title: The Effects of Benthic Organisms on Intertidal Sediment Erodibility

authors: Harris, Rachel Joy

subjects: macrofauna

abstract: On intertidal sandflats, the dispersal of juvenile organisms can rely on bedload transport, a critical process during small-scale disturbance recovery. The erosion of surface sediments is also vital to benthic-pelagic coupling, where resuspended microbes and organic material become available to suspension feeders and/or transported to adjacent habitats. On sandflats, the organisms living within sediments have been proven to be key drivers of ecological function, such as benthic-pelagic coupling and biogeochemical cycling. Although benthic organisms have been recognized as important to ecological function, the role of multiple species and their interactions on sediment movement is rarely described in non-cohesive sandflats. Furthermore, the role of benthic organisms in sediment movement can vary with environmental conditions, making general sediment-benthos relationships difficult to establish.
In this thesis, I examined subtle variations in the biotic and abiotic factors that influence sediment movement on intertidal sandflats. The thesis comprises three research chapters, each evaluating the relationships between benthic community structure and sediment properties. I used a backdrop of environmental stressors common to intertidal sandflats in order to incorporate the natural variations in sediment-benthos relationships that occur under environmental stress. Throughout this thesis, erosion potential was characterized by: erosion thresholds (Ʈc; N m⁻²), erosion rates (ER; g m⁻² s⁻¹), and change in erosion rate with increasing bed shear stress (me; g N⁻¹ s⁻¹). When describing erosion, a decrease in (-) Ʈc signifies an increase in initial bed erosion and an increase in (+) ER represents an increase in surface erosion. Therefore -Ʈc and +ER demonstrate surface erosion. In contrast, me was recorded during a higher bed shear stress, so that an increase in (+) me denotes more rapid changes in subsurface erosion.
In chapter 2, I used a spatial gradient of increasing sediment mud (≤ 63 μm) content (0-56 %) to represent temporal increases in fine sediments that can occur as a result of terrestrial inputs. Samples were collected from intertidal flats in three estuaries (n = 45), and data pooled across estuaries to achieve the increasing mud gradient. Distance-based linear modeling (DistLM) was employed to account for the variation in erodibility using biotic and abiotic sediment characteristics. Small bioturbating macrofauna, predominantly freely motile species < 5 mm in size, destabilized surface sediments (-Ʈc and +ER), whereas microbes and organic matter were resuspended during surface erosion. In contrast, increasing mud and mean grain size stabilized subsurface sediments (+me) explaining 61 % of the variation. This study highlights the importance of abundant small bioturbating macrofauna to surface erosion, and describes the natural variation in erosion measures that occur with changes in biotic and abiotic sediment properties. 
In chapter 3, I manipulated macrofaunal deposit feeding grazing pressure (i.e., Macomona liliana density, hereafter Macomona) and added shade to stress the microphytobenthic community on an exposed sandflat. Biotic and abiotic properties of sediments were measured, and DistLM used to account for the variation in erosion measures with increasing grazing pressure. In this study, the density of abundant shallow-dwelling bioturbators was linked to initial bed erosion (-Ʈc), whereas density of larger deep-dwelling adult Macomona was linked to stabilization (+Ʈc). This study also confirmed several positive feedbacks between abundant shallow-dwelling macrofauna and microbial biomass. However, despite positive feedbacks, net results demonstrate the importance of bioturbating macrofauna to initiating sediment transport in a tidally driven wave dominated system.
In chapter 4, I used a disturbance-recovery experiment to measure changes in benthic macrofaunal community structure and sediment erosion after exposure to decomposing macroalgae (Ulva spp). Since a small-scale disturbance response can be influenced by pre-disturbance benthic community structure, I considered the effects of decomposing macroalgae at two sites: mixed (deposit feeding, suspension feeding, and predators) and Macomona (grazing deposit feeder) dominated. After 30 d, decomposing Ulva was removed, and multivariate measures of sediment properties, microbial biomass, and macrofaunal functional groups (based on feeding mode) compared to changes in erosion measures. Despite similarities in sediment properties and microbial biomass, erosion was greater (-Ʈc, +ER, and +me) at the Macomona dominated site than in control plots. After Ulva exposure, I measured a difference in surface erosion by site, with an increase in surface erosion (-Ʈc and +ER) at the mixed site (1 d post-Ulva removal) and more stable surface sediments (+Ʈc and -ER) at the Macomona site (up to 2 weeks post-Ulva removal). This study highlights the importance of benthic macrofaunal community structure to surface erosion and suggests that the small-scale variations may aid in larger-scale disturbance recovery.
Throughout this thesis, I describe the role of abundant bioturbating macrofauna in enhancing surface erosion (-Ʈc and +ER) on intertidal sandflats. I also demonstrate positive feedbacks between macrofauna and microbial biomass, which typically resulted in surface erosion (-Ʈc and +ER). Subsurface erosion (+me) was distinct, and more accurately predicted by sediment grain size characteristics. When considering anthropogenic inputs (e.g., terrestrial fine sediments or excess macroalgae), these results suggest that benthic infaunal organisms play a key role in regulating their sedimentary environment, and that areas with a healthy abundance of small bioturbating macrofauna may exhibit greater resilience.

text: The Effects of Benthic Organisms on Intertidal Sediment Erodibility On intertidal sandflats, the dispersal of juvenile organisms can rely on bedload transport, a critical process during small-scale disturbance recovery. The erosion of surface sediments is also vital to benthic-pelagic coupling, where resuspended microbes and organic material become available to suspension feeders and/or transported to adjacent habitats. On sandflats, the organisms living within sediments have been proven to be key drivers of ecological function, such as benthic-pelagic coupling and biogeochemical cycling. Although benthic organisms have been recognized as important to ecological function, the role of multiple species and their interactions on sediment movement is rarely described in non-cohesive sandflats. Furthermore, the role of benthic organisms in sediment movement can vary with environmental conditions, making general sediment-benthos relationships difficult to establish.
In this thesis, I examined subtle variations in the biotic and abiotic factors that influence sediment movement on intertidal sandflats. The thesis comprises three research chapters, each evaluating the relationships between benthic community structure and sediment properties. I used a backdrop of environmental stressors common to intertidal sandflats in order to incorporate the natural variations in sediment-benthos relationships that occur under environmental stress. Throughout this thesis, erosion potential was characterized by: erosion thresholds (Ʈc; N m⁻²), erosion rates (ER; g m⁻² s⁻¹), and change in erosion rate with increasing bed shear stress (me; g N⁻¹ s⁻¹). When describing erosion, a decrease in (-) Ʈc signifies an increase in initial bed erosion and an increase in (+) ER represents an increase in surface erosion. Therefore -Ʈc and +ER demonstrate surface erosion. In contrast, me was recorded during a higher bed shear stress, so that an increase in (+) me denotes more rapid changes in subsurface erosion.
In chapter 2, I used a spatial gradient of increasing sediment mud (≤ 63 μm) content (0-56 %) to represent temporal increases in fine sediments that can occur as a result of terrestrial inputs. Samples were collected from intertidal flats in three estuaries (n = 45), and data pooled across estuaries to achieve the increasing mud gradient. Distance-based linear modeling (DistLM) was employed to account for the variation in erodibility using biotic and abiotic sediment characteristics. Small bioturbating macrofauna, predominantly freely motile species < 5 mm in size, destabilized surface sediments (-Ʈc and +ER), whereas microbes and organic matter were resuspended during surface erosion. In contrast, increasing mud and mean grain size stabilized subsurface sediments (+me) explaining 61 % of the variation. This study highlights the importance of abundant small bioturbating macrofauna to surface erosion, and describes the natural variation in erosion measures that occur with changes in biotic and abiotic sediment properties. 
In chapter 3, I manipulated macrofaunal deposit feeding grazing pressure (i.e., Macomona liliana density, hereafter Macomona) and added shade to stress the microphytobenthic community on an exposed sandflat. Biotic and abiotic properties of sediments were measured, and DistLM used to account for the variation in erosion measures with increasing grazing pressure. In this study, the density of abundant shallow-dwelling bioturbators was linked to initial bed erosion (-Ʈc), whereas density of larger deep-dwelling adult Macomona was linked to stabilization (+Ʈc). This study also confirmed several positive feedbacks between abundant shallow-dwelling macrofauna and microbial biomass. However, despite positive feedbacks, net results demonstrate the importance of bioturbating macrofauna to initiating sediment transport in a tidally driven wave dominated system.
In chapter 4, I used a disturbance-recovery experiment to measure changes in benthic macrofaunal community structure and sediment erosion after exposure to decomposing macroalgae (Ulva spp). Since a small-scale disturbance response can be influenced by pre-disturbance benthic community structure, I considered the effects of decomposing macroalgae at two sites: mixed (deposit feeding, suspension feeding, and predators) and Macomona (grazing deposit feeder) dominated. After 30 d, decomposing Ulva was removed, and multivariate measures of sediment properties, microbial biomass, and macrofaunal functional groups (based on feeding mode) compared to changes in erosion measures. Despite similarities in sediment properties and microbial biomass, erosion was greater (-Ʈc, +ER, and +me) at the Macomona dominated site than in control plots. After Ulva exposure, I measured a difference in surface erosion by site, with an increase in surface erosion (-Ʈc and +ER) at the mixed site (1 d post-Ulva removal) and more stable surface sediments (+Ʈc and -ER) at the Macomona site (up to 2 weeks post-Ulva removal). This study highlights the importance of benthic macrofaunal community structure to surface erosion and suggests that the small-scale variations may aid in larger-scale disturbance recovery.
Throughout this thesis, I describe the role of abundant bioturbating macrofauna in enhancing surface erosion (-Ʈc and +ER) on intertidal sandflats. I also demonstrate positive feedbacks between macrofauna and microbial biomass, which typically resulted in surface erosion (-Ʈc and +ER). Subsurface erosion (+me) was distinct, and more accurately predicted by sediment grain size characteristics. When considering anthropogenic inputs (e.g., terrestrial fine sediments or excess macroalgae), these results suggest that benthic infaunal organisms play a key role in regulating their sedimentary environment, and that areas with a healthy abundance of small bioturbating macrofauna may exhibit greater resilience.

year: 2015

title: Vegetational change along an altitudinal gradient, Mount Egmont, New Zealand

authors: Clarkson, Bruce D.

subjects: Botany

abstract: A direct gradient analysis was conducted on Mt Egmont, New Zealand, firstly to examine quantitatively changes in composition, physiognomy and structure of the vegetation along the altitudinal gradient in order to investigate the accepted notions of vegetation zonation, and secondly to relate such an analysis to other New Zealand gradient analyses and to the two views on vegetation description and analysis, the continuum view and the discrete community (association) view. 
Vegetation data was collected at altitudinally defined sites on five major ridges on Mt Egmont; North Egmont (Blundell’s Track, Ngatoro Track and the Razorback), York Road Track Ridge, Stratford (Summit Road), Dawson Falls (Summit Track), and Lake Dive Track Ridge. The data collected on the York Road Track Ridge provided the basis for describing altitudinal change while the remainder was used to examine in detail the tree-shrub and shrub-tussock interfaces. 
Sample size (quadrat and line transect) was determined after minimal area checks to ensure that a representative combination of species was sampled at each site. Data from a total of sixty plots was collected and preliminary analysis, including graphing of the major species distributions and calculation of similarity matrices to compare quadrats, revealed a tendency toward discontinuity in species distributions. This allowed a classificatory rather than ordinatory strategy of data analysis to be followed. Cluster analyses based on statistical tests of species association were used to determine "natural" groupings of positively associated species and qualitative and quantitative classifications of samples were used to define vegetation zones or groupings at specific similarity index levels. 
Tree-shrub interfaces and tussock-shrub interfaces were compared on the basis of species complement, the degree of floristic, physiognomic and structural discontinuity in the vegetation, and differences in species interaction at each of the locations. 
The effects of data amalgamation, altitudinal interval employed, altitudinal range encountered, and classificatory versus ordinatory techniques, on the conclusions drawn were examined. 
Graphing of species distributions, cluster analyses, and classifications supported in part previously described zonation patterns but enabled a refinement of the generally accepted notions of vegetation zonation on Mt Egmont. In contrast to previous research the vegetation zones identified have a quantitative and objective basis. 
Comparison of the results with those of other New Zealand gradient analyses enabled elucidation of several major species distributions and species interactions because of the unique species complement found on Mt Egmont. 
Comparison of different data collection and manipulation techniques indicated that decisions made may cause data to conform to one or other of the two major approaches (continuum or discrete community types) to vegetation description and analysis. 
The study of the tree-shrub interfaces and shrub-tussock inter­faces showed that the vegetation on Mt Egmont exhibits a spectrum of species distributions ranging from continua through to discontinuities at different locations and specific examples of each are described. Possible explanations advanced include differences in species complement and species interaction, the non-equivalence of the altitudinal gradient at different locations, and differences in environmental factors including slope and aspect.

text: Vegetational change along an altitudinal gradient, Mount Egmont, New Zealand A direct gradient analysis was conducted on Mt Egmont, New Zealand, firstly to examine quantitatively changes in composition, physiognomy and structure of the vegetation along the altitudinal gradient in order to investigate the accepted notions of vegetation zonation, and secondly to relate such an analysis to other New Zealand gradient analyses and to the two views on vegetation description and analysis, the continuum view and the discrete community (association) view. 
Vegetation data was collected at altitudinally defined sites on five major ridges on Mt Egmont; North Egmont (Blundell’s Track, Ngatoro Track and the Razorback), York Road Track Ridge, Stratford (Summit Road), Dawson Falls (Summit Track), and Lake Dive Track Ridge. The data collected on the York Road Track Ridge provided the basis for describing altitudinal change while the remainder was used to examine in detail the tree-shrub and shrub-tussock interfaces. 
Sample size (quadrat and line transect) was determined after minimal area checks to ensure that a representative combination of species was sampled at each site. Data from a total of sixty plots was collected and preliminary analysis, including graphing of the major species distributions and calculation of similarity matrices to compare quadrats, revealed a tendency toward discontinuity in species distributions. This allowed a classificatory rather than ordinatory strategy of data analysis to be followed. Cluster analyses based on statistical tests of species association were used to determine "natural" groupings of positively associated species and qualitative and quantitative classifications of samples were used to define vegetation zones or groupings at specific similarity index levels. 
Tree-shrub interfaces and tussock-shrub interfaces were compared on the basis of species complement, the degree of floristic, physiognomic and structural discontinuity in the vegetation, and differences in species interaction at each of the locations. 
The effects of data amalgamation, altitudinal interval employed, altitudinal range encountered, and classificatory versus ordinatory techniques, on the conclusions drawn were examined. 
Graphing of species distributions, cluster analyses, and classifications supported in part previously described zonation patterns but enabled a refinement of the generally accepted notions of vegetation zonation on Mt Egmont. In contrast to previous research the vegetation zones identified have a quantitative and objective basis. 
Comparison of the results with those of other New Zealand gradient analyses enabled elucidation of several major species distributions and species interactions because of the unique species complement found on Mt Egmont. 
Comparison of different data collection and manipulation techniques indicated that decisions made may cause data to conform to one or other of the two major approaches (continuum or discrete community types) to vegetation description and analysis. 
The study of the tree-shrub interfaces and shrub-tussock inter­faces showed that the vegetation on Mt Egmont exhibits a spectrum of species distributions ranging from continua through to discontinuities at different locations and specific examples of each are described. Possible explanations advanced include differences in species complement and species interaction, the non-equivalence of the altitudinal gradient at different locations, and differences in environmental factors including slope and aspect.

year: 1977

title: Te Raupatu o Tauranga Moana : Volume 2, Documents relating to tribal history, confiscation and reallocation of Tauranga lands.

authors: Stokes, Evelyn

subjects: Tauranga lands

abstract: A report providing a historical and geographical overview on the confiscation of Tauranga lands. In two volumes, volume one comprises a narrative of the events described as the raupatu, the confiscation of lands in the Tauranga Moana tribal area under the New Zealand Settlements Act 1863.  Volume two is a collection of documents, edited and annotated which were compiled in support of the report. These documents include personal accounts, tribal history, land purchases, lands returned and crown transactions.

text: Te Raupatu o Tauranga Moana : Volume 2, Documents relating to tribal history, confiscation and reallocation of Tauranga lands. A report providing a historical and geographical overview on the confiscation of Tauranga lands. In two volumes, volume one comprises a narrative of the events described as the raupatu, the confiscation of lands in the Tauranga Moana tribal area under the New Zealand Settlements Act 1863.  Volume two is a collection of documents, edited and annotated which were compiled in support of the report. These documents include personal accounts, tribal history, land purchases, lands returned and crown transactions.

year: 1993