Seabirds as monitors of marine plastic pollution

Small buoyant plastic items are one of the most pervasive and abundant marine pollutants. They pose significant environmental impacts, including threatening the health of marine life through plastic ingestion, necessitating efforts to reduce plastic leakage into the sea. To evaluate the effectiveness of mitigation strategies, it is essential to understand trends in marine plastic densities, types, and sources, which requires a reliable baseline for repeated assessments. While sea-surface net trawls are commonly used to monitor trends in small floating plastics at sea, they face several challenges. Seabirds, particularly petrels and albatrosses (order Procellariiformes), offer a practical alternative to net sampling as they often ingest and retain buoyant plastics encountered while foraging at sea, making them valuable indicators of this type of plastic pollution. However, few studies have thoroughly tested their utility. Larger species, such as albatrosses and giant petrels, typically ingest macroplastics items like bags, bottle lids, and fishery-related debris, which can often be traced back to specific sources. In contrast, smaller petrels, including storm petrels, prions, and shearwaters, tend to ingest smaller items like industrial pellets and fragments of larger plastic objects, whose sources are more challenging to identify. Due to their high propensity for ingesting plastics and their tendency to consume larger volumes, these smaller petrels may be particularly well- suited for monitoring ingested plastic loads over time. In Chapter 2, I assess trends in litter items collected at the nests of albatrosses and giant petrels breeding on Marion Island in the southwestern Indian Ocean, from 1996 to 2018. Temporal variation in litter composition and amounts were compared to data on Patagonian toothfish Dissostichus eleginoides fishing intensity in the area. Fishery-related litter abundance peaked during industry's height, declining in the following two decades. Other litter items increased over the last decade, when the most frequently recorded identifiable litter items were drink bottle lids from Indonesia. Long-distance drift of buoyant plastic items from Southeast Asia, mainly Indonesia, is a major source of litter to the western Indian Ocean. In Chapter 3, I assess the use of an indirect method to sample plastics ingested by seabirds by examining regurgitated Brown Skua Catharacta antarctica (Stercorariidae) pellets containing prey remains of petrels at Inaccessible Island in the central South Atlantic Ocean. I compare the size of plastics in skua pellets to those collected directly from seabird carcasses, to assess the validity of this method. I also compare the composition of plastics ingested within each seabird taxon to small buoyant plastics sampled with a neuston net, to understand how the ingested plastic compares with that found in the environment. I found that as a community, petrels reflected the composition of small buoyant plastics at sea, providing support for their use as biomonitors of marine plastic pollution. In Chapter 4, I assess how plastic loads in four petrels have changed from 1987 to 2018 in roughly decadal time periods and years. More than 3 700 regurgitated Brown Skua pellets, each containing the remains of a single petrel, indicated fluctuations in plastic loads between periods and years, but no overall clear trend was evident in any species. The number and proportions of industrial pellets among ingested plastics decreased over the study period, indicating that industry initiatives to reduce pellet leakage have been at least partly successful. In Chapter 5, I assess whether the size, mass, and polymer types of ingested plastic items have changed over the study period (1987 – 2018) to help interpret the results from Chapter 4. I found little change in the size and mass of ingested plastics since the 1980s. The ratio of polypropylene to polyethylene has increased consistently among hard fragments of user items over time. Overall, the limited change in plastic characteristics is consistent with the absence of clear trends in plastic loads over time (Chapter 4). In Chapter 6, which also serves as my synthesis, I investigate whether plastics sampled on beaches along the southern Cape coastline of South Africa from 1984 to 2023 exhibit the same trends in composition as small buoyant plastics ingested by petrels from 1987 to 2018. The findings show minimal changes in beached hard fragment sizes, with a recent increase in industrial pellet mass due to two major spills at sea off South Africa in 2017 and 2020. Polymer ratios in hard fragments mirrored those ingested by seabirds in the South Atlantic, indicating common influencing variables. More data are needed to understand the increase in the ratios of polypropylene to polyethylene over time, and how this may influence retention rates of plastics on the sea surface. In summary, this thesis demonstrates that sampling plastics ingested by seabirds provides a comprehensive assessment of marine litter composition and sources. Seabirds offer valuable insights into temporal trends in plastic loads and characteristics which align with variations observed in beached plastics. The lack of clear patterns in plastic loads over time suggests that initiatives to reduce the influx of plastics, and remove existing litter, may be preventing a rapid increase in the density of floating plastics at sea, despite the ongoing increase in global plastic production. However, the possible egestion of plastics by seabirds while out at sea, may also account for the lack of clear trends. More empirical data are needed to assess this, and how turnover rates of floating plastics will change under different plastic emission scenarios, to help interpret patterns in the loads and sizes of plastics in the marine environment. These insights are crucial for assessing the efficacy of mitigation strategies to reduce plastic waste leakage into the marine environment

Are high elevation crag lizards sensitive to climate change?

Crag lizards are restricted to montane areas where biota are strongly exposed to the effects of climate change. We investigated the factors shaping the distribution of Drakensberg crag lizards (Pseudocordylus melanotus melanotus; Cordylidae) by quantifying their elevational ranges, availability of shelter and prey as well as the thermal environment at three elevations. We recorded expected body temperatures using copper models of the lizards at each elevation in the field and in the laboratory, estimating the duration for which lizards must shelter from high temperatures. This correlated strongly with field observations of lizard activity during winter, spring and summer. Our models predicted that at lower elevations, lizards would shelter for longer periods each day, resulting in a marked reduction in time available for essential activities such as feeding and breeding, possibly explaining why these animals do not occur at lower elevations. The distribution and survival of these animals therefore appear to be impacted by the degree to which daytime temperatures limit their activity. Modelling future climate change scenarios at the high elevation site indicates that crag lizards would be resilient against small to moderate warming reflected by RCP4.5 climate change predictions, but populations are unlikely to persist under conditions predicted in the RCP8.5 scenario. This study is important as, unlike broader-scope studies that cannot quantify climate change impacts on individual species, we combine detailed field data with laboratory measurements and modelling of a single species to assess the ecological constraints to which crag lizards are exposed.The University of Pretoria and the National Research Foundation.https://onlinelibrary.wiley.com/journal/14429993hj2022Geography, Geoinformatics and MeteorologyPhysicsZoology and Entomolog

Birds of a feather eat plastic together: high levels of plastic ingestion in Great Shearwater adults and juveniles across their annual migratory cycle

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Robuck, A. R., Hudak, C. A., Agvent, L., Emery, G., Ryan, P. G., Perold, V., Powers, K. D., Pedersen, J., Thompson, M. A., Suca, J. J., Moore, M. J., Harms, C. A., Bugoni, L., Shield, G., Glass, T., Wiley, D. N., & Lohmann, R. Birds of a feather eat plastic together: high levels of plastic ingestion in Great Shearwater adults and juveniles across their annual migratory cycle. Frontiers in Marine Science, 8, (2022): 719721, https://doi.org/10.3389/fmars.2021.719721.Limited work to date has examined plastic ingestion in highly migratory seabirds like Great Shearwaters (Ardenna gravis) across their entire migratory range. We examined 217 Great Shearwaters obtained from 2008–2019 at multiple locations spanning their yearly migration cycle across the Northwest and South Atlantic to assess accumulation of ingested plastic as well as trends over time and between locations. A total of 2328 plastic fragments were documented in the ventriculus portion of the gastrointestinal tract, with an average of 9 plastic fragments per bird. The mass, count, and frequency of plastic occurrence (FO) varied by location, with higher plastic burdens but lower FO in South Atlantic adults and chicks from the breeding colonies. No fragments of the same size or morphology were found in the primary forage fish prey, the Sand Lance (Ammodytes spp., n = 202) that supports Great Shearwaters in Massachusetts Bay, United States, suggesting the birds directly ingest the bulk of their plastic loads rather than accumulating via trophic transfer. Fourier-transform infrared spectroscopy indicated that low- and high-density polyethylene were the most common polymers ingested, within all years and locations. Individuals from the South Atlantic contained a higher proportion of larger plastic items and fragments compared to analogous life stages in the NW Atlantic, possibly due to increased use of remote, pelagic areas subject to reduced inputs of smaller, more diverse, and potentially less buoyant plastics found adjacent to coastal margins. Different signatures of polymer type, size, and category between similar life stages at different locations suggests rapid turnover of ingested plastics commensurate with migratory stage and location, though more empirical evidence is needed to ground-truth this hypothesis. This work is the first to comprehensively measure the accumulation of ingested plastics by Great Shearwaters over the last decade and across multiple locations spanning their yearly trans-equatorial migration cycle and underscores their utility as sentinels of plastic pollution in Atlantic ecosystems.This project was supported by the NOAA Fisheries National Seabird Program and the Volgenau Foundation. AR acknowledges support from the National Oceanic and Atmospheric Administration Dr. Nancy Foster Scholarship Program (NOAA Award Number NA17NOS4290028), the Robert and Patricia Switzer Foundation, the STEEP Superfund Research Program (NIEHS Award Number P42ES027706), and the Oak Ridge Institute for Science and Education (ORISE) program. LB was funded by INCT-Mar COI and PQ Grant No. 311409/2018-0, both by the Brazilian National Research Council (CNPq). JS was funded by the National Science Foundation Graduate Research Fellowship program

The effect of long-term climate change on the vertebrate fauna of Mariepskop South Africa

Climate change is leading to loss of global and local biodiversity through changes in the ecology of fauna and flora. Changes in environmental temperature influence species distributional ranges. They respond by either migrating along with the shift in ecological zones or adapting to the new environmental conditions within a habitat. If neither adaptation nor migration is possible, local extinction of the species can result. This study was performed at Mariepskop mountain which served as the ideal environment for quantifying species distribution along an altitudinal gradient within different vegetation types. The information collected was used to quantify the factors shaping species distribution and to predict the fate of these species at Mariepskop with future climate change scenarios. In this study I identified vertebrate taxa with restricted distribution along the altitudinal gradient representing low, high and generalist species. Regional geographical distribution and temperature data were analysed to create geographical distribution and temperature profiles for each species. Local distribution data and temperature profiles created from data recorded at automated weather stations within the study area and long-term interpolated data were compared to the geographical profiles for each species. Habitat requirements at a geographical scale were investigated for each species and related to the local habitat selection rationale at Mariepskop. Quantifying vegetation types and land types in the study area I predicted the possible shifts in vegetation zones with future climate change. Using this rationale we predicted which species at Mariepskop were most likely to be affected by future temperature increases and to what extent. A detailed study focussing on the factors shaping the local restricted altitudinal distribution of the Drakensberg crag lizard (Pseudocordylus melanotus melanotus) to the highest altitudinal site was also performed. Factors investigated were suitable shelter and prey availability, ambient temperature conditions and operative temperatures recorded with copper lizard models. A behaviour study on focal lizards at the highest altitudinal sites was also performed to create diurnal activity pattern profiles for crag lizards. Activity profiles were related to temperature data and diurnal activity time budgets were calculated. We established that the restriction provided by the upper thermal limit of this species is the factor most likely responsible for limiting it to the highest altitudinal site. A temperature simulation model based on laboratory experiments and field data was designed to simulate future increased temperature scenarios at Mariepskop. It revealed a reduction in the diurnal activity time budget for P. m. melanotus with increased temperature. In summation we predicted that future climate change could affect three vertebrate species at Mariepskop due to shifts in vegetation zones. The Drakensberg crag lizard is however unlikely to be affected by a future 2?C increase in environmental temperature.Dissertation (MSc)--University of Pretoria, 2016.tm2016Zoology and EntomologyMScUnrestricte

Monitoring marine plastics – will we know if we are making a difference?

In the context of marine anthropogenic debris management, monitoring is essential to assess whether mitigation measures to reduce the amounts of waste plastic entering the environment are being effective. In South Africa, baselines against which changes can be assessed include data from the 1970s to the 1990s on microplastics floating at sea, on macro- and microplastic beach debris, and interactions with biota. However, detecting changes in the abundance of microplastics at sea is complicated by high spatial and temporal heterogeneity in net samples. Beach debris data are easier to gather, but their interpretation is complicated by the dynamic nature of debris fluxes on beaches and the increase in beach cleaning effort over time. Sampling plastic ingested by biota is a powerful approach, because animals that retain ingested plastic for protracted periods integrate plastics over space and time, but there are ethical issues to using biota as bioindicators, particularly for species that require destructive sampling (e.g. turtles, seabirds). Bioindicators could be established among fish and invertebrates, but there are technical challenges with sampling microplastics smaller than 1 mm. Fine-scale debris accumulation on beaches provides an index of macroplastic abundance in coastal waters, and offers a practical way to track changes in the amounts and composition of debris in coastal waters. However, upstream flux measures (i.e. in catchments, rivers and storm-water run-off) provide a more direct assessment of mitigation measures for land-based sources. Similarly, monitoring refuse returned to port by vessels is the best way to ensure compliance with legislation prohibiting the dumping of plastics at sea.&#x0D; Significance:&#x0D; &#x0D; Monitoring is required to assess whether mitigation measures to reduce waste plastics at sea are making a difference.&#x0D; Monitoring the leakage of plastic from land-based sources is best addressed on land (e.g. in storm drains and river run-off) before the plastic reaches the sea.&#x0D; Illegal dumping from ships is best addressed by monitoring the use of port waste reception facilities.&#x0D; Sampling plastic ingested by biota is a powerful approach, using fish and invertebrates as bioindicators for larger microplastic fragments.&#x0D; </jats:p