Doctoral Theses
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The Doctoral Theses collection contains digital copies of AUT doctoral theses deposited with the Library since 2004 and made available open access. All theses for doctorates awarded from 2007 onwards are required to be deposited in Tuwhera Open Theses unless subject to an embargo.
For theses submitted prior to 2007, open access was not mandatory, so only those theses for which the author has given consent are available in Tuwhera Open Theses. Where consent for open access has not been provided, the thesis is usually recorded in the AUT Library catalogue where the full text, if available, may be accessed with an AUT password. Other people should request an Interlibrary Loan through their library.
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Browsing Doctoral Theses by Supervisor "Alfaro, Andrea C."
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- ItemDevelopment and Optimisation of a Sustainable Feed Formulation for the New Zealand Farmed Abalone (Haliotis iris)(Auckland University of Technology, 2023) Bullon Zegarra, Elizabeth NataliaThe expansion of aquaculture depends on the availability and sustainability of aquafeeds. The development of aquafeeds is hampered by the lack of more eco-friendly ingredients that promote animal growth and contribute to animal welfare simultaneously. The common ingredients of aquafeeds (e.g., fishmeal and plant meals) are highly nutritious due to a well-balanced amino acid profile, fatty acid, and micronutrients. However, these ingredients are considered unsustainable due to the utilisation of wild fish stocks and extensive land and energy use for their cultivation. Alternative ingredients such as insect meals and waste-by products are of interest due to their high nutritional profile and contribution to a more circular economy. Tenebrio molitor (mealworm) is one species of insect with high digestibility and high levels of polyunsaturated fatty acids. Grape marc is a waste-by product from the wine production industry which disposal is becoming problematic. Grape marc is rich in antioxidants and is a potential prebiotic source. The aim of this thesis is to evaluate the inclusion of two alternative ingredients, insect meal and grape marc, on somatic growth, nutritional profile, health, shell colour and flavour of the New Zealand farmed abalone (Haliotis iris). Initially, the nutritional profile and metabolomic variations were assessed in a farm in Northland (Ruakaka) over a year (Chapter 3). Data collected from this chapter showed that the nutritional profile of juvenile abalone is subject to age and seasonal variations although feed remained the same. The protein levels were the most affected during the year of grow-out whereas carbohydrate, ash, and moisture did not show extreme variations. The metabolite profiles corroborated the presence of some amino acids related to flavour and tenderness, and fatty acids related to temperature regulation showing higher levels in summer compared to winter months. The study of the nutritional profile of the commercial feed allowed us to develop four experimental diets which included fishmeal at some extent and included insect meal and grape marc to reduce the nitrogen and phosphorus load in the uneaten feed while improving physical and chemical characteristics (Chapter 4). The experimental diets were encapsulated in alginate beads to promote better seawater stability. The physical and chemical properties of encapsulated feeds revealed improved seawater stability compared to commercial feed and advantages in their frozen delivery form in terms of the texture profile. Encapsulated diets with grape marc inclusion resulted in an improved resistance to abrasion, and the encapsulation with the inclusion of both, insect meal and grape marc, significantly reduced the phosphorus and nitrogen waste in uneaten feed. In addition, the inclusion of insect meal and grape marc showed growth promotion and comparable feed intake to commercial feed in 14-days. After acceptable feed intake of the experimental diets in a 14-day feeding trial, the encapsulated diets were trialled in an abalone farm in Southland (Bluff, Invercargill) over 165 days. The nutritional profile and nutrient digestibility were assessed on the experimental diets, and growth parameters, proximate composition, amino acids, and fatty acids were assessed in juvenile abalone tissue (Chapter 5). Results showed that the inclusion of insect meal and grape marc did not affect the growth of abalone after 165 days compared to diets without the inclusion. However, the inclusion of grape marc reduced the digestibility of the diets significantly, while insect meal did not. The fatty acid profile of abalone was significantly affected mainly in the α-linolenic acid, arachidonic acid, and eicosapentaenoic acid content, while the amino acid profile was not significantly modified by the inclusion of insect meal nor grape marc. The flavour-volatile compounds and shell coloration were also assessed after six months of feeding (Chapter 6). The results showed that the inclusion of insect meal did not significantly affect the flavour volatile profile, whereas the inclusion of grape marc significantly reduced the production of most of the volatile compounds. This reduction indicated an antioxidant effect of grape marc in the meat of abalone, suggesting a reduced oxidation of lipids. In addition, the inclusion of both insect meal and grape marc affected did not affect the lightness, redness/greenness, and yellowness/blueness coloration of the shells. The study also evaluated the effect of insect meal and grape marc inclusion on the gut health and muscle metabolome of abalone (Chapter 7). The results showed that the inclusion of insect meal and grape marc did not significantly affect the gut microbial diversity nor the intestinal morphology, indicating a capacity of abalone to adapt to those ingredients maintaining a good intestinal condition. In addition, the relative abundance of gut bacteria fluctuated with the dietary inclusion of insect meal and grape marc, suggesting a possible increase of beneficial species. This study also corroborated the relevant role of fatty acids in abalone metabolism and growth as described in Chapter 5. In conclusion, this thesis has successfully performed a holistic evaluation of the effects of insect meal and grape marc inclusion in feeds for abalone aquaculture. The different angles of animal nutrition described in this thesis go beyond traditional growth evaluation, which has been considered as the gold standard. The insights from this thesis contribute to the development of more sustainable aquafeeds to be used in the abalone industry to promote growth and animal welfare, improve the quality of the meat, reduce environmental impact, has adequate physical properties for commercialization and represents a steppingstone for the development of a blue aquaculture in New Zealand.
- ItemDietary protein requirements of the New Zealand Black-footed Abalone (Haliotis iris, Martyn 1784)(Auckland University of Technology, 2010) Tung, Che-HuangThe aim of this thesis is to evaluate the nutritional aspects of dietary protein for the New Zealand black-footed abalone (Haliotis iris) as an aquaculture species, and thus provide an affordable option for formulated feeds to be used in this abalone industry. Young (4 hours) and mature (7 days) and nine of twenty strains were mixed to each other microalgal biofilms were tested for their effectiveness on H. iris larval early developmental processes (attachment, metamorphosis, settlement and survival). Amino acid profiles and percent biofilm cover of microalgae also were monitored. Significantly better effects on attachment, metamorphosis, settlement and survival were found when abalone were exposed to mature microalgal biofilms compared to young biofilms, but few significant differences were found among biofilms composed of different microalgal species. Attachment and metamorphosis did not appear to be affected by differences in essential or non-essential amino acid profiles in the diets, but positive correlations were found between developmental processes and total amino acid content and percent biofilm cover. Similar results were also found in dual strains experiment. Nine commercially available protein sources (white fish, red fish, blood, meat and bone, casein, soybean, gluten, maize protein, Spirulina) were used as sole protein sources in formulated diets, which was fed to juvenile H. iris at 18 °C for five months. Juvenile abalone fed with diets containing white fish, red fish, casein, soybean and Spirulina had significantly better growth than those of fed other protein sources, thus indicating that these diets could be suitable as sole protein sources for H. iris formulated feeds. Abalone juveniles fed soybean diets (with extremely low methionine content) had similar growth results as those fed fish meal diets, and did not show a decrease in certain amino acid content (such as methionine) in their soft body tissues. However, dietary amino acid profiles did affect the amino acid profiles of both soft bodies and shells, which may have caused changes in shell bio-mineralization. Red fish protein had the best performance and it was therefore used to determine protein requirements under two different temperature regimes (13-21°C and 8-16°C) that simulated the temperature regimes of the South and North Islands in New Zealand. Six different dietary protein levels (0, 10, 20, 30, 40, and 45%) made from red fish meal were fed to juvenile abalone for four months. Growth performance increased steadily with increasing dietary protein. A second-order polynomial curve fit showed differences in protein requirements between the two temperature regimes, which were 42-53% in low temperatures and 38-39% in high temperature regimes. Shell morphology of previous two dietary experiments shown that: dietary protein sources and levels strongly affected H. iris shell morphology. Significantly wider, higher and heavier shells were found in animals fed casein diets. Both fish meal diets resulted in abalone with flatter and heavier shells. High dietary protein levels also promoted the enhancement of shell width and shell weight, and high temperature environments produced heavier and thicker shells. In conclusion, dietary protein is an important factor for H. iris aquaculture. The content of dietary protein strongly affects settlement of larvae and growth of juveniles in H. iris. Dietary amino acid profiles can change amino acid profiles in both soft bodies and shells, which may cause changes in shell morphology. A dietary protein content above 40%, as can be provided with red fish meal in formulated diets, is recommended to improve H. iris production. Raising dietary protein contents can effectively recover the decreased growth that results from a low cultivation water temperature regime.
- ItemEffect of Nutrients and Salinity on Growth of Temperate Mangroves (Avicennia marina var australasica) in Northern New Zealand(Auckland University of Technology, 2019) Gritcan, IanaEstuarine environmental conditions in New Zealand have changed greatly due to human catchment activity (e.g., deforestation, intensive agricultural activity, and urbanisation). These factors have led to additional accretion of sediment (sedimentation) and nutrients (eutrophication) throughout New Zealand waterways and coast waters. In recent years, New Zealand mangroves (Avicennia marina var australasica) have shifted their distribution within estuaries and rapidly spread into areas where they have never been found before. Many local communities and councils are worried that mangroves have replaced sandy bare tidal flats and other estuarine habitats (i.e., seagrass beds, marshlands) and will turn them into muddy sites. Researchers have proposed several reasons for the spread of temperate mangroves, including estuary infilling, increased nutrient inputs, climate warming, changes in sea level and a combination of some of these factors. Indeed, it has been shown that increased sedimentation correlates well with rapid mangrove accretion in New Zealand through the emergence of additional mangrove habitat space, but the effect of the nutrient uploads has received less attention. Additionally, there is almost no information on the salinity levels that are characteristic for temperate New Zealand mangrove ecosystems. Indeed, it is well documented that salinity is an important controlling factor for mangrove growth in tropical mangrove ecosystems, but there is almost no such studies in temperate mangrove areas. Current research is highly relevant to on-going controversial discussions regarding management versus conservation of New Zealand mangroves, because it provides the review and experimental work on the cycling of nutrients in temperate mangrove and ecosystems as well as how salinity levels affect mangrove growth. This study presents previously missing information on the sources of nutrients in New Zealand estuarine ecosystems, as well as how these nutrients are conserved and stored in below ground biomass of A. marina. Field fertilisation experiments were conducted to describe nutrient availability as a primary driver for the difference in growth forms of mangrove plants (tall plants at the edge and stunted inland) in temperate New Zealand conditions. Controlled laboratory experiments were conducted to demonstrate how nutrient availability changes metabolite profiles of individual mangrove plants. The present research also provides novel information on how seasonal changes in salinity distribution patterns across the intertidal gradient in temperate mangrove ecosystems affect sodium composition of mangrove leaves. Results of the growth trial also suggest that moderate salinity has beneficial effects on A. marina seedling growth. Overall, results suggest that a unique combination of factors can increase growth and spread of temperate mangroves in estuarine and coastal territories in northern New Zealand. One of the most important factors is the cooler and wetter New Zealand climate, which is, due to high precipitation rate and low temperature. These conditions result in lower salinity levels, which are beneficial for A. marina growth. Another factor impinging on these mangroves is the natural nutrient deficiency state of these coastal ecosystems, and anthropogenic influences. These anthropogenic influences are mainly due to the increasing nutrient input over the past 100 years, originating from fertilisation, livestock urine runoff from dairy and meat farming, and human sewage inputs, which promotes growth and survival of mangrove seedlings. In addition, it can be concluded that the presence of mangrove plants at the interface between anthropogenically affected terrestrial lands and coastal ecosystems may mangrove habitats may act as nutrient sinks, thus mitigating coastal and marine eutrophication.
- ItemExtraction and Characterisation of Bioactive Compounds From New Zealand Black-footed Abalone(Auckland University of Technology, 2023) Mohammadi, SoniyaThere is expanding interest in marine organisms as a source of new bioactive chemicals for development of novel health-promoting products. Marine species account for half of the world’s biodiversity making them a rich source of new chemicals and the largest remaining source of beneficial natural molecules that might be exploited as functional ingredients in various food, cosmetic and pharmaceutical products. Abalone, a marine organism, have believed to provide health benefit with consumption for many years. Recent research has shown that abalone contain physiologically active chemicals with diverse modes of action, including antioxidant, antibacterial, anticancer, anti-hyaluronidase, anti-collagenase activities, and collagen. Thus, this thesis aimed to explore the extraction of bioactive compounds from Zealand black-footed abalone using novel environmentally friendly extraction techniques in order to make it an ideal candidate as a natural active ingredient for health promoting products. Bioactive compounds were extracted from New Zealand black-footed abalone using subcritical water extraction (SWE), an environmentally friendly extraction technique. Abalone subcritical water extracts are promising sources of bioactive compounds, including antioxidants, glycogen, phenolic compounds, carbohydrates, proteins, and amino acids, based on the overall findings. Furthermore, the findings demonstrate that the efficiency of SWE is affected by temperature, which is a critical factor in demonstrating extraction efficiency. Antioxidant and antiageing properties of bioactive compounds were recovered from wild and farmed black-footed abalone using SWE. The black-footed abalone extracts obtained by SWE, were found to be rich in majority of essential and non-essential amino acids and exhibited broad antioxidant and antiageing properties such as anti-hyaluronidase and anti-collagenase activity without causing significant toxicity at the high doses evaluated. It was also demonstrated that there was a strong correlation between antioxidant, antiageing and total phenolic compounds in both farmed and wild abalone extracts. Consequently black-footed abalone extracts were found as promising sources of novel anti-aging agents due to their high antioxidant, anti-collagenase and anti-hyaluronidase activities that could be incorporated into cosmetics. In addition, collagen type I was isolated from farmed and wild black-footed abalone using ultrasound assisted extraction (UAE) and CO2 water extraction (CO2-WE). Both techniques yield comparable SDS-Page, FTIR, and cytotoxicity results. However, CO2-WE had higher collagen extraction yield, shorter extraction time and used water instead of organic solvent. Therefore, CO2-WE could be an alternative promising technique than UAE with higher sustainability for enhancing the non-toxic extraction efficiency of collagen type I from black-footed abalone with applications in the cosmetic, biomedical, and pharmaceutical industries. The overall findings of this study, have confirmed the feasibility of using SWE and CO2-WE to produce high-quality abalone extracts from black-footed abalone. This study has also proved that New Zealand black-footed abalone possesses vast unexploited potential to be used to make high value products. This research resulted in a better understanding of the composition and bioactivity of black-footed abalone that can inspire to further research of this native abalone and accordingly, deriving high value products and expand it’s applications.
- ItemImmunological and Metabolomics Tools for Health Assessment of Farmed New Zealand Chinook Salmon (Oncorhynchus tshawytscha)(Auckland University of Technology, 2022) Lulijwa, RonaldNew Zealand’s Chinook salmon (Oncorhynchus tshawytscha) farming started in 1976 and has developed to become the number one farmed finfish in the country. New Zealand is the leading global producer and supplier of farmed O. tshawytscha. New Zealand’s O. tshawytscha production remains free from diseases that have devastated global salmon farming (Diggles, 2016). However, the recent emergence of New Zealand rickettsia-like organism (NZ-RLO) (Brosnahan et al., 2017), continued industry growth, and climate change, necessitates the development of health assessment tools. The aim of this thesis was to develop immunological and metabolomic tools for farmed O. tshawytscha health assessment. Farmed O. tshawytscha peripheral blood was characterised for cellular composition and a micro-volume blood technique was developed for isolation of fish peripheral blood mononuclear cells (PBMCs) using Lymphoprep. Differential cell counts identified five cell types including erythrocytes, lymphocytes, thrombocytes, monocytes and unquantifiable neutrophils, important in future health assessments. Isolated PBMCs enable field on-farm sampling for longitudinal studies and allow in vitro immunological assessments. Findings provided the possibility to make fish health assessments in the field without fish euthanisation. The developed micro-volume blood technique was used to isolate O. tshawytscha PBMCs. These PBMCs were used to model the functional and targeted immune cytokine responses to Gram-negative bacterial lipopolysaccharide (LPS) from Escherichia coli in vitro. Bacterial LPS stimulated biphasic reactive oxygen species (ROS) production enhanced by interferon (ifn) inducible cytokines, and phagocytosis. LPS also upregulated pro-inflammatory interferon gamma (ifnγ), tumour necrosis factor alpha (tnf-α), and anti-inflammatory interleukin-10 (il-10) 24 h post-stimulus. This provided the first report of LPS induced immunomodulation in O. tshawytscha in vitro. The results have high application potential in modelling response mechanisms to emerging NZ-RLO pathogenesis. The response mechanisms of O. tshawytscha to polyinosinic: polycytidylic acid [poly (I:C)] were investigated 24 h post-in vivo stimulation. The most striking results were observed at the metabolomic level. Poly (I:C) upregulated metabolites involved in branched‐chain amino acid (BCAA)/glutathione and transsulphuration pathways and phospholipid metabolism, while those involved in energy metabolism were downregulated. At the molecular level, poly (I:C) enhanced antiviral ifnγ in head kidney (HK) and Mx1 protein in head kidney (HK), spleen (SP) and red blood cells (RBCs). Findings provide insights into poly (I:C) induced immune‐related biomarkers at metabolic and molecular levels important in future investigations. The effects of poly (I:C) in vivo on O. tshawytscha haematology, innate immunity, serum and liver metabolite profiles, HK, and SP cytokine transcript expression, over a 5-day period post-injection were studied. Important responses included enhanced neutrophil counts and PBMC ROS production. Metabolically, poly (I:C) upregulated liver and serum metabolites involved in BCAA at day one and returned to normal by day five, while metabolites involved in glycolysis were persistently depleted. Metabolic results suggest that poly (I:C) induced response mechanisms similar to those observed in viral-infected fish, where the host metabolome is hijacked to favour viral replication. At the molecular level, poly (I:C) promoted antiviral ifnγ and Mx1, and anti-inflammatory il-10 in fish lymphoid organs, depict O. tshawytscha immune defence against infection. Results may act as a primer for developing amelioration strategies against viral infections in aquaculture. Finally, O. tshawytscha were subjected to a three-month thermal stress challenge (17°C vs 19°C-20°C) to identify blood biomarkers of thermal tolerance and growth performance (weight loss vs weight gain). Independent of growth performance, thermal stress induced leucocyte apoptosis, minor immune responses, and disturbed plasma osmoregulation via reduced Na+/K+-ATPase activity. Irrespective of culture temperature, fish that lost weight were characterised by several biomarker alterations in cellular haematology and plasma clinical chemistries suggestive of suppressed feed intake. Findings provide insights into physiological and growth effects of thermal stress on O. tshawytscha, useful in selective breeding strategies. Overall, depending on resource availability, this thesis has demonstrated the usage of classical haematology, novel flow cytometry, molecular and metabolomic tools in farmed O. tshawytscha health assessment. The thesis thus recommends an integrated approach of classical assays with the more recent flow cytometry and metabolomics approaches to promote holistic farmed teleost health assessments. Keywords Farmed Salmon; Aquaculture; Oncorhynchus tshawytscha; Metabolomics; Immunology; Flow Cytometry; Peripheral Blood Mononuclear Cells; Haematology; Biomarkers
- ItemMetabolomic Applications in Marine Mollusc Development and Aquaculture(Auckland University of Technology, 2016) Young, TimMetabolomics is a rapidly emerging discipline within functional genomics to better understand biochemical phenotypes across a range of biological systems. The approach has many demonstrated applications in aquatic biology, but has not yet been applied to study early lifestages of marine molluscs. This Thesis evaluates metabolomics as an approach to characterise early lifestage phenotypes of molluscs, and demonstrates unique applications in aquaculture, developmental biology, immunology, and toxicology. GC/MS-based metabolomics was first tested for its capacity to classify good and bad quality mussel larvae (i.e., slow- vs fast-growing organisms). Based on the composition of metabolites, larval classes could clearly be discriminated and the data indicated differences energy metabolism, osmotic regulation, immune function and cell–cell communication. Mussel larvae which had been subjected to handling stress and different culture conditions were also assessed. A decrease in succinate and an increase in alanine were observed after the water exchange, which indicated alterations in energy production and osmotic balance. However, these variations were subtle and it is unlikely that the water exchange practice had any lasting negative effects on larval physiology and performance. A culture condition classification model was also constructed which revealed that larvae from flowthrough vs static systems differed in terms of energy, protein and lipid metabolism. The data also suggests that growth performance is metabolically buffered through an adaptive physiological mechanism to provide similar developmental characteristics under these conditions. Oyster larvae were assessed during a viral (OsHV-1 μVar) infection to characterise the host-virus interaction at a metabolic level. Responses included a coordinated disruption of the TCA cycle in accordance with mammalian macrophage stimulation via activation of immunoresponsive gene 1 and production of itaconic acid, induction of a Warburg-like effect, and production of free fatty acids for virion assembly, among others. These results provide new insights into the pathogenic mechanisms of OsHV-1 infection in oyster larvae, which may be applied for selective breeding programmes aiming to enhance viral resistance. Lastly, metabolomics was applied to investigate mechanisms of toxicity in mussel larvae exposed to copper contamination. At sublethal dose levels, metabolic trajectory analysis indicated that larvae were successfully employing various endogenous mechanisms involving biosynthesis of antioxidants and a restructuring of energy-related metabolism in an attempt to alleviate the toxic effects on cells and developing tissues. This was partly confirmed by a targeted analysis of oxidative stress biomarkers (e.g., enzymes). A lethal copper dose induced severe metabolic dysregulation after 3 hrs exposure which worsened with time, substantially delayed embryonic development, initiated the apoptotic pathway, provided many evidences for the occurrence of oxidative stress (validated via oxidative stress biomarkers), and resulted in cell/organism death shortly after 18 hrs exposure. In summary, this Thesis provides strong support for the application of metabolomics to assess the health status of marine mollusc embryos and larvae.
- ItemMulti-omics Approaches to Investigate Responses of New Zealand Green-lipped™ Mussels to Environmental Stress and Pathogen Loads(Auckland University of Technology, 2023) Azizan, AwanisGreenshellTM mussels are important ecosystem engineers, with an established position in the aquaculture sector of New Zealand. Significant industry losses have been experienced, in terms of mass mortalities, on mussel farms in recent years. The exact cause of these mortalities is unknown, however association with increased water temperatures experienced during summer months have been deemed as a likely cause. Literature suggests that summer mortality involves intrinsic (immune dysfunction, gametogenesis, and spawning) and extrinsic (frequency and duration of heatwaves) factors, causing a physiological tipping point resulting in mussel death. Pathogen loads seem to proliferate during the summer months resulting in disease outbreaks. Novel research is required to study the impact of these mortalities and to mitigate disease outbreaks to assure health and sustainability for this industry. In this study, a multi-disciplinary approach, along with physiological evaluations, were employed to investigate the investigate the interplay of selected bacterial pathogens Photobacterium spp. and Vibrio spp. and temperature changes threatening the health status of adult, green-lipped mussels, Perna canaliculus. This thesis consists of two literature reviews (Chapter 2 and Chapter 3) and six experimental chapters (Chapter 4 -Chapter 9). Chapter 2 evaluates the immune status of GreenshellTM mussels and Chapter 3 explores physiological biomarkers relating to Vibrio sp. infections in mussels. Building upon the insights gained from extensive literature reviews, the focus now shifts to the experimental chapters, aiming to illuminate potential intersections and broader implications within the research framework. The first experimental chapter of this thesis (Chapter 4) assesses the effect of magnesium chloride (MgCl2) on adult GreenshellTM mussels’ physiology and metabolic response. MgCl2 significantly impacted the haemolymph metabolome in anesthetised mussels, indicating major physiological dysregulation. In Chapter 5, four bacterial isolates retrieved from moribund P. canaliculus, from a previous summer mortality event, were identified as V. celticus, P. swingsii, P. rosenbergii and P. proteolyticum using whole genome sequencing. Additionally, mussels injected with P. swingsii showed high mortality, along with expression of virulence genes (hsp60, zm, vcpA, toxR, ompU, mshA, chi, lip, and plp), suggesting pathogenesis of this bacterium to GreenshellTM mussels. Bacterial progression utilising P. swingsii was further investigated to better understand the mussel immune response and bacterial effect on mussel mortalities (Chapter 6). This study showed that the most profound effects of bacterial infection on mussels were seen at 48 hours post challenge (hpc) where mussel mortality, haemocyte counts and haemolymph colony forming units were the highest. The quantification of P. swingsii via targeted PCR showed highest levels of bacterial DNA at 12 hpc in the adductor muscle, gill, and digestive gland. Histopathological observations suggested a non-specific inflammatory response in all mussels associated with a general stress response. This study highlights the physiological effects of P. swingsii infection in GreenshellTM mussels and provides histopathological insight into the tissue injury caused by the action of injection into the adductor muscle. In Chapter 7, the impact of temperature stress on the metabolome of mussels was investigated utilising metabolomics. Mussels were exposed to two temperatures, 16 °C and 24 °C for five-days, creating a controlled laboratory marine heatwave environment. The metabolite changes in the presence of temperature stress provided insights into several pathways involved in defence and repair mechanisms, which reallocated energy away from organismal growth towards maintenance. Since all mussels in this experiment survived, this suggests that P. canaliculus has the potential to adapt to heat stress up to 24°C, by regulating their energy metabolism, balancing nucleotide production, and implementing oxidative stress mechanisms overtime. In the next chapter (Chapter 8), an experiment was performed to investigate the effects of thermal stress, bacteria, and combined stressors on selected immunological parameters and the survival of mussels. The total haemocyte count, viability, bacterial counts, total antioxidant capacity, and lipid peroxidation were used as indicators to measure an immune response of infected mussels to different temperatures. Water temperature at 24°C significantly affected immune functions and led to oxidative stress and reduction of immunosurveillance in the P. swingsii infected mussels. The combination of temperature-pathogen stress affected the survival of mussels with highest mortality at 24°C in the presence of bacteria. This chapter demonstrated that mussels have lower tolerance to the combined effects of high temperature stress and pathogen infection. Chapter 9 investigated the effect of bacterial coinfection, on mussel size, bacterial clearance efficiency and metabolic response, considering juvenile and adult mussels. This study showed greater mortality in juvenile mussels within the bacterial coinfection group, suggesting that susceptibility of small mussels to bacterial infections are greater than in adults. Large decreases in energy metabolites were detected in mussels when exposed to multiple bacterial pathogens. Potentially due to high energy expenditure and metabolite functions to support immunity and protein synthesis during this pathogen interactions. Collectively, these findings demonstrated a rigorous exploration of complex biological processes within New Zealand Greenshell™ mussels (P. canaliculus) and deepened the understanding of their general health, disease progression, transmission mechanism and host-pathogen interactions. These findings can be used to help assess P. swingsii transmission risk within and among GreenshellTM mussels’ populations and facilitate appropriate management and restoration strategies for both wild and cultured mussel species.
- ItemNutrition and Reproductive Condition of Wild and Cultured New Zealand Scallops (Pecten novaezelandiae)(Auckland University of Technology, 2016) Wong, Ka Lai ClaraThe New Zealand native scallop, Pecten novaezelandiae, is a species with a high economic value as a wild catch and has good potential for cultivation. As a mean to enhance the future of this growing shellfish industry, this thesis set out to investigate the nutritional requirements of P. novaezelandiae in relation to reproductive conditions, and determined the physical and biological factors that affect the condition of this scallop species in the wild and cultivated environments. Adult scallops (Pecten novaezelandiae) were sampled from six populations in the Hauraki Gulf (Auckland, New Zealand) in the spawning season (October 2014), in order to evaluate the scallop reproductive condition and nutritional state across the populations. Results showed a spatial variation in reproduction condition (VGI and gonad index), with a higher number of mature scallops in populations closer to the shoreline, where higher food availability may be found. Conversely, nutrient content in scallop somatic tissues (adductor muscle carbohydrates and digestive gland lipids) did not vary across the populations, but was strongly associated with reproductive status of individual scallops (VGI). Nutrient (carbohydrates, proteins and lipids) storage and utilization were investigated within scallops from two sites in the Hauraki Gulf, bi-monthly over a year (2012−2013). In addition, sediment samples were also taken to evaluate the potential for re-suspended nutrients as a food source for scallops. Water samples were collected for seston and chlorophyll a analyses. Isotope analyses (carbon and nitrogen) and proximate analyses were conducted for the gonad, adductor muscle and digestive gland of wild P. novaezelandiae, sediment samples and the seston (1.2−5μm, >5μm). Isotope analyses revealed distinctly different signatures in suspended sediment and scallop tissues, indicating that re-suspended nutrients were unlikely to contribute to the diet of scallops. Nevertheless, seston (particularly the small fractions) signatures were closely related to scallop tissue samples, suggesting that it is likely to be the main food source for the wild P. novaezelandiae. Scallops from the two sampling sites exhibited similar reproductive cycles and utilization of nutrients. Gametogenesis started in winter, and took place at the expense of carbohydrates stored in adductor muscles. Spawning events were recorded in spring (October−November) and summer (January−March), and the energy demand required during spawning events was supported by digestive gland protein. Gonad re-maturation between spring and summer spawnings were supported by the utilization of digestive gland lipids. The reproductive condition and nutrient content of scallops were then studied during the spawning season (October 2013) in wild populations and within experimental conditions (fed with a commercial microalgal diet; Shellfish Diet 1800®) in an aquaculture laboratory, in order to identify condition and nutrient requirements for scallop cultivation in New Zealand. Field scallops (feeding on natural food sources) spawned just before the end of the experiment, while experimental animals reached gonad maturity at the end of the experiment, but did not spawn. The trend in gonad maturation for field and experimental animals indicates that there was a lag time of about 2 weeks, and that this lag is likely due to nutritional stress associated with the shift from natural food sources to the mixed microalgal formulated diet provided in the laboratory. Results indicate that experimental scallops had lower nutrient (carbohydrates, protein, lipids and total energy) reserves stored in adductor muscle tissues compared to wild animals, but both field and experimental animals utilized muscular reserves (especially carbohydrates and protein) to support reproductive activity. The fatty acid profiles revealed that polyunsaturated fatty acids (PUFA) were found in significantly lower quantities in gonad tissues of scallops from the laboratory compared to those in the field. This thesis shows that P. novaezelandiae utilizes energy reserves from both adductor muscle and digestive gland to cover the full cost of gametogenesis. In addition, cultivation environments using microalgal diets are conducive to condition P. novaezelandiae, but the optimal nutrient requirements for an efficient aquaculture production of this species needs further investigation. It is recommended by this thesis that future investigation on the conditioning requirements for P. novaezelandiae will be the next step for New Zealand scallop fisheries.
- ItemRegional spread of marine non-indigenous species, a pathway modelling approach in New Zealand(Auckland University of Technology, 2013) Acosta Cajiao, HernandoThe devastating ecological and socio-economic impacts of non-indigenous species (NIS) have been documented worldwide, highlighting the need for effective management. In contrast to terrestrial and freshwater ecosystems, management of marine NIS is relatively new and usually focused on preventing initial introductions at national (e.g., in New Zealand) and state (e.g., in the United States, Australia) borders. However, the intrinsic ‘leakiness’ of these borders and thus, inevitable arrival of new NIS, in addition to the potential spread of those already established, makes regional management an integral component of marine biosecurity programmes. Even in New Zealand, a leading country in marine biosecurity, the implementation of regional strategies has been difficult, putting New Zealand’s iconic values such as marine biodiversity and aquaculture, at risk. This thesis aims to model and analyse recreational boating, aquaculture and natural currents as pathways for the regional spread of NIS within New Zealand. It uses Golden Bay and Tasman Bay as a case study and applies existing and new modelling and prioritisation approaches. Chapter 1 presents a succinct introduction to some basic concepts of marine invasions and risk assessment. The term biosecurity is presented, followed by an outline of this system in New Zealand, with an emphasis on the post-border component. The chapter describes Golden Bay and Tasman Bay, including aspects related to its marine biosecurity. Chapter 2 develops a comprehensive conceptual model representing a range of sequential events that could lead to the release of a NIS into the environment when transported by a recreational vessel to a new area. The model was developed using fault tree analysis and expert input. The results show the complexity of the marine invasion process via recreational vessels, even when only one step of the process is considered. They also highlight the role that other components of the vessel besides the hull could have in the spread of NIS and identify user awareness as a determining factor in the release of a NIS into a new area. Chapter 3 characterises recreational boating in Golden Bay and Tasman Bay. It introduces the connectivity ranking value and priority ranking value concepts to identify areas within the study region where marine biosecurity surveillance should be a priority. The information required for this analysis was generated through a mail survey with recreational boat users and estimates from a group of experts, which were combined using interval type–2 fuzzy logic. The results show that areas such as Nelson and the Abel Tasman National Park would be comparatively more important than other regions in the spread of NIS within the region. Chapter 4 uses the Greenshell mussel aquaculture industry to model its potential role as a pathway for NIS. The results identify the components (e.g., farms, hatcheries) and processes, as well as potential vectors (vessels, gear, spat) that define mussel aquaculture as a potential pathway for NIS in this region. The results show that, based on the likelihood of 1) movement between locations, 2) retention of fouling, sediment and/or water, and 3) cleaning between locations, spat is the most important vector of this pathway and thus, a management priority. This chapter also describes some overlaps between mussel aquaculture and other potential pathways such as commercial shipping, recreational boating, public aquaria, and coastal currents. Chapter 5 presents a 2D advection-diffusion model that was used to investigate the role of currents in the spread of NIS within Golden Bay and Tasman Bay. A current field of 13 years of hourly data is used to analyse the dispersal patterns for four planktonic propagule durations (PPD) between 1–30 days released at 11 different locations. High variability in the results associated with release location, PPD and time period, indicates that the fate of propagules will be species and spatio-temporally dependent. The results present the connectivity pattern for each release location, identifying the role of these locations as source and/or recipients. Chapter 6 presents a brief summary of previous chapters, highlighting their main aspects. It conducts an initial integral assessment across the pathways recreational boating, aquaculture, and natural currents in the study region by combining the connectivity patterns identified in previous chapters. The results show that when considering all these pathways together, the entire region is interconnected creating a potentially ‘efficient NIS pathway’ (i.e., with the ability to spread a NIS from any region throughout the entire region). Future application of the concepts and results are suggested.
- ItemTrace Metal Dynamics in Mangrove Sediments Within Temperate Estuaries(Auckland University of Technology, 2019) Bastakoti, UjwalMangrove sediments have a high capacity to retain organic matter because of the low mineralization processes induced by the waterlogged conditions around them. The accumulation of organic matter and deposition of fine particles within mangrove forests are favorable for anaerobic metabolic processes that produce inorganic sulphur, which has a high capacity to sequester trace metals. This means that mangrove sediments have the ability to protect surrounding environments from trace metal contamination. However, changes in redox conditions in mangrove sediments as a result of natural or anthropogenic activities may result in trace metals being released to overlying waters. The released metals from mangrove sediments are a serious environmental threat worldwide because of their persistent nature, and they tend to accumulate in estuarine food chains. Such complex dynamics of metal cycling within temperate mangroves and their effects on surrounding ecosystems require further investigation. Thus, a comprehensive field-based study on the factors influencing the redox conditions of mangrove sediments is needed to understand trace metal dynamics in these habitats, especially in temperate areas, such as New Zealand. Hence, this study aims to enhance our knowledge on the process involved in metal cycling induced by natural and anthropogenic factors in temperate mangrove sediments, which could be a useful benchmark for estuarine management in temperate regions, including New Zealand. Such estuarine management approach should consider several physical and ecological factors because the distribution of trace metals in mangrove sediments may exclusively vary on a site-by-site basis. Hence, in this study, four different mangrove stands at Mangawhai Harbour and two stands at Manukau Harbour, both located in northern New Zealand, were selected as study locations, which represent rural and urban temperate mangrove stands, respectively. The study aims to understand trace metal distributions up to 30 cm sediment depth, representing the majority of mangrove live root zone which may influence metal distribution patterns. Overall, the results indicate that organic matter highly controls trace metal cycling in mangrove sediments and the variation of organic matter within the system is influenced by several natural and anthropogenic factors. Especially, local weather pattern, fluctuations in anthropogenic inputs, and hydrographic condition are major factors controlling organic matter and trace metal distributions in these mangrove sediments. The results also revealed significant variations in trace metal levels between mangrove sediments and adjacent mudflats, which indicate that mangrove sediments have the inherent sequestering capacity. However, the results also indicate that there are possible impacts of trace metal contamination to surrounding environments during pre- and post-mangrove removal assessment. Hence, the study utilizes a unique and rare opportunity especially during the mangrove removal period to provide field-based scientific information that physical disturbances in the mangrove ecosystem could change the habitat from a sink to a source of trace metals. In summary, the findings of the study show that mangrove sediments could act as both natural filters and secondary sources of trace metals depending on several factors influencing sediment redox conditions. Thus, mangrove ecosystems may be important agents to minimize trace metal contamination in estuarine and coastal ecosystems worldwide. Overall, the outcomes of the study provide essential scientific information on trace metal cycling in mangrove sediments, which is likely to assist with estuarine management and conservation strategies in New Zealand and worldwide. Also, the study highlights the necessity for periodic scientific assessments on trace metals in mangrove ecosystems, especially before making management decisions involving their removal in New Zealand and worldwide.