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Search Results: 1 - 10 of 4716 matches for " Laurent Seuront "
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Marine Biology: A Sub-Sample of a Vast Topic  [PDF]
Laurent Seuront
Open Journal of Marine Science (OJMS) , 2013, DOI: 10.4236/ojms.2013.32A001
Abstract:

Marine Biology: A Sub-Sample of a Vast Topic

Hydrocarbon Contamination Decreases Mating Success in a Marine Planktonic Copepod
Laurent Seuront
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0026283
Abstract: The mating behavior and the mating success of copepods rely on chemoreception to locate and track a sexual partner. However, the potential impact of the water-soluble fraction of hydrocarbons on these aspects of copepod reproduction has never been tested despite the widely acknowledged acute chemosensory abilities of copepods. I examined whether three concentrations of the water-soluble fraction of diesel oil (0.01%, 0.1% and 1%) impacts (i) the swimming behavior of both adult males and females of the widespread calanoid copepod Temora longcornis, and (ii) the ability of males to locate, track and mate with females. The three concentrations of the water-soluble fraction of diesel oil (WSF) significantly and non-significantly affect female and male swimming velocities, respectively. In contrast, both the complexity of male and female swimming paths significantly decreased with increasing WSF concentrations, hence suggesting a sex-specific sensitivity to WSF contaminated seawater. In addition, the three WSF concentrations impacted both T. longicornis mating behavior and mating success. Specifically, the ability of males to detect female pheromone trails, to accurately follow trails and to successfully track a female significantly decreased with increasing WSF concentrations. This led to a significant decrease in contact and capture rates from control to WSF contaminated seawater. These results indicate that hydrocarbon contamination of seawater decreases the ability of male copepods to detect and track a female, hence suggest an overall impact on population fitness and dynamics.
Virally-Mediated Versus Grazer-Induced Mortality Rates in a Warm-Temperate Inverse Estuary (Spencer Gulf, South Australia)  [PDF]
Laurent Seuront, Mark Doubell, Paul Van Ruth
Open Journal of Marine Science (OJMS) , 2014, DOI: 10.4236/ojms.2014.44024
Abstract: We investigated the seasonal dynamics of flow cytometrically-defined populations of viruses, heterotrophic bacteria, and the picoeukaryotic and prokaryotic phytoplankton at three sites in the temperate oligotrophic inverse estuary of Spencer Gulf (South Australia). We consistently identified two sub-populations of viruses, three sub-populations of heterotrophic bacteria, one population of picoeukaryotic phytoplankton and two populations of prokaryotic phytoplankton (cyanobacteria Prochlorococcus and Synechococcus). Both the cytometric community composition and the abundance of viruses, heterotrophic bacteria and both prokaryotic (Synechococcus and Prochlorococcus) and eukaryotic picophytoplankton were consistent with previous observations conducted in South Australian continental shelf waters. Noticeably LDNA bacteria (i.e. inactive or dormant cells) were consistently significantly the most abundant group of heterotrophic bacteria (totaling from 29% to 68% of total bacterial abundance) and were up to 10-fold more abundant than that previously reported in South Australian continental shelf waters, including the nearby Saint Vincent Gulf. These results suggest an overall low activity of the microbial community, and are consistent with previous evidence that LDNA cells may play a greater role in heterotrophic processes than HDNA cells in oligotrophic waters. In an attempt to further assess the qualitative and quantitative nature of the mortality of these organisms, we used a specific dilution assay to assess the relative contribution of viruses and microzooplankton grazers to the mortality rates of heterotrophic bacteria, and picoeukaryotic and prokaryotic phytoplankton. We consistently reported site-specific, population specific and sea-son-specific viral lysis and grazing rates of heterotrophic bacteria and the picoeukaryotic and prokaryotic (cyanobacteria Prochlorococcus and Synechococcus) phytoplankton across sites and seasons. Specifically, both viral lysis and micro-zooplankton grazing rates of heterotrophic bacteria were consistently relatively low across sites and seasons, even though their seasonality suggested an overall dominance of grazing over viral lysis in both summer and winter. In contrast, no seasonality is found in either lysis or grazing rates of prokaryotic and eukaryotic picophytoplankton, which are comparable to previous observations conducted in oligotrophic waters, suggesting the mortality dynamics of these populations is similar to those encountered in other oligotrophic waters. The
Towards a Standardized Approach of Cetacean Habitat: Past Achievements and Future Directions  [PDF]
Nardi Cribb, Cara Miller, Laurent Seuront
Open Journal of Marine Science (OJMS) , 2015, DOI: 10.4236/ojms.2015.53028
Abstract: The understanding of what habitat means for an organism as well as the underlying factors driving patterns of habitat use is still unknown for many species. Cetacean habitat has been described using a range of methodologies and variables measured over various temporal and spatial scalesthat are often author-dependent. However, in order to develop an objective and sound understanding of what habitat actually means for cetaceans, a standardized approach needs to be developed. Here, after briefly reviewing the fundamental differences between terrestrial and marine habitats, we highlight the difficulty in defining a marine habitat, with a special focus on marine mammals. We subsequently provide six recommendations by which future cetacean habitat studies might be approached. This recommended approach aims to amend the way in which we think about and undertake investigations into cetacean habitat. It is believed that through this broadened approach, future cetacean habitat studies will increase our understanding of underlying driving factors of cetacean habitat, rather than just describing distribution patterns. Finally, it is stressed how the proposed approach will be more directly applicable within management frameworks and of benefit to conservation initiatives.
New Evidence for Bottlenose Dolphin (Tursiops spp.) Population Connectivity between Kangaroo Island and South Australian Mainland Waters  [PDF]
Nardi Cribb, Phyll Bartram, Tony Bartram, Laurent Seuront
Open Journal of Marine Science (OJMS) , 2017, DOI: 10.4236/ojms.2018.81003
Abstract:
Limited information still exists on the movements of bottlenose dolphins in South Australian coastal waters. There is, however, a need to overcome this paucity of information for an effective development and implementation of conservation and management initiatives in these waters that are increasingly threatened by anthropogenic activities. This study infers potential movements of bottlenose dolphins (Tursiops spp.) between Kangaroo Island that separate and shelter South Australian coastal waters from the Southern Ocean swell, and the South Australian mainland (The Fleurieu Peninsula and The Adelaide Dolphin Sanctuary). Bottlenose dolphins were identified from three separate photo-identification catalogues collated from around the South Australian coastline. Of the 3518, 654 and 181 dolphins sighted in Kangaroo Island, Fleurieu Peninsula and the Adelaide Dolphin Sanctuary, 233, 74 and 40 individuals were recognizable, respectively. Resighting rates were similar in Kangaroo Island (70.4%) and Fleurieu Peninsula (75.7%), but much lower in the Adelaide Dolphin Sanctuary (35%). Ten individuals were resighted between Kangaroo Island and the Fleurieu Peninsula, whilst no matches were made between these two locations and the Adelaide Dolphin Sanctuary catalogue. This suggests a longitudinal connectivity between Kangaroo Island and South Australian mainland waters, but a lack of latitudinal connectivity that may result from the physical stratification processes that separate northern and southern South Australian waters. Our results also demonstrate the highly mobile nature of this species within South Australian waters as well as establish photo-identification as an effective non-invasive tool in which to monitor long-term movement patterns).
Multifractal random walk in copepod behavior
Francois G. Schmitt,Laurent Seuront
Physics , 2001, DOI: 10.1016/S0378-4371(01)00429-0
Abstract: A 3D copepod trajectory is recorded in the laboratory, using 2 digital cameras. The copepod undergoes a very structured type of trajectory, with successive moves displaying intermittent amplitudes. We perform a statistical analysis of this 3D trajectory using statistical tools developed in the field of turbulence and anomalous diffusion. We show that the walk belongs to "multifractal random walks", characterized by a nonlinear moment scaling function for the distance versus time. To our knowledge, this is the first experimental study of multifractal anomalous diffusion. We then propose a new type of stochastic process reproducing these multifractal scaling properties. This can be directly used for stochastic numerical simulations, and is thus of important potential applications in the field of animal movement study, and more generally of anomalous diffusion studies.
Indo-Pacific bottlenose dolphin (Tursiops aduncus) habitat preference in a heterogeneous, urban, coastal environment
Cribb Nardi,Miller Cara,Seuront Laurent
Aquatic Biosystems , 2013, DOI: 10.1186/2046-9063-9-3
Abstract: Background Limited information is available regarding the habitat preference of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) in South Australian estuarine environments. The need to overcome this paucity of information is crucial for management and conservation initiatives. This preliminary study investigates the space-time patterns of habitat preference by the Indo-Pacific bottlenose dolphin in the Port Adelaide River-Barker Inlet estuary, a South Australian, urbanised, coastal environment. More specifically, the study aim was to identify a potential preference between bare sand substrate and seagrass beds, the two habitat types present in this environment, through the resighting frequency of recognisable individual dolphins. Results Photo-identification surveys covering the 118 km2 sanctuary area were conducted over 2 survey periods May to August 2006 and from March 2009 to February 2010. Sighting frequency of recognisable individual Indo-Pacific bottlenose dolphins established a significant preference for the bare sand habitat. More specifically, 72 and 18% of the individuals sighted at least on two occasions were observed in the bare sand and seagrass habitats respectively. This trend was consistently observed at both seasonal and annual scales, suggesting a consistency in the distinct use of these two habitats. Conclusions It is anticipated that these results will benefit the further development of management and conservation strategies.
The impact of turbulence and phytoplankton dynamics on foam formation, seawater viscosity and chlorophyll concentration in the eastern English Channel
Irma Kesaulya,Sophie C. Leterme,James G. Mitchell,Laurent Seuront
Oceanologia , 2008,
Abstract: The space-time dynamics of chlorophyll a concentration and seawater excess viscosity has been investigated in the hydrographically contrasting inshore and offshore water masses of the eastern English Channel. This was done during the phytoplankton spring bloom dominated by Phaeocystis globosa before and after the very large-scale formation of foam induced by an increase in wind-driven turbulence and the related wave breakings. The results suggest that the dynamics of chlorophyll a concentration and seawater excess viscosity are differentially controlled by the formation of foam through the intensity of the spring bloom and wind-generated turbulence.
Distribution of picophytoplankton communities from brackish to hypersaline waters in a South Australian coastal lagoon
Mathilde Schapira, Marie-Jeanne Buscot, Thomas Pollet, Sophie C Leterme, Laurent Seuront
Aquatic Biosystems , 2010, DOI: 10.1186/1746-1448-6-2
Abstract: Highest picophytoplankton abundances were recorded under salinity conditions ranging between 8.0% and 11.0% (1.3 × 106 to 1.4 × 106 cells ml-1). Two populations of picocyanobacteria (likely Synechococcus and Prochlorococcus) and 5 distinct populations of pico-eukaryotes were identified along the salinity gradient. The picophytoplankton cytometric-richness decreased with salinity and the most cytometrically diversified community (4 to 7 populations) was observed in the brackish-marine part of the lagoon (i.e. salinity below 3.5%). One population of pico-eukaryote dominated the community throughout the salinity gradient and was responsible for the bloom observed between 8.0% and 11.0%. Finally only this halotolerant population and Prochlorococcus-like picocyanobacteria were identified in hypersaline waters (i.e. above 14.0%). Salinity was identified as the main factor structuring the distribution of picophytoplankton along the lagoon. However, nutritive conditions, viral lysis and microzooplankton grazing are also suggested as potentially important players in controlling the abundance and diversity of picophytoplankton along the lagoon.The complex patterns described here represent the first observation of picophytoplankton dynamics along a continuous gradient where salinity increases from 1.8% to 15.5%. This result provides new insight into the distribution of pico-autotrophic organisms along strong salinity gradients and allows for a better understanding of the overall pelagic functioning in saline systems which is critical for the management of these precious and climatically-stress ecosystems.The ubiquitous distribution of picophytoplankton and their importance in terms of biomass and production, make them a critical component of food web and carbon cycling in marine systems [1-3]. In particular the partitioning between picophytoplankton and larger cells reflects the source and cycling of nutrients [4] and influences the pathway of matter transfer to higher trophic
Prokaryotic aminopeptidase activity along a continuous salinity gradient in a hypersaline coastal lagoon (the Coorong, South Australia)
Thomas Pollet, Mathilde Schapira, Marie-Jeanne Buscot, Sophie C Leterme, James G Mitchell, Laurent Seuront
Aquatic Biosystems , 2010, DOI: 10.1186/1746-1448-6-5
Abstract: Dissolved proteins and peptides are important sources of energy and nitrogen in aquatic systems [1,2], but they must be hydrolysed to amino acids and oligopeptides to be useable by prokaryotes. Following the development of sensitive methods using fluorogenic substrates [3], proteolytic activity in natural aquatic systems has been assessed by measuring the activity of leucine-aminopeptidase as a model enzyme [4]. However, microbial cells living in aquatic systems are influenced by a variety of environmental factors which affect the molecular control of their enzyme synthesis. Among these variables, salinity has been identified as a major driving force in both the composition of bacterioplankton and their efficiency in degrading dissolved organic carbon (DOC) [5]. Previous studies focusing on the effect of salinity on the composition and metabolic activity of bacterial communities were mainly conducted in estuaries where salinity typically did not exceed 5% [6] and the effect of higher salinity conditions was mainly investigated in highly saline ponds from solar salterns [7]. To our knowledge, little is still known about the dynamic of prokaryotic aminopeptidase activity along natural continuous hypersaline gradients. The objective of this study was to investigate the changes in aminopeptidase activity of prokaryotic communities identified using flow cytometry from brackish to hypersaline waters.The Coorong is a South Australian shallow coastal lagoon characterized by a strong salinity gradient with salinity continuously ranging from brackish (1.8%) to hypersaline (15.5%). Constrained between the last interglacial dune and the modern dune that has been established from the mid-holocene, this lagoon receives inputs from the ocean through the Murray Mouth and from underground and freshwater inputs from Lake Alexandrina and Lake Albert, which are the terminal system of the River Murray (Fig. 1). If freshwater inputs lead to lower salinities in the northwest part of the C
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