Publicação

Coral reef microbiota and the potential of humic substances to improve reef resilience

Detalhes bibliográficos
Resumo:	Coral reef ecosystems are renowned for their biodiversity and for their socioeconomic and ecological significance. In recent decades, however, the ecological balance within coral reefs has been disrupted leading to large-scale loss of coral reef habitat. El Niño Southern Oscillation (ENSO)-induced elevated temperatures and intense UVB radiation have resulted in global coral bleaching events. Meanwhile, large-scale urbanisation of coastal areas has further degraded reef ecosystems at local scales by increasing the inflow of nutrients and pollutants, and favoring the proliferation of benthic cyanobacterial mats over corals. To effectively protect and restore coral reefs, it is crucial to improve our understanding of these emerging microbial colonizers. Additionally, it is of paramount importance to identify local factors, which influence coral reef microbial communities and reef resilience. Previous observational studies have suggested that terrestrially-derived compounds, particularly humic substances (HS), can protect coral reefs from thermal stress. However, no study has, until now, systematically tested this hypothesis. This thesis addresses this gap by investigating 1) the diversity, distribution and biofouling activity of benthic cyanobacterial mats, 2) the suitability of an experimental life support system (ELLS) to study coral reef microbial communities under controlled conditions, 3) the effects of terrestriallyderived HS on coral reef microbial communities and 4) the potential of HS in augmenting coral reef resilience to elevated temperatures and UVB radiation. The goals were achieved by employing a comprehensive approach that combined field surveys, the development and subsequent utilization of an experimental life support system (ELSS), and chemical and microbial community analyses. Field surveys were performed to document and sample benthic cyanobacterial mats at reefs surrounding the island of Koh Tao (Gulf of Thailand). To obtain information on the bacterial community composition, samples were analysed using 16S rRNA gene high-throughput sequencing (HTS). The results of this study are discussed in chapter two and showed that mat colour (morphotype), substrate type and geographic location only explained a small part of the total variation in bacterial composition. Proteobacteria, Cyanobacteria, Bacteroidetes and Planctomycetes were the four most abundant phyla and occurred in all samples. Mats, moreover, were composed of potentially toxin producing bacteria, including the cyanobacterial genera Blennothrix, Hormoscilla, and the related proteobacterial species Vibrio harveyi and Vibrio neptunius. These findings improved our understanding of cyanobacterial mat ecology, which will help to guide conservation efforts aimed at improving coral reef health, especially in the light of future climate conditions which have been predicted to enhance mat proliferation at the expense of coral growth. In chapter three, the ELSS is described in detail. The system consisted of 32 independent microcosms, each containing coral reef sediment, artificial seawater, and five reef organisms. These included two hard corals Montipora digitata and Montipora capricornis, a soft coral Sarcophyton glaucum, a zoanthid Zoanthus sp., and a sponge Chondrilla sp.. The system was validated by comparing physiochemical conditions, coral photosynthetic efficiency and both environmental and host-associated bacterial communities sampled in microcosms and natural reef sites. The results supported the suitability of the ELSS to study coral reef biotopes and their associated bacterial communities exposed to a suite of environmental parameters. The developed ELSS was subsequently used to test to what extent HS are able to mitigate the adverse effects of elevated temperature and UVB radiation on coral photosynthetic activity, and environmental and host-associated bacterial communities. Photosynthetic activity was estimated by measuring the chlorophyll fluorescence of the corals and bacterial communities were studied using 16S rRNA gene HTS analysis. The results are described in chapters four, five and six and indicate that corals in HS-supplemented microcosms had significantly higher photosynthetic activities than those in microcosms subjected to elevated temperature and UVB radiation. HS supplementation, furthermore, significantly influenced the composition of sediment, water and host-associated bacterial communities. Individuals of M. digitata, S. glaucum and Chondrilla sp. in HS supplemented microcosms contained unique bacterial communities enriched with groups of potentially beneficial bacteria. In the hard coral M. digitata, we observed a significant interactive effect of HS, UVB, and temperature, whereby bacterial communities were more resilient to the combined effects of temperature and UVB radiation in microcosms supplemented with HS. These findings have significant repercussions for reef resilience in the face of increasing climate-induced stressors and highlight the importance of restoring coastal forests, known as the main sources of HS in coastal environments, to protect coral reefs.
Autores principais:	Stuij, Tamara Maria
Assunto:	Cyanobacteria Microbial mat 16S rRNA gene amplicon sequencing Bacterial communities Humic substances Terrestrial organic matter ENSO Climate change Montipora digitata Montipora capricornis Sarcophyton glaucum Chondrilla sp.
Ano:	2024
País:	Portugal
Tipo de documento:	tese de doutoramento
Tipo de acesso:	acesso aberto
Instituição associada:	Universidade de Aveiro
Idioma:	inglês
Origem:	RIA - Repositório Institucional da Universidade de Aveiro