title: Sea ice dynamics drive benthic microbial communities in McMurdo Sound, Antarctica

authors: Currie, Ashleigh Ann

subjects: Bacteria

abstract: Globally, Earth’s warming climate is evidently driving sea ice variability in high latitude regions. In the Arctic, older and thicker multi-year sea ice is declining and transitioning into younger and more ephemeral first-year sea ice. Whereas in Antarctica, sea ice extent is increasing around the continent, masking strong regional reductions around the Western Antarctic Peninsula. Models predict that sea ice will continue to decline into the 21ˢᵗ Century globally. Reduced sea ice cover is expected to impact marine ecosystem functioning through increased primary productivity at the sea surface and increased flux of organic matter to the seafloor. Seafloor sediments are a critical component of the marine ecosystem as sites of organic matter remineralisation and nutrient regeneration, processes which are driven by microorganisms. Despite their importance, our understanding of sediment biogeochemical processes, their connectivity to the water column and to primary productivity at the surface is limited, particularly in polar regions. This impedes our ability to predict the impacts of climate change on marine ecosystem functioning. This study sampled marine sediments from two strategically chosen sites ~60 km apart in McMurdo Sound, Antarctica, where organic matter concentrations were high due to firstyear ice conditions and productive open ocean source waters (Cape Evans), and low due to multi-year ice and oligotrophic source waters (New Harbour). Using high-throughput 16S rRNA gene amplicon sequencing and sediment geochemistry data (chlorophyll-α, phaeophytin, TOC, TN, δ13C, δ15N) this study compared the structure and composition of the sediment microbial communities at these two contrasting sites. The bacterial richness and evenness (alpha diversity) was comparatively greater in the low organic matter sediments underneath the multi-year ice cover than in the high organic matter sediments underneath first-year ice. Significant site-based compositional differences between the two study sites were found. Compositional differences in the high organic matter sediments were driven by known heterotrophic algal biopolymer degrading taxa Flavobacteriales, Cytophagales, and Verrucomicrobiales, and sulfate-reducing bacteria Desulfobulbales, potentially reflecting a sediment legacy of high algal-derived organic matter flux. Whereas the low organic matter sediment communities were driven by chemoautotrophic taxa Nitrosopumilaeles, Nitrospirales, and Steroidobacterales which are known to be involved in carbon fixation and nitrogen cycling, reflecting the legacy of oligotrophic conditions in these sediments. The marine sediments at New Harbour and Cape Evans were not influenced by wind-blown terrestrial surface sediments from the neighbouring Taylor Valley. Additionally, this study supported the hypothesis that subsurface brine channels from the Taylor Valley could be discharging into McMurdo Sound at New Harbour by detecting low abundances of taxa associated with high saline environments (e.g. Thiohalorhabdales). Overall, the findings from this study suggest that climate driven sea ice reductions and increased organic matter flux may shift sediment communities from autotrophy towards heterotrophy, thus impacting sediment biogeochemistry. This study contributes towards our understanding of marine sediment processes and marine ecosystem functioning. Additionally, this study provides a baseline of understanding of sediment microbial communities in McMurdo Sound which will support future research further examining community functional capabilities. Finally, this study contributes a first report of the direct impacts of climate driven sea ice change on sediment microbial communities in Antarctica.

text: Sea ice dynamics drive benthic microbial communities in McMurdo Sound, Antarctica Globally, Earth’s warming climate is evidently driving sea ice variability in high latitude regions. In the Arctic, older and thicker multi-year sea ice is declining and transitioning into younger and more ephemeral first-year sea ice. Whereas in Antarctica, sea ice extent is increasing around the continent, masking strong regional reductions around the Western Antarctic Peninsula. Models predict that sea ice will continue to decline into the 21ˢᵗ Century globally. Reduced sea ice cover is expected to impact marine ecosystem functioning through increased primary productivity at the sea surface and increased flux of organic matter to the seafloor. Seafloor sediments are a critical component of the marine ecosystem as sites of organic matter remineralisation and nutrient regeneration, processes which are driven by microorganisms. Despite their importance, our understanding of sediment biogeochemical processes, their connectivity to the water column and to primary productivity at the surface is limited, particularly in polar regions. This impedes our ability to predict the impacts of climate change on marine ecosystem functioning. This study sampled marine sediments from two strategically chosen sites ~60 km apart in McMurdo Sound, Antarctica, where organic matter concentrations were high due to firstyear ice conditions and productive open ocean source waters (Cape Evans), and low due to multi-year ice and oligotrophic source waters (New Harbour). Using high-throughput 16S rRNA gene amplicon sequencing and sediment geochemistry data (chlorophyll-α, phaeophytin, TOC, TN, δ13C, δ15N) this study compared the structure and composition of the sediment microbial communities at these two contrasting sites. The bacterial richness and evenness (alpha diversity) was comparatively greater in the low organic matter sediments underneath the multi-year ice cover than in the high organic matter sediments underneath first-year ice. Significant site-based compositional differences between the two study sites were found. Compositional differences in the high organic matter sediments were driven by known heterotrophic algal biopolymer degrading taxa Flavobacteriales, Cytophagales, and Verrucomicrobiales, and sulfate-reducing bacteria Desulfobulbales, potentially reflecting a sediment legacy of high algal-derived organic matter flux. Whereas the low organic matter sediment communities were driven by chemoautotrophic taxa Nitrosopumilaeles, Nitrospirales, and Steroidobacterales which are known to be involved in carbon fixation and nitrogen cycling, reflecting the legacy of oligotrophic conditions in these sediments. The marine sediments at New Harbour and Cape Evans were not influenced by wind-blown terrestrial surface sediments from the neighbouring Taylor Valley. Additionally, this study supported the hypothesis that subsurface brine channels from the Taylor Valley could be discharging into McMurdo Sound at New Harbour by detecting low abundances of taxa associated with high saline environments (e.g. Thiohalorhabdales). Overall, the findings from this study suggest that climate driven sea ice reductions and increased organic matter flux may shift sediment communities from autotrophy towards heterotrophy, thus impacting sediment biogeochemistry. This study contributes towards our understanding of marine sediment processes and marine ecosystem functioning. Additionally, this study provides a baseline of understanding of sediment microbial communities in McMurdo Sound which will support future research further examining community functional capabilities. Finally, this study contributes a first report of the direct impacts of climate driven sea ice change on sediment microbial communities in Antarctica.

year: 2020

title: Detecting anthropogenic impacts on estuarine benthic communities

authors: Clark, Dana

subjects: Macroinvertebrates

abstract: Our estuaries, and the benefits that we derive from them, are threatened by the cumulative effects of interacting stressors. Separating the impacts of anthropogenic stressors from natural variability in the marine environment is extremely difficult. This is particularly true for estuaries, due to their inherent complexity and the prevalence of difficult-to-manage diffuse stressors. Successful management and protection of these valuable ecosystems requires innovative monitoring approaches that can reliably detect anthropogenic stressor impacts. In this thesis, I examined approaches for detecting the effects of three diffuse land-derived stressors (sedimentation, nutrient loading, and heavy metal contamination) on estuarine benthic communities.

Using Gradient Forest analysis, I explored the relative importance of environmental factors, operating across multiple spatio-temporal scales, in influencing patterns of compositional turnover in estuarine benthic macroinvertebrate communities across New Zealand. Both land-derived stressors (sediment mud content and total sediment nitrogen and phosphorus content) and natural environmental variables (sea surface temperature, Southern Oscillation Index, and wind-wave exposure) were important predictors of compositional turnover, reflecting a matrix of processes interacting across space and time. Generalized linear models were used to link these turnover values to measures of benthic macroinvertebrate diversity, which are commonly used as indicators of ecological health. Based on compositional turnover, I could disentangle the negative effects of land-derived stressors from natural environmental variability. Critical stressor levels associated with high rates of compositional turnover were identified, providing a useful contribution to the current knowledge on land-derived stressor effects.

Once I had determined that anthropogenic impacts could be disentangled from natural variability, I developed indicators (Benthic Health Models; BHMs) to assess estuary health in response to two dominant coastal stressors (sedimentation and heavy metal contamination). Benthic macroinvertebrate community data were used in separate canonical analyses of principal coordinates to create multivariate models of community responses to these stressors. Both models performed well (R² = 0.81, 0.71), and were unaffected by regional and estuarine typology differences. They offer a sensitive and standardised approach to assessing estuarine health that allows separation of the two stressors.

I also examined the potential for emerging molecular approaches to inform estuary health assessment. Recent advances in environmental genomics allow characterization of less visible forms of benthic biodiversity, offering a more holistic view of the ecosystem and potentially providing early warning signals of disturbance. A manipulative nutrient enrichment experiment was conducted in two estuaries and environmental DNA (eDNA) metabarcoding was used to examine the response of eukaryotic (18S rRNA), diatom only (rbcL) and bacterial (16S rRNA) communities. Multivariate analyses demonstrated differential changes in examined communities between sites, suggesting a context dependent response to nutrient enrichment. These patterns aligned with changes in morphologically identified macroinvertebrate communities, confirming concordance between eDNA-based and current monitoring approaches. This work represents a first step towards the development of molecular estuary monitoring tools, which could transform current approaches to ecosystem health assessment.

This thesis demonstrates that the detection of anthropogenic impacts on estuarine benthic communities requires an understanding of the response of communities to stressors and how this response is modified by natural environmental processes operating at different spatio-temporal scales. My research contributes to the management and protection of estuaries by improving knowledge on the processes generating broad scale patterns in benthic macroinvertebrate communities, developing indicators that can be used to assess estuary health and demonstrating the potential of eDNA metabarcoding as a new tool for estuary health assessment.

text: Detecting anthropogenic impacts on estuarine benthic communities Our estuaries, and the benefits that we derive from them, are threatened by the cumulative effects of interacting stressors. Separating the impacts of anthropogenic stressors from natural variability in the marine environment is extremely difficult. This is particularly true for estuaries, due to their inherent complexity and the prevalence of difficult-to-manage diffuse stressors. Successful management and protection of these valuable ecosystems requires innovative monitoring approaches that can reliably detect anthropogenic stressor impacts. In this thesis, I examined approaches for detecting the effects of three diffuse land-derived stressors (sedimentation, nutrient loading, and heavy metal contamination) on estuarine benthic communities.

Using Gradient Forest analysis, I explored the relative importance of environmental factors, operating across multiple spatio-temporal scales, in influencing patterns of compositional turnover in estuarine benthic macroinvertebrate communities across New Zealand. Both land-derived stressors (sediment mud content and total sediment nitrogen and phosphorus content) and natural environmental variables (sea surface temperature, Southern Oscillation Index, and wind-wave exposure) were important predictors of compositional turnover, reflecting a matrix of processes interacting across space and time. Generalized linear models were used to link these turnover values to measures of benthic macroinvertebrate diversity, which are commonly used as indicators of ecological health. Based on compositional turnover, I could disentangle the negative effects of land-derived stressors from natural environmental variability. Critical stressor levels associated with high rates of compositional turnover were identified, providing a useful contribution to the current knowledge on land-derived stressor effects.

Once I had determined that anthropogenic impacts could be disentangled from natural variability, I developed indicators (Benthic Health Models; BHMs) to assess estuary health in response to two dominant coastal stressors (sedimentation and heavy metal contamination). Benthic macroinvertebrate community data were used in separate canonical analyses of principal coordinates to create multivariate models of community responses to these stressors. Both models performed well (R² = 0.81, 0.71), and were unaffected by regional and estuarine typology differences. They offer a sensitive and standardised approach to assessing estuarine health that allows separation of the two stressors.

I also examined the potential for emerging molecular approaches to inform estuary health assessment. Recent advances in environmental genomics allow characterization of less visible forms of benthic biodiversity, offering a more holistic view of the ecosystem and potentially providing early warning signals of disturbance. A manipulative nutrient enrichment experiment was conducted in two estuaries and environmental DNA (eDNA) metabarcoding was used to examine the response of eukaryotic (18S rRNA), diatom only (rbcL) and bacterial (16S rRNA) communities. Multivariate analyses demonstrated differential changes in examined communities between sites, suggesting a context dependent response to nutrient enrichment. These patterns aligned with changes in morphologically identified macroinvertebrate communities, confirming concordance between eDNA-based and current monitoring approaches. This work represents a first step towards the development of molecular estuary monitoring tools, which could transform current approaches to ecosystem health assessment.

This thesis demonstrates that the detection of anthropogenic impacts on estuarine benthic communities requires an understanding of the response of communities to stressors and how this response is modified by natural environmental processes operating at different spatio-temporal scales. My research contributes to the management and protection of estuaries by improving knowledge on the processes generating broad scale patterns in benthic macroinvertebrate communities, developing indicators that can be used to assess estuary health and demonstrating the potential of eDNA metabarcoding as a new tool for estuary health assessment.

year: 2021

title: How Pākehā in not-for-profit organisations implement Te Tiriti o Waitangi

authors: Newcombe, Nicolina Isabel

subjects: Decolonisation

abstract: The aims of this research are to understand what is happening in not-for-profit organisations in relation to our obligation to honour Te Tiriti o Waitangi, and to describe some strategies Pākehā can use to implement Te Tiriti o Waitangi in our work in the not-for-profit sector.  

The history of, and current circumstances affecting, the not-for-profit sector have formed a disabling context, diverting energy away from deepening relationships with local hapū (subtribe). Compounding this situation, the core texts about Te Tiriti and not-for-profit organisations are inconsistent and mainly focus on the first steps of the journey: Treaty education and self assessment.  

After writing about my own experiences with Te Tiriti and working in the not-for-profit sector and comparing my stories with the stories of other Pākehā, I recorded and transcribed conversations with six anonymous Pākehā not-for-profit workers and analysed our commonalities. All participants and their organisations wanted to enact best practice, although 
this aspiration was challenged by many factors, including: a spectrum of understandings about Te Tiriti which often led to piecemeal attempts at power sharing; concerns about the effectiveness of self-assessment by Pākehā about our own Treaty work because of inevitable and inbuilt biases; experience of minimisation or exclusion for speaking up about Te Tiriti at work; box ticking Treaty policies; Māori employees being treated differently to other staff; and confusion between cultural expression and genuine power sharing.  

Protective factors that came through in interviews included: cultural practices that were woven through organisations in a way that was beneficial and welcoming to Māori; relationships with kaumātua (elders); appropriate and emotionally engaging Treaty education; Māori governance members, Māori led research in the community, and Māori involvement in all projects; te reo (Māori language) being a commonly used language in the work place; acknowledgment of our own privilege as Pākehā; and engagement in continuous dialogue about racism. 

Reflections on these issues led to recommendations for how to move forward with implementing Te Tiriti in not-for-profit organisations. These recommendations hinge on a set of actions underpinned by a set of values. Three change management strategies are also described to assist organisations with this transformation. 

This research is intended to be a building block towards empowering Pākehā allies to identify practices, policies, and power structures that could be developed to transform our organisations, and embody our obligations to Te Tiriti, leading to more effective outcomes for all New Zealanders.

text: How Pākehā in not-for-profit organisations implement Te Tiriti o Waitangi The aims of this research are to understand what is happening in not-for-profit organisations in relation to our obligation to honour Te Tiriti o Waitangi, and to describe some strategies Pākehā can use to implement Te Tiriti o Waitangi in our work in the not-for-profit sector.  

The history of, and current circumstances affecting, the not-for-profit sector have formed a disabling context, diverting energy away from deepening relationships with local hapū (subtribe). Compounding this situation, the core texts about Te Tiriti and not-for-profit organisations are inconsistent and mainly focus on the first steps of the journey: Treaty education and self assessment.  

After writing about my own experiences with Te Tiriti and working in the not-for-profit sector and comparing my stories with the stories of other Pākehā, I recorded and transcribed conversations with six anonymous Pākehā not-for-profit workers and analysed our commonalities. All participants and their organisations wanted to enact best practice, although 
this aspiration was challenged by many factors, including: a spectrum of understandings about Te Tiriti which often led to piecemeal attempts at power sharing; concerns about the effectiveness of self-assessment by Pākehā about our own Treaty work because of inevitable and inbuilt biases; experience of minimisation or exclusion for speaking up about Te Tiriti at work; box ticking Treaty policies; Māori employees being treated differently to other staff; and confusion between cultural expression and genuine power sharing.  

Protective factors that came through in interviews included: cultural practices that were woven through organisations in a way that was beneficial and welcoming to Māori; relationships with kaumātua (elders); appropriate and emotionally engaging Treaty education; Māori governance members, Māori led research in the community, and Māori involvement in all projects; te reo (Māori language) being a commonly used language in the work place; acknowledgment of our own privilege as Pākehā; and engagement in continuous dialogue about racism. 

Reflections on these issues led to recommendations for how to move forward with implementing Te Tiriti in not-for-profit organisations. These recommendations hinge on a set of actions underpinned by a set of values. Three change management strategies are also described to assist organisations with this transformation. 

This research is intended to be a building block towards empowering Pākehā allies to identify practices, policies, and power structures that could be developed to transform our organisations, and embody our obligations to Te Tiriti, leading to more effective outcomes for all New Zealanders.

year: 2019