The effect of olivine in the tropical coral Montipora digitata: toxicological assessment and resilience to thermal stress

• Autor(a) principal: Latães, Ana Catarina Estima
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/30818
• topic: Scleractinia; Bleaching; Coral reef; Olivine mineral; Photosynthetic efficiency; Oxidative stress; Cellular energy allocation; Global warming; SEM

The future of coral reefs is already being shaped by the resilience, or lack of it, of different species to climate change. Corals are currently undergoing a major ecological threat as result of ocean warming and acidification and anthropogenic activities. Marine protected areas and reduced carbon emissions are certainly relevant although likely insufficient to preserve this ecosystem. Therefore, additional conservation strategies are required. Olivine weathering, proposed as a CO2 removal strategy, is expected to increase seawater alkalinity while consuming CO2 from the atmosphere. Although verified the potential of increase pH values and alkalinity, the impact on marine organisms and ecosystem is still to be understood. Our study aimed to evaluate olivine exposure effects on tropical coral Montipora digitata, assessing molecular biomarkers of oxidative stress and damage and metabolic profiles, as well as photosynthetic efficiency, coral growth, pH and dissolved oxygen variations. Firstly, our study assessed sub-lethal effects of different olivine concentrations, 6.00, 9.00, 13.50, 20.25, 30.38, 45.56, 68.35 and 102.5 mg L-1 under an acute experiment of 96h. Primary results did not show a general dose-response tendency, although photosynthetic efficiency was impaired for increasing concentrations. HSP70 levels and protein content decreased for higher concentrations, while lipid content showed higher values as well as pH and DO. A second experiment was performed assessing chronic exposure effects on M. digitata to a concentration of 20.25 mg L-1 of olivine sand, of which we can conclude that a long-term exposure to olivine facilitates M. digitata relative growth and photosynthetic efficiency as well as significantly higher pH values. M. digitata experienced moderate oxidative stress efficiently tackled by antioxidant enzymes and a higher relative growth rate through the expense of tissue lipid content, but no additional energy demands to maintain defence mechanisms or metabolic activity. Additionally, coral macrostructures were not affected by olivine exposure. The final stage of this study aimed to assess biological responses of the coral M. digitata to increase temperature (30 ºC) for 24h, while exposed to 20.25 mg L-1 of olivine sand. Besides, we evaluated if previous olivine exposure enhances coral resilience to rising temperatures. Overall, biological response of M. digitata, associated with antioxidant pathways and cellular energy allocation and consumption was not indicative of induced thermal stress. Photosynthetic efficiency exhibited significantly higher values when exposed to olivine at 30 ºC, although being impaired in both treatments at the higher temperature. Therefore, we cannot conclude that olivine exposure enhances resilience mechanisms in the coral M. digitata whilst abnormal temperatures.