In recent years there has been growing environmental concern regarding ‘microplastics’: microscopic plastic granules, fibres and fragments, categorised as <1 or <5 mm diameter. Microplastics are manufactured to be of a microscopic size, or derive from the photo- and mechanical degradation and subsequent fragmentation of larger plastic litter. Microplastics debris has been identified in the water column and sediments of marine and freshwater ecosystems across the globe, although difficulties in sampling and isolating smaller particulates has resulted in the abundance of <333 µm microplastics being under-reported. Microplastics are bioavailable to a range of aquatic organisms, including fish, seabirds and benthic invertebrates, and can be trophically transferred. The consumption of plastic debris can result in gut blockages, heightened immune response and a loss of lipid reserves. The potential risk to food security, and thereby human health, has led regulators to call for better understanding of the fate and effects of microplastic debris on marine life. Here I tested the hypothesis that microplastics can be ingested by and may negatively impact upon zooplankton. Zooplankton encompass a range of aquatic animals that form a key trophic link between primary producers and the rest of the marine food web. I used a suite of feeding experiments, bio-imaging techniques and ecotoxicological studies to explore the interactions and impacts of polystyrene microplastics on marine zooplankton. My results demonstrate that a range of filter-feeding zooplankton taxa, including copepods and bivalve and decapod larvae, have the capacity to ingest microplastics. Microplastics significantly reduced algal feeding in the copepods Centropages typicus and Calanus helgolandicus. With prolonged microplastic exposure C. helgolandicus produced smaller eggs with reduced hatching success, and had reduced survival owing to declining energetic reserves. Microplastics egested by copepods significantly altered the properties and sinking rates of faecal pellets, with potential repercussions for marine nutrient flux. This investigative work highlights that microplastics pose a significant risk to the health of animals at the base of the marine food web.

Methods of studying the interaction between fish viruses with inanimate surfaces were developed and used to explore several variables. Viral hemorrhagic septicemia virus (VHSV) was used as the model virus. The EPC cell line, which is now known to be from Fathead Minnow, was used to detect the virus through the development of cytopathic effect (CPE); this allowed virus levels to be titrated and expressed as tissue culture infectious dose (TCID50). The labour and tedium of scoring hundreds of wells for CPE was overcome through the use of the fluorescent indicator dye, Alamar Blue, which is reduced by living cells and not by dead cells to yield a fluorescent product that can be measured as relative fluorescence units (RFUs) with a fluorescent microwell plate reader. Microsoft Excel 2007 was used to compare RFU values of wells and to create a scoring template in the computer program that allowed for easy summation of the total number of wells with infectious virus. With this system and as well as with conventional scoring, surface-virus interactions were studied in the following general way. Surfaces were incubated with a solution (L-15 with 2% fetal bovine serum or FBS) of virus, rinsed, and then incubated under various conditions, either wet or dry, before being evaluated for infectious virus. The transfer of viruses through their elution from surfaces is termed elution transfer (ET) and was investigated in two ways: agitated elution and static elution. Agitated elution was done through the repeated action of pipetting up and down on either glass or plastic surfaces with different eluting solutions. The best eluting solution was 2% FBS/L-15 and the worst was tissue culture grade water. Regardless of the eluting solution, no infectious virus could be removed by agitated elution from glass Petri dishes. Static elution was demonstrated through a two-compartment culture system linked by 3.0 m pores. L-15 with 2% FBS eluted VHSV from the surface of the top chamber to infect cells in the bottom chamber and from the surface of the bottom chamber to infect cells in the top chamber. The ability of different objects to carry infectious VHSV to a new culture vessel was investigated in a protocol termed object-associated transfer (OAT). The objects were incubated with VHSV, rinsed, and then incubated wet or dry for various periods before being transferred to EPC cultures. After up to ten days of wet incubation, pieces of glass, fishing line, plastic water bottle, and pop can were able to transfer infectious virus. In contrast, when the same objects were incubated dry, they were able to transfer VHSV after only one day of drying. Fishing hooks kept wet for a day were able to transfer VHSV but dry hooks had no capacity to transfer infectious virus. A third experimental protocol was used to detect infectious viruses on surfaces and involves the surface to cell transfer (SCT) of viruses. For this protocol, EPC cells were plated directly onto plastic or glass surfaces that previously had been exposed to virus, rinsed, and incubated dry or wet at various temperatures for up to 15 days. After 15 days being kept dry at 4 °C, infectious VHSV was still found to be present on both glass and plastic surfaces. At 14 °C and room temperature, the virus was found to survive longer on plastic than on glass, and at 26 °C both surfaces retained infectious VHSV for only one day of being dry. Survival time on plastic surfaces at different temperatures was compared for wet and dry incubation. VHSV kept on plastic surface in a dry state was more susceptible to temperature inactivation, with inactivation of the virus being detected clearly after 1 day 37 °C, 10 days at 26 °C, and 15 days at room temperature.

Methods of studying the interaction between fish viruses with inanimate surfaces were developed and used to explore several variables. Viral hemorrhagic septicemia virus (VHSV) was used as the model virus. The EPC cell line, which is now known to be from Fathead Minnow, was used to detect the virus through the development of cytopathic effect (CPE); this allowed virus levels to be titrated and expressed as tissue culture infectious dose (TCID50). The labour and tedium of scoring hundreds of wells for CPE was overcome through the use of the fluorescent indicator dye, Alamar Blue, which is reduced by living cells and not by dead cells to yield a fluorescent product that can be measured as relative fluorescence units (RFUs) with a fluorescent microwell plate reader. Microsoft Excel 2007 was used to compare RFU values of wells and to create a scoring template in the computer program that allowed for easy summation of the total number of wells with infectious virus. With this system and as well as with conventional scoring, surface-virus interactions were studied in the following general way. Surfaces were incubated with a solution (L-15 with 2% fetal bovine serum or FBS) of virus, rinsed, and then incubated under various conditions, either wet or dry, before being evaluated for infectious virus. The transfer of viruses through their elution from surfaces is termed elution transfer (ET) and was investigated in two ways: agitated elution and static elution. Agitated elution was done through the repeated action of pipetting up and down on either glass or plastic surfaces with different eluting solutions. The best eluting solution was 2% FBS/L-15 and the worst was tissue culture grade water. Regardless of the eluting solution, no infectious virus could be removed by agitated elution from glass Petri dishes. Static elution was demonstrated through a two-compartment culture system linked by 3.0 m pores. L-15 with 2% FBS eluted VHSV from the surface of the top chamber to infect cells in the bottom chamber and from the surface of the bottom chamber to infect cells in the top chamber. The ability of different objects to carry infectious VHSV to a new culture vessel was investigated in a protocol termed object-associated transfer (OAT). The objects were incubated with VHSV, rinsed, and then incubated wet or dry for various periods before being transferred to EPC cultures. After up to ten days of wet incubation, pieces of glass, fishing line, plastic water bottle, and pop can were able to transfer infectious virus. In contrast, when the same objects were incubated dry, they were able to transfer VHSV after only one day of drying. Fishing hooks kept wet for a day were able to transfer VHSV but dry hooks had no capacity to transfer infectious virus. A third experimental protocol was used to detect infectious viruses on surfaces and involves the surface to cell transfer (SCT) of viruses. For this protocol, EPC cells were plated directly onto plastic or glass surfaces that previously had been exposed to virus, rinsed, and incubated dry or wet at various temperatures for up to 15 days. After 15 days being kept dry at 4 °C, infectious VHSV was still found to be present on both glass and plastic surfaces. At 14 °C and room temperature, the virus was found to survive longer on plastic than on glass, and at 26 °C both surfaces retained infectious VHSV for only one day of being dry. Survival time on plastic surfaces at different temperatures was compared for wet and dry incubation. VHSV kept on plastic surface in a dry state was more susceptible to temperature inactivation, with inactivation of the virus being detected clearly after 1 day 37 °C, 10 days at 26 °C, and 15 days at room temperature.

In the United Nations Convention on the Law of the Sea, the environmental protection of the marine environment was first addressed in a comprehensive manner on an international level. However, the Convention distinguishes between four different sorts of pollution depending on which source the pollution originates from. Still, one of these sources play a more crucial role in the protection of the marine environment than the other since that source is estimated to stand for 80 percent of all the marine pollution; namely marine pollution from land-based sources. As the throw-away culture has led to products being disposed of at a faster rate than ever before, in particular plastic products, the amount of land-based debris has also substantially increased over the last decades. This increased disposal rate of products in combination with poor waste treatment has consequently led to many kinds of wastes ending up in the ocean and causing severe harm, not only to the marine environment and its living species, but also to humans that eat the fish and use the many other ecosystem services of the Sea. In this thesis, some prominent international conventions on marine pollution from land-based sources are examined; namely the United Nations Convention on the Law of the Sea, the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal, as well as the Stockholm Convention on Persistent Organic Pollutants. To achieve United Nations Sustainable Development Goal number 14.1 to significantly reduce marine pollution from land-based sources by 2025, this thesis claims that international laws addressing this sort of pollution need to be implemented. Moreover, this thesis rests on the belief that regional implementation is a crucial component in making states align with international law. However, while regional implementation has been ambitious in the European Union Law, many regions still lack enforceable frameworks that aim to reduce and prevent marine pollution from land-based sources.