{"id":{"repo_id":"unsw","oai_identifier":"oai:unsworks.library.unsw.edu.au:1959.4/108254"},"canonical_url":"https://search.dev.ndltd.org/etd/unsw/oai:unsworks.library.unsw.edu.au:1959.4/108254","repository":{"repo_id":"unsw","name":"University of New South Wales","base_url":"https://unsworks.unsw.edu.au/oai/provider"},"display":{"title":"Potent but forgotten: nitrous oxide contributions by an ascidian on warming reefs","abstract":"Increasing emissions of greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are driving global climate change and greatly impacting ecosystems. Although N2O has approximately 300 times the warming potential of carbon dioxide, mitigation strategies are lagging in comparison, and our understanding of natural production sources is somewhat limited, especially in the ocean. Coastal zones are widely recognised as hotspots of N2O production, especially in sediments within estuarine and upwelling systems. However, recent studies suggest that marine filter feeders are also important producers of N2O, with only a limited number of taxa investigated for their N2O potential. This thesis uses an interdisciplinary lens to study coastal N2O production in a warming world, linking emerging sources of microbial N2O production on temperate reefs with their ecological implications and quantifying general levels of public awareness about N2O via a media analysis. I focus on the habitat-forming ascidian Herdmania grandis, which I show is increasing in abundance on warming temperate reefs where carbon-capturing kelp forests have declined. My findings reveal that H. grandis’ microbiota produces the most N2O under present-day summer extreme temperatures compared to winter and predicted summer extremes. By combining in situ ascidian densities with spatial modelling of warming reefs, I found that H. grandis-dominated reefs may already be producing more N2O than adjacent estuaries, which are a recognised source of coastal N2O which are included in greenhouse gas budgets. I characterised the microbiome of H. grandis to identify potential microbial contributors to N2O production. H. grandis hosts distinct body-section specific microbial communities, which are dominated by two previously undescribed microorganisms that were present across all ascidians. Warming altered H. grandis’ section-specific microbiomes and I found large relative abundances of ammonia oxidising archaea on H. grandis’ exterior, suggesting a possible pathway for N2O production. Next, I found that H. grandis aggregations support abundant epibiota assemblages with comparable biodiversity to kelp forests, demonstrating their importance as habitat-formers on temperate reefs. I show that the presence of these epibiota does not influence H. grandis’ N2O production. Finally, given that public awareness of N2O is crucial for mitigation efforts, I also examined media coverage of this greenhouse gas across six media outlets. I found that media coverage of N2O was significantly lower than the coverage of CO2 and CH4 over the last 25 years. Articles that mentioned N2O generally reflected the broader science on climate change but rarely elaborated on N2O’s role in it specifically. Given the role of media coverage in shaping public concern, this relative silence on N2O as a greenhouse gas is problematic. Together, these findings show that although climate-mediated shifts to H. grandis-dominated ecosystems support high levels of epifaunal biodiversity, they are also generating an overlooked source of coastal N2O.","abstract_html":"Increasing emissions of greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are driving global climate change and greatly impacting ecosystems. Although N2O has approximately 300 times the warming potential of carbon dioxide, mitigation strategies are lagging in comparison, and our understanding of natural production sources is somewhat limited, especially in the ocean. Coastal zones are widely recognised as hotspots of N2O production, especially in sediments within estuarine and upwelling systems. However, recent studies suggest that marine filter feeders are also important producers of N2O, with only a limited number of taxa investigated for their N2O potential. This thesis uses an interdisciplinary lens to study coastal N2O production in a warming world, linking emerging sources of microbial N2O production on temperate reefs with their ecological implications and quantifying general levels of public awareness about N2O via a media analysis. I focus on the habitat-forming ascidian Herdmania grandis, which I show is increasing in abundance on warming temperate reefs where carbon-capturing kelp forests have declined. My findings reveal that H. grandis’ microbiota produces the most N2O under present-day summer extreme temperatures compared to winter and predicted summer extremes. By combining in situ ascidian densities with spatial modelling of warming reefs, I found that H. grandis-dominated reefs may already be producing more N2O than adjacent estuaries, which are a recognised source of coastal N2O which are included in greenhouse gas budgets. I characterised the microbiome of H. grandis to identify potential microbial contributors to N2O production. H. grandis hosts distinct body-section specific microbial communities, which are dominated by two previously undescribed microorganisms that were present across all ascidians. Warming altered H. grandis’ section-specific microbiomes and I found large relative abundances of ammonia oxidising archaea on H. grandis’ exterior, suggesting a possible pathway for N2O production. Next, I found that H. grandis aggregations support abundant epibiota assemblages with comparable biodiversity to kelp forests, demonstrating their importance as habitat-formers on temperate reefs. I show that the presence of these epibiota does not influence H. grandis’ N2O production. Finally, given that public awareness of N2O is crucial for mitigation efforts, I also examined media coverage of this greenhouse gas across six media outlets. I found that media coverage of N2O was significantly lower than the coverage of CO2 and CH4 over the last 25 years. Articles that mentioned N2O generally reflected the broader science on climate change but rarely elaborated on N2O’s role in it specifically. Given the role of media coverage in shaping public concern, this relative silence on N2O as a greenhouse gas is problematic. Together, these findings show that although climate-mediated shifts to H. grandis-dominated ecosystems support high levels of epifaunal biodiversity, they are also generating an overlooked source of coastal N2O.","abstract_has_math":false,"creators":["Dindar, Zuhairah"],"institution":"UNSW, Sydney","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2026,"date_issued":"2026","date_published":"2026","updated_at":"2026-07-24T05:33:43Z","subjects":["climate change","nitrogen cycling","marine invertebrate","greenhouse gas","anzsrc-for: 31 BIOLOGICAL SCIENCES"],"languages":["en"],"rights":["open access","CC BY 4.0","free_to_read"],"rights_urls":["https://purl.org/coar/access_right/c_abf2","https://creativecommons.org/licenses/by/4.0/"],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://doi.org/10.26190/unsworks/32500"],"render_values":[{"text":"https://doi.org/10.26190/unsworks/32500","href":"https://doi.org/10.26190/unsworks/32500","code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/1959.4/108254","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Dindar, Zuhairah"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2026"]},{"key":"dc:publisher","label":"Institution","values":["UNSW, Sydney"]},{"key":"dc:type","label":"Dc Type","values":["doctoral thesis","http://purl.org/coar/resource_type/c_db06"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["climate change","nitrogen cycling","marine invertebrate","greenhouse gas","anzsrc-for: 31 BIOLOGICAL SCIENCES"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["open access","https://purl.org/coar/access_right/c_abf2","CC BY 4.0","https://creativecommons.org/licenses/by/4.0/","free_to_read"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/1959.4/108254","https://unsworks.unsw.edu.au/bitstreams/3f4f0655-2878-4d85-98ba-30373fb2366a/download","https://doi.org/10.26190/unsworks/32500"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Increasing emissions of greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are driving global climate change and greatly impacting ecosystems. Although N2O has approximately 300 times the warming potential of carbon dioxide, mitigation strategies are lagging in comparison, and our understanding of natural production sources is somewhat limited, especially in the ocean. Coastal zones are widely recognised as hotspots of N2O production, especially in sediments within estuarine and upwelling systems. However, recent studies suggest that marine filter feeders are also important producers of N2O, with only a limited number of taxa investigated for their N2O potential. This thesis uses an interdisciplinary lens to study coastal N2O production in a warming world, linking emerging sources of microbial N2O production on temperate reefs with their ecological implications and quantifying general levels of public awareness about N2O via a media analysis. I focus on the habitat-forming ascidian Herdmania grandis, which I show is increasing in abundance on warming temperate reefs where carbon-capturing kelp forests have declined. My findings reveal that H. grandis’ microbiota produces the most N2O under present-day summer extreme temperatures compared to winter and predicted summer extremes. By combining in situ ascidian densities with spatial modelling of warming reefs, I found that H. grandis-dominated reefs may already be producing more N2O than adjacent estuaries, which are a recognised source of coastal N2O which are included in greenhouse gas budgets. I characterised the microbiome of H. grandis to identify potential microbial contributors to N2O production. H. grandis hosts distinct body-section specific microbial communities, which are dominated by two previously undescribed microorganisms that were present across all ascidians. Warming altered H. grandis’ section-specific microbiomes and I found large relative abundances of ammonia oxidising archaea on H. grandis’ exterior, suggesting a possible pathway for N2O production. Next, I found that H. grandis aggregations support abundant epibiota assemblages with comparable biodiversity to kelp forests, demonstrating their importance as habitat-formers on temperate reefs. I show that the presence of these epibiota does not influence H. grandis’ N2O production. Finally, given that public awareness of N2O is crucial for mitigation efforts, I also examined media coverage of this greenhouse gas across six media outlets. I found that media coverage of N2O was significantly lower than the coverage of CO2 and CH4 over the last 25 years. Articles that mentioned N2O generally reflected the broader science on climate change but rarely elaborated on N2O’s role in it specifically. Given the role of media coverage in shaping public concern, this relative silence on N2O as a greenhouse gas is problematic. Together, these findings show that although climate-mediated shifts to H. grandis-dominated ecosystems support high levels of epifaunal biodiversity, they are also generating an overlooked source of coastal N2O."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Potent but forgotten: nitrous oxide contributions by an ascidian on warming reefs"]}]}],"canonical_facts":{"dc:creator":["Dindar, Zuhairah"],"dc:date":["2026"],"dc:description":["Increasing emissions of greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are driving global climate change and greatly impacting ecosystems. Although N2O has approximately 300 times the warming potential of carbon dioxide, mitigation strategies are lagging in comparison, and our understanding of natural production sources is somewhat limited, especially in the ocean. Coastal zones are widely recognised as hotspots of N2O production, especially in sediments within estuarine and upwelling systems. However, recent studies suggest that marine filter feeders are also important producers of N2O, with only a limited number of taxa investigated for their N2O potential. This thesis uses an interdisciplinary lens to study coastal N2O production in a warming world, linking emerging sources of microbial N2O production on temperate reefs with their ecological implications and quantifying general levels of public awareness about N2O via a media analysis. I focus on the habitat-forming ascidian Herdmania grandis, which I show is increasing in abundance on warming temperate reefs where carbon-capturing kelp forests have declined. My findings reveal that H. grandis’ microbiota produces the most N2O under present-day summer extreme temperatures compared to winter and predicted summer extremes. By combining in situ ascidian densities with spatial modelling of warming reefs, I found that H. grandis-dominated reefs may already be producing more N2O than adjacent estuaries, which are a recognised source of coastal N2O which are included in greenhouse gas budgets. I characterised the microbiome of H. grandis to identify potential microbial contributors to N2O production. H. grandis hosts distinct body-section specific microbial communities, which are dominated by two previously undescribed microorganisms that were present across all ascidians. Warming altered H. grandis’ section-specific microbiomes and I found large relative abundances of ammonia oxidising archaea on H. grandis’ exterior, suggesting a possible pathway for N2O production. Next, I found that H. grandis aggregations support abundant epibiota assemblages with comparable biodiversity to kelp forests, demonstrating their importance as habitat-formers on temperate reefs. I show that the presence of these epibiota does not influence H. grandis’ N2O production. Finally, given that public awareness of N2O is crucial for mitigation efforts, I also examined media coverage of this greenhouse gas across six media outlets. I found that media coverage of N2O was significantly lower than the coverage of CO2 and CH4 over the last 25 years. Articles that mentioned N2O generally reflected the broader science on climate change but rarely elaborated on N2O’s role in it specifically. Given the role of media coverage in shaping public concern, this relative silence on N2O as a greenhouse gas is problematic. Together, these findings show that although climate-mediated shifts to H. grandis-dominated ecosystems support high levels of epifaunal biodiversity, they are also generating an overlooked source of coastal N2O."],"dc:format":["application/pdf"],"dc:identifier":["http://hdl.handle.net/1959.4/108254","https://unsworks.unsw.edu.au/bitstreams/3f4f0655-2878-4d85-98ba-30373fb2366a/download","https://doi.org/10.26190/unsworks/32500"],"dc:language":["en"],"dc:publisher":["UNSW, Sydney"],"dc:rights":["open access","https://purl.org/coar/access_right/c_abf2","CC BY 4.0","https://creativecommons.org/licenses/by/4.0/","free_to_read"],"dc:subject":["climate change","nitrogen cycling","marine invertebrate","greenhouse gas","anzsrc-for: 31 BIOLOGICAL SCIENCES"],"dc:title":["Potent but forgotten: nitrous oxide contributions by an ascidian on warming reefs"],"dc:type":["doctoral thesis","http://purl.org/coar/resource_type/c_db06"]},"updated_at":"2026-07-24T05:33:43Z"}