Differences in the Feeding Ecology of Two Seagrass-Associated Snails     

Kimberly K. Holzer  José L. Rueda  Karen J. McGlathery 《Estuaries and Coasts》2011,34(6):1140-1149

Grazing by small epifauna on live seagrass leaves was formerly viewed as unimportant in controlling plant biomass and growth, instead researchers focused on the indirect benefits of small invertebrates that crop algal competitors. Recent evidence shows that the emerald nerite Smaragdia viridis preferentially ingests seagrass leaf tissue. In contrast, the button snail Modulus modulus feeds on epiphytes and periphyton coating the leaves. We conducted laboratory microcosm and field experiments to investigate how the different feeding preferences of these seagrass-associated snails affect turtlegrass Thalassia testudinum primary production. Data revealed that after 24 h S. viridis reduced foliar biomass (25%) and chlorophyll (30%) and injured the equivalent of 50% of daily seagrass growth per shoot. Conversely, M. modulus did not affect these variables. Our results emphasize that in subtropical seagrass communities not all small epifauna browse off leaf surfaces and some can have important direct negative impacts on their seagrass host.  相似文献   

Biophysical controls on accretion and elevation change in Caribbean mangrove ecosystems     

Karen L. McKee   《Estuarine, Coastal and Shelf Science》2011,91(4):259

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Actinian dominated intertidal mudflats: A new case of an extraordinary rare phenomenon from Southern Chile     

Dirk Schories  Karsten Reise  Karen Sanamyan  Nadya Sanamyan  Elena Clasing  Anneken Reise 《Journal of Sea Research》2011,65(2):304-314

Generally, estuarine intertidal mudflats constitute important nurseries for fish and foraging grounds for coastal birds by providing a plenitude of mollusks, worms, and crustaceans as prey, which in turn mostly feed on suspended and benthic microalgae, bacteria, and detritus. Despite the high productivity of such habitats, pronounced variability in both salinity and temperature results typically in low diversity. The only sea anemone reported from estuarine mud is the edwardsiid Nematostella vectensis Stephenson, 1935. It occurs widely in the northern hemisphere, and occasionally in extremely high density. Here we document another sea anemone from estuarine mud and muddy sand found in Southern Chile which has similar ecological attributes. Taxonomic confusion has impeded the reporting on this small but prominent member in a macrozoobenthic assemblage, the brooding Anthopleura hermaphroditica (Carlgren, 1899; Anthozoa: Actiniidae). It differs from N. vectensis by the presence of symbiotic algae. Average density under poly- to euhaline conditions in mud and muddy sand at around mid tide level was about 3 actinians per cm². An average abundance of 11,000 m^? 2, a biovolume of 487 cm³ m^? 2, and a biomass of 35.5 g dry organic weight m^? 2 were found in mud and muddy sand in two surveys 20 years apart. The mean fishing area of fully expanded individuals covers 42 ± 25 mm², corresponding to a circular area with a diameter of 7.3 ± 5.7 mm. Preliminary experiments indicate that associated benthos may be relegated to life below surface by the net of tentacles above the sediment. As no predators on A. hermaphroditica could be found on the mudflat, the success of this mixotrophic sea anemone may entail a trophic dead end.  相似文献   

A search for amino acids and nucleobases in the Martian meteorite Roberts Massif 04262 using liquid chromatography‐mass spectrometry     

Michael P. Callahan  Aaron S. Burton  Jamie E. Elsila  Eleni M. Baker  Karen E. Smith  Daniel P. Glavin  Jason P. Dworkin 《Meteoritics & planetary science》2013,48(5):786-795

The investigation into whether Mars contains signatures of past or present life is of great interest to science and society. Amino acids and nucleobases are compounds that are essential for all known life on Earth and are excellent target molecules in the search for potential Martian biomarkers or prebiotic chemistry. Martian meteorites represent the only samples from Mars that can be studied directly in the laboratory on Earth. Here, we analyzed the amino acid and nucleobase content of the shergottite Roberts Massif (RBT) 04262 using liquid chromatography‐mass spectrometry. We did not detect any nucleobases above our detection limit in formic acid extracts; however, we did measure a suite of protein and nonprotein amino acids in hot‐water extracts with high relative abundances of β‐alanine and γ‐amino‐n‐butyric acid. The presence of only low (to absent) levels of several proteinogenic amino acids and a lack of nucleobases suggest that this meteorite fragment is fairly uncontaminated with respect to these common biological compounds. The distribution of straight‐chained amine‐terminal n‐ω‐amino acids in RBT 04262 resembled those previously measured in thermally altered carbonaceous meteorites (Burton et al. 2012; Chan et al. 2012). A carbon isotope ratio of ?24‰ ± 6‰ for β‐alanine in RBT 04262 is in the range of reduced organic carbon previously measured in Martian meteorites (Steele et al. 2012). The presence of n‐ω‐amino acids may be due to a high temperature Fischer‐Tropsch‐type synthesis during igneous processing on Mars or impact ejection of the meteorites from Mars, but more experimental data are needed to support these hypotheses.  相似文献   

Composition and petrology of HED polymict breccias: The regolith of (4) Vesta     

David W. Mittlefehldt  Jason S. Herrin  Julie E. Quinn  Stanley A. Mertzman  Julia A. Cartwright  Karen R. Mertzman  Zhan X. Peng 《Meteoritics & planetary science》2013,48(11):2105-2134

We have done petrologic and compositional studies on a suite of polymict eucrites and howardites to better understand regolith processes on their parent asteroid, which we accept is (4) Vesta. Taking into account noble gas results from companion studies, we interpret five howardites to represent breccias assembled from the true regolith: Elephant Moraine (EET) 87513, Grosvenor Mountains (GRO) 95535, GRO 95602, Lewis Cliff (LEW) 85313, and Meteorite Hills (MET) 00423. We suggest that EET 87503 is paired with EET 87513, and thus is also regolithic. Pecora Escarpment (PCA) 02066 is dominated by melt‐matrix clasts, which may have been formed from true regolith by impact melting. These meteorites display a range in eucrite:diogenite mixing ratio from 55:45 to 76:24. There is no correlation between degree of regolith character and Ni content. The Ni contents of howardite, eucrite, and diogenites (HEDs) are mostly controlled by the distribution of coarse chondritic clasts and metal grains, which in some cases resulted from individual, low‐velocity accretion events, rather than extensive regolith gardening. Trace element compositions indicate that the mafic component of HED polymict breccias is mostly basalt similar to main‐group eucrites; Stannern‐trend basaltic debris is less common. Pyroxene compositions show that some trace element‐rich howardites contain abundant debris from evolved basalts, and that cumulate gabbro debris is present in some breccias. The scale of heterogeneity varies considerably; regolithic howardite EET 87513 is more homogeneous than fragmental howardite Queen Alexandra Range (QUE) 97001. Individual samples of a given howardite can have different compositions even at roughly 5 g masses, indicating that obtaining representative meteorite compositions requires multiple or large samples.  相似文献   

It starts at home? Climate policies targeting household consumption and behavioral decisions are key to low-carbon futures     

Ghislain Dubois  Benjamin Sovacool  Carlo Aall  Maria Nilsson  Carine Barbier  Alina Herrmann  Sébastien Bruyère  Camilla Andersson  Bore Skold  Franck Nadaud  Florian Dorner  Karen Richardsen Moberg  Jean Paul Ceron  Helen Fischer  Dorothee Amelung  Marta Baltruszewicz  Jeremy Fischer  Françoise Benevise  Rainer Sauerborn 《Chemie der Erde / Geochemistry》2013

Through their consumption behavior, households are responsible for 72% of global greenhouse gas emissions. Thus, they are key actors in reaching the 1.5 °C goal under the Paris Agreement. However, the possible contribution and position of households in climate policies is neither well understood, nor do households receive sufficiently high priority in current climate policy strategies. This paper investigates how behavioral change can achieve a substantial reduction in greenhouse gas emissions in European high-income countries. It uses theoretical thinking and some core results from the HOPE research project, which investigated household preferences for reducing emissions in four European cities in France, Germany, Norway and Sweden. The paper makes five major points: First, car and plane mobility, meat and dairy consumption, as well as heating are the most dominant components of household footprints. Second, household living situations (demographics, size of home) greatly influence the household potential to reduce their footprint, even more than country or city location. Third, household decisions can be sequential and temporally dynamic, shifting through different phases such as childhood, adulthood, and illness. Fourth, short term voluntary efforts will not be sufficient by themselves to reach the drastic reductions needed to achieve the 1.5 °C goal; instead, households need a regulatory framework supporting their behavioral changes. Fifth, there is a mismatch between the roles and responsibilities conveyed by current climate policies and household perceptions of responsibility. We then conclude with further recommendations for research and policy.  相似文献   

Smallholder groundwater irrigation in sub-Saharan Africa: an interdisciplinary framework applied to the Usangu plains, Tanzania     

Karen G. Villholth  Jegan Ganeshamoorthy  Christian M. Rundblad  Theis S. Knudsen 《Hydrogeology Journal》2013,21(7):1481-1495

A simple but comprehensive framework for analysing the potential for and constraints to groundwater development for irrigated agriculture in sub-Saharan Africa is proposed. The framework, based on food value chain principles, is applied to the sub-Saharan context and a specific catchment in Tanzania, the Usangu plains, where groundwater has been proposed as a strategic resource for augmenting food production and smallholder livelihoods and to alleviate seasonal water scarcity. The novel contribution of the work is the presentation of a tool that can be applied to support an interdisciplinary approach to systematically identify most significant barriers and most critical water management and development interventions for sustainable development of groundwater irrigation. The result of the case study shows that farmer economics, capacity, and pump and well drilling market constraints limit groundwater irrigation in the Usangu plains rather than hydrogeological conditions.  相似文献   

Transboundary aquifer mapping and management in Africa: a harmonised approach     

Yvan Altchenko  Karen G. Villholth 《Hydrogeology Journal》2013,21(7):1497-1517

Recent attention to transboundary aquifers (TBAs) in Africa reflects the growing importance of these resources for development in the continent. However, relatively little research on these aquifers and their best management strategies has been published. This report recapitulates progress on mapping and management frameworks for TBAs in Africa. The world map on transboundary aquifers presented at the 6th World Water Forum in 2012 identified 71 TBA systems in Africa. This report presents an updated African TBA map including 80 shared aquifers and aquifer systems superimposed on 63 international river basins. Furthermore, it proposes a new nomenclature for the mapping based on three sub-regions, reflecting the leading regional development communities. The map shows that TBAs represent approximately 42 % of the continental area and 30 % of the population. Finally, a brief review of current international law, specific bi- or multilateral treaties, and TBA management practice in Africa reveals little documented international conflicts over TBAs. The existing or upcoming international river and lake basin organisations offer a harmonised institutional base for TBA management while alternative or supportive models involving the regional development communities are also required. The proposed map and geographical classification scheme for TBAs facilitates identification of options for joint institutional setups.  相似文献   

Does Magnetic Flux Submerge at Flux Cancelation Sites?     

Harvey  Karen L.  Jones  Harrison P.  Schrijver  Carolus J.  Penn  Matthew J. 《Solar physics》1999,190(1-2):35-44

Simultaneous measurements of the magnetic fields in the photosphere and chromosphere were used to investigate if magnetic flux is submerging at sites between adjacent opposite polarity magnetic network elements in which the flux is observed to decrease or `cancel'. These data were compared with chromospheric and coronal intensity images to establish the timing of the emission structures associated with these magnetic structures as a function of height. We found that most of the cancelation sites show either that the bipole is observed longer in the photosphere than in the chromosphere and corona (44%) or that the timing difference of the disappearance of the bipole between these levels of the atmosphere is unresolved. The magnetic axis lengths of the structures associated with the cancelation sites are on average slightly smaller in the chromosphere than the photosphere. These observations suggest that magnetic flux is retracting below the surface for most, if not all, of the cancelation sites studied.  相似文献   

Coming to Terms with “Integrated Coastal Management”: Problems of Meaning and Method in a New Arena of Resource Regulation     

Karen Nichols 《The Professional geographer》1999,51(3):388-399

This paper traces the emergence of coastal management in the late twentieth century and assesses the social and spatial implications of the new Integrated Coastal Management (ICM) philosophy that guides national regulatory programs worldwide. A review of the epistemology of ICM reveals its link to the United Nations marine regulatory regime (the Law of the Sea) and the sustainable development paradigm embraced at the 1992 United Nations Conference on Environment and Development. I suggest that the resulting regulatory regime facilitates the opening of coastal zones worldwide to aggressive state and global capital investment. By promoting the overhaul of existing social and spatial organization in coastal zones and by asserting the primacy of resource access for modern economic interests, ICM may introduce more rather than less social conflict and ecological degradation. To illustrate this dynamic, I examine the case of coral reef management in general, and in the context of the Sri Lankan ICM program.  相似文献