A Delicate Balance between Copper Necessity and Toxicity

Recent human activities, such as urbanisation, industrialisation and agricultural intensification, have produced a concerning increase in the concentrations of trace metals in the aquatic environment. While metals such as copper are essential micro-nutrients to aqueous organisms, they become toxicants when surpassing a critical concentration threshold in the aquatic environment. The copper concentration of many natural water masses and tissue of aquatic organisms have been found to exceed essential levels. These elevated levels of copper lead to sub-lethal or toxic effects on adults or, more crucially, their larval stages, drastically impacting the diversity, health, structure and functioning of affected ecosystems. The detection, monitoring and assessment of copper concentrations are therefore key to the integrity of aquatic environments and are becoming increasingly important as a result of legislation and increasing public awareness

Copper speciation in different marine ecosystems around New Zealand

Copper (Cu) is an important bioactive trace metal in the marine environment, acting as an essential micronutrient for many marine species. However, it can also be harmful at elevated concentrations, triggering sub-lethal and toxic effects. During the last few decades, studies using electrochemical techniques have established that it is the particular chemical form of Cu, its so-called chemical speciation, and not its total concentration that controls the geochemical and biological behaviour and thus the bioavailability and toxicity of Cu in marine systems. The majority of dissolved Cu in the marine environment is strongly complexed by a heterogeneous mixture of Cu-binding organic ligands (L), reducing the free ionic Cu concentration ([Cu2+]) to femto- and picomolar levels. Free ionic Cu is generally considered the most bioavailable and thus the most beneficial or toxic form to marine organisms. Organic complexation reduces [Cu2+] in most marine systems to levels harmless, but above limitation, to many marine microorganisms. Measuring the inorganic, organic, and free Cu forms in the dissolved phase is critical to assess the fate (i.e., distribution, cycling, and reactivity) and the biological effects of Cu in the marine environment. However, the chemical speciation of Cu in natural saline waters is complex and is technically challenging to evaluate, resulting in cost-intensive and time-consuming analyses. Consequently, despite the recognised importance, little data exists for Cu speciation and Cu-binding ligands in the marine environment, and ligand sources and chemical identities are generally understudied. Additionally, environmental processes and factors influencing and controlling Cu speciation in marine systems are still poorly understood. As a result, four different marine systems (i.e., estuarine, coastal and open ocean waters, as well as a shallow low-temperature hydrothermal vent system) were studied around New Zealand in an effort to advance the current understanding of Cu speciation processes and Cu-binding ligands in the marine environment. Total dissolved Cu concentrations were analysed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), while Cu speciation was assessed with adsorptive cathodic stripping voltammetry (AdCSV) with salicylaldoxime (SA) as the competing ligand. It was found that more than 99.7 % of the total dissolved Cu (CuT) in the sampled marine waters was complexed with organic and inorganic (i.e., sulfides) ligands, demonstrating the decisive role of ligands in controlling Cu speciation, bioavailability, and toxicity in the marine environment. AdCSV detected only one L-class with concentrations of up to 47.4 nM for low CuT areas, such as the region of the Hauraki Gulf and White Island/Whakaari, and L-concentrations ([L]) of up to 114.8 nM for areas enriched in CuT like the Astrolabe Reef and the Whau Estuary. Conditional stability constants (logK) of the CuL-complexes were relatively uniform in the working areas and ranged from 11.4 to 13.6, suggesting a similar chemical nature and source of the prevalent Cu-binding ligands in the sampled marine environments. On the basis of the ligand distribution in the water column, with higher [L] in the photic zone and decreasing [L] with depth, Cu-binding organic ligands were suggested to predominantly originate from passive or active biological in-situ production of planktonic species or life stages. This assumption was supported by the 48 h bioassay in Chapter 6, during which Cu-stressed mussel embryos actively produced ligands, with logK values similar to those observed in the sampled natural saline waters, to mitigate the toxic effects of the Cu2+ in their environment. The current study also pointed out that the heterogeneous ligand pool in the marine environment might also include some organic ligands of terrestrial nature (i.e., humic substances (HS)), organic ligands derived from chemoautotrophic microorganisms, organic ligands formed abiotically under hydrothermal conditions, organic ligands which originate from yet unknown allochthonous and autochthonous sources, and in the case of hydrothermal systems can include substantial amounts of inorganic ligands such as sulfides. Further, [L] was always in excess of the [CuT] and as a result [Cu2+] were buffered to femto- and picomolar levels in the Hauraki Gulf region, White Island/Whakaari, and the Whau Estuary. These Cu2+ levels were below the toxicity threshold and above the deficiency threshold of Cu for many marine microorganisms. Only at the Astrolabe Reef, with highly elevated [CuT] in the vicinity of the MV Rena wreck, was the Cu complexation capacity of the natural organic ligands saturated, which led to toxic levels of [Cu2+] in the system. Consequently, the benthic invertebrate recruitment was lower, and different types of organisms were recruiting the high Cu2+ areas, leading to an alteration in the community diversity, structure, and functionality of the Astrolabe Reef. This output indicates the importance of organic ligand production by organisms as a strategy to maintain the delicate balance between ecosystem health and degradation. Temperature, pH, sample depth, chlorophyll a, particulate organic matter, and nutrient concentrations (i.e., nitrogen oxides, phosphate) had a poor correlation with Cu speciation parameters in the water column of the working areas. Salinity was found to increase Cu toxicity to M. galloprovincialis embryos, while higher dissolved organic carbon (DOC) concentrations decreased Cu toxicity to the mussel embryos. These outputs suggest that the biogeochemical cycling of Cu and its impact on marine life is intricate, dependent on the interactions between interrelated physical, chemical, and biological properties of the water column and the affected organism itself (e.g., ligand production, osmoregulation, and ionoregulation). This complexity precludes a generalisation of Cu speciation, bioavailability, and toxicity for the marine environment and thus highlights the urgent need to develop a site-specific saltwater Biotic Ligand Model (BLM) to assure adequate protection of aquatic life in various marine systems. Further, one of the most interesting findings of this thesis was that DOC and ligand quality (i.e., competition of several metals for the same ligand binding sites (non-specific metal binding affinities) or multidentate binding) were significantly more important in determining Cu bioavailability and toxicity in the sampled natural marine environments relative to DOC and ligand quantity. This finding highlights the necessity to elucidate the sources and chemical natures of organic Cu-binding ligands in order to improve the current understanding of the biogeochemical behaviour of Cu in marine systems. Moreover, it was demonstrated that the excessive Cu-loss during laboratory-based bioassays owing to container adsorption and bioaccumulation processes of the test organisms, together with the detoxification effect of extracellular Cu, and the variability of intracellular Cu, can lead to a significant misunderstanding of Cu toxicity mechanisms and a misrepresentation of Cu toxicity to test organisms. This latter output questions the reliability of current marine water quality criteria (WQC), which were extrapolated from laboratory-based bioassay tests that did not account for the Cu-loss in solution under laboratory conditions. Overall, the results from this study added to the body of current knowledge about Cu speciation, bioavailability, and toxicity in marine systems. This study thus provides a good basis to supplement the refinement of marine biogeochemical models of Cu, the establishment of a functional saltwater BLM, and the improvement of environmental risk assessments (i.e., WQC) of Cu in marine environments. As a result of this work, two papers have already been published, one is accepted, subject to minor changes, and three are under preparation

Review of the scientific and institutional capacity of small island developing states in support of a bottom-up approach to achieve sustainable development goal 14 targets

Capacity building efforts in Small Island Developing States (SIDS) are indispensable for the achievement of both individual and collective ocean-related 2030 agenda priorities for sustainable development. Knowledge of the individual capacity building and research infrastructure requirements in SIDS is necessary for national and international efforts to be effective in supporting SIDS to address nationally-identified sustainable development priorities. Here, we present an assessment of human resources and institutional capacities in SIDS United Nations (UN) Member States to help formulate and implement durable, relevant, and effective capacity development responses to the most urgent marine issues of concern for SIDS. The assessment highlights that there is only limited, if any, up-to-date information publicly available on human resources and research capacities in SIDS. A reasonable course of action in the future should, therefore, be the collection and compilation of data on educational, institutional, and human resources, as well as research capacities and infrastructures in SIDS into a publicly available database. This database, supported by continued, long-term international, national, and regional collaborations, will lay the foundation to provide accurate and up-to-date information on research capacities and requirements in SIDS, thereby informing strategic science and policy targets towards achieving the UN sustainable development goals (SDGs) within the next decade

Climate change driven effects on transport, fate and biogeochemistry of trace element contaminants in coastal marine ecosystems

Human activities and climate change substantially threaten coastal areas, impacting ecosystem functions, services, and human-wellbeing. Trace elements, from both natural and anthropogenic sources, can contaminate coastal regions, and at high concentrations may become toxic to marine biota. Climate change is likely to affect the sources, sinks and cycling of trace elements in coastal systems: for example, riverine runoff is set to increase as precipitation in the Arctic intensifies, and more frequent extreme floods are expected to activate previously deeply buried trace elements. Furthermore, changes in human activity under a warming climate, such as increased Arctic shipping and potential geoengineering projects such as ocean alkalinity enhancement, will likely introduce more trace elements to coastal ecosystems. Advancing our understanding of trace element cycling is at present limited by factors including lack of data coverage in the Global South, challenges in studying multi-stressor effects and ecosystem responses, lack of long-term data, and the difficulty in parametrizing robust models in coastal environments

Parameters Governing the Community Structure and Element Turnover in Kermadec Volcanic Ash and Hydrothermal Fluids as Monitored by Inorganic Electron Donor Consumption, Autotrophic CO2 Fixation and 16S Tags of the Transcriptome in Incubation Experiments

The microbial community composition and its functionality was assessed for hydrothermal fluids and volcanic ash sediments from Haungaroa and hydrothermal fluids from the Brothers volcano in the Kermadec island arc (New Zealand). The Haungaroa volcanic ash sediments were dominated by epsilonproteobacterial Sulfurovum sp. Ratios of electron donor consumption to CO2 fixation from respective sediment incubations indicated that sulfide oxidation appeared to fuel autotrophic CO2 fixation, coinciding with thermodynamic estimates predicting sulfide oxidation as the major energy source in the environment. Transcript analyses with the sulfide-supplemented sediment slurries demonstrated that Sulfurovum prevailed in the experiments as well. Hence, our sediment incubations appeared to simulate environmental conditions well suggesting that sulfide oxidation catalyzed by Sulfurovum members drive biomass synthesis in the volcanic ash sediments. For the Haungaroa fluids no inorganic electron donor and responsible microorganisms could be identified that clearly stimulated autotrophic CO2 fixation. In the Brothers hydrothermal fluids Sulfurimonas (49%) and Hydrogenovibrio/Thiomicrospira (15%) species prevailed. Respective fluid incubations exhibited highest autotrophic CO2 fixation if supplemented with iron(II) or hydrogen. Likewise catabolic energy calculations predicted primarily iron(II) but also hydrogen oxidation as major energy sources in the natural fluids. According to transcript analyses with material from the incubation experiments Thiomicrospira/Hydrogenovibrio species dominated, outcompeting Sulfurimonas. Given that experimental conditions likely only simulated environmental conditions that cause Thiomicrospira/Hydrogenovibrio but not Sulfurimonas to thrive, it remains unclear which environmental parameters determine Sulfurimonas’ dominance in the Brothers natural hydrothermal fluids

Aqueous copper bioavailability linked to shipwreck-contaminated reef sediments

Pollution from the grounding or sinking of ships can have long lasting effects on the recovery and dynamics of coastal ecosystems. Research on the impact of copper (Cu) pollution from the 2011 MV Rena shipwreck at the Astrolabe Reef (Otaiti), New Zealand, 5 years after the grounding, followed a multi-method and multi-disciplinary approach. Three independent measures of aqueous Cu using trace-element-clean-techniques substantiate the presence of high total, total dissolved (<2 µm) and elevated bioavailable Cu in the water column immediately above the aft section of the wreck where the highest sedimentary load of Cu was located. Intermittently elevated concentrations of strong Cu-binding ligands occurred in this location, and their binding strength was consistent with ligands actively produced by organisms in response to Cu induced stress. The recruitment of benthic invertebrates was modified at the high-Cu location. Taxonomic groups usually considered robust to pollution were restricted to this site (e.g. barnacles) or were the most abundant taxa present (e.g. foraminifera). Our results demonstrate that Cu-contaminated sediments can impose a persistent point source of Cu pollution in high-energy reef environments, with the potential to modify the composition and recovery of biological communities

Trace Metal Dynamics in Shallow Hydrothermal Plumes at the Kermadec Arc

Hydrothermal vents are a source of many trace metals to the oceans. Compared to mid-ocean ridges, hydrothermal vent systems at arcs occur in shallower water depth and are much more diverse in fluid composition, resulting in highly variable water column trace metal concentrations. However, only few studies have focused on trace metal dynamics in hydrothermal plumes at volcanic arcs. During R/V Sonne cruise SO253 in 2016/2017, hydrothermal plumes from two hydrothermally active submarine volcanoes along the Kermadec arc in the Southwest Pacific Ocean were sampled: (1) Macauley, a magmatic dominated vent site located in water depths between 300 and 680 m, and (2) Brothers, located between 1,200 and 1,600 m water depth, where hydrothermalism influenced by water rock interactions and magmatically influenced vent sites occur near each other. Surface currents estimated from satellite-altimeter derived currents and direct measurements at the sites using lowered acoustic Doppler current profilers indicate the oceanic regime is dominated by mesoscale eddies. At both volcanoes, results indicated strong plumes of dissolved trace metals, notably Mn, Fe, Co, Ni, Cu, Zn, Cd, La, and Pb, some of which are essential micronutrients. Dissolved metal concentrations commonly decreased with distance from the vents, as to be expected, however, certain element/Fe ratios increased, suggesting a higher solubility of these elements and/or their stronger stabilization (e.g., for Zn compared to Fe). Our data indicate that at the magmatically influenced Macauley and Brothers cone sites, the transport of trace metals is strongly controlled by sulfide nanoparticles, while at the Brothers NW caldera wall site iron oxyhydroxides seem to dominate the trace metal transport over sulfides. Solution stabilization of trace metals by organic complexation appears to compete with particle adsorption processes. As well as extending the generally sparse data set for hydrothermal plumes at volcanic arc systems, our study presents the first data on several dissolved trace metals in the Macauley system, and extends the existing plume dataset of Brothers volcano. Our data further indicate that chemical signatures and processes at arc volcanoes are highly diverse, even on small scales

Trace Metal Chemistry in the Water Column of the Angola Basin - A Contribution to the International GEOTRACES Program - Cruise No. M121, November 22, – December 27, 2015, Walvis Bay (Namibia) – Walvis Bay (Namibia)

Meteor Cruise M121 was dedicated to the investigation of the distribution of dissolved and particulate trace metals and their isotopic compositions (TEIs) in the full water column of the Angola Basin and the northernmost Cape Basin. A key aim was to determine the driving factors for the observed distributions, which includes the main external inputs, as well as internal cycling and ocean circulation. The research program of the cruise is official part of the international GEOTRACES program (www.geotraces.org) and cruise M121 corresponds to GEOTRACES cruise GA11. Subject of the cruise was the trace metal clean and contamination-free sampling of waters and particulates for subsequent analyses of the TEIs in the home laboratories of the national and international participants. Besides a standard rosette for the less contaminant prone metals, trace metal clean sampling was realized by using for the first time a new dedicated, coated trace metal clean rosette equipped with Teflon-coated GO-FLO bottles operated via a plastic coated cable from a mobile winch of GEOMAR Kiel. The particulate samples were collected under trace metal clean conditions using established in-situ pump systems operated from Meteor’s Aramid line. The cruise track led from Walvis Bay northwards along the West African margin until 3°S, then turned west until the Zero Meridian, which was followed southwards until 30°S. Then the cruise track turned east again until the Namibian margin was reached and then completed the near shore track northwards until Walvis Bay. The track crossed areas of major external inputs including dust from the Namib Desert and exchange with the west African continental margin and with the oxygen depleted shelf sediments of the Benguela upwelling, as well as with the plume of the Congo outflow, that was followed from its mouth northwards. Our investigations of internal cycling included the extremely high productivity associated with the Benguela Upwelling and the elevated productivity of the Congo plume contrasting with the extremely oligotrophic waters of the southeastern Atlantic Gyre. The links between TEI biogeochemistry and the nitrogen cycle forms an important aspect of our study. The major water masses contributing the Atlantic Meridional Overturning Circulation were sampled in order to investigate if particular TEI signatures are suitable as water mass tracers, in particular near the ocean margin and in the restricted deep Angola Basin. A total of 51 full water column stations were sampled for the different dissolved TEIs, which were in most cases accompanied by sampling for particulates and radium isotopes using the in-situ pumps. In addition, surface waters were continuously sampled under trace metal clean conditions using a towed fish and aerosol and rain samples were continuously collected

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

Copper speciation in different marine ecosystems around New Zealand

Copper (Cu) is an important bioactive trace metal in the marine environment, acting as an essential micronutrient for many marine species. However, it can also be harmful at elevated concentrations, triggering sub-lethal and toxic effects. During the last few decades, studies using electrochemical techniques have established that it is the particular chemical form of Cu, its so-called chemical speciation, and not its total concentration that controls the geochemical and biological behaviour and thus the bioavailability and toxicity of Cu in marine systems. The majority of dissolved Cu in the marine environment is strongly complexed by a heterogeneous mixture of Cu-binding organic ligands (L), reducing the free ionic Cu concentration ([Cu2+]) to femto- and picomolar levels. Free ionic Cu is generally considered the most bioavailable and thus the most beneficial or toxic form to marine organisms. Organic complexation reduces [Cu2+] in most marine systems to levels harmless, but above limitation, to many marine microorganisms. Measuring the inorganic, organic, and free Cu forms in the dissolved phase is critical to assess the fate (i.e., distribution, cycling, and reactivity) and the biological effects of Cu in the marine environment. However, the chemical speciation of Cu in natural saline waters is complex and is technically challenging to evaluate, resulting in cost-intensive and time-consuming analyses. Consequently, despite the recognised importance, little data exists for Cu speciation and Cu-binding ligands in the marine environment, and ligand sources and chemical identities are generally understudied. Additionally, environmental processes and factors influencing and controlling Cu speciation in marine systems are still poorly understood. As a result, four different marine systems (i.e., estuarine, coastal and open ocean waters, as well as a shallow low-temperature hydrothermal vent system) were studied around New Zealand in an effort to advance the current understanding of Cu speciation processes and Cu-binding ligands in the marine environment. Total dissolved Cu concentrations were analysed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), while Cu speciation was assessed with adsorptive cathodic stripping voltammetry (AdCSV) with salicylaldoxime (SA) as the competing ligand. It was found that more than 99.7 % of the total dissolved Cu (CuT) in the sampled marine waters was complexed with organic and inorganic (i.e., sulfides) ligands, demonstrating the decisive role of ligands in controlling Cu speciation, bioavailability, and toxicity in the marine environment. AdCSV detected only one L-class with concentrations of up to 47.4 nM for low CuT areas, such as the region of the Hauraki Gulf and White Island/Whakaari, and L-concentrations ([L]) of up to 114.8 nM for areas enriched in CuT like the Astrolabe Reef and the Whau Estuary. Conditional stability constants (logK) of the CuL-complexes were relatively uniform in the working areas and ranged from 11.4 to 13.6, suggesting a similar chemical nature and source of the prevalent Cu-binding ligands in the sampled marine environments. On the basis of the ligand distribution in the water column, with higher [L] in the photic zone and decreasing [L] with depth, Cu-binding organic ligands were suggested to predominantly originate from passive or active biological in-situ production of planktonic species or life stages. This assumption was supported by the 48 h bioassay in Chapter 6, during which Cu-stressed mussel embryos actively produced ligands, with logK values similar to those observed in the sampled natural saline waters, to mitigate the toxic effects of the Cu2+ in their environment. The current study also pointed out that the heterogeneous ligand pool in the marine environment might also include some organic ligands of terrestrial nature (i.e., humic substances (HS)), organic ligands derived from chemoautotrophic microorganisms, organic ligands formed abiotically under hydrothermal conditions, organic ligands which originate from yet unknown allochthonous and autochthonous sources, and in the case of hydrothermal systems can include substantial amounts of inorganic ligands such as sulfides. Further, [L] was always in excess of the [CuT] and as a result [Cu2+] were buffered to femto- and picomolar levels in the Hauraki Gulf region, White Island/Whakaari, and the Whau Estuary. These Cu2+ levels were below the toxicity threshold and above the deficiency threshold of Cu for many marine microorganisms. Only at the Astrolabe Reef, with highly elevated [CuT] in the vicinity of the MV Rena wreck, was the Cu complexation capacity of the natural organic ligands saturated, which led to toxic levels of [Cu2+] in the system. Consequently, the benthic invertebrate recruitment was lower, and different types of organisms were recruiting the high Cu2+ areas, leading to an alteration in the community diversity, structure, and functionality of the Astrolabe Reef. This output indicates the importance of organic ligand production by organisms as a strategy to maintain the delicate balance between ecosystem health and degradation. Temperature, pH, sample depth, chlorophyll a, particulate organic matter, and nutrient concentrations (i.e., nitrogen oxides, phosphate) had a poor correlation with Cu speciation parameters in the water column of the working areas. Salinity was found to increase Cu toxicity to M. galloprovincialis embryos, while higher dissolved organic carbon (DOC) concentrations decreased Cu toxicity to the mussel embryos. These outputs suggest that the biogeochemical cycling of Cu and its impact on marine life is intricate, dependent on the interactions between interrelated physical, chemical, and biological properties of the water column and the affected organism itself (e.g., ligand production, osmoregulation, and ionoregulation). This complexity precludes a generalisation of Cu speciation, bioavailability, and toxicity for the marine environment and thus highlights the urgent need to develop a site-specific saltwater Biotic Ligand Model (BLM) to assure adequate protection of aquatic life in various marine systems. Further, one of the most interesting findings of this thesis was that DOC and ligand quality (i.e., competition of several metals for the same ligand binding sites (non-specific metal binding affinities) or multidentate binding) were significantly more important in determining Cu bioavailability and toxicity in the sampled natural marine environments relative to DOC and ligand quantity. This finding highlights the necessity to elucidate the sources and chemical natures of organic Cu-binding ligands in order to improve the current understanding of the biogeochemical behaviour of Cu in marine systems. Moreover, it was demonstrated that the excessive Cu-loss during laboratory-based bioassays owing to container adsorption and bioaccumulation processes of the test organisms, together with the detoxification effect of extracellular Cu, and the variability of intracellular Cu, can lead to a significant misunderstanding of Cu toxicity mechanisms and a misrepresentation of Cu toxicity to test organisms. This latter output questions the reliability of current marine water quality criteria (WQC), which were extrapolated from laboratory-based bioassay tests that did not account for the Cu-loss in solution under laboratory conditions. Overall, the results from this study added to the body of current knowledge about Cu speciation, bioavailability, and toxicity in marine systems. This study thus provides a good basis to supplement the refinement of marine biogeochemical models of Cu, the establishment of a functional saltwater BLM, and the improvement of environmental risk assessments (i.e., WQC) of Cu in marine environments. As a result of this work, two papers have already been published, one is accepted, subject to minor changes, and three are under preparation