381023 research outputs found
Sort by
Identifying drivers of microbial dynamics in aquaculture : from single-cell technology to metagenomics
No full textThe growing world population necessitates a reliable supply of high-quality protein, which is increasingly provided through aquatic animal products. The frequent outbreaks of diseases and the economic losses associated with these outbreaks is one of the main restraints for a further sustainable expansion of the aquaculture sector. To meet the increasing demand, aquaculture systems must become more efficient through sustainable, long-term biosecurity management strategies that reduce the occurrence of diseases. In light of these diseases, bacterial pathogens are of major concern. Over the years, it has become clear that bacteria do not only play a role in the emergence of diseases, but that they are of great importance for many functional aspects in the aquaculture ecosystem, in which they are involved in cycling of nutrients, degradation of organic matter etc.Therefore, a holistic approach where not only the potential pathogens, but the entire microbial community is monitored and manipulated, is needed to effectively manage aquaculture ecosystems. To develop and perform this management in practice we need, on the one hand, to understand which microbiomes lead to optimal performance and how we can steer microbiomes towards that state, and on the other hand, to be able to monitor the microbial communities during the cultivation. It is widely accepted that rearing water has a strong influence on the host microbiomes, and, hence, plays an essential role in the emergence of diseases. Therefore, proper management of the rearing water microbiome is considered crucial for obtaining productive systems. The research presented in this dissertation has aimed to acquire insights into the microbial community ecology of rearing water bacterial communities and their community members, and in the process, to contribute to the development of tools that can be used for investigating and monitoring these rearing water microbiomes.
In Chapter 2, we have acquired new insights in the dynamics, assembly and sources of rearing water communities of a Litopenaeus vannamei larviculture farm. We tracked the bacterial densities of the rearing water microbiomes of 5 replicate cultivation tanks through a high-resolution sampling campaign and show that bacterial densities increased with 2 log-units over an 18 day cultivation. When studying the dynamics of the community composition of these microbiomes, we determined two community shifts that could be related to the dynamics of the algae in the water. Hence, our study illustrates that even when algae are added in low abundance to be used as a feed product, they can have a steering role on the bacterial community. We found that stochastic processes dominated the community assembly in the water over time, which could be linked to the high observed heterogeneity between the replicate tanks. Through a better understanding of the community assembly processes that are prevailing in an ecosystem, we should be able to make informed decisions about optimal monitoring schemes and management practices, such as dosing of probiotics. Hence, further investigations regarding how widespread this dominance of stochastic community assembly is across farm layout and in relation to different farm management practices, will be a crucial step to improve management practices.
During the sampling campaign, we additionally investigated the microbial communities present in the live (algae and Artemia) and dry feed products, and the exchange water. For each of these peripheral microbiomes we found a high batch-to-batch variability, both in terms of bacterial abundance and community composition. Additionally, for the live feeds, we found a high within-batch variability in bacterial densities. The most striking dynamics were those of the Artemia storage basins where in each batch, bacterial growth was observed over 24 hours, leading up to a 10-fold difference in bacterial densities for samples originating from the same batch. We have quantified the contributions of these peripheral microbiomes to the rearing water and found that ± 10 % of the rearing water operational taxonomic units (OTUs) were introduced through these sources. Together, these OTUs were responsible for 37 % of the rearing water community over the entire cultivation. These results illustrate the importance of peripheral microbiomes. Given this large contribution, careful preparation and storage of these inputs will be paramount to maintain stable, healthy systems.
Determining the composition of microbial communities is an essential step in both microbiome management and research. In Chapter 3, we have developed a new pipeline that allows to predict the presence and abundance of taxa in environmental communities based on flow cytometric measurements. Using cell-sorting, we validated that the model correctly associates taxa to regions in the cytometric fingerprint, where they are detected using 16S rRNA gene amplicon sequencing, illustrating the reliability of the constructed models. This pipeline expands the existing flow cytometric toolbox for the assessment of community status in a fast, cheap and high-throughput manner. While some further validation of the developed models is recommended, this pipeline holds great potential to be integrated in routine monitoring schemes and early warning systems for the aquaculture sector.
Rearing water microbiomes contain a large diversity of bacterial taxa. In Chapter 4, we investigated the in situ life strategies of 67 taxa present in the rearing water. We found evidence for niche separation between r- and K-strategists in the communities, with r-strategists typically encoding for more and more diverse transporters and metabolic pathways and having a higher fitness for exploitation of spatially structured nutrient hotspots. This niche separation provides an explanation for the coexistence of r- and K-strategists in the rearing water. Additionally, we found that the in situ growth activity of r-strategists could be linked better with the cultivation performance as compared to the distribution of relative abundances of r- and K-strategists in the rearing water. Although we could not provide a mechanistic understanding of this relationship between the growth activity of r-strategists and host health based on our study, these findings open a future for further research into the in situ functionalities of r- and K-strategists, and their potential role in mediating the host performance.
In conclusion, during this dissertation several insights in the ecology of bacterial communities in rearing water of aquaculture ecosystems were obtained. These insights contribute to the knowledge base that is needed to develop effective management strategies to reduce the occurrence of diseases. Our findings include insights with direct practical implications (e.g. optimization of live feed preparation and storage protocols), as well as insights that can be translated into management strategies after further research (e.g. the implications of stochastic changes in community composition for determining optimal protocols for administering probiotics or optimizing monitoring schemes; management strategies to direct the growth activities of r-strategists). In parallel, a new method was developed that allows to predict the presence and abundance of bacterial taxa via flow cytometric fingerprinting. This method contributes to the toolbox of available pipelines for assessing the status of a microbial community in a fast, cheap manner
Listening to children in vulnerable situations : rethinking voice through intra-active pedagogical encounters
No full text'It was never made for TV' : niche sports in the age of digital plenitude : a case of the World Rally Championship (WRC)
No full textIn this dissertation, a case study is formed about the sport of rallying, and in particular, the World Rally Championship (WRC) and its media strategy. Traditionally, media rights have been sold to free-to-air television or pay-television networks in individual markets across the world. The premise became to sell the media rights to a sporting contest to the highest bidder, who would recoup their money through advertising and subscriptions to audiences. It is a system that brought great financial rewards to many sports. However, not all could make this model work. The WRC was one such sport as it was run over several days and in non-centralised geographic locations. It ensured the sport was not television-friendly and therefore could not generate significant media-driven financialisation. After a change in ownership, the WRC Promoter GmbH was formed and in 2013 a new media strategy was created, and then reinforced in 2018. They launched an over-the-top streaming service called WRC+ All Live. To do this, the WRC Promoter GmbH abandoned the notion of selling its product exclusively and primarily to a television partner, rather it went with a direct-to-consumer streaming service. The product available across the world without geoblocking restrictions. Along with the stream, the media rights are sold on a non-exclusive basis meaning that multiple media companies in the same marketplace can air the sport at the same time. It resulted in another shift for the WRC Promoter GmbH as they transitioned from a sports management concern to a sports media company with total responsibility for the media. The shift affected the fans as it changed their relationship with the sport and its media product and for sports media researchers, as the generally accepted sports rights model was abandoned.
The case study, therefore, focuses aspects pertaining to decisions made, with regards to the streaming media product. The case study seeks to understand the effect that the change had on the economic aspects of the sport. As the media product has become of vital importance to the financial models of many sports, understanding how the WRC+ All Live and the effect on media-driven financialisation is the first area to be explored. It is followed by understanding how the shift from selling media rights to external broadcasters to that of becoming a media broadcaster in their own right and how that has affected the way the sport is operated. Finally, the way the fans engage with the sport under the new media delivery methods is understood. The streaming product had several effects on fan engagement. The first was that fans across the world could watch the same show at the same time. Secondly, the sport was delivered live for the first time, in what was a dramatic increase in programming, going from just a couple of hours of highlights per round, to more than 25 hours of live coverage. As the sport launched the product, it was unclear how the fans would react, and therefore understanding that reaction is important. The case of the WRC is important to understand, as technology and fan behaviours are changing which results in different opportunities for many niche sports in their media rights and media delivery models.
The change to the media service and the WRC+ All Live is understood through multiple theoretical lenses. The first is that of the media-sport triangle. The triangle was conceived to help explain the financial and cultural success of some sports, with the relationship between sport, the media, and business. With popular sports on linear television, a culturally popular sport could be sold to television stations as they wanted the content and the audiences. Those audiences could be financialised through subscriptions or advertising, for example. However, the model must change for niche sports undertaking a direct-to-consumer model, where targeted audiences, and their attention can be commodified. The notions of digital plenitude are explored as internet-enabled technologies allow sports to undertake streaming media and with it, many barriers to delivery no longer exist. However, to create and distribute a streaming service requires a sport to rapidly professionalise and create an organisational culture to allow such a change to occur and become normalised in the organisation. Though the history of sports on television, a broadcast company has, generally, been the intermediary between the sport and the fans, providing their own services to create a product that was acceptable to these audiences. While elite sport has utilised professionals to play the game and to manage the sport, they now needed professionalise in new areas of sport media. Here, the WRC Promoter GmbH culturally enabled sport-entrepreneurial characteristics to take place that allowed a revolutionary media model to be created and normalised within its structures. Finally, the relationship with the fans is explored as without the fan having a willingness to pay for the service, and enjoying the mediated sport, the streaming product cannot obtain sufficient financial success.
To ensure that sufficient reliable information could be found for the exploratory case study, a three-sided methodological approach was formed. The first method utilised was expert interviews. In total 27 expert interviews were conducted with key stakeholders in the sport, like senior managers, on-air talent and key people involved in media sales for the sport. Through these interviews, a complex and deep understanding of the decision-making processes could be formed. Importantly, the impact of the change of the media product to the sporting product itself could be understood, enabling a clear picture regarding the pressures, successes and necessary changes that were made to the sport to emerge. However, it was important to consolidate the validity of these findings through other methods. Observational research at nine WRC events over four years provided insight into how WRC events operated in different regions and how the media influenced the operation and standardisation of each event. Finally, desk research provided historical perspectives on decisions that were made prior to the research taking place, and to inform the research on decisions and attitudes throughout the execution of the case study.
These theoretical perspectives and research techniques provided many key outcomes. It became clear that the transition away from traditional media strategies altered the power relationship between the sport, broadcasters and fans. The sport now guaranteed its position in every market across the world and its direct relationship with the fans. However, the culture and history of the sport played an important role in what actions the WRC Promoter GmbH could undertake. It was not a case of having a new owner, and therefore they could impose their own culture on the sport. To ensure fan enjoyment, the historical element of the event, the media product and the way the sport was run needed to be maintained. As the streaming market continues to develop, more niche sports seek to control their own media futures, and as promotion rights to sports are being bought and sold, the outcomes from the WRC+ All Live product can contain important lessons for other sports, and researchers into the future
Building towards a culture-sensitive pain neuroscience education for African (Hausa-speaking) chronic pain patients
No full textExpanding the scope of prone breast radiotherapy with the prone crawl position : prone alone?
No full textOn becoming a green kid : how to effectively design climate messages to encourage children's intention to adopt pro-environmental behavior through message framing and emotions
No full textIndirect effects of soil texture on organic matter mineralization through mediation of soil moisture
No full textAs the largest carbon pool in most terrestrial ecosystems, soil organic carbon (SOC) forms a critical component of the global carbon cycle and its preservation is crucial to further halt the buildup of CO2 in the atmosphere. Among many controlling factors, soil texture is a key soil trait determining SOC content. In addition, soil texture determines soil water balance, and such textural control may in turn influence organic matter (OM) mineralization indirectly. However, such indirect mechanisms induced by soil texture are often overlooked when interpreting and modeling the overall control of soil texture on SOC. In this PhD dissertation, we conducted two lab-scale experiments and two field-scale experiments to systematically investigate to what extent soil texture impacts OM mineralization indirectly through mediation of moisture. Overall, it was shown that there is a potentially significant indirect influence of soil texture on OM degradation through its impact on soil moisture balance and location of moisture in the soil matrix. These findings clearly suggest that the feedback mechanism induced by soil texture needs to be incorporated into soil C models to accurately predict future evolution of SOC stocks
