title: Dispersal and remineralisation of biodeposits: Ecosystem impacts of mussel aquaculture

authors: Giles, Hilke

subjects: faeces

abstract: Suspension-feeding bivalves produce biodeposits (faeces and pseudofaeces) that have much higher sinking velocities than their constituent particles. Consequently they cause sedimentation of material that might otherwise not be deposited. The benthic remineralisation of biodeposits increases sediment oxygen demand and nutrient regeneration, thus enhancing the benthic-pelagic coupling of nearshore ecosystems. In New Zealand the mussel Perna canaliculus has a high natural abundance and is also intensively cultured. This thesis examines the dispersal and remineralisation characteristics of mussel P. canaliculus biodeposits and the impacts of sedimentation from a mussel farm in the Firth of Thames on sediment biogeochemistry by combining laboratory, field and modelling studies. 

Dispersal characteristics were examined in the laboratory by measuring sinking velocities and erosion thresholds of biodeposits produced by mussels of a wide size range fed three experimental diets. The results show that biodeposit dispersal is a function of mussel diet and size and thus could differ significantly between locations and seasons. Estimates of dispersal distances based on these results demonstrated that the initial dispersal of biodeposits produced by cultured mussels is not far. Depending on the hydrodynamic conditions, secondary dispersal via resuspension potentially plays a more important role in the dispersal of biodeposits from mussel farms than initial dispersal and almost certainly serves as the major means of transport of biodeposits from natural mussel beds.

Biodeposit mineralisation was studied by incubating coastal sediments with added biodeposits and measuring oxygen and nutrient fluxes as well as sediment characteristics over an 11 d period. Sediment oxygen consumption and ammonium release increased immediately after biodeposit addition and remained elevated compared to control cores without additions for the incubation period. A biodeposit decay rate (0.16 d-1) was calculated by fitting a first-order G model to the observed increase in oxygen consumption. This rate is 1 - 2 orders of magnitude higher than published decay rates of coastal sediments without organic enrichment or plant material. Nutrient fluxes during the incubation period illustrated that biodeposit remineralisation alters the stoichiometry of the nutrients released from the sediments which may potentially be more significant than the changes of the individual fluxes.

To determine the impact of a mussel farm in the Firth of Thames I measured sediment oxygen and nutrient fluxes by deploying benthic chambers, sediment characteristics by collecting sediment cores and sedimentation rates by deploying sediment traps in four seasons. Oxygen consumption and sediment nutrient release rates were generally higher under the farm compared to a reference site, demonstrating the typical response to increased organic input. Unusually low nitrogen release rates measured in summer may indicate enhanced denitrification under the farm. A simple budget demonstrated the importance of benthic nutrient regeneration in maintaining primary production in this region and that mussel culture can lead to a redistribution of nutrients. This study showed that site-specific hydrodynamic and biogeochemical conditions have to be taken into account when planning new mussel farms to prevent excessive modifications of nutrient dynamics.

Results of the laboratory and field studies conducted in this thesis were used to parameterise, calibrate and validate models of mussel biodeposit dispersal and remineralisation. A particle tracking model showed that the maximum initial dispersal of faecal pellets from the mussel farm is approximately 300 m and that pellets can be transported several times this distance via resuspension. The remineralisation model was able to simulate the increased nitrogen fluxes from the sediments well and highlighted the need for thorough calibration and parameterisation of the model. 

This thesis contributed to the current understanding of the ecosystem impacts of mussel culture and provided numerical models and model parameters that will assist in the assessment of mussel culture sustainability and the contribution of mussels to the nutrient cycling in nearshore ecosystems.

text: Dispersal and remineralisation of biodeposits: Ecosystem impacts of mussel aquaculture Suspension-feeding bivalves produce biodeposits (faeces and pseudofaeces) that have much higher sinking velocities than their constituent particles. Consequently they cause sedimentation of material that might otherwise not be deposited. The benthic remineralisation of biodeposits increases sediment oxygen demand and nutrient regeneration, thus enhancing the benthic-pelagic coupling of nearshore ecosystems. In New Zealand the mussel Perna canaliculus has a high natural abundance and is also intensively cultured. This thesis examines the dispersal and remineralisation characteristics of mussel P. canaliculus biodeposits and the impacts of sedimentation from a mussel farm in the Firth of Thames on sediment biogeochemistry by combining laboratory, field and modelling studies. 

Dispersal characteristics were examined in the laboratory by measuring sinking velocities and erosion thresholds of biodeposits produced by mussels of a wide size range fed three experimental diets. The results show that biodeposit dispersal is a function of mussel diet and size and thus could differ significantly between locations and seasons. Estimates of dispersal distances based on these results demonstrated that the initial dispersal of biodeposits produced by cultured mussels is not far. Depending on the hydrodynamic conditions, secondary dispersal via resuspension potentially plays a more important role in the dispersal of biodeposits from mussel farms than initial dispersal and almost certainly serves as the major means of transport of biodeposits from natural mussel beds.

Biodeposit mineralisation was studied by incubating coastal sediments with added biodeposits and measuring oxygen and nutrient fluxes as well as sediment characteristics over an 11 d period. Sediment oxygen consumption and ammonium release increased immediately after biodeposit addition and remained elevated compared to control cores without additions for the incubation period. A biodeposit decay rate (0.16 d-1) was calculated by fitting a first-order G model to the observed increase in oxygen consumption. This rate is 1 - 2 orders of magnitude higher than published decay rates of coastal sediments without organic enrichment or plant material. Nutrient fluxes during the incubation period illustrated that biodeposit remineralisation alters the stoichiometry of the nutrients released from the sediments which may potentially be more significant than the changes of the individual fluxes.

To determine the impact of a mussel farm in the Firth of Thames I measured sediment oxygen and nutrient fluxes by deploying benthic chambers, sediment characteristics by collecting sediment cores and sedimentation rates by deploying sediment traps in four seasons. Oxygen consumption and sediment nutrient release rates were generally higher under the farm compared to a reference site, demonstrating the typical response to increased organic input. Unusually low nitrogen release rates measured in summer may indicate enhanced denitrification under the farm. A simple budget demonstrated the importance of benthic nutrient regeneration in maintaining primary production in this region and that mussel culture can lead to a redistribution of nutrients. This study showed that site-specific hydrodynamic and biogeochemical conditions have to be taken into account when planning new mussel farms to prevent excessive modifications of nutrient dynamics.

Results of the laboratory and field studies conducted in this thesis were used to parameterise, calibrate and validate models of mussel biodeposit dispersal and remineralisation. A particle tracking model showed that the maximum initial dispersal of faecal pellets from the mussel farm is approximately 300 m and that pellets can be transported several times this distance via resuspension. The remineralisation model was able to simulate the increased nitrogen fluxes from the sediments well and highlighted the need for thorough calibration and parameterisation of the model. 

This thesis contributed to the current understanding of the ecosystem impacts of mussel culture and provided numerical models and model parameters that will assist in the assessment of mussel culture sustainability and the contribution of mussels to the nutrient cycling in nearshore ecosystems.

year: 2006

title: Pasifika in the news: the portrayal of Pacific peoples in the New Zealand press

authors: Loto, Robert

subjects: psychology

abstract: Pacific Islanders have faced discrimination in New Zealand particularly since the 1960s when communities began to be transplanted from their home nations to Aotearoa as cheap immigrant labour. Subsequently, the New Zealand vernacular has contained references to Pacific Islanders as  overstayers ,  coconuts ,  bungas  and  fresh off the boat  [FOB]. However, the legacy of a domineering relationship between the Palagi[Note 1] majority group and Pacific minorities[Note 2] that is captured by such derogatory terms is still evident in public forums such as the media. Using a quantitative content and qualitative narrative analysis, this paper documents portrayals of Pacific Islanders in New Zealand print media reports (n = 65) published over a 3 month period. Findings reveal that Pacific people are predominantly portrayed as unmotivated, unhealthy and criminal others who are overly dependent on Palagi support. We consider this offered pacific identity formation with that implied for Palagi, which is active, independent, competent and caring. Issues in coverage are discussed in relation to how Pacific Islanders are encouraged to see themselves, and the health and social consequences of dominant practices in press coverage. We offer some suggestions as to how more equitable representations of Pacific people could be fostered in news media.

text: Pasifika in the news: the portrayal of Pacific peoples in the New Zealand press Pacific Islanders have faced discrimination in New Zealand particularly since the 1960s when communities began to be transplanted from their home nations to Aotearoa as cheap immigrant labour. Subsequently, the New Zealand vernacular has contained references to Pacific Islanders as  overstayers ,  coconuts ,  bungas  and  fresh off the boat  [FOB]. However, the legacy of a domineering relationship between the Palagi[Note 1] majority group and Pacific minorities[Note 2] that is captured by such derogatory terms is still evident in public forums such as the media. Using a quantitative content and qualitative narrative analysis, this paper documents portrayals of Pacific Islanders in New Zealand print media reports (n = 65) published over a 3 month period. Findings reveal that Pacific people are predominantly portrayed as unmotivated, unhealthy and criminal others who are overly dependent on Palagi support. We consider this offered pacific identity formation with that implied for Palagi, which is active, independent, competent and caring. Issues in coverage are discussed in relation to how Pacific Islanders are encouraged to see themselves, and the health and social consequences of dominant practices in press coverage. We offer some suggestions as to how more equitable representations of Pacific people could be fostered in news media.

year: 2006

title: Consciousness-centered stewardship: An indigenous standpoint

authors: Spiller, Chellie

abstract: Dominion-driven stewardship, which stages human interventions with an anthropocentric lens, externalises problems. We present consciousness-centered stewardship, seen through the Māori ethic of kaitiakitanga, as the missing connective tissue that looks to fix ourselves. We advocate an approach that appreciates a collective self-intelligence in the world and being a steward with a “conscious mind” as part of a transformative way forward. Sustainable development from this perspective thus includes paying attention to personal growth.

text: Consciousness-centered stewardship: An indigenous standpoint Dominion-driven stewardship, which stages human interventions with an anthropocentric lens, externalises problems. We present consciousness-centered stewardship, seen through the Māori ethic of kaitiakitanga, as the missing connective tissue that looks to fix ourselves. We advocate an approach that appreciates a collective self-intelligence in the world and being a steward with a “conscious mind” as part of a transformative way forward. Sustainable development from this perspective thus includes paying attention to personal growth.

year: 2025