with the surface of a check dam immediately upstream of a sediment retention basin. We compare PBIS data with long-term sedimentation records obtained from repeated surveys of material stored in the sediment retention basin, with artificial sediment input under controlled conditions in the field, and also with laboratory experiments. The rate of bedload transport is proportional to the number of impacts on the sensor per unit time. The reliability of the calibration relationship increases with the length of the observation period, e.g. for higher numbers of impacts and larger bedload volumes. Sediment volumes for individual flood events estimated with the PBIS method are in agreement with volumes estimated using an independent empirical method based on the effective runoff volume of water, the peak water discharge, and the critical discharge for the onset of sediment transport. Copyright (c) 2007 John Wiley & Sons, Ltd. Earth Surface Processes and Landforms, 2007, V32, N9, AUG, pp 1362-1378. 08.1-272 Cadmium isotope fractionation in seawater - A signature of biological activity Ripperger S, Rehkamper M, Porcelli D, Halliday A N Switzerland, England Oceanography , Geochemistry & Geophysics , Marine & Freshwater Biology Investigations of cadmium isotope variations in the oceans may provide new insights into the factors that control the marine distribution and cycling of this element. Here we present the results of Cd isotope and concentration analyses for 22 seawater samples from the Atlantic, Southern, Pacific, and Arctic Oceans. The results reveal, for the first time, large and well resolved Cd isotope fractionations in the marine environment. The majority of the seawater samples display an inverse relationship between dissolved Cd contents and isotope compositions, which range from epsilon Cd-114 /110 approximate to +3 +/- 0.5 for Cd-rich waters (0.8-1.0 nmol/kg) to epsilon Cd-114/110 approximate to 38 +/- 6 for surface water with a Cd concentration of only 0.003 nmol/kg (all epsilon Cd-114/110 data are reported relative to the JMC Cd Munster standard). This suggests that the Cd isotope variations reflect kinetic isotope effects that are generated during closed system uptake
Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems of dissolved seawater Cd by phytoplankton. A few samples do not follow this trend, as they exhibit extremely low Cd contents (= 900 in depth, despite of Cd concentrations that display the expected increase along the global deep-water pathway from the Atlantic (similar to 0.3 nmol/kg) to the Pacific Ocean (similar to 0.9 nmol /kg). This indicates that the biomass, which is remineralized in the deeper ocean, is also characterized by a very constant Cd isotope composition. This observation is in accord with the interpretation that the Cd distribution in surface waters is primarily governed by Rayleigh fractionation during near-quantitative uptake of dissolved seawater Cd. Earth and Planetary Science Letters, 2007, V261, N3-4, SEP 30, pp 670-684. 08.1-273 Density-dependent life history differences in a stream mayfly (Deleatidium) inhabiting permanent and intermittent stream reaches Robinson C T, Buser T Switzerland Marine & Freshwater Biology , Ecology , Zoology A life-history response by the mayfly Deleatidium (Ephemeroptera: Leptophlebiidae) from a permanent-fl owing and an intermittent- flowing reach of the Selwyn River, New Zealand, to failing water conditions was examined using field populations and laboratory experiments in January 2006. Field populations had similar densities under flowing water conditions, but size distributions were skewed towards larger larvae in the intermittent reach relative to the permanent reach. Under field conditions of falling water at the intermittent reach, more larvae were caught in the drift during the day and more adults at dusk at the intermittent than at the permanent reach. A desiccation study in the laboratory showed that larvae survived up to 3 days under moist conditions, whereas larvae died within 3 h under dry conditions. Another laboratory experiment revealed that both populations increased emergence under falling water in the high density treatment but not in the ambient density treatment. We conclude that a density increase caused by falling water cues late instar larvae to hasten emergence, 141 an adaptive trait that may reduce population mortality from stream drying. New Zealand Journal of Marine and Freshwater Research, 2007, V41, N3, SEP, pp 265-271. 08.1-274 Macroinvertebrate assemblages of a high elevation stream/lake network with an emphasis on the Chironomidae Robinson C T, Hieber M, Wenzelides V, Lods Crozet B Switzerland Limnology , Marine & Freshwater Biology , Hydrology , Zoology Macroinvertebrate assemblages of inlet and outlet streams were examined in a high elevation cirque comprising two basins in the Swiss Alps. Average taxon richness, with chironomids included as a single taxon, was < 8 at most sites. Chironomids represented between 26 and 85 % of the individuals and at least 50 % of the species collected at the different sites with over 22 chironomid species identified in total. No differences in the relative abundance of common macroinvertebrate taxa were found between inlet and outlet streams, but composition differed between the north and south basin of the cirque. The north basin was mostly fed by groundwater and snowmelt, whereas the south basin was dominated by glacier-melt from rock glaciers. Chironomids were 26 % more abundant and had more species in south basin than north basin streams, whereas the simuliid Prosimulium latimucro was 24 % more abundant in north basin streams. Other common taxa, e.g., Nemoura sp., Dicranota sp., Crenobia alpina and Pseudopsilopteryx zimmeri, also showed substantial differences in abundance between the two basins. Diamesinae and Orthocladiinae were the most common chironomid subfamilies collected with Diamesa zernyilcinerella, Pseudodianiesa branickii, Pseudodiamesa arctica, Corynoneura scutellata, and Tvetenia calvescens together representing on average > 10 % of the assemblage at most sites. Chironomid abundance typically was higher in outlets than inlets. An exception was Diamesa zernyilcinerella, which had greater relative abundances in inlets (24 %) than outlets (6 %). The results suggest that alpine macroinvertebrates, chironomids in particular, are sensitive to subtle differences in habitat conditions and may thus make good sentinels of environmental change to alpine waters. Fundamental and Applied Limnology, 2007, V169, N1, pp 25-36.
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