title: The impact of macrophyte mats on biodiversity and ecosystem functioning of benthic communities

authors: Niemand, Clarisse

subjects: bivalves

abstract: Macroalgal blooms, such as Ulva spp., are a common disturbance to estuarine benthic fauna worldwide. As large quantities of macroalgae break free from growing substrates, drifting mats are formed that eventually deposit in low energy environments, including intertidal sandflats. The mats will typically settle on the sediment surface as large sheets. Once these sheets start to decompose, detritus is formed, which is eventually incorporated into the benthic food web; however, the ability to process detritus is dependent on the species present. This thesis examined the impacts of Ulva on the benthic macrofaunal communities and ecosystem functions, at different phases of decomposition; firstly, as large sheets (Chapter 2), then as detritus (Chapter 3), and finally as the Ulva detritus is incorporated and reworked into the sediment and foodweb (Chapters 4 and 5). 

The impacts of intact macroalgal mats on the sediment characteristics, community composition and ecosystem functions (i.e. benthic primary production, metabolism, and nutrient cycling) associated with an intertidal macrofaunal community in Tauranga Harbour were measured in a manipulative field experiment. Temporal changes and recovery of the community and the ecosystem functions they provide were measured twice over a 14-day period. Subtle treatment effects were observed in the macrofaunal community and sediment characteristics, which in turn resulted in subtle shifts in chlorophyll a (chl a) corrected gross primary production. However, there were no significant impacts on the key benthic species (the suspension-feeder Austrovenus stutchburyi and the deposit-feeder Macomona liliana) at this site, which is likely the reason more significant treatment effects were not observed in the measures of ecosystem function. Significant temporal variation was measured in most sediment properties (all except for phaeophytin), and also in benthic primary production. This study emphasized the importance of temporal variability when measuring ecosystem functions in shallow intertidal environments.

A second manipulative field experiment examined the impact of different quantities of Ulva detritus (low [60 g dw m-2], medium [120 g dw m-2] and high [240 g dw m-2]) on the sediment properties, benthic community composition and ecosystem functions of an estuarine benthic community. Plots were sampled on three occasions over an 8-week period, to examine changes in macrofauna and/or ecosystem functions over time. The only significant treatment effect was less gross ammonium flux from the sediment in procedural controls compared to low density treatments. Although no further significant treatment effects were detected, important temporal variation was observed. The macrofaunal community varied significantly between all three the sampling dates, while gross primary production, sediment oxygen consumption, and nutrient efflux from the light and dark chambers varied between at least two of the sampling dates. The results from this study again highlighted the important temporal changes that can be observed over relatively short time scales, and the importance of measuring temporal variation, particularly when measuring ecosystem functions such as primary production and benthic metabolism.

Finally, in a laboratory study, I examined the density dependent effects of two key intertidal bivalve species (A. stutchburyi and M. liliana) and their associated communities on the breakdown, loss, burial and uptake of Ulva detritus. Results showed that the site dominated by A. stutchburyi (AS) had higher overall chl a biomass and chl a was distributed evenly throughout the sediment profile, whilst less labelled Ulva was retained in the sediment. Both chl a biomass and the amount of Ulva recovered were correlated with the density of M. liliana, but only in cores collected from AS sites. Cores collected from the M. liliana dominated site (ML) showed an exponential decline in chl a with depth, and chl a biomass was negatively correlated with species richness. In ML cores (which had very low A. stutchburyi abundances), M. liliana densities showed no correlation with chl a biomass or the amount of Ulva that was recovered, which suggested that the community present in cores from AS is important in facilitating the impact by M. liliana on the mixing and the reworking of organic matter. These results emphasize the value of considering whole communities, and not just key species, when trying to understand sediment mixing and organic matter processing.

Although the addition of Ulva did not result in large and obvious shifts in community composition or ecosystem function, small subtle shifts were observed. These results underpinned the complex nature of biotic and abiotic interactions in dynamic systems like estuaries, but show that for the most part, ecosystem functions are robust. Temporal variations in ecosystem functions appeared to be largely driven by environmental conditions such as light availability, and were a more prominent driver in the differences observed in ecosystem function compared to treatment effects of Ulva addition. The results also highlighted the importance of community composition in the processing and reworking of macroalgal detritus, which further emphasized the complexity of estuarine systems. The results from this research suggest that on intertidal sandflats, providing the abundances of key species remain intact, the benthic community composition can shift, and species can be lost, without a significant loss or shift in overall ecosystem function.

text: The impact of macrophyte mats on biodiversity and ecosystem functioning of benthic communities Macroalgal blooms, such as Ulva spp., are a common disturbance to estuarine benthic fauna worldwide. As large quantities of macroalgae break free from growing substrates, drifting mats are formed that eventually deposit in low energy environments, including intertidal sandflats. The mats will typically settle on the sediment surface as large sheets. Once these sheets start to decompose, detritus is formed, which is eventually incorporated into the benthic food web; however, the ability to process detritus is dependent on the species present. This thesis examined the impacts of Ulva on the benthic macrofaunal communities and ecosystem functions, at different phases of decomposition; firstly, as large sheets (Chapter 2), then as detritus (Chapter 3), and finally as the Ulva detritus is incorporated and reworked into the sediment and foodweb (Chapters 4 and 5). 

The impacts of intact macroalgal mats on the sediment characteristics, community composition and ecosystem functions (i.e. benthic primary production, metabolism, and nutrient cycling) associated with an intertidal macrofaunal community in Tauranga Harbour were measured in a manipulative field experiment. Temporal changes and recovery of the community and the ecosystem functions they provide were measured twice over a 14-day period. Subtle treatment effects were observed in the macrofaunal community and sediment characteristics, which in turn resulted in subtle shifts in chlorophyll a (chl a) corrected gross primary production. However, there were no significant impacts on the key benthic species (the suspension-feeder Austrovenus stutchburyi and the deposit-feeder Macomona liliana) at this site, which is likely the reason more significant treatment effects were not observed in the measures of ecosystem function. Significant temporal variation was measured in most sediment properties (all except for phaeophytin), and also in benthic primary production. This study emphasized the importance of temporal variability when measuring ecosystem functions in shallow intertidal environments.

A second manipulative field experiment examined the impact of different quantities of Ulva detritus (low [60 g dw m-2], medium [120 g dw m-2] and high [240 g dw m-2]) on the sediment properties, benthic community composition and ecosystem functions of an estuarine benthic community. Plots were sampled on three occasions over an 8-week period, to examine changes in macrofauna and/or ecosystem functions over time. The only significant treatment effect was less gross ammonium flux from the sediment in procedural controls compared to low density treatments. Although no further significant treatment effects were detected, important temporal variation was observed. The macrofaunal community varied significantly between all three the sampling dates, while gross primary production, sediment oxygen consumption, and nutrient efflux from the light and dark chambers varied between at least two of the sampling dates. The results from this study again highlighted the important temporal changes that can be observed over relatively short time scales, and the importance of measuring temporal variation, particularly when measuring ecosystem functions such as primary production and benthic metabolism.

Finally, in a laboratory study, I examined the density dependent effects of two key intertidal bivalve species (A. stutchburyi and M. liliana) and their associated communities on the breakdown, loss, burial and uptake of Ulva detritus. Results showed that the site dominated by A. stutchburyi (AS) had higher overall chl a biomass and chl a was distributed evenly throughout the sediment profile, whilst less labelled Ulva was retained in the sediment. Both chl a biomass and the amount of Ulva recovered were correlated with the density of M. liliana, but only in cores collected from AS sites. Cores collected from the M. liliana dominated site (ML) showed an exponential decline in chl a with depth, and chl a biomass was negatively correlated with species richness. In ML cores (which had very low A. stutchburyi abundances), M. liliana densities showed no correlation with chl a biomass or the amount of Ulva that was recovered, which suggested that the community present in cores from AS is important in facilitating the impact by M. liliana on the mixing and the reworking of organic matter. These results emphasize the value of considering whole communities, and not just key species, when trying to understand sediment mixing and organic matter processing.

Although the addition of Ulva did not result in large and obvious shifts in community composition or ecosystem function, small subtle shifts were observed. These results underpinned the complex nature of biotic and abiotic interactions in dynamic systems like estuaries, but show that for the most part, ecosystem functions are robust. Temporal variations in ecosystem functions appeared to be largely driven by environmental conditions such as light availability, and were a more prominent driver in the differences observed in ecosystem function compared to treatment effects of Ulva addition. The results also highlighted the importance of community composition in the processing and reworking of macroalgal detritus, which further emphasized the complexity of estuarine systems. The results from this research suggest that on intertidal sandflats, providing the abundances of key species remain intact, the benthic community composition can shift, and species can be lost, without a significant loss or shift in overall ecosystem function.

year: 2018

title: A Predictive Model for the Parallel Processing of Digital Libraries

authors: Thompson, John Matthew

subjects: Digital Library

abstract: The computing world is facing the problem of a seemingly exponential increase in the amount of raw digital data, and the speed at which it is being collected, is eclipsing our ability to manage it manually. Combine this with the increasing expectations of a growing number of experienced computer users—including real-time access and a demand for expensive-to-process file types such as multimedia—and it is not hard to understand why managing data of this scale and providing timely access to useful information requires specialized algorithms, techniques, and software.

Digital libraries are being used to help address these challenges. Drawing upon knowledge learned through traditional library science, digital libraries excel in providing structured user access to a wide variety of documents. They increasingly include tools for managing, moderating, and marking up these documents. Furthermore, they often feature phases where documents are independently processed and so can benefit from the application of parallel processing techniques—the focus of this thesis. Whether a digital library collection can benefit from parallel processing depends on considerations such as document type, processing cost per document, number of documents, and file-system input/output.

To aid in deciding when to apply parallel processing techniques to digital libraries, this thesis explores the creation a model for predicting key outcomes of leveraging such techniques. It does so by implementing parallel processing in three distinct open-source digital library tools, undertaking experiments designed to measure key processing features (such as processing time versus number of compute nodes), and applying machine learning techniques to these features in order to derive a predictive model.

The model created predicts parallel processing performance at 96% accuracy (adjusted r-squared) for a number of exemplar collection types. The result is a generally applicable tool for estimating the benefits of applying parallel processing to a wide range of digital collections.

text: A Predictive Model for the Parallel Processing of Digital Libraries The computing world is facing the problem of a seemingly exponential increase in the amount of raw digital data, and the speed at which it is being collected, is eclipsing our ability to manage it manually. Combine this with the increasing expectations of a growing number of experienced computer users—including real-time access and a demand for expensive-to-process file types such as multimedia—and it is not hard to understand why managing data of this scale and providing timely access to useful information requires specialized algorithms, techniques, and software.

Digital libraries are being used to help address these challenges. Drawing upon knowledge learned through traditional library science, digital libraries excel in providing structured user access to a wide variety of documents. They increasingly include tools for managing, moderating, and marking up these documents. Furthermore, they often feature phases where documents are independently processed and so can benefit from the application of parallel processing techniques—the focus of this thesis. Whether a digital library collection can benefit from parallel processing depends on considerations such as document type, processing cost per document, number of documents, and file-system input/output.

To aid in deciding when to apply parallel processing techniques to digital libraries, this thesis explores the creation a model for predicting key outcomes of leveraging such techniques. It does so by implementing parallel processing in three distinct open-source digital library tools, undertaking experiments designed to measure key processing features (such as processing time versus number of compute nodes), and applying machine learning techniques to these features in order to derive a predictive model.

The model created predicts parallel processing performance at 96% accuracy (adjusted r-squared) for a number of exemplar collection types. The result is a generally applicable tool for estimating the benefits of applying parallel processing to a wide range of digital collections.

year: 2015

title: Hoea Te Waka ki Uta: Critical Kaupapa Māori Research and Mormon Studies Moving Forward

authors: Simon, Hemopereki

abstract: The following is a reflective commentary on the place of Critical Indigenous Studies, with a focus on Kaupapa Māori Research, within Mormon Studies. Specifically, the piece explores the following questions: What does Kaupapa Māori Research look like when engaging in Mormon Studies? What positionality needs to be taken by Kaupapa Māori researchers and Critical Indigenous scholars when engaging in Mormon Studies? What are the main areas Critical Indigenous scholars and Kaupapa Māori scholars should engage when tackling issues around Mormonism? These questions are important in light of the growing importance of the cultural renaissance in Te Ao Māori and the rise of Kaupapa Māori Research.

text: Hoea Te Waka ki Uta: Critical Kaupapa Māori Research and Mormon Studies Moving Forward The following is a reflective commentary on the place of Critical Indigenous Studies, with a focus on Kaupapa Māori Research, within Mormon Studies. Specifically, the piece explores the following questions: What does Kaupapa Māori Research look like when engaging in Mormon Studies? What positionality needs to be taken by Kaupapa Māori researchers and Critical Indigenous scholars when engaging in Mormon Studies? What are the main areas Critical Indigenous scholars and Kaupapa Māori scholars should engage when tackling issues around Mormonism? These questions are important in light of the growing importance of the cultural renaissance in Te Ao Māori and the rise of Kaupapa Māori Research.

year: 2021