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The algae Gelidium corneum is the dominant species in a large part of the infralittoral rocky habitats of the North Atlantic demarcation, belonging to the Natura 2000 Network. In addition, it is part of descriptors 1 (biodiversity) and 6 (seabed) established in the Marine Strategy Framework Directive (MSFD) to determine the environmental status of marine waters. It is also one of the biological quality elements considered in the European Water Framework Directive (WFD).

Despite its relevance in the conservation of the marine environment, the Foundation Institute of Environmental Hydraulics of Cantabria indicates that knowledge about its distribution and state of conservation is still very limited. In addition, it has suffered a significant setback in certain regions of Spain (e.g. the Basque Country), which is attributed to the interaction between climate change and anthropogenic pressures (i.e. the impact caused on the environment by human activities). Among these pressures, its commercial exploitation for the extraction of agar-agar (an ingredient widely used especially for vegetarian and vegan cuisine), using different uprooting and harvesting techniques, stands out. For all these reasons, there is a need to deepen our knowledge of its ecology and main threats.

The general objective of the project has been to know the potential distribution of Gelidium corneum and to analyse the main pressures that threaten its conservation in the medium and long term.

The specific objectives were as follows:

• To know the potential distribution of Gelidium corneum on the Spanish coasts.
• To assess possible changes in their biogeographic distribution as a result of climate change.
• To analyse the interaction between the different techniques for exploiting the resource.
• To bring knowledge of the species (biology, distribution) and the community that houses its habitat (richness of algae, invertebrates) closer to the managers and professionals of the resource (shipowners, divers, collectors), to improve its management and raise awareness among the different groups of its role in maintaining the biodiversity of the marine environment and the need for its sustainable management.
• To disseminate the project and raise awareness of the importance of the species in maintaining biodiversity and conserving the marine environment.

• Preparation of a map of the potential distribution of the algae Gelidium corneum on the Spanish Atlantic coasts, especially in the North Atlantic demarcation, which is its preferred distribution.
• Analysis of the change in the biogeographic distribution of the species due to climate change, considering two climate change scenarios defined by the IPCC (RCP 4.5 and RCP 8.5) for the medium term (2040‐2069) and long term (2070‐2100). This action has made it possible to estimate the probability of occurrence of the species in the study area and to know the magnitude of the potential change in its biogeographical distribution and to identify the most vulnerable areas of the Cantabrian coast.
• To evaluate the interaction between the exploitation of the resource through uprooting techniques and collection of coastal landings (i.e., collection of algae detached from the seabed and that have been dragged by the waves to the shore, where they accumulate).
• Training and awareness raising for professionals in the sector, through the preparation of a guide of good practices aimed at managers and professionals in the sector. This guide was prepared with a double purpose: on the one hand, to facilitate the preparation of resource management plans for the competent authorities; and, on the other hand, to contribute to the training, information and awareness of professionals in the sector, in addition to making the ecological and economic value of the resource known to the general population. The guide has also collected specific information on the fields and the collection of arrivals carried out in Cantabria, and has included information on the biology, ecology, current and future distribution, commercial uses, main threats, techniques and general recommendations for the exploitation of the resource.
• Dissemination and communication of the project (publications on the project website and on the entity’s social networks, etc.). The preparation of an informative brochure with the objectives of the project and its main actions is highlighted.

On a general level, in this project distribution models of the species Gelidium corneum have been developed, generating a cartography of its habitat in its current situation and an estimate of the changes in its future biogeographic distribution as a result of climate change. Likewise, an analysis of the interaction between the exploited fields and the areas of accumulation of arrival has been carried out, based on the modelling of their detachment, dispersion, transport and accumulation on the coast. Finally, a guide of good practices on the exploitation of the resource has been drafted and distributed for its knowledge and management.

All the scenarios analysed in the mapping work show significant reductions in habitat suitability in the inland area of the Bay of Biscay, which affects practically all the coastal communities in the north of the peninsula, with the exception of Galicia. This reduction in the interior of the Bay of Biscay is accompanied by an increase in the probability of occurrence in the south of Galicia and practically in the entire Portuguese coast (with the exception of the southernmost region). Therefore, everything seems to indicate, according to the Foundation Institute of Environmental Hydraulics of Cantabria, that the limit of distribution of the species in the Cantabrian Sea is moving westwards, that is, towards the Atlantic coasts.

On the other hand, with regard to environmental variability, a greater dispersion of the algae is observed, due, on the one hand, to the greater release of particles to the coast and, on the other, to a greater distance from the trajectory described by the particles due to the action of the wind and the tide.