Diversidade taxonômica, funcional e trófica de corais e respostas ao estresse térmico

Abstract

Coral reefs play unique roles and are critically important ecosystems, but they are threatened by rising ocean temperatures causing bleaching events that can lead to loss of coral cover and diversity, and a reduction in reef complexity. Considering that approaches based on functional attributes can inform about organism responses to environmental disturbances, understanding coral diversity patterns, their attributes, and responses to climate change is crucial. In Chapter 1, we describe the taxonomic and functional diversity of corals in Brazil, assessing species composition and functional space occupation across regions. We observe clustering of eight regions, where Bahia holds the highest species richness and proportion of occupied functional space, both decreasing with distance from this region. Species and region compositions are influenced by environmental barriers and filters, related to coral attributes. In Chapter 2, we investigate variation in concentration and composition of fatty acids in shallow-water zooxanthellate corals along 21° of latitude in the Southwest Atlantic (SWA) to indicate their predominant trophic mode and assess potential geographic variations. Species identity and location explain most of the fatty acid composition variation in SWA corals, associated with available photosynthetic radiation (PAR), sea surface temperature (SST), and particulate organic carbon (POC). Fatty acid composition of Favia gravida, Siderastrea stellata, Mussismilia harttii, and Mussismilia hispida varies among locations, while Madracis decactis, Montastraea cavernosa, and Porites astreoides show consistent patterns across all sites. Additionally, based on the concentration of the heterotrophic marker (CGA), P. astreoides is the most autotrophic species, and Mu. hispida is the most heterotrophic coral. In Chapter 3, we experimentally evaluate the relative contribution of autotrophy and heterotrophy-based feeding modes to the growth of Millepora alcicornis and Mo. cavernosa and how they respond to thermal stress. We observe a higher growth rate for Mi. alcicornis than Mo. cavernosa. Dissolved organic matter (DOM) feeding initially positively influences coral growth, sustained for Mo. cavernosa and delayed for Mi. alcicornis. Thermal stress has little impact on the growth and dominant trophic mode of both species. However, it negatively affects the maximum photochemical efficiency (Fv/Fm) and coloration of Mi. alcicornis, which proves more temperature-sensitive. Corals subjected to DOM treatment exhibit greater resilience and recovery after thermal stress. The health of Mo. cavernosa is unaffected by thermal stress. The results demonstrate how species and environmental variables are related, resulting in taxonomic, functional, and trophic heterogeneity along the Brazilian coast. Rising temperatures in climate change scenarios result in different coral responses to bleaching, primarily modulated by heterotrophic feeding, which may lead to changes in species distribution and current patterns.