title: The distribution and dynamics of planktonic rotifera in the North Island, New Zealand

authors: Duggan, Ian C.

abstract: The distribution and dynamics of planktonic rotifers, at various spatial and temporal scales, were investigated in lakes of the North Island, New Zealand. The overall aim was to provide a better understanding of the relative influence of various environmental gradients in determining the composition of planktonic rotifer communities in New Zealand.

Potential methods for collection and concentration of samples were assessed. For investigating seasonal and vertical distributions in lakes, sedimentation provided significantly greater (P>0.01) estimates of total and abundant rotifer densities than filtration with 40 μm mesh. For collection of depth integrated samples, various net designs and a tube sampler gave differing estimates of the proportions of species. Overall nets were preferred because they required less time and effort than tubes, and nets with reducing cones provided results more similar to tubes than those without.

The seasonal and vertical dynamics of rotifer communities were investigated in four central North Island lakes of contrasting trophic state and mixing regime: Lakes Tikitapu, Rotoiti, Okaro and Ngaroto. Total rotifer abundances were consistently lowest in winter. The temporal occurrence of species assemblages within lakes related to mixing pattern, with different communities in stratified (or relatively stable) and holomictic periods. Multivariate techniques (Cluster analysis, MDS, CCA) indicated that species distributions were most strongly associated with temperature. The predominant warm monomictic mixing pattern in New Zealand is likely to have prevented the occurrence of truly cold-water assemblages. No distinct hypolimnetic community was recognised in any lake, indicating that New Zealand’s frequently strong winds are likely to prevent persistence of winter species in the hypolimnion. Rotifer densities were lower in the hypolimnion. Total rotifer abundance was generally greater in lakes of higher trophic state.

The geographical distribution of rotifer species in 42 North Island lakes was investigated using multivariate techniques. Distribution patterns were most strongly associated with trophic state gradients. Based on this relationship, bioindicator indices were developed using Weighted Averaging techniques using rotifer communities for inferring trophic state. Some species, for example Keratella australis and Conochilus exiguus, appear to be limited in distribution by poor dispersal abilities. Rotifer diversity within lakes, previously thought to be low in New Zealand, was found to be comparable with that of northern temperate lakes.

The methods for estimating rotifer resting egg densities from lake sediment, and the use of emergence for determining community composition from lakes, were investigated in Lakes Tikitapu and Okaro. Significantly lower (P<0.01) estimates of resting egg densities were obtained by incubation of sediments than egg counts. Significantly higher (P<0.01) densities of resting eggs were found from the eutrophic Lake Okaro sediments. Incubation of sediments did not result in the emergence of all the planktonic species found in the seasonal study.

The taxonomy and biogeography of North Island and New Zealand species were investigated based on the species recorded from the current study and from New Zealand to date. The level of endemism in New Zealand appears to be low. Fewer species have been recorded from the North Island than the South Island, and fewer in New Zealand than Australia. This variation can be largely explained by differences in sampling effort or biogeographical processes. No typically cold-water species, e.g., Notholca species, are known from the North Island. New Zealand species records have affinities with the Australian fauna.

text: The distribution and dynamics of planktonic rotifera in the North Island, New Zealand The distribution and dynamics of planktonic rotifers, at various spatial and temporal scales, were investigated in lakes of the North Island, New Zealand. The overall aim was to provide a better understanding of the relative influence of various environmental gradients in determining the composition of planktonic rotifer communities in New Zealand.

Potential methods for collection and concentration of samples were assessed. For investigating seasonal and vertical distributions in lakes, sedimentation provided significantly greater (P>0.01) estimates of total and abundant rotifer densities than filtration with 40 μm mesh. For collection of depth integrated samples, various net designs and a tube sampler gave differing estimates of the proportions of species. Overall nets were preferred because they required less time and effort than tubes, and nets with reducing cones provided results more similar to tubes than those without.

The seasonal and vertical dynamics of rotifer communities were investigated in four central North Island lakes of contrasting trophic state and mixing regime: Lakes Tikitapu, Rotoiti, Okaro and Ngaroto. Total rotifer abundances were consistently lowest in winter. The temporal occurrence of species assemblages within lakes related to mixing pattern, with different communities in stratified (or relatively stable) and holomictic periods. Multivariate techniques (Cluster analysis, MDS, CCA) indicated that species distributions were most strongly associated with temperature. The predominant warm monomictic mixing pattern in New Zealand is likely to have prevented the occurrence of truly cold-water assemblages. No distinct hypolimnetic community was recognised in any lake, indicating that New Zealand’s frequently strong winds are likely to prevent persistence of winter species in the hypolimnion. Rotifer densities were lower in the hypolimnion. Total rotifer abundance was generally greater in lakes of higher trophic state.

The geographical distribution of rotifer species in 42 North Island lakes was investigated using multivariate techniques. Distribution patterns were most strongly associated with trophic state gradients. Based on this relationship, bioindicator indices were developed using Weighted Averaging techniques using rotifer communities for inferring trophic state. Some species, for example Keratella australis and Conochilus exiguus, appear to be limited in distribution by poor dispersal abilities. Rotifer diversity within lakes, previously thought to be low in New Zealand, was found to be comparable with that of northern temperate lakes.

The methods for estimating rotifer resting egg densities from lake sediment, and the use of emergence for determining community composition from lakes, were investigated in Lakes Tikitapu and Okaro. Significantly lower (P<0.01) estimates of resting egg densities were obtained by incubation of sediments than egg counts. Significantly higher (P<0.01) densities of resting eggs were found from the eutrophic Lake Okaro sediments. Incubation of sediments did not result in the emergence of all the planktonic species found in the seasonal study.

The taxonomy and biogeography of North Island and New Zealand species were investigated based on the species recorded from the current study and from New Zealand to date. The level of endemism in New Zealand appears to be low. Fewer species have been recorded from the North Island than the South Island, and fewer in New Zealand than Australia. This variation can be largely explained by differences in sampling effort or biogeographical processes. No typically cold-water species, e.g., Notholca species, are known from the North Island. New Zealand species records have affinities with the Australian fauna.

year: 1999

title: Exploring the dynamic behaviour of commodity market tail risk connectedness during the negative WTI pricing event

authors: Hu, Yang

abstract: Using a TVP-VAR analytical framework, this study explores the change and persistence of the dynamic connectedness of international energy and carbon credit markets. The overall destabilising effects generated by recent political and epidemiological events, and the subsequent consequences of shocks such as the negative WTI pricing event, have the potential to be disruptive to the continued growth and development of several regional oil markets. Results are presented via a comprehensive analysis of the dynamics of extreme risk spillovers for particular commodity pairs. In particular, WTI and Brent crude oil are found to have transmitted significant tail uncertainty shocks to other energy markets. However, Shanghai crude oil and carbon credit markets typically function as shock absorbers. The remaining energy-related commodities primarily function as tail uncertainty receivers. Further, by incorporating EGARCH-based robustness procedures, tests for significant market connectedness within international energy markets adds further validity to the results. Specifically, results relating to the substantial rebalancing of information to Shanghai crude oil futures and EUA carbon futures merit special consideration, as dynamic interactions strengthen evidence supporting their continued maturation into significant international markets. These findings are particularly interesting to policymakers and market participants who use such products to hedge against and diversify regional oil market fluctuations.

text: Exploring the dynamic behaviour of commodity market tail risk connectedness during the negative WTI pricing event Using a TVP-VAR analytical framework, this study explores the change and persistence of the dynamic connectedness of international energy and carbon credit markets. The overall destabilising effects generated by recent political and epidemiological events, and the subsequent consequences of shocks such as the negative WTI pricing event, have the potential to be disruptive to the continued growth and development of several regional oil markets. Results are presented via a comprehensive analysis of the dynamics of extreme risk spillovers for particular commodity pairs. In particular, WTI and Brent crude oil are found to have transmitted significant tail uncertainty shocks to other energy markets. However, Shanghai crude oil and carbon credit markets typically function as shock absorbers. The remaining energy-related commodities primarily function as tail uncertainty receivers. Further, by incorporating EGARCH-based robustness procedures, tests for significant market connectedness within international energy markets adds further validity to the results. Specifically, results relating to the substantial rebalancing of information to Shanghai crude oil futures and EUA carbon futures merit special consideration, as dynamic interactions strengthen evidence supporting their continued maturation into significant international markets. These findings are particularly interesting to policymakers and market participants who use such products to hedge against and diversify regional oil market fluctuations.

year: 2023

title: Te Mauri o te Kaitiaki - Exploring Te Ao Māori in environmental relations and kaitiakitanga  in Aotearoa New Zealand

authors: Wareka, Mona-Lisa

subjects: Te Ao Māori

abstract: Indigenous environmental empowerment is on the rise as humans look at ways to slow the adverse effects of anthropogenic environmental degradation. In the context of Aotearoa New Zealand, the concept and practice of ‘kaitiaki’ and ‘kaitiakitanga’, respectfully, play a significant role in the co-existence of Māori with the natural world. Previous research shows the innate connections and responsibilities encompassed in being kaitiaki which extend beyond the human element to encompass nonhumans and spiritual manifestations. This research aims to illustrate how Māori use cultural values, concepts and practices in local-level conservational practices through ethnographic research in Matapōuri. I investigate the conflicts and convergences of a rāhui recently placed on two cultural significant areas to the local hapū, and through this, I analyse the practical and spiritual application of kaitiakitanga. Based on this ethnography, I discuss a model for relating environmental degradation with the wellbeing of Māori within Aotearoa New Zealand today. Here, I wish to highlight the ecological and cultural threats present from continuing in the current system. Lastly, I argue that the assertion of kaitiakitanga at the local-level is also an assertion of Indigenous autonomy for Māori and the environment.

text: Te Mauri o te Kaitiaki - Exploring Te Ao Māori in environmental relations and kaitiakitanga  in Aotearoa New Zealand Indigenous environmental empowerment is on the rise as humans look at ways to slow the adverse effects of anthropogenic environmental degradation. In the context of Aotearoa New Zealand, the concept and practice of ‘kaitiaki’ and ‘kaitiakitanga’, respectfully, play a significant role in the co-existence of Māori with the natural world. Previous research shows the innate connections and responsibilities encompassed in being kaitiaki which extend beyond the human element to encompass nonhumans and spiritual manifestations. This research aims to illustrate how Māori use cultural values, concepts and practices in local-level conservational practices through ethnographic research in Matapōuri. I investigate the conflicts and convergences of a rāhui recently placed on two cultural significant areas to the local hapū, and through this, I analyse the practical and spiritual application of kaitiakitanga. Based on this ethnography, I discuss a model for relating environmental degradation with the wellbeing of Māori within Aotearoa New Zealand today. Here, I wish to highlight the ecological and cultural threats present from continuing in the current system. Lastly, I argue that the assertion of kaitiakitanga at the local-level is also an assertion of Indigenous autonomy for Māori and the environment.

year: 2020