title: The ecological role of the suspension feeding bivalve, Austrovenus stutchburyi, in estuarine ecosystems

authors: Jones, Hannah Frances Emily

subjects: ecosystem function

abstract: Suspension feeding bivalves are described as key species in many aquatic ecosystems, where they can influence primary productivity and nutrient dynamics, are food for higher trophic levels, and may be harvested in commercial or recreational fisheries. In many areas where bivalve populations have declined, substantial changes to ecosystem structure and function have occurred. High-density beds of the infaunal suspension feeding bivalve, Austrovenus stutchburyi, are a dominant feature on intertidal flats in many New Zealand estuaries, but populations are declining in some areas, likely due to anthropogenic stressors such as overharvesting and sedimentation. This thesis examines the influence of Austrovenus on estuarine ecosystem function using laboratory, field and modelling studies.
The effects of bed density and flow speed on boundary layer dynamics and Austrovenus clearance rates (CR) were investigated in annular flumes. Bed shear stress increased with increasing bivalve density, and under certain conditions was also increased when Austrovenus were feeding, compared to when they were not. The bed roughness and siphonal currents generated by the bivalves may therefore influence food supply to the bed. Both individual and bed CR were significantly greater at the high flow speed. Bed CR did not scale proportionally with density, in part because individual CR decreased with increasing density, but also because the proportion of bivalves actively feeding decreased at high densities. Thus, scaling up individual CR obtained from animals at low densities will significantly overestimate population filtration capacity.
The effect of Austrovenus on ecosystem function was examined at two sites, one sandy, the other composed of muddy-sand, to determine whether sedimentary environment alters this key species’ role. Gross primary production (likely corresponding to microphytobenthos production) and ammonium uptake were significantly increased, and denitrification potential was also elevated, when Austrovenus was added, relative to removed, at the sandy site. In contrast, there was no effect of Austrovenus on any of these variables at the muddy-sand site. These results reveal the importance of considering sedimentary environment when examining the effect of key species on ecosystem function, and suggest that even moderate levels of sedimentation may reduce the positive effect of Austrovenus on primary productivity.
A food-web model was used to quantify the interactions between Austrovenus and other estuarine species, and to determine the effect of reducing Austrovenus biomass on ecosystem properties. The model revealed an estuarine system dominated by benthic species, characterised as a developing, rather than a mature ecosystem. Detritus production and export were high, while transfer efficiency and internal recycling were low. Decreasing Austrovenus biomass decreased system maturity, suggesting that reductions in Austrovenus populations may decrease ecosystem stability. The model also confirmed that within these estuarine systems Austrovenus and microphytobenthos are key species which impact greatly on all other trophic levels.
This thesis demonstrates that Austrovenus populations exert considerable influence on benthic communities and processes, and play a key role in the functioning of estuarine ecosystems. Reductions in Austrovenus populations will likely negatively impact on microphytobenthos and higher trophic levels, and may also reduce ecosystem maturity and stability.

text: The ecological role of the suspension feeding bivalve, Austrovenus stutchburyi, in estuarine ecosystems Suspension feeding bivalves are described as key species in many aquatic ecosystems, where they can influence primary productivity and nutrient dynamics, are food for higher trophic levels, and may be harvested in commercial or recreational fisheries. In many areas where bivalve populations have declined, substantial changes to ecosystem structure and function have occurred. High-density beds of the infaunal suspension feeding bivalve, Austrovenus stutchburyi, are a dominant feature on intertidal flats in many New Zealand estuaries, but populations are declining in some areas, likely due to anthropogenic stressors such as overharvesting and sedimentation. This thesis examines the influence of Austrovenus on estuarine ecosystem function using laboratory, field and modelling studies.
The effects of bed density and flow speed on boundary layer dynamics and Austrovenus clearance rates (CR) were investigated in annular flumes. Bed shear stress increased with increasing bivalve density, and under certain conditions was also increased when Austrovenus were feeding, compared to when they were not. The bed roughness and siphonal currents generated by the bivalves may therefore influence food supply to the bed. Both individual and bed CR were significantly greater at the high flow speed. Bed CR did not scale proportionally with density, in part because individual CR decreased with increasing density, but also because the proportion of bivalves actively feeding decreased at high densities. Thus, scaling up individual CR obtained from animals at low densities will significantly overestimate population filtration capacity.
The effect of Austrovenus on ecosystem function was examined at two sites, one sandy, the other composed of muddy-sand, to determine whether sedimentary environment alters this key species’ role. Gross primary production (likely corresponding to microphytobenthos production) and ammonium uptake were significantly increased, and denitrification potential was also elevated, when Austrovenus was added, relative to removed, at the sandy site. In contrast, there was no effect of Austrovenus on any of these variables at the muddy-sand site. These results reveal the importance of considering sedimentary environment when examining the effect of key species on ecosystem function, and suggest that even moderate levels of sedimentation may reduce the positive effect of Austrovenus on primary productivity.
A food-web model was used to quantify the interactions between Austrovenus and other estuarine species, and to determine the effect of reducing Austrovenus biomass on ecosystem properties. The model revealed an estuarine system dominated by benthic species, characterised as a developing, rather than a mature ecosystem. Detritus production and export were high, while transfer efficiency and internal recycling were low. Decreasing Austrovenus biomass decreased system maturity, suggesting that reductions in Austrovenus populations may decrease ecosystem stability. The model also confirmed that within these estuarine systems Austrovenus and microphytobenthos are key species which impact greatly on all other trophic levels.
This thesis demonstrates that Austrovenus populations exert considerable influence on benthic communities and processes, and play a key role in the functioning of estuarine ecosystems. Reductions in Austrovenus populations will likely negatively impact on microphytobenthos and higher trophic levels, and may also reduce ecosystem maturity and stability.

year: 2011

title: Sentence initial lexical bundles in Chinese and New Zealand PhD theses in the discipline of General and Applied Linguistics

authors: Li, Liang

abstract: Lexical bundles are recurrent multiword combinations and often function as discourse building blocks. Lexical bundles have been analysed in university students’ writing to detect linguistic errors, measure writing competence, and investigate the divergence between L1 and L2 writing. Few studies, however, have focused on the high-stakes genre of PhD thesis and investigated the bundle productions of the same genre within the same level and discipline. This paper compares sentence initial lexical bundles in the corpora of English theses written by Chinese and New Zealand PhD students in the discipline of General and Applied Linguistics. Forty-six bundles from a Chinese corpus and forty-two bundles from a New Zealand corpus were generated. Among them, 94% of sentence initial bundles were identified as metadiscursive bundles. Chinese and New Zealand doctoral students showed considerably different preferences in their bundle selection. The paper examines the possible impact of these preferences and suggests there is a need to extend the metadiscourse knowledge of doctoral students in terms of lexical bundles.

text: Sentence initial lexical bundles in Chinese and New Zealand PhD theses in the discipline of General and Applied Linguistics Lexical bundles are recurrent multiword combinations and often function as discourse building blocks. Lexical bundles have been analysed in university students’ writing to detect linguistic errors, measure writing competence, and investigate the divergence between L1 and L2 writing. Few studies, however, have focused on the high-stakes genre of PhD thesis and investigated the bundle productions of the same genre within the same level and discipline. This paper compares sentence initial lexical bundles in the corpora of English theses written by Chinese and New Zealand PhD students in the discipline of General and Applied Linguistics. Forty-six bundles from a Chinese corpus and forty-two bundles from a New Zealand corpus were generated. Among them, 94% of sentence initial bundles were identified as metadiscursive bundles. Chinese and New Zealand doctoral students showed considerably different preferences in their bundle selection. The paper examines the possible impact of these preferences and suggests there is a need to extend the metadiscourse knowledge of doctoral students in terms of lexical bundles.

year: 2022-09-21

title: My journey with te reo Māori: From primary schooling in the mid 20th century to retirement from full-time academic service in the early years of the 21st Century

authors: Houia-Roberts, Ngaere

subjects: New Zealand

abstract: This is not an academic article in the traditional sense. It is a personal account of my experiences, as a first language speaker of te reo Māori, of New Zealand's educational system from the middle of the 20th century to the early years of the 21st century, from the early days of my primary schooling, through my service as a teacher, teacher trainer and academic researcher until my retirement from full-time academic service in 2005. A great deal has been written about the ways in which attitudes and approaches to te reo Māori have changed over that period of time but very little has been written about how it felt to be part of these changes. Our society is based on facts and feelings. If our mokopuna are to understand the fabric of our society, they need to have access to feelings as well as to facts. In this paper, weft and warp, facts and feelings, are woven together. This personal account is dedicated to our mokopuna, to all of our mokopuna, whatever their origin and whatever their colour. The future of our society depends upon their understanding.

text: My journey with te reo Māori: From primary schooling in the mid 20th century to retirement from full-time academic service in the early years of the 21st Century This is not an academic article in the traditional sense. It is a personal account of my experiences, as a first language speaker of te reo Māori, of New Zealand's educational system from the middle of the 20th century to the early years of the 21st century, from the early days of my primary schooling, through my service as a teacher, teacher trainer and academic researcher until my retirement from full-time academic service in 2005. A great deal has been written about the ways in which attitudes and approaches to te reo Māori have changed over that period of time but very little has been written about how it felt to be part of these changes. Our society is based on facts and feelings. If our mokopuna are to understand the fabric of our society, they need to have access to feelings as well as to facts. In this paper, weft and warp, facts and feelings, are woven together. This personal account is dedicated to our mokopuna, to all of our mokopuna, whatever their origin and whatever their colour. The future of our society depends upon their understanding.

year: 2006-02