Impacts of plastic ingestion on seabirds
Creators: name: Puskic, Peter
Publisher: name: University of Tasmania
Year: 2024

description: The pollution of the marine environment with plastics, presents a global grand challenge which requires coordinated efforts to address. In order to galvanise a global response, the United Nations Agenda for Sustainable Development dedicated one of the 17 sustainable development goals (SDGs) to protecting and understanding the marine environment (SDG 14: Life Below Water). Specifically, SDG target 14.1 aims to, “prevent and significantly reduce marine pollution of all kinds, particularly from land-based activities, including marine debris.” Additionally, the UN Decade of Ocean Science for Sustainable Development (2021-2030) has dedicated one of its seven Ocean Outcomes to addressing marine pollution (including marine debris) as “A Clean Ocean: in which the sources of pollution are identified and removed.” To “understand and beat marine pollution” as encouraged by the Ocean Decade agenda, we will require collaborative and transdisciplinary approaches. Plastic has been adrift at sea for over 60 years. The interactions between these particles and animals is largely negative, often causing entanglement and ingestion injuries. When ingested, marine plastics and their associated chemicals may lead to sub-lethal impacts on an individual. Sub-lethal impacts do not always lead to mortality, but effect animal function and physiology. Typically, research on the impacts of plastic ingestion on animal health focuses on single responses or indicators of health such as body condition. Historically, seabirds have been the most studied organisms to assess the impacts of plastic on animal health. Seabirds, particularly procellariiformes (taxonomic order representing albatrosses, petrels, and shearwaters), are at high risk of marine debris ingestion. There is a growing body of research suggesting that chemicals associated with (but not intrinsic to) plastics leach inside the stomachs of seabirds, thus supporting the environmental management advantages of monitoring plastics within these species and signs of physiological health impacts. Typically, plastics consumed by and retained in the upper digestive tract of adult birds are offloaded to their chicks during the provisioning and chick rearing period, making pre-fledged birds ideal case studies in which to explore the potential impacts of plastic on their health, growth, and survival. While our knowledge is increasing at the endpoints of harm, such as mortality, there is a deficit of knowledge about the sub-lethal health consequences of ingested plastic at environmentally relevant background levels in the broader population. This thesis explores the impacts of plastic pollution across a range of organism functional levels, using two seabird species as a case study, Short-tailed Shearwater <i>(Ardenna tenurositris</i>) and Flesh-footed Shearwaters (<i>Ardenna carneipes</i>) both known to frequently ingest plastics. By partnering with yula mulaka (muttonbird harvesters) and parks managers on their breeding islands, we were able to explore the impacts of these environmentally relevant loads of plastic on the growth of healthy chicks and assess fledging survivability. In comparison, the Flesh-footed Shearwaters breeding on Lord Howe Island are among some of the largest consumers of marine plastic debris among seabirds globally. Previous studies on these birds suggest that plastics may impact both the development and survival of Flesh-footed Shearwater fledglings. This thesis applies a range of tools to assess the impact of plastics on two comparative shearwater species with varying amounts of plastic ingestion to further develop our understanding of the threat that marine debris poses to wildlife. Chapter one, a systematic literature review, acts as a broad introduction to this work and the relevant literature in the plastic pollution space. Specifically, it reviews the sub-lethal impacts of plastic ingestion on marine vertebrates (excluding fish). Of the 290 papers returned by our systematic literature search, just 34 studies quantified the impact of plastic on the health of their target species. The most common tools used to quantify health impact were visual observations and body condition indices. Tools that explore physiological indices, such as histopathology, fatty acid analysis, and molecular techniques appear in the literature as promising future techniques to further explore this issue and are therefore explored within the context of this thesis. Chapter two aims to determine if plastic negatively impacts an individual bird’s fledging success using a multiple-tool approach. Chapter two explores blood chemistry, trace element analysis, and broadscale growth metrics (using bird morphometrics as a proxy for seabird health). Examining over 500 shearwater chicks collected by traditional harvests, this chapter explores links between bird size and plastic load. It then examines the difference in plastic load between failed fledglings (collected as beach cast) and those collected as rescued animals by park managers and seabird rehabilitation clinics. Finally, chapter 2 compares data from this thesis to a literature search of plastic in seabird chicks globally to understand at what levels plastic loads may present a threat to other similar-size seabirds. We found beached birds to be smaller (by wing length and body mass) compared to rescued fledglings, with slightly higher plastic loads in the beach-cast birds. However, no significant links between bird size, trace element burden, or blood chemistry and plastic ingestion was found for this species. These results suggest that birds at this level of exposure may not be physically impacted by the ingestion of plastics. Chapter three assesses cellular level harm caused by the ingestion of plastic and associated chemicals through histopathological analysis. This chapter employs histopathology to assess tissue damage on the digestive, renal, and endocrine organs of shearwaters that have been exposed to plastic litter in their diet. In birds with extreme plastic loads (i.e., ~ 100 pieces), perforation and physical abrasion of the gastrointestinal tract could be seen through gross pathology. Nanoplastics (&lt;1mm) were identified in the proventriculus of shearwaters, confirming that our understanding of plastic loads at these smaller size ranges may be underestimated for seabirds, however, no host-response could be demonstrated in association to this plastic. Microplastic ingestion could not be linked to changes visible through histopathology of liver, kidney, muscle, or stomach in birds at this age and range of plastic exposure. The results of this analysis suggest the need to look at multiple stressors on wild animals (i.e., disease and parasites) to understand anthropogenic threats. &gt;&lt;1mm) were identified in the proventriculus of shearwaters, confirming that our understanding of plastic loads at these smaller size ranges may be underestimated for seabirds, however, no host-response could be demonstrated in association to this plastic. Microplastic ingestion could not be linked to changes visible through histopathology of liver, kidney, muscle, or stomach in birds at this age and range of plastic exposure. The results of this analysis suggest the need to look at multiple stressors on wild animals (i.e., disease and parasites) to understand anthropogenic threats. Finally, chapter four uses next generation, metagenomic sequencing to understand how the gut microbiome of seabirds may change in response to increased ingested plastic load. This work is the first to fully document the oral, cloacal and stomach microbial communities of both shearwaters and provides insights into how plastics may disrupt gut function if consumed in high quantities. We document a number of bacteria previously associated with flotsam plastic assemblages which have been described as harmful or pathogenic. We also detected a weak negative relationship with alpha abundance of bacteria plastics ingested by Short-tailed Shearwaters only. We suggest that our null-result regarding plastic ingestion and microbial community composition may also reflect the low incidences of plastics documented in the Flesh-footed Shearwaters in this particular study. This thesis is bookended by both a preface and discussion chapter. The preface was part of a major interdisciplinary project and has been published in the journal of Reviews in Fish Biology and Fisheries as part of the Future Seas 2030 special issue, Future Seas: Cleaner Seas. The discussion is intended to be a reflection on the multi-stakeholder, interdisciplinary approach to conducting this research. Together, this body of work acts as a comprehensive assessment of the impacts of plastics on seabird health across a range of health indicators and across a range of functional levels. This body of work acts as a comprehensive assessment of the impacts of plastics on seabird health across a range of health indicators and functional levels. Each chapter of this thesis employs a distinct multidisciplinary approach to understand the physiology of seabirds in relation to plastic ingestions with samples and data generated through many interdisciplinary partnerships. The findings from this thesis further our understanding of the complexities of seabird physiology and the various pathways in which plastic may interact with wildlife health.