Teses/Dissertações reconhecidas pela UMa - Portaria 43-2020
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- Assessing the extent and impact of plastic pollution in coral reefsPublication . Vered, Gal; Shenkar, NoaDespite the growing awareness of the harmful effects, the continuous increase in plastic influx into natural environments still poses a constant threat, endangering unique marine ecosystems such as coral reefs. These reefs, which are essential ecologically and sustain livelihoods for over a billion people worldwide, face severe degradation due to anthropogenic activities, climate change and the pervasive issue of plastic pollution. Plastic enters the oceans through various land- and sea-based human activities, breaking down into microplastics and releasing chemical additives into the environment. Marine plastic debris has detrimental effects on corals, increasing their vulnerability to pathogens and causing issues like entanglement, suffocation and the ingestion of microplastics, resulting in energy loss. Additionally, plastic additives leaching into the environment can harm marine organisms, with chemicals such as bisphenols and phthalates disrupting endocrine systems. The primary motivation of my research was to address the main knowledge gaps identified by the United Nations Environment Programme concerning plastic pollution in coral-reef ecosystems. I achieved this by conducting controlled experiments and comprehensive field surveys, seeking to understand the extent and impact of plastic pollution in coral reefs. My research encompasses an examination of the effects of plastic additives on coral reef organisms; the characterization of plastic debris levels in the Gulf of Aqaba; and an exploration of plastic additives in coral-reef invertebrates residing on natural substrates compared to those residing on plastic debris. The findings from my study contribute to the development of a comprehensive understanding of marine plastic pollution and its implications for coral-reef ecosystems. In Chapter 1, I examine the reproductive products of four tropical coral-reef invertebrates exposed to environmentally-relevant concentrations in seawater of four prevalent plastic additives: dibutyl phthalate (DBP), dimethyl phthalate (DMP), 4 nonylphenol (4-NP) and bisphenol A (BPA), as well as to 10 3 higher laboratory concentrations of these four plastic additives. The findings reveal that apart from the -NP on the settlement of the soft coral Rhytisma fulvum, none of the other tested materials demonstrated a significant effect on the exposed organisms at environmentally relevant concentrations in the seawater. Regarding the high laboratory concentrations: the 4-gnificant negative effects on all the success in the solitary ascidian Herdmania momus, up to its complete failure to reproduce; ad a significant negative effect on planulae settlement of the stony coral Stylophora pistillata. The study's findings demonstrate the negative and selective effects of plastic additives on the development and reproduction of coral-reef organisms; and, specifically, the significant effect found following exposure to 4-NP. Consequently, if we wish to fully understand the impact of these contaminants on this endangered ecosystem, their actual concentrations within the living organism tissues need to be determined in order to produce relevant risk assessments for brooding coral species. The Gulf of Aqaba in the northern Red Sea is considered a potential coral-reef refuge from climate change. However, it is subjected to increasing levels of plastic contamination. In Chapter 2, I characterized the levels of benthic plastic debris, microplastics and plasticizers within the coral 2 years. I found that concentrations of benthic plastic debris lay within the level of the reported data from other tropical coral reefs, with boating and fishing debris comprising the most abundant categories. Unlike other studies that have investigated the relationship between depth and the extent of plastic pollution, I found that the deep mesophotic reefs featured significantly higher levels of benthic plastic debris compared to the shallower concentrations to those reported for the central Red Sea surface seawater, with none of the studied plasticizers exceeding the limits of quantification. These findings provide an important scientific database for developing regional policies and management strategies for battling plastic pollution and making the reefs of the northern Red Sea a coral refuge protected from both global and local anthropogenic stressors. In Chapter 3, I explore the differences in the presence of plastic additives among coral reef invertebrates, particularly by comparing organisms residing on natural substrates with those on plastic debris. The connection between the occurrence of plastic additives in corals and encrusting invertebrates residing on plastic debris has not been explored to date, nor contrasted with those residing on natural substrates. My analytical approach involved utilizing Accelerated Solvent Extraction (ASE), Gas Chromatography-Mass Spectrometry (GCMS), and High-Performance Liquid Chromatography coupled to both UV and Mass Spectrometry (HPLC/UV/MS). These methodologies were applied to explore the occurrence of seven targeted plastic additives in samples of three prevalent coral-reef invertebrate species: Stylophora pistillata, Rhytisma fulvum and Crella cyathophora, collected from both a protected reef within a marine nature reserve and an adjacent reef outside the reserve. The study not only scrutinized the presence of plastic additives but also investigated potential patterns across various species, substrates and sites. My findings revealed the widespread presence of plastic additives in 52% of the examined organisms, encompassing all the studied species and substrates, with Dibenzylamine and bis (2 ethylhexyl) phthalate (DEHP) emerging as the only detected compounds. Statistical analyses indicated no significant difference in their presence between the natural substrate and plastic debris. However, a statistically significant difference was observed in pollution levels between sites, with the protected reef site exhibiting lower contamination. Notably, R. fulvum within the marine reserve demonstrated significantly reduced pollution levels compared to its counterparts in the unprotected adjacent reef. This underscores the protective role of marine reserves in mitigating the impact of chemical pollutants on coral reef ecosystems. The findings from this research add to the growing body of evidence regarding the widespread presence of plastic-related chemicals, and highlight the protective role of marine reserves in mitigating the impact of chemical pollutants on coral-reef ecosystems. The data acquired and presented in my dissertation contribute to promoting a global understanding of the extent and impact of plastic pollution on coral-reef ecosystems. They provide essential support for the science-based management of marine plastic pollution and, consequently, may play a crucial role in the preservation of coral reefs.