Search results for "Ocean"
showing 10 items of 2919 documents
Database of diazotrophs in global ocean: abundance, biomass and nitrogen fixation rates
2012
Marine N<sub>2</sub> fixing microorganisms, termed diazotrophs, are a key functional group in marine pelagic ecosystems. The biological fixation of dinitrogen (N<sub>2</sub>) to bioavailable nitrogen provides an important new source of nitrogen for pelagic marine ecosystems and influences primary productivity and organic matter export to the deep ocean. As one of a series of efforts to collect biomass and rates specific to different phytoplankton functional groups, we have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling about 12 000 direct field measurements of cyanobacterial diazotroph abundances (based on microscopic …
Reproductive strategy as a piece of the biogeographic puzzle: a case study using Antarctic sea stars (Echinodermata, Asteroidea)
2017
13 pages; International audience; AimTo describe and analyse asteroid biogeographic patterns in the Southern Ocean (SO) and test whether reproductive strategy (brooder versus broadcaster) can explain distribution patterns at the scale of the entire class. We hypothesize that brooding and broadcasting species display different biogeographic patterns.LocationSouthern Ocean, south of 45 °S.MethodsOver 14,000 asteroid occurrences are analysed using bootstrapped spanning network (BSN), non-metrical multidimensional scaling (nMDS) and clustering to uncover the spatial structure of faunal similarities among 25 bioregions.ResultsMain biogeographic patterns are congruent with previous works based on…
Benthic mats offer a potential subsidy to pelagic consumers in tundra pond food webs
2014
We quantified the potential nutritional contribution of benthic mats to pelagic consumers in tundra ponds using three approaches. (1) We compared benthic and pelagic habitats based on their algal biomass and community composition and assessed the dietary quality in terms of fatty acid (FA) concentrations in both habitats. The algal community compositions differed significantly between habitats. Both benthic and pelagic habitats contained saturated and unsaturated FAs, but on average there were more FAs relative to carbon in the pelagic habitat (44 6 29 m gm g C21) than the benthic habitat (23 6 18 m gm g C21) across all studied ponds. (2) We quantified the contribution of benthic mats to th…
Development of picoplankton during natural and enhanced mixing under late-winter ice
2014
We studied the development of autotrophic picophytoplankton and heterotrophic bacterioplankton during the tran- sition from winter ice cover to open water under natural and manipulated mixing conditions in eutrophic Lake Vesijarvi. During the melting of the snow and ice cover, a convection layer developed which eventually met the che- mocline at the interface between the oxic and anoxic water masses. However, in the years with mechanically enhanced mixing, the whole water column remained well oxygenated and the deepening of penetrative convection was facilitated. Stochastic variations in weather, primarily the thickness of the snow cover, likely determined the timing of picophytoplankton gr…
Influence of biotic variables on invertebrate size structure and diversity in coastal wetlands of Southeastern Spain
2016
Abstract Biomass and size-based estimations provide relevant information regarding ecosystem functioning and biotic interactions. Our aims were to study the effect of fish and macrophytes on the size structure of invertebrate assemblages (from rotifers to insects) in a set of coastal water bodies, estimating the biomass (total and main invertebrate groups), the biomass-size spectra (model of Pareto) and size diversity. In fishless ponds, cladoceran and ostracod biomass were higher, and they presented greater size diversity. In fish ponds, rotifer biomass presented greater proportion; while in fishless ponds, cladocerans were usually the most abundant taxa and the largest organisms. The biom…
Plant and sediment properties in seagrass meadows from two Mediterranean CO2 vents: Implications for carbon storage capacity of acidified oceans
2019
Abstract Assessing the status of important carbon sinks such as seagrass meadows is of primary importance when dealing with potential climate change mitigation strategies. This study examined plant and sediment properties in seagrass meadows (Cymodocea nodosa (Ucria) Asch.) from two high pCO2–low pH Mediterranean vent systems, located at Milos (Greece) and Vulcano (Italy) Islands, providing insights on carbon storage potential in future acidified oceans. Contrary to what has been suggested, carbon content (both inorganic and organic) and its surficial accumulation decreased at high pCO2–low pH in comparison with controls. The decrease in inorganic carbon may result from the higher solubilit…
Seagrass ecosystem response to long-term high CO2 in a Mediterranean volcanic vent
2014
We examined the long-term effect of naturally acidified water on a Cymodocea nodosa meadow growing at a shallow volcanic CO2 vent in Vulcano Island (Italy). Seagrass and adjacent unvegetated habitats growing at a low pH station (pH = 7.65 ± 0.02) were compared with corresponding habitats at a control station (pH = 8.01 ± 0.01). Density and biomass showed a clear decreasing trend at the low pH station and the below- to above-ground biomass ratio was more than 10 times lower compared to the control. C content and δ13C of leaves and epiphytes were significantly lower at the low pH station. Photosynthetic activity of C. nodosa was stimulated by low pH as seen by the significant increase in Chla…
Seguimiento del fenómeno blanco de la laguna de la Cruz (Cuenca, España)
2020
[EN] In the present study, a five-year follow-up was performed by remote sensing of the calcium carbonate precipitation in La Gitana karstic lake also known as La Cruz (located on the province of Cuenca, Spain). The important role that calcium carbonate precipitation plays in the ecology of the lake is well known for its influence on the vertical migrations of phytoplankton, the concentration of bioavailable phosphorus and, therefore, the eutrophication and quality of the waters. Whiting take place between the months of July and August, and it can be studied at this time through its optical properties, with the main objective of offering updated data on a phenomenon traditionally studied an…
Standardization proposal for the mapping of Caulerpa taxifolia expansion in the Mediterranean sea
1999
Fourteen years after the first observation of Caulerpa taxifolia (Valh) C. Agardh in the northwestern Mediterranean Sea, this green alga of tropical origin is now present in five countries (Spain, France, Monaco, Italy and Croatia). By the end of 1997, more than 46 km(2), at depths of between 0 and 50 m, were found to be affected by this expansion. A standardization of the cartographic procedure is proposed here. Such a standardization is necessary to compare maps produced by various organizations from different countries. For a given independent station, it is based on the definition of three levels of colonization:Level I refers to a station where one or several colonies less than 100 m a…
The Impact of Variations in the Climate on Seasonal Dynamics of Phytoplankton
2009
Phytoplankton, an assemblage of suspended, primarily autotrophic single cells and colonies, forms part of the base of the pelagic food chain in lakes. The responses of phytoplankton to anthropogenic pressures frequently provide the most visible indication of a long-term change in water quality. Several attributes related to the growth and composition of phytoplankton, such as their community structure, abundance as well as the frequency and the intensity of blooms, are included as indicators of water quality in the Water Framework Directive. The growth and seasonal succession of phytoplankton is regulated by a variety of external as well as internal factors (Reynolds et al., 1993; Reynolds,…