title: Increasing Microcystis cell density enhances microcystin synthesis: a mesocosm study

authors: Wood, Susanna A.

subjects: cell abundance

abstract: An experimental protocol using mesocosms was established to study the effect of Microcystis sp. cell abundance on microcystin production. The mesocosms (55 L) were set up in a shallow eutrophic lake and received either no (control), low (to simulate a moderate surface accumulation), or high (to simulate a dense surface scum) concentrations of Microcystis sp. cells collected from the lake water adjacent to the mesocosms. In the low- and high-cell addition mesocosms (2 replicates of each), the initial addition of Microcystis sp. cells doubled the starting cell abundance from 500 000 to 1 000 000 cells mL⁻¹, but there was no detectable effect on microcystin quotas. Two further cell additions were made to the high-cell addition mesocosms after 60 and 120 min, increasing densities to 2 900 000 and 7 000 000 cells mL-1, respectively. Both additions resulted in marked increases in microcystin quotas from 0.1 pg cell-1 to 0.60 and 1.38 pg cell⁻¹, respectively, over the 240 min period. Extracellular microcystins accounted for <12% of the total microcystin load throughout the whole experiment. The results of this study indicate a relationship between Microcystis cell abundance and/or mutually correlated environmental parameters and microcystin synthesis.

text: Increasing Microcystis cell density enhances microcystin synthesis: a mesocosm study An experimental protocol using mesocosms was established to study the effect of Microcystis sp. cell abundance on microcystin production. The mesocosms (55 L) were set up in a shallow eutrophic lake and received either no (control), low (to simulate a moderate surface accumulation), or high (to simulate a dense surface scum) concentrations of Microcystis sp. cells collected from the lake water adjacent to the mesocosms. In the low- and high-cell addition mesocosms (2 replicates of each), the initial addition of Microcystis sp. cells doubled the starting cell abundance from 500 000 to 1 000 000 cells mL⁻¹, but there was no detectable effect on microcystin quotas. Two further cell additions were made to the high-cell addition mesocosms after 60 and 120 min, increasing densities to 2 900 000 and 7 000 000 cells mL-1, respectively. Both additions resulted in marked increases in microcystin quotas from 0.1 pg cell-1 to 0.60 and 1.38 pg cell⁻¹, respectively, over the 240 min period. Extracellular microcystins accounted for <12% of the total microcystin load throughout the whole experiment. The results of this study indicate a relationship between Microcystis cell abundance and/or mutually correlated environmental parameters and microcystin synthesis.

year: 2012

title: Ecology of aquatic hyphomycetes in New Zealand streams

authors: Aimer, Robyn Denise

abstract: This work investigated the occurrence of aquatic hyphomycetes in stream ecosystems in New Zealand. It provided evidence for the potential importance of detrital cycles in such ecosystems and of the role of aquatic hyphomycetes in the decay of leaf litter. Leaves from a representative range of plant species were enclosed in mesh bags in two undisturbed streams flowing through different forest types at different altitudes, and fungal population dynamics followed during leaf decay. A method was developed, using pure cultures of appropriate aquatic hyphomycetes, which enabled the mycelial content of leaf material (m mycelium/g) attributable to individual fungal species to be quickly and easily determined from the spore production measured from leaf samples. Antibiotics were used to quantify the relative fungal and bacterial contributions to microbial activity of leaf samples through the selective inhibition of respiration. Fungi accounted for about half of the total microbial respiration, and on average 80 % of this fungal respiration was attributable to aquatic hyphomycetes.

Three major patterns were apparent from the data for aquatic hyphomycete population dynamics. 1) A successional pattern was identified among aquatic hyphomycetes, with the species falling into three groups on the basis of the order of their period of abundance. 2) Aquatic hyphomycete abundance varied among leaf types, with soft-rotting types (hangehange, young kanono) being poorly colonised compared to firmer, darker-rotting types (old kanono, kamahi, silver beech, tawa, kauri, and rimu). Nikau (palm) and ponga (fern) leaves, although not soft-rotting, were also poorly colonised by aquatic hyphomycetes, but bore a rich alternative mycoflora. 3) The occurrence of many aquatic hyphomycetes showed seasonal preferences and a distinct geographical distribution which followed that of higher plants. Both seasonal and geographical patterns were probably related to temperature.

Laboratory evidence was obtained of the potential importance of oxygen in determining aquatic hyphomycete occurrence, with the dominant species in most New Zealand streams (Lunulospora cymbiformis) being extremely intolerant of low oxygen conditions. Two new species of aquatic hyphomycetes were isolated in the course of the work.

text: Ecology of aquatic hyphomycetes in New Zealand streams This work investigated the occurrence of aquatic hyphomycetes in stream ecosystems in New Zealand. It provided evidence for the potential importance of detrital cycles in such ecosystems and of the role of aquatic hyphomycetes in the decay of leaf litter. Leaves from a representative range of plant species were enclosed in mesh bags in two undisturbed streams flowing through different forest types at different altitudes, and fungal population dynamics followed during leaf decay. A method was developed, using pure cultures of appropriate aquatic hyphomycetes, which enabled the mycelial content of leaf material (m mycelium/g) attributable to individual fungal species to be quickly and easily determined from the spore production measured from leaf samples. Antibiotics were used to quantify the relative fungal and bacterial contributions to microbial activity of leaf samples through the selective inhibition of respiration. Fungi accounted for about half of the total microbial respiration, and on average 80 % of this fungal respiration was attributable to aquatic hyphomycetes.

Three major patterns were apparent from the data for aquatic hyphomycete population dynamics. 1) A successional pattern was identified among aquatic hyphomycetes, with the species falling into three groups on the basis of the order of their period of abundance. 2) Aquatic hyphomycete abundance varied among leaf types, with soft-rotting types (hangehange, young kanono) being poorly colonised compared to firmer, darker-rotting types (old kanono, kamahi, silver beech, tawa, kauri, and rimu). Nikau (palm) and ponga (fern) leaves, although not soft-rotting, were also poorly colonised by aquatic hyphomycetes, but bore a rich alternative mycoflora. 3) The occurrence of many aquatic hyphomycetes showed seasonal preferences and a distinct geographical distribution which followed that of higher plants. Both seasonal and geographical patterns were probably related to temperature.

Laboratory evidence was obtained of the potential importance of oxygen in determining aquatic hyphomycete occurrence, with the dominant species in most New Zealand streams (Lunulospora cymbiformis) being extremely intolerant of low oxygen conditions. Two new species of aquatic hyphomycetes were isolated in the course of the work.

year: 1989

title: Academic success amongst a cohort of gifted and talented Māori and Pasifika secondary school boys: Elements that have contributed to their achievement

authors: Miller, Graeme Oliver

subjects: Māori

abstract: In recent years Māori and Pasifika students have been the focus of much discussion and a significant amount of research relating to underachievement. Despite this, many Māori and Pasifika secondary school boys are achieving highly in the academic sphere within the context of mainstream boys’ state secondary schools in New Zealand. Achievement aside, evidence shows that Māori and Pasifika secondary school boys are seriously under-represented in programmes for the gifted and talented. This enquiry examines factors in relation to identifying gifted and talented students, and investigates how their abilities are forged and nurtured. The reasons for student success merit serious investigation because of how the multiple elements contributing to their achievement are likely to be applicable to others, and are a pressing concern for academic attainment in the New Zealand education system. 
 
This qualitative study examines why 30 academically successful Māori and Pasifika secondary school boys achieved highly in the mainstream education system. The boys ranged from 13 to 19 years, the youngest being in his first year at high school as a Year 9 student, and the oldest being in his second year at university. The thesis argues their academic success was due to the complex interplay of home and school environmental elements, and the boys’ intrapersonal characteristics. The study explored the boys’ and parents’ narratives to explain why students had achieved highly, and examined both the parents’ and boys’ perceptions of how well the schools had provided for their intellectual, emotional and cultural needs. Sociocultural learning theory is the main theoretical lens through which the findings are viewed. The methodology is primarily built upon narrative inquiry. The main method of data collection was by semi-structured interview, both individually and in focus groups. Supplementary methods utilised were questionnaires and observation.  
  
An issue in the research was the disparity between the cultural and ethnic background of the participants and myself as the researcher. However, an endeavour was made to mitigate this by consulting with Māori and Pasifika educators, a kaumatua (elder) and iwi (tribal) representative prior to the research commencing. In addition, models developed through this study were submitted to Māori and Pasifika educators for their comment and approval prior to being included. 
 
With its focus specifically on highly-achieving Māori and Pasifika secondary school boys, this thesis makes an original contribution to the national and international discussion about raising student achievement. It provides a platform for further research to 	address the particular concerns around the underachievement of Māori and Pasifika secondary school boys. 
 
While there are several implications arising from the research, all are linked to the need for policy makers and educators to address the issue of the underrepresentation of Māori and Pasifika students in programmes for the gifted and talented. Policies, practices and relationships need to be examined to evaluate how effectively they contribute to gifted and talented Māori and Pasifika students receiving the academic opportunities they deserve. A key part of this examination will need to include consultation with students and their whānau.

text: Academic success amongst a cohort of gifted and talented Māori and Pasifika secondary school boys: Elements that have contributed to their achievement In recent years Māori and Pasifika students have been the focus of much discussion and a significant amount of research relating to underachievement. Despite this, many Māori and Pasifika secondary school boys are achieving highly in the academic sphere within the context of mainstream boys’ state secondary schools in New Zealand. Achievement aside, evidence shows that Māori and Pasifika secondary school boys are seriously under-represented in programmes for the gifted and talented. This enquiry examines factors in relation to identifying gifted and talented students, and investigates how their abilities are forged and nurtured. The reasons for student success merit serious investigation because of how the multiple elements contributing to their achievement are likely to be applicable to others, and are a pressing concern for academic attainment in the New Zealand education system. 
 
This qualitative study examines why 30 academically successful Māori and Pasifika secondary school boys achieved highly in the mainstream education system. The boys ranged from 13 to 19 years, the youngest being in his first year at high school as a Year 9 student, and the oldest being in his second year at university. The thesis argues their academic success was due to the complex interplay of home and school environmental elements, and the boys’ intrapersonal characteristics. The study explored the boys’ and parents’ narratives to explain why students had achieved highly, and examined both the parents’ and boys’ perceptions of how well the schools had provided for their intellectual, emotional and cultural needs. Sociocultural learning theory is the main theoretical lens through which the findings are viewed. The methodology is primarily built upon narrative inquiry. The main method of data collection was by semi-structured interview, both individually and in focus groups. Supplementary methods utilised were questionnaires and observation.  
  
An issue in the research was the disparity between the cultural and ethnic background of the participants and myself as the researcher. However, an endeavour was made to mitigate this by consulting with Māori and Pasifika educators, a kaumatua (elder) and iwi (tribal) representative prior to the research commencing. In addition, models developed through this study were submitted to Māori and Pasifika educators for their comment and approval prior to being included. 
 
With its focus specifically on highly-achieving Māori and Pasifika secondary school boys, this thesis makes an original contribution to the national and international discussion about raising student achievement. It provides a platform for further research to 	address the particular concerns around the underachievement of Māori and Pasifika secondary school boys. 
 
While there are several implications arising from the research, all are linked to the need for policy makers and educators to address the issue of the underrepresentation of Māori and Pasifika students in programmes for the gifted and talented. Policies, practices and relationships need to be examined to evaluate how effectively they contribute to gifted and talented Māori and Pasifika students receiving the academic opportunities they deserve. A key part of this examination will need to include consultation with students and their whānau.

year: 2015