University of Tasmania
Serra_Gonçalves_whole_thesis.pdf (4.48 MB)

Assessing temporal trends of marine debris and the effectiveness of individual plastic debris mitigation strategies at a national and local level in Australia

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Version 2 2023-12-21, 00:34
Version 1 2023-05-27, 19:48
posted on 2023-12-21, 00:34 authored by Ana Catarina Serra-Gonçalves

Plastic pollution is an increasing threat to our environment, being of particular concern in coastal and marine ecosystems, where it represents 60-80% of the marine litter. Plastic debris is expected to have long lasting negative, if not permanent or irreversible, consequences for ecosystems. These particles are widely documented to affect habitats and wildlife (more than 1450 marine species), economies, and industries.
Community science plays a crucial role in addressing environmental issues that have impact at an international scale, such as marine pollution, by providing not only large datasets at a temporal and geographical scale but also by engaging the communities and raising public awareness. The Tangaroa Blue Foundation coordinates the Australian Marine Debris Initiative (AMDI), an established network of communities, schools, industries, government agencies, and individuals (national and international) who aim to quantify and reduce marine debris in our communities and oceans. More than a decade of community-driven data collected through AMDI (primarily through beach clean-ups) has identified areas of high debris accumulation and problematic debris types. The AMDI dataset can be used at local, state, national, and international levels to identify items of significant concern and the potential sources can be linked.
Additionally, due to the diversity of sources responsible for plastic pollution in our environment (e.g., sewage, storm-water outfalls, fishing), the development of mitigation strategies is extremely complex; there is not one simple or unique solution. The applied strategies for reducing these differ according to the source, type of item, location, and stakeholders involved. A wide range of approaches have been applied at different organizational levels (e.g., international, national, local) worldwide to minimise and reduce plastic pollution in the environment, comprising legislative actions (e.g., international, and national policies) and non-legislative actions (e.g., behaviour change campaigns, organised clean-ups). However, consultation with scientists identified the development of regulatory strategies aimed at reducing and preventing debris at the source (Source Reduction Plans (SRPs)) as the most effective strategy. Globally, few data are available in relation to the challenges associated with the implementation of plastic debris mitigation strategies, such as policy considerations and costs. Most importantly, the effectiveness of individual strategies with a measurable outcome to reduce marine pollution has never been assessed rigorously. The key to any mitigation program is to determine if they actually work. Therefore, there is a need to measure the effectiveness of such programs with quantifiable pre- and post- implementation data.
The present thesis aims to assess (1) the temporal trends, seasonal patterns, and characteristics of marine macro-debris in Australia, (2) the effectiveness of mitigation strategies in reducing marine debris in the environment at a national level, using as a case study the international agreement MARPOL Annex V and, (3) the effectiveness of reduction strategies at a local level, using Source Reduction Plans as case studies.
1.This chapter analyses community-collected data from the AMDI Database between 2004 and 2020 to investigate whether the number and/or frequency of clean-ups translates into a local decrease and change in the composition of beach debris at ten Australian costal sites. Along the Australian coast, 48.27% of debris items recorded by the community were originated on land, 41.72% were plastic fragments (i.e.,from unknown sources) and only 10.01% originated from ocean-sources. There was a significant decline in the mass and number of debris items over the sampling period, likely a reflection, in part, of Tangaroa Blue Foundation’s and the Australian communities’ continuous efforts to remove and control marine pollution in Australia.
The International Convention for the Prevention of Pollution from Ships (MARPOL) is one of the most well-known and important agreements focused on reducing all types of ship-sourced marine pollution. The Annex V of the International Convention for the Prevention of Pollution from Ships (MARPOL 73/78) was established in 1978 to reduce solid waste pollution from ships. Revisions in 2011 (MEPC.201(62)) banned the discharge of these pollutants from all ships since 1 January 2013.
2.This chapter will evaluate whether if at a national level, MARPOL Annex V translated into a decrease in ship-sourced plastic debris on Australian beaches using AMDI data collected during 2006-2020, more specifically after the amendment made in 2013. There was a significant change over time in the density of fishing and shipping debris on Australian beaches; debris density increased up to 2013followed by a decrease until mid-2017. Although the new regulation started in January 2013, the decrease in density wasn’t recorded until one year later. The decline is only observed for 4 years, reinforcing the existence of lags between the implementation of international agreements and the corresponding potential reduction in debris in the environment.
In Australia, several SRPs have been trialled and applied by communities and the Tangaroa Blue Foundation. Each SRP follows the same implementation template and framework proposed by Tangaroa Blue Foundation: pre-SRP training workshops are held with members of the community, where the group identifies debris hotspots and problematic items in their area and is guided through the SRP implementation process (e.g., how to identify alternative products, how to approach different stakeholders). This allowed the communities to tackle different items, from consumer (e.g., cigarette butts) to industrial products (e.g., strapping bands). After SRP implementation, a second round of follow-up workshops are held to show the community how to monitor its progress by collecting post-SRP data (e.g., monthly beach-based monitoring).
3.This chapter assessed the effectiveness of two very different SRPs (plastic items consumed at the industrial and consumer level) between 2005-2021. We show a decline in strapping bands on beaches (-0.001 bands/day), and a reduction in the number of cigarette butts per spectator at a sporting venue after the implementation of the SRP, decreasing by more than 40%, from 0.11 (n=1) to 0.06 ± 0.05 (n = 18)cigarette butts per spectator. The outcomes differ depending on the type of SRP (i.e.,type of item targeted), possibly due to the different source (consumer vs industrial)and the respective SRP implementation mechanism. Therefore, we propose a framework to compile these into a SRPs online library made available to the community on the Blue Foundation website to guide the implementation of a successful Source Reduction Plan in other communities.
We link our results to discuss the best solution to stopping marine debris from entering the environment and the importance of community science activities as an important tool to avert marine debris in the environment. Our research findings provide strong evidence that international agreements and policies by themselves are not enough to solve the debris problem. Additionally, we were able to show the enormous potential of SRPs in effectively reducing specific items of debris in the environment, at industrial (e.g., strapping bands originating from the commercial fishing industry) and at consumer level (e.g., cigarette butts). We discuss future perspectives and solutions to reduce ocean-sourced litter inputs into the ocean and highlight the urgent need for action. Our findings will help to identify common aspects, challenges, and most importantly, keys to success in order to recommend and implement the best (i.e., most effective) plastic debris reduction strategies in the future.



  • PhD Thesis


xxiv, 245 pages


Institute for Marine and Antarctic Studies


University of Tasmania

Publication status

  • Unpublished

Event title


Date of Event (Start Date)


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Copyright 2022 the author.


Chapter 1 appears to be, in part, the equivalent of a pre-print version of an article published as: Serra-Gonçalves, C., Lavers, J. L., Bond, A. L., 2019. Global review of beach debris monitoring and future recommendations, Environmental science and technology, 53, 21 12158-12167. Chapter 3 appears to be the equivalent of a pre-print version of an article published as: Serra-Gonçalves, C., Lavers, J. L., Tait, H. L., Fischer, A. M., Bond, A. L., 2023. Assessing the effectiveness of MARPOL Annex V at reducing marine debris on Australia beaches, 191 114929. © 2023 The Author(s). Published by Elsevier Ltd. The article is an open access article under the CC BY-NC-ND license ( Chapter 4 appears to be the equivalent of a pre-print version of an article published as: Serra-Gonçalves, C., Lavers, J. L., Fischer, A. M., Tait, H., Bond, A. L., 2023. Stopping marine debris at the source: effectiveness of source reduction plans in Australia, Marine policy, 155, 105776. 597X/© 2023 The Author(s). Published by Elsevier Ltd. The article is an open access article under the CC BY license (

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