Search results for "14"

Carbon, iron and sulphur cycling in the sediments of a Mediterranean lagoon (Ghar El Melh, Tunisia)

2019

Coastal lagoon sediments are important for the biogeochemical carbon cycle at the land-ocean transition, as they form hotspots for organic carbon burial, as well as potential sites for authigenic carbonate formation. Here, we employ an early diagenetic model to quantify the coupled redox cycling of carbon, iron and sulphur in the sediments of the shallow Ghar El Melh (GEM) lagoon (Tunisia). The model simulated depth profiles show a good correspondence with available pore water data (dissolved inorganic carbon, NH 4 + , total alkalinity, Ca 2+ , Fe 2+ and SO 4 2− ) and solid phase data (organic matter, pyrite, calcium carbonate and iron (oxyhydr)oxides). This indicates that the model is abl…

Factors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off Peru

2020

Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organ…

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 …

Revision of the pentacrinid stalked crinoids of the genus Endoxocrinus (Echinodermata, Crinoidea), with a study of environmental control of character…

2006

A revision of the stalked crinoid species attributed to the genus Endoxocrinus A.H. Clark, 1908 (Diplocrininae, Pentacrinitidae, Crinoidea, Echinodermata) is conducted using studies on phenotype variation and its relation with environment. Specimens collected via submersible at five sites in the Bahamas exhibit distinct phenotypes that correlate with different apparent ecological niches and serve as references for interpreting specimens dredged in Atlantic and Pacific Oceans where detailed information on their benthic environment is unknown. Documentation of ecophenotypic convergences or divergences allows us to distinguish between adaptive characters and those revealing genetic affinities,…

Extinction and recolonization of maritime Antarctica in the limpet Nacella concinna (Strebel, 1908) during the last glacial cycle: toward a model of …

2013

Quaternary glaciations in Antarctica drastically modified geographical ranges and population sizes of marine benthic invertebrates and thus affected the amount and distribution of intraspecific genetic variation. Here, we present new genetic information in the Antarctic limpet Nacella concinna, a dominant Antarctic benthic species along shallow ice-free rocky ecosystems. We examined the patterns of genetic diversity and structure in this broadcast spawner along maritime Antarctica and from the peri-Antarctic island of South Georgia. Genetic analyses showed that N. concinna represents a single panmictic unit in maritime Antarctic. Low levels of genetic diversity characterized this population…

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…

Fish community structure in mesotrophic and eutrophic lakes of southern Finland: the relative abundances of percids and cyprinids along a trophic gra…

2002

In 36 south Finnish lakes, the number of species, as well as the cyprinids:percids ratio, was dependent, not only on total phosphorus (TP), but also on lake size. Total fish biomass and cyprinid biomass increased along the TP gradient, whereas the dependence of percid biomass was less evident. Perch Perca fluviatilis and roach Rutilus rutilus strongly dominated mesotrophic lakes; in eutrophic lakes the proportion of other cyprinids and percids, such as white bream Blicca bjoerkna, bream Abramis brama, pikeperch Stizostedion lucioperca and ruffe Gymnocephalus cernuus, increased. Perch biomass was weakly related to abiotic factors but depended on roach biomass. Lake size and fish species comp…

Response of zooplankton to nutrient enrichment and fish in shallow lakes: a pan-European mesocosm experiment

2004

1. Responses of zooplankton to nutrient enrichment and fish predation were studied in 1998 and 1999 by carrying out parallel mesocosm experiments in six lakes across Europe. 2. Zooplankton community structure, biomass and responses to nutrient and fish manipulation showed geographical and year-to-year differences. Fish had a greater influence than nutrients in regulating zooplankton biomass and especially the relative abundances of different functional groups of zooplankton. When fish reduced the biomass of large crustaceans, there was a complementary increase in the biomasses of smaller crustacean species and rotifers. 3. High abundance of submerged macrophytes provided refuge for zooplank…

2021

Fisheries exploitation can cause genetic changes in heritable traits of targeted stocks. The direction of selective pressure forced by harvest acts typically in reverse to natural selection and selects for explicit life histories, usually for younger and smaller spawners with deprived spawning potential. While the consequences that such selection might have on the population dynamics of a single species are well emphasized, we are just beginning to perceive the variety and severity of its propagating effects within the entire marine food webs and ecosystems. Here, we highlight the potential pathways in which fisheries-induced evolution, driven by size-selective fishing, might resonate throu…