The Experts below are selected from a list of 5049 Experts worldwide ranked by ideXlab platform
Karin A F Zonneveld - One of the best experts on this subject based on the ideXlab platform.
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atlas of modern organic walled dinoflagellate cyst distribution
Review of Palaeobotany and Palynology, 2003Co-Authors: Fabienne Marret, Karin A F ZonneveldAbstract:This Atlas summarises the global distribution of extant organic-walled dinoflagellate cysts in the form of 61 maps illustrated by the relative abundance of individual cyst taxa in recent marine sediments from the Atlantic Ocean and adjacent basins, the Antarctic region (South Atlantic, southwestern Pacific and southern Indian Ocean sections), the Arabian Sea and the northwestern Pacific. This synthesis is based on the integration of literature sources together with data from 835 marine surface sediments prepared on a comparable methodology and taxonomy. The relationships between distribution patterns of cyst species and the surface-water parameters (temperature, salinity, phosphate and nitrate concentrations) are documented with graphs depicting the relative abundance of species in relation to seasonal and annual values of the above mentioned parameters at the sample sites. Two Ordination Techniques (detrended correspondence analysis and canonical correspondence analysis) have been carried out to statistically illustrate the relationships between species distribution and sea-surface conditions. Results have been compared with previously published records and an overview of the ecological significance of each individual species is presented. Characterisations of selected environments as well as a discussion about how additional processes such as preservation and transport could have affected the present dataset are included. This Atlas forms the basic printed version of an international database that will be freely available within the PANGAEA database: http://www.pangaea.de and on the web site www.pangea.de/projects/dino-atlas.
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geographical distributions of organic walled dinoflagellate cysts in surficial sediments of the benguela upwelling region and their relationship to upper ocean conditions
Progress in Oceanography, 2001Co-Authors: Karin A F Zonneveld, Ramses P Hoek, Henk Brinkhuis, Helmut WillemsAbstract:The organic walled cyst content of 41 surface sediment samples from the south-eastern South Atlantic Ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions. In order to obtain insight into which environmental factors influence the distribution of individual cyst species, the cyst associations have been compared with oceanographic characteristics of the overlying water masses, i.e. temperature, salinity, density and stratification gradients. The associations and relationships have been established by visual examination of the dataset and the multivariate Ordination Techniques, Detrended Correspondence Analysis and Canonical Correspondence Analysis. Special attention has been given to the factors of transport and preservation of the cysts. Five associations have been recognised as being characteristic of (1) areas influenced by coastal upwelling and/or river outflow, (2) open ocean, (3) Agulhas Current and southern Benguela Current, (4) Benguela Current and (5) Walvis Bay, shelf break area. The factors dominant in influencing either directly or indirectly the cyst distributions appear to be the stratification in the upper 50 m of the water column, nutrient concentration and seasonality. Variations in sea surface temperatures and salinities have only minor effect on cyst distribution.
Fabienne Marret - One of the best experts on this subject based on the ideXlab platform.
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atlas of modern organic walled dinoflagellate cyst distribution
Review of Palaeobotany and Palynology, 2003Co-Authors: Fabienne Marret, Karin A F ZonneveldAbstract:This Atlas summarises the global distribution of extant organic-walled dinoflagellate cysts in the form of 61 maps illustrated by the relative abundance of individual cyst taxa in recent marine sediments from the Atlantic Ocean and adjacent basins, the Antarctic region (South Atlantic, southwestern Pacific and southern Indian Ocean sections), the Arabian Sea and the northwestern Pacific. This synthesis is based on the integration of literature sources together with data from 835 marine surface sediments prepared on a comparable methodology and taxonomy. The relationships between distribution patterns of cyst species and the surface-water parameters (temperature, salinity, phosphate and nitrate concentrations) are documented with graphs depicting the relative abundance of species in relation to seasonal and annual values of the above mentioned parameters at the sample sites. Two Ordination Techniques (detrended correspondence analysis and canonical correspondence analysis) have been carried out to statistically illustrate the relationships between species distribution and sea-surface conditions. Results have been compared with previously published records and an overview of the ecological significance of each individual species is presented. Characterisations of selected environments as well as a discussion about how additional processes such as preservation and transport could have affected the present dataset are included. This Atlas forms the basic printed version of an international database that will be freely available within the PANGAEA database: http://www.pangaea.de and on the web site www.pangea.de/projects/dino-atlas.
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control of modern dinoflagellate cyst distribution in the irish and celtic seas by seasonal stratification dynamics
Marine Micropaleontology, 2003Co-Authors: Fabienne Marret, James D ScourseAbstract:Abstract Surface sediments from seven stations located in the seasonally stratified, frontal and mixed water regions in the Celtic and Irish seas have been analysed for their dinoflagellate cyst assemblages and dinosterol content. A total of 45 dinoflagellate cyst taxa have been identified and the assemblages related to surface and sediment conditions. Sediments from the mixed water region, at 30 m water depth, are characterised by a relatively low cyst concentration (∼2300 cysts/g dry weight) and high relative abundances of Lingulodinium machaerophorum accompanied by Spiniferites membranaceus , Brigantedinium spp. and Dubridinium caperatum . Assemblages from stratified and frontal water stations are dominated by Spiniferites ramosus associated with Operculodinium centrocarpum , Brigantedinium spp., cysts of Polykrikos schwartzii and Selenopemphix quanta . Ordination Techniques performed on a restricted number of 35 taxa from the assemblages differentiated the stratified and frontal assemblages based on the abundance of the less abundant species Bitectatodinium tepikiense and Spiniferites elongatus . Among the environmental parameters (sea-surface temperature and salinity, stratification index, chlorophyll concentration and sediment grain-size classes), the seasonal stratification and sedimentological context, itself a function of tidal dynamics, explain most of the variance in the environmental conditions. These results indicate that dinoflagellate cyst analyses of shelf sediment records can be used to document the planktonic signal of seasonal stratification dynamics.
Helmut Willems - One of the best experts on this subject based on the ideXlab platform.
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geographical distributions of organic walled dinoflagellate cysts in surficial sediments of the benguela upwelling region and their relationship to upper ocean conditions
Progress in Oceanography, 2001Co-Authors: Karin A F Zonneveld, Ramses P Hoek, Henk Brinkhuis, Helmut WillemsAbstract:The organic walled cyst content of 41 surface sediment samples from the south-eastern South Atlantic Ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions. In order to obtain insight into which environmental factors influence the distribution of individual cyst species, the cyst associations have been compared with oceanographic characteristics of the overlying water masses, i.e. temperature, salinity, density and stratification gradients. The associations and relationships have been established by visual examination of the dataset and the multivariate Ordination Techniques, Detrended Correspondence Analysis and Canonical Correspondence Analysis. Special attention has been given to the factors of transport and preservation of the cysts. Five associations have been recognised as being characteristic of (1) areas influenced by coastal upwelling and/or river outflow, (2) open ocean, (3) Agulhas Current and southern Benguela Current, (4) Benguela Current and (5) Walvis Bay, shelf break area. The factors dominant in influencing either directly or indirectly the cyst distributions appear to be the stratification in the upper 50 m of the water column, nutrient concentration and seasonality. Variations in sea surface temperatures and salinities have only minor effect on cyst distribution.
Vigdis Vandvik - One of the best experts on this subject based on the ideXlab platform.
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succession after prescribed burning in coastal calluna heathlands along a 340 km latitudinal gradient
Journal of Vegetation Science, 2014Co-Authors: Liv Guri Velle, Vigdis VandvikAbstract:Questions The coastal heathlands of northwest Europe are classified as highly endangered and a habitat of high conservation importance throughout their geographic range. Previous research into heathland vegetation dynamics has typically been carried out within single sites or regions, and hence little is known about the variability of land-use effects and successional dynamics along biogeographic gradients. We test the hypothesis that the bioclimatic gradient is a key factor shaping post-fire regeneration dynamics in Calluna heathlands, with progressively slower regrowth and lower post-fire pioneer species richness towards colder climates. Location Wet and dry Calluna heath vegetation in five sites spanning a 340-km latitudinal gradient along the west coast of Norway (60.70°–63.79° N). Methods A repeated measures design was used, with floristic data recorded from permanent plots in a number of experimental post-fire successions over a 3-yr period (n = 344). The data were analysed using multivariate Ordination Techniques: detrended correspondence analysis, partial redundancy analysis and principal response curves, and mixed effects models. Results Regeneration rates decrease from south to north and the wet heath stands regenerate faster towards the pre-fire community composition than the dry stands. Calluna decreases immediately after fire in all sites, but increases from the second year onwards, with the southernmost site having the fastest return. Regeneration of grasses, herbs, mosses and lichens is also faster in the south. Across all sites, species richness decreased the first year after fire, followed by an increase that exceeds pre-fire levels by the second year. The number of pioneer species entering the heathlands after fire decreases northwards. Conclusions We found considerable geographic variation, not only in species composition, but also in post-fire successional trends and dynamics. This is probably linked to higher productivity and larger pools of pioneer species in southern sites, and higher growth rates of shrubs and mosses in the wet heath habitat. This calls for conservation of a geographically diverse set of heathland sites, as well as development of regional- and site-specific management plans.
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the age of calluna stands moderates post fire regeneration rate and trends in northern calluna heathlands
Applied Vegetation Science, 2012Co-Authors: Liv Guri Velle, Liv S Nilsen, Vigdis VandvikAbstract:Questions: Does stand age influence the direction and rate of post-fire successional dynamics in coastal Calluna heaths and can old degraded heath vegetation be restored through reintroduction of fire? Location: Coastal heaths in the Tarva archipelago, central Norway. Methods: We investigated revegetation dynamics after experimental fires set in young (8 years since last fire) and old (>50 years since last fire) grazed heath stands. A repeated measures design was used, with floristic data recorded in permanent plots in the post-fire successions (n=12) over a 7-year period. The data were analysed using multivariate Ordination Techniques (PCA, RDA and PRC) and mixed effects models. Results: The age of Calluna stands strongly influenced post-fire succession, different trends due to age explained 10.4% of variation in floristic data. Young heath showed faster succession towards pre-fire community composition than old heath, and this could partially be explained by succession-related factors: young heath had lower cover of mosses and lichens in the pre-burned vegetation, and lower cover of litter early in succession. Young heath had a less pronounced overall community response to fire than old heath. Vegetative regeneration of C. vulgaris was absent in both old and young heath, but Calluna still re-established as the dominant species within 5–7 years in both young and old stands. Regeneration dynamics were also affected by habitat conditions, different trends due to habitat explained 6% of variation. Conclusions: Our study demonstrates that old stands do develop characteristic heathland vegetation and structure after fire, and while potential invasives into the system such as trees and rhizomatous species are present, they do not impair Calluna regeneration or vegetation development towards the target heathland community composition and structure. Further, as our young stands are only in their second fire rotation after restoration, we suggest that characteristic dynamics of managed heathlands can re-establish relatively rapidly, even in severely degenerated sites (>50 years since last fire). Site-specific factors also need to be considered. We conclude that there is restoration potential in old heaths, despite slow dynamics in the first rotation.
P Leeuwangh - One of the best experts on this subject based on the ideXlab platform.
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Ordination Techniques for analysing response of biological communities to toxic stress in experimental ecosystems
Ecotoxicology, 1995Co-Authors: R P A Van Wijngaarden, P J Van Den Brink, J Oude H Voshaar, P LeeuwanghAbstract:The Ordination Techniques principal component analysis (PCA) and redundancy analysis (RDA) are considered to be useful tools for evaluating community responses in experimental ecotoxicology. Concepts and interpretation of these Techniques are summarized. Application of PCA and RDA is illustrated in a case study. In this study, the effects of a single application of the insecticide Dursban® 4E (a.i. chlorpyrifos) on an aquatic macroinvertebrate community in microcosms were analysed. Four treatment (nominal chlorpyrifos concentration: 35 μg l-1) and four control microcosms were used. PCA visualized a change in species composition with time. Immediately after treatment, a major shift in species composition occurred in treated microcosms. RDA demonstrated that this shift was due to the treatment. RDA also showed that non-arthropods were generally insusceptible to chlorpyrifos; most arthropods were affected. Dynamics of separate taxa were visualized, giving indications of possible primary and secondary effects for these taxa. A Monte Carlo permutation test was used to decide whether treatment had a significant effect on the species composition and to investigate the state of recovery in time. In general, the RDA results gave an adequate condensation of detailed information on abundance and effects obtained by more conventional univariate statistical analysis for some individual taxa of the community. In combination with toxicity and ecological data, Ordination Techniques can provide insight into effects of toxic substances in complex biological communities.