Search results for "106"

Accuracy of IKONOS for mapping benthic coral-reef habitats: a case study from the Puerto Morelos Reef National Park, Mexico

2012

International audience; Reefs are being threatened by global warming, natural disasters, and the increased pressure of the global population. These habitats are in urgent need of mapping at high resolution so that these threats can be quantified. Remote sensing can potentially provide such quantitative data. In this article, we attempt to map benthic coral-reef habitats at the Puerto Morelos Reef National Park in Yucatan Peninsula (Mexico) and to assess the accuracy of the technique in providing a baseline data for future monitoring of changes and evolution of the reef system. An IKONOS image was used in combination with checkpoint ground sampling and classified using a supervised maximum l…

Mn/Ca in shells of Arctica islandica (Baltic Sea) – A potential proxy for ocean hypoxia?

2021

Oxygen depletion threatens an increasing number of shallow water environments, specifically habitats below the seasonal halocline in coastal settings of the Baltic Sea. To understand the natural variations of dissolved oxygen levels on seasonal and inter-annual time-scales prior to the instrumental era, high-resolution archives are urgently required. The present study evaluates the potential use of Mn/Ca values in shells of the bivalve, Arctica islandica to infer concentrations of past dissolved oxygen concentrations. This study is based on laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) data of six contemporaneous specimens and demonstrates that background varia…

The stoichiometry of particulate nutrients in Lake Tanganyika — implications for nutrient limitation of phytoplankton

1999

We studied the potential nutrient limitation of phytoplankton by means of seston nutrient stoichiometry and nutrient enrichment bioassays in the epilimnion of Lake Tanganyika. In most cases, the particulate carbon to phosphorus (C:P) ratio was high and indicated moderate P deficiency, while the respective C:N ratio mainly suggested moderate N deficiency. The N:P ratios of seston indicated rather balanced N and P supply. In three two-day enrichment bioassays in April—May 1995, a combined addition of P, N and organic carbon (glucose) always increased primary production in comparison to untreated controls. Primary production also slightly increased after the addition of phosphate-P, while the …

Oxygen respiration rates of benthic foraminifera as measured with oxygen microsensors

2011

Abstract Oxygen respiration rates of benthic foraminifera are still badly known, mainly because they are difficult to measure. Oxygen respiration rates of seventeen species of benthic foraminifera were measured using microelectrodes and calculated on the basis of the oxygen fluxes measured in the vicinity of the foraminiferal specimens. The results show a wide range of oxygen respiration rates for the different species (from 0.09 to 5.27 nl cell−1 h−1) and a clear correlation with foraminiferal biovolume showed by the power law relationship: R = 3.98 10−3 BioVol0.88 where the oxygen respiration rate (R) is expressed in nl O2 h−1 and in μm3 biovolume (BioVol) (n = 44, R2 = 0.72, F = 114, p

Molecular composition of dissolved organic matter from a wetland plant (Juncus effusus) after photochemical and microbial decomposition (1.25 yr): Co…

2013

We hypothesized that microbial and photochemical processing of dissolved organic matter (DOM) determines its molecular formula composition in aquatic systems to a greater degree than does the original source of the DOM. To test this hypothesis, we exposed DOM from a leachate of a wetland plant (Juncus effusus) to solar radiation or incubated it in the dark for 1.25 yr. Analysis of the extracted DOM of the leachates via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) identified 2800 molecular formulae. Of the formulae in the initial DOM, 11% were lost during microbial decomposition in the dark and 54% under solar radiation. Solar radiation also produced a large number…

Are aquatic and semiaquatic true bugs (Hemiptera: Nepomorpha; Gerromorpha) distinct aquatic communities? A case study in homogeneous habitats

2019

We investigated the environmental factors influencing Nepomorpha and Gerromorpha in lentic, highly vegetated habitats from the Danube Delta. We collected 7032 individuals from 12 species from 23 ha...

Insights from sodium into the impacts of elevated pCO2 and temperature on bivalve shell formation

2017

Ocean acidification and warming are predicted to affect the ability of marine bivalves to build their shells, but little is known about the underlying mechanisms. Shell formation is an extremely complex process requiring a detailed understanding of biomineralization processes. Sodium incorporation into the shells would increase if bivalves rely on the exchange of Na+/H+ to maintain homeostasis for shell formation, thereby shedding new light on the acid-base and ionic regulation at the calcifying front. Here, we investigated the combined effects of seawater pH (8.1, 7.7 and 7.4) and temperature (16 and 22 °C) on the growth and sodium composition of the shells of the blue mussel, Mytilus edul…

2018

Climatically controlled allocation to reproduction is a key mechanism by which climate influences tree growth and may explain lagged correlations between climate and growth. We used continent-wide datasets of tree-ring chronologies and annual reproductive effort in Fagus sylvatica from 1901 to 2015 to characterise relationships between climate, reproduction and growth. Results highlight that variable allocation to reproduction is a key factor for growth in this species, and that high reproductive effort ('mast years') is associated with stem growth reduction. Additionally, high reproductive effort is associated with previous summer temperature, creating lagged climate effects on growth. Con…

Cod at drift in the North Sea

2018

Abstract There has been a large-scale geographical re-distribution of the North Sea cod stock over the past century, and recent surveys indicate a north-eastern modal distribution. Here we assess the consequences of the contemporary distribution of North Sea cod (Gadus morhua) spawning biomass to inter-ocean recruitment potential. By simulations of drifting cod eggs and larvae spawned in the northern North Sea over 16 spawning seasons (in the period 1995–2016), we show that a large portion of the North Sea produced pelagic juveniles most likely settle along the Norwegian Sea shelf. For example during the early 2000s when the North Sea cod spawning biomass was at its lowest, 20% to 27% of la…

Effects of host abundance on larch budmoth outbreaks in the European Alps

2017

Outbreaks of the larch budmoth (LBM) in the European Alps are among the most documented population cycles and their historical occurrence has been reconstructed over 1200 years. Causes and consequences of cyclic LBM outbreaks are poorly understood and little is known about populations near the margin of the host's distribution range. In the present study, we quantify historical LBM outbreaks and associated growth reductions in host trees (European larch). Tree-ring data collected from 18 sites between approximately 500 and 1700 m a.s.l. in the Northern pre-Alps are compared with data from the Western Alps and Tatra Mountains, as well as with nonhost Norway spruce. Highly synchronized host a…