title: The phytoplankton communities of nine lakes, Waikato, New Zealand: a comparative study of floristics, seasonal dynamics and the influence of herbivory

authors: Etheredge, Margaret Kay

abstract: The structure and seasonal dynamics of the phytoplankton communities of nine shallow lakes located in relatively close proximity to one another within the Waikato Basin, and of similar age and origin, were studied for one year (July 1983 to July 1984); the lakes were Kainui, Mangahia, Mangakaware, Maratoto, Ngaroto, Rotokauri, Rotomanuka North and South, and Rotoroa. There was a broad range of physico-chemical regimes, a direct result of differing morphometries and quantities of allochthonous dissolved humic material from adjacent peatland and/or swamps, and varying degrees of exposure to wind.
Community structure was markedly influenced by humic content, in terms of both α diversity and distribution of species within the major classes, with total numbers of species found per lake ranging from 113 to 210.
Temporal patterns of community composition were directly related to specific mixing regimes and morphometry. Lakes which had minimal thermal stability throughout summer were dominated throughout the entire year by one or two algal classes, and it was shown statistically that the major phytoplankters were large, K- selected species (e.g., Botryococcus braunii and Microcystis aeruginosa). Unpredictable sequences of domination, one class replacing another after brief periods of importance, were recorded in lakes where ephemeral periods of summer stratification alternated with either equally short periods of holomixis or weakly developed stratification; the dominant species in these lakes were r- strategists such as Asterionella formosa, Acanthoceras zachariasi and Tetrastrum triangulare. Marked seasonal periodicity (including autogenic succession) occurred in Lake Rotomanuka North, the only warm monomictic lake within the series.
Total α diversity (402 species) was higher than that of any other group of intensively studied New Zealand lakes, but compositional overlap at both generic and specific levels was low, with only 24 species being found in all nine lakes. Of these, the most common and ecologically versatile phytoplankters were Closterium acutum var. variabile, Cryptomonas marssonii and C. ovata, Cyclotella stelligera, Monoraphidium contortum and Trachelomonas volvocina. 
Mean total phytoplankton biomass and density ranged from 0.7 to 72.2 g m³ and 0.4 to 11.6 pu 1⁻¹, respectively, and comparisons with other quantitative phytoplankton studies indicate that some of the study lakes (Maratoto, Ngaroto and Rotomanuka South) are the most productive recorded in New Zealand to date. Eutrophic waters and rich organic sediments, together with a combination of both stratified and frequently mixed water columns, resulted in relatively high euglenophyte species diversity. Conversely, the number of desmid species was relatively low.
Zooplankton exclusion experiments using limnocorrals were carried out in an almost clear-water lake (Rotomanuka North) and in a darkly-stained lake (Maratoto). The results suggest that a reduction in grazing pressure markedly influenced phytoplankton community structure in the former, causing shifts (in terms of biomass) from communities dominated by K- strategists (Microcystis aeruginosa or Peridinium cinctum) to smaller, fast-growing species (Cyclotella stelligera or Coelastrum microporum). Reduced herbivory also permitted increases in the number of taxa and total biomass of small edible phytoplankters (GALDs ≤ 20 μm), together with an increase in the number of euchlorophyte species. Similar responses were not apparent in dystrophic Lake Maratoto, suggesting that the stressful physico-chemical regime was the major regulator of community structure, and that trophic organisation within the two systems differed markedly, with energy transfer in the latter operating largely through a heterotrophic-based food chain.

text: The phytoplankton communities of nine lakes, Waikato, New Zealand: a comparative study of floristics, seasonal dynamics and the influence of herbivory The structure and seasonal dynamics of the phytoplankton communities of nine shallow lakes located in relatively close proximity to one another within the Waikato Basin, and of similar age and origin, were studied for one year (July 1983 to July 1984); the lakes were Kainui, Mangahia, Mangakaware, Maratoto, Ngaroto, Rotokauri, Rotomanuka North and South, and Rotoroa. There was a broad range of physico-chemical regimes, a direct result of differing morphometries and quantities of allochthonous dissolved humic material from adjacent peatland and/or swamps, and varying degrees of exposure to wind.
Community structure was markedly influenced by humic content, in terms of both α diversity and distribution of species within the major classes, with total numbers of species found per lake ranging from 113 to 210.
Temporal patterns of community composition were directly related to specific mixing regimes and morphometry. Lakes which had minimal thermal stability throughout summer were dominated throughout the entire year by one or two algal classes, and it was shown statistically that the major phytoplankters were large, K- selected species (e.g., Botryococcus braunii and Microcystis aeruginosa). Unpredictable sequences of domination, one class replacing another after brief periods of importance, were recorded in lakes where ephemeral periods of summer stratification alternated with either equally short periods of holomixis or weakly developed stratification; the dominant species in these lakes were r- strategists such as Asterionella formosa, Acanthoceras zachariasi and Tetrastrum triangulare. Marked seasonal periodicity (including autogenic succession) occurred in Lake Rotomanuka North, the only warm monomictic lake within the series.
Total α diversity (402 species) was higher than that of any other group of intensively studied New Zealand lakes, but compositional overlap at both generic and specific levels was low, with only 24 species being found in all nine lakes. Of these, the most common and ecologically versatile phytoplankters were Closterium acutum var. variabile, Cryptomonas marssonii and C. ovata, Cyclotella stelligera, Monoraphidium contortum and Trachelomonas volvocina. 
Mean total phytoplankton biomass and density ranged from 0.7 to 72.2 g m³ and 0.4 to 11.6 pu 1⁻¹, respectively, and comparisons with other quantitative phytoplankton studies indicate that some of the study lakes (Maratoto, Ngaroto and Rotomanuka South) are the most productive recorded in New Zealand to date. Eutrophic waters and rich organic sediments, together with a combination of both stratified and frequently mixed water columns, resulted in relatively high euglenophyte species diversity. Conversely, the number of desmid species was relatively low.
Zooplankton exclusion experiments using limnocorrals were carried out in an almost clear-water lake (Rotomanuka North) and in a darkly-stained lake (Maratoto). The results suggest that a reduction in grazing pressure markedly influenced phytoplankton community structure in the former, causing shifts (in terms of biomass) from communities dominated by K- strategists (Microcystis aeruginosa or Peridinium cinctum) to smaller, fast-growing species (Cyclotella stelligera or Coelastrum microporum). Reduced herbivory also permitted increases in the number of taxa and total biomass of small edible phytoplankters (GALDs ≤ 20 μm), together with an increase in the number of euchlorophyte species. Similar responses were not apparent in dystrophic Lake Maratoto, suggesting that the stressful physico-chemical regime was the major regulator of community structure, and that trophic organisation within the two systems differed markedly, with energy transfer in the latter operating largely through a heterotrophic-based food chain.

year: 1987

title: The influence of interacting stressors on soft sediment ecosystem function

authors: Mangan, Stephanie

subjects: Turbidity

abstract: Soft sediment intertidal habitats provide valuable ecosystem services to millions of people worldwide yet are under intense anthropogenic pressure. In particular, the intensification of land derived sediment and nutrient delivery has resulted in elevated water column turbidity and nutrient over-enrichment, both of which can diminish ecosystem functionality. Identifying how these stressors interact and influence benthic ecosystems is crucial to understanding the resilience of these valuable habitats and to help manage effectively to prevent shifts towards ecological tipping points. This thesis therefore investigates the response of benthic primary production and biogeochemical cycling to two pervasive stressors; increasing water column turbidity and sediment nutrient enrichment.
Water column turbidity directly restricts the availability of light to microphytobenthos (MPB), a key primary producer in soft sediment intertidal habitats. However, the degree to which turbidity may limit primary production across New Zealand was largely unknown. I recorded light availability at the seafloor over a 9-month period at 22 sites situated within 14 estuaries. Coupled with a global literature compilation of photosynthesis-irradiance curves, the proportion of time MPB were light limited during submergence ranged from a median of 55–100 %. For estuaries close to 100 % light limitation, emerged intertidal areas represent a refuge for MPB production which is vulnerable to sea-level rise. Using hypsometric curves, the intertidal area of my study estuaries was predicted to decrease by 27–94 % under a 1.4 m rise in sea-level. The combination of high light limitation during submergence and large losses of intertidal area will increase vulnerability to the loss of MPB production and the associated ecosystem services, which can push these ecosystems towards tipping points.
Anthropogenic stressors often occur concomitantly, and therefore understanding how differing degrees of water column turbidity may interact with other stressors, such as increasing nutrient enrichment and influence benthic productivity over alternating periods of submergence and emergence were investigated. A field manipulation study was designed to enrich porewaters at three levels for 20 months, at six sites that spanned a gradient in water column turbidity. While nutrient enrichment had no detectable effect on MPB primary production, water column turbidity had a significant influence, explaining up to 40 % of the variability during tidal submergence, followed by temperature and sediment characteristics. In addition, negative net primary production (NPP) and therefore net heterotrophy for the most turbid estuaries during tidal submergence resulted in an increased reliance on production during emerged periods. This study highlights the prominent role of turbidity over porewater nutrient enrichment in moderating MPB production and supports earlier conclusions of the increasing importance of emerged periods to maintain the health and functioning of coastal habitats.
Soft sediment intertidal habitats are not only hot spots for benthic productivity, but they also play a fundamental role in biogeochemical cycling. The influence of increased nutrient availability on nitrogen and carbon cycling was investigated after 15 and 20 months of nitrogen enrichment. This study highlighted the limited capacity for denitrification, a key process in removing bioavailable nitrogen, to mitigate large increases in nitrogen availability, as evidenced through the consistent rates of net denitrification and reductions in the efficiency at which nitrogen was removed. Denitrification rate was most strongly correlated to carbon supply, trophic status and to a lesser extent, macrofaunal diversity. In addition, analysis of factor-ceiling relationships revealed the vulnerability of estuaries to increasing stressor loads. The appearance of significant nonlinearities with increasing nitrogen enrichment suggests alterations to the interactions of intrinsic dynamics and drivers which can fundamentally alter biogeochemical cycling within soft sediments and increase the likelihood of abrupt non-linear shifts.
Overall, the findings of my thesis demonstrate how the health and functioning of coastal ecosystems can be significantly diminished under increasing anthropogenic stress, and that the vulnerability of coastal ecosystems to the loss of ecosystem functionality will change in the future as global scale stressors intensify.

text: The influence of interacting stressors on soft sediment ecosystem function Soft sediment intertidal habitats provide valuable ecosystem services to millions of people worldwide yet are under intense anthropogenic pressure. In particular, the intensification of land derived sediment and nutrient delivery has resulted in elevated water column turbidity and nutrient over-enrichment, both of which can diminish ecosystem functionality. Identifying how these stressors interact and influence benthic ecosystems is crucial to understanding the resilience of these valuable habitats and to help manage effectively to prevent shifts towards ecological tipping points. This thesis therefore investigates the response of benthic primary production and biogeochemical cycling to two pervasive stressors; increasing water column turbidity and sediment nutrient enrichment.
Water column turbidity directly restricts the availability of light to microphytobenthos (MPB), a key primary producer in soft sediment intertidal habitats. However, the degree to which turbidity may limit primary production across New Zealand was largely unknown. I recorded light availability at the seafloor over a 9-month period at 22 sites situated within 14 estuaries. Coupled with a global literature compilation of photosynthesis-irradiance curves, the proportion of time MPB were light limited during submergence ranged from a median of 55–100 %. For estuaries close to 100 % light limitation, emerged intertidal areas represent a refuge for MPB production which is vulnerable to sea-level rise. Using hypsometric curves, the intertidal area of my study estuaries was predicted to decrease by 27–94 % under a 1.4 m rise in sea-level. The combination of high light limitation during submergence and large losses of intertidal area will increase vulnerability to the loss of MPB production and the associated ecosystem services, which can push these ecosystems towards tipping points.
Anthropogenic stressors often occur concomitantly, and therefore understanding how differing degrees of water column turbidity may interact with other stressors, such as increasing nutrient enrichment and influence benthic productivity over alternating periods of submergence and emergence were investigated. A field manipulation study was designed to enrich porewaters at three levels for 20 months, at six sites that spanned a gradient in water column turbidity. While nutrient enrichment had no detectable effect on MPB primary production, water column turbidity had a significant influence, explaining up to 40 % of the variability during tidal submergence, followed by temperature and sediment characteristics. In addition, negative net primary production (NPP) and therefore net heterotrophy for the most turbid estuaries during tidal submergence resulted in an increased reliance on production during emerged periods. This study highlights the prominent role of turbidity over porewater nutrient enrichment in moderating MPB production and supports earlier conclusions of the increasing importance of emerged periods to maintain the health and functioning of coastal habitats.
Soft sediment intertidal habitats are not only hot spots for benthic productivity, but they also play a fundamental role in biogeochemical cycling. The influence of increased nutrient availability on nitrogen and carbon cycling was investigated after 15 and 20 months of nitrogen enrichment. This study highlighted the limited capacity for denitrification, a key process in removing bioavailable nitrogen, to mitigate large increases in nitrogen availability, as evidenced through the consistent rates of net denitrification and reductions in the efficiency at which nitrogen was removed. Denitrification rate was most strongly correlated to carbon supply, trophic status and to a lesser extent, macrofaunal diversity. In addition, analysis of factor-ceiling relationships revealed the vulnerability of estuaries to increasing stressor loads. The appearance of significant nonlinearities with increasing nitrogen enrichment suggests alterations to the interactions of intrinsic dynamics and drivers which can fundamentally alter biogeochemical cycling within soft sediments and increase the likelihood of abrupt non-linear shifts.
Overall, the findings of my thesis demonstrate how the health and functioning of coastal ecosystems can be significantly diminished under increasing anthropogenic stress, and that the vulnerability of coastal ecosystems to the loss of ecosystem functionality will change in the future as global scale stressors intensify.

year: 2021

title: Maori and epilepsy: Personal perceptions of the cause, treatment and consequences of epilepsy by Maori in the Bay of Plenty

authors: Simonsen, Kiri

subjects: Maori

abstract: This paper discusses the perceptions of epilepsy held by Maori in the Bay of Plenty. The paper
begins by introducing the purpose and rationale of the research. It then moves on to describe the
aims and qualitative research methods that were used to collect the data. Finally the paper
discusses the findings of the research, this includes: a close look at the unique perceptions of
epilepsy that were reported by Maori in the Bay of Plenty; the lack of resources and services
available in a small rural town of the Bay of Plenty; the services desired by Maori; attitudes
towards medication and the inappropriate behaviour many of the participants experienced by the
medical profession.

text: Maori and epilepsy: Personal perceptions of the cause, treatment and consequences of epilepsy by Maori in the Bay of Plenty This paper discusses the perceptions of epilepsy held by Maori in the Bay of Plenty. The paper
begins by introducing the purpose and rationale of the research. It then moves on to describe the
aims and qualitative research methods that were used to collect the data. Finally the paper
discusses the findings of the research, this includes: a close look at the unique perceptions of
epilepsy that were reported by Maori in the Bay of Plenty; the lack of resources and services
available in a small rural town of the Bay of Plenty; the services desired by Maori; attitudes
towards medication and the inappropriate behaviour many of the participants experienced by the
medical profession.

year: 1999