In the framework of the RESTORE project, two crustose coralline algae (CCA) species observed to live associated with octocoral juveniles in the area of Banyuls-sur-Mer (France) were identified to be Macroblastum dendrospermum and Lithophyllum stictiforme through barcoding (Sanger) analysis. The 16S rDNA metabarcoding analysis of the bacteria communities associated with the two CCA species showed that the two algal species are characterized by species-specific bacterial assemblages. Despite this specificity, both CCA species predominantly host bacterial taxa that have been observed to characterize the microbial communities of many CCA species and to have a potential role in favouring tropical coral larvae settlement. Through an experimental test in aquaria and control conditions, the two CCA species and their bacteria were tested for their capability of promoting the settlement of larvae of the white gorgonian E. singularis, also after being subjected to climate change effects. Replicates of each CCA species were subjected to three different experimental conditions for two months: 1 - Control conditions. Normal conditions of pH (pHT≈8.1) and temperature (T≈16.1°C) for control CCA samples. Three bare rock fragments were also exposed to the control conditions and used as experimental control samples. 2 - Treatment 1 (T1). Acidified and warming conditions projected in the RCP8.5 scenario foreseen at the end of the 21st century with pH value corresponding to 7.70 and a temperature increase of 2.5°C; 3 - Treatment 2 (T2). same conditions of water acidification and warming followed by the reproduction of a heatwave phenomenon at 26°C foreseen in the area starting from 2050. At the end of the treatment period, part of the algae was sampled to explore potential changes in their bacterial community composition, algae exo-metabolites were sampled for metabolomic analysis, and the water conditions in each aquarium were restored to normal conditions. Octocoral larvae were then equally distributed in the aquaria and checked every day for two months to count the number of settlers.
Extracts of grounded CCA fragments were subsequently used to obtain purified bacterial strains that were identified by means of barcoding analysis of the 16S rDNA gene. Most of the bacterial strains were successfully identified. The capability of each strain to produce biofilm was assessed by crystal violet staining technique, and all bacterial strains were found to be biofilm producers. Biofilms were used in a second octocoral larval settlement test.
The RESTORE project also explored the effect of climate change on the presence and spatial distribution of the red coral C. rubrum in the Western Mediterranean by implementing predictive models of species distribution. Spatial data searching and gathering of coral presence and environmental parameters were carried out by using open-access data portals. The environmental parameters known to influence C. rubrum distribution and presence were selected. Environmental data were found in CMEMS and EMODnet data portals with 200 m spatial resolution. As for temperature, dissolved oxygen, and current velocity, data were also collected for climate change scenarios’ analysis starting from the IPCC scenario SSP5-8.5 predicted for 2100. The data were analyzed, processed, and used to build and test the performances of three species distribution models, GAM, Maxent, and Random Forest.
