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The ability to acclimatize and adapt define the evolutionary potential of organisms and the likelihood that they will resist, thrive or become extinct in a dynamic and constantly changing world. These changes range from major paleogeological and paleoclimatic events to cyclical fluctuations on the human scale and have determined the patterns of distribution and composition of biodiversity on the planet. In this sense, the processes of extinction, expansion, regression, invasion or competition have increased enormously in recent times.

The presence of invasive exotic species is of special relevance in these processes and is one of the descriptors included in the Marine Strategies for the determination of good environmental status. This project will study the case, in order to address its better conservation and management, of Cladocora caespitosa, a threatened and regressing coral on our coasts (currently included in the List of Wild Species under Special Protection) that faces the expansion of the invasive species Oculina patagonica.

The general objective of the project has been to analyse the dynamics of changes and their demographic and genetic consequences in the interaction between the coral species Cladocora caespitosa (endemic to the Mediterranean) and Oculina paedonia (invasive), as an example of the interaction between native and invasive species, in order to foresee what evolutionary, conservation and management implications they may have in the short to long term.

The specific objectives were as follows:

• To compile the existing information on the corals Cladocora caespitosa and Oculina patagonica in the coasts of the Iberian Peninsula and nearby areas.
• Collect the necessary samples for molecular analysis.
• Analyze and contrast demographic histories, population structures and connectivity patterns.
• Establish possible correlations between genetic and habitat parameters.
• Communication and dissemination of the current state of knowledge and results.

• Bibliographic review and web pages of official local, state and international organizations, as well as scientific societies and NGOs related to the conservation and monitoring of marine biodiversity or own observations, on the coexistence of these species in the study area.
• Sampling in areas of the Mediterranean and near Atlantic of populations where the interaction between the selected species and single occurrence reference populations is taking place.
• Obtaining informative molecular markers for the analysis of molecular variation.
• Genotyping of markers developed in the samples obtained.
• Data analysis for different genetic and population structure parameters.
• Translation of the parameters obtained on maps with geographic information system (GIS) tools.
• Exploration of correlations of genetic diversity with environmental parameters (temperature, currents, winds, waves, pH, salinity or chlorophyll, for example).
• Dissemination and communication of the project, through 2 scientific publications and a contribution to a congress, as well as the carrying out of different dissemination actions: an online talk on invasive species; a temporary exhibition in Los Yébenes (Toledo); 6 workshops aimed at children, schools and various institutes in the Community of Madrid, Alicante and Utah (United States); 2 informative videos on invasive species, a video on the species studied in the project and 2 presentations on invasive species to master’s students.

Thanks to the Coralien project, the diversity and genetic structures of two coral species have been compared: one endemic to the Mediterranean(Cladocora caespitosa), and one cryptogenic, i.e. of unknown origin, and expanding(Oculina patagonica). For the study, populations in the east of the Iberian Peninsula (from Almería to Tarragona) and the Balearic Islands where both species coexisted were analyzed, as well as a couple of localities where only one of them was present. These analyses have confirmed that, although the true origin of Oculina patagonica is unknown, its invasive behavior is causing a displacement of Cladorora caespitosa, a native species of coral in regression on the Spanish Mediterranean coasts.

Likewise, the results of the project show that there is no great differentiation between the populations of Cladocora caespitosa, although within this homogeneity, the populations of Aguadulce (Almería) and Formentera are genetically distinguishable from the other Iberian coastal populations. As for the invasive species, Oculina patagonica, the populations located in the northeast of the peninsula (Tarragona) are clearly different from the rest of the populations located further south. Regarding intraspecific genetic diversity, it has been found to be higher in Cladocora caespitosa than in Oculina patagonica, so that the native species shows a greater genetic balance in its populations and the invasive species a higher index of inbreeding (inbreeding) associated with the deficit of heterozygotes, which can be associated with a small number of founding individuals of Oculina patagonica. As for the population structure of both species, the Formentera and Almeria populations of Cladocora caespitosa differ genetically from the rest, while in the case of Oculina patagonica the populations of Tarragona are the ones that differ the most from the other populations located south of the sampling area.

In this case, according to the organization, it is possible that there is a correlation between genetic differentiation and some environmental factors such as salinity, since their values are higher in the populations of Tarragona and Aguadulce (Almeria). Therefore, it is proposed that the study of environmental factors and their relationship with genetic parameters could be of practical application in the management of the populations of these species, since they indicate a genetic dynamics and connectivity of interest to establish management measures, especially for the control of the invasive species Oculina patagonica.

On the other hand, one of the most worrying conclusions of the project has been the discovery of hybridization between both species due to their coexistence, specifically in the population of Aguadulce (Almeria), as it could represent a serious threat to the genetic integrity and survival of Cladocora caespitosa. This exemplifies, according to the entity, that hybridization is one of the fundamental problems for native species (in general) facing invaders, since they may lose the cohesion of their genome, and the introgression of genetic material from another species may even represent their disappearance as a unique and differentiated entity.

Finally, it is worth mentioning that different communication and dissemination actions have been carried out on the project and on the problem of invasive species, including the holding of 6 workshops aimed at schoolchildren from schools and several institutes in the Community of Madrid, Alicante and Utah (United States). Two informative videos on invasive species, a video on the species studied in the project and two presentations on invasive species to master’s degree students were also produced.