Tropical corals under climate changeunravelling ecological insight from varying methodological strategies

Laburpena

Tropical coral reefs are one of the most diverse ecosystems on Earth. However, their main structural components, i.e. corals (scleractinian and hydrocorals), are highly threaten by climate change and local perturbations. Climate change is altering corals distributions worldwide, and predictions of corals habitat suitability, based on the IPCC climatic scenarios, can help to early detect range contractions and expansions. This thesis aims to predict these potential distributional changes. To accomplish this goal, the main environmental factors driving corals distribution are explored. Then, modelling techniques as ‘Species Distribution Models’ are used to predict current and future corals habitat suitability. However, future climatic scenarios usually represent conditions that do not exist in the current world, and extrapolations are needed. Corals currently live close to their upper thermal tolerance thresholds, and their response curves are truncated; thus, the detection of their future habitat decline is a challenge. In this thesis, a new Hybrid method, integrating the complete physiological response of a hydrocoral into a correlative model, is proposed. The hybrid model eliminates the uncertainty of extrapolations and allows robust predictions, detecting future corals habitat suitability declines, undetected by classical methods. Additionally, this thesis explores potential future changes in the richness, phylogenetic diversity and phylogenetic species variability of Atlantic coral communities; this information is key to select the most important areas and species for conservation purposes. Lastly, this thesis resolves the genetic relationships of a hydrocoral and its symbionts on both sides of the Atlantic. Results demonstrated a genetic mismatch between the coral host and their symbionts, which clears up an adaptation strategy to climate change by acquiring new symbionts from the environment, or by shuffling their internal symbionts density depending on environmental conditions. In conclusion, this thesis contributes to an integrative knowledge, based on different methodological approaches, to explore the most relevant ecological responses of tropical corals under climate change scenarios