The coral corridor: A rewilding approach for the conservation of orange coral (Astroides calycularis) in the western Mediterranean Sea.

Alexis Terrón-Sigler^1,2, Patricio Peñalver Duque¹, David León-Muez¹

¹Hombre y Territorio Association, Spain - ²Universidad de Sevilla, Spain

Over the past five years, it has been estimated that more than 35% of the populations of orange coral (Astroides calycularis) have disappeared. This coral, which is both endemic and endangered, is perhaps the most emblematic of the shallow coral ecosystems of the western Mediterranean, and it is currently facing a critical situation in this region. Unfortunately, this trend is expected to worsen. Within the Mediterranean, Astroides calycularis is one of the most severely affected coral species, along with the habitats it supports. Presently, populations of A. calycularis are struggling to adapt to ongoing environmental stressors. Recurrent mass mortality events (MMEs) affecting macroinvertebrates), combined with the impact of non-native algal species such as Rugulopteryx okamurae, are primary contributors to the decline of coral populations in the Alborán Sea. Thus, the isolation of populations can lead to their collapse due to the absence of genetic exchange and the subsequent depletion of genetic diversity. Therefore, our research has focused on rewilding orange coral populations through the transplantation of detached colonies and the seeding of collected larvae (pioneering techniques in Europe). Through this approach, we are generating coral reefs on artificial substrates, which will facilitate the connectivity of populations once established among isolated groups, support the establishment of self-sustaining colonies, and enhance local biodiversity, thereby contributing to the conservation of the most endangered orange coral populations in the Mediterranean Sea. This conservation strategy, which we have named the Coral Corridor, aims to establish a 600 km connection between coral populations in the northern Alboran Sea. Initial results are promising, as we have already created two coral reefs that connect 57 km of orange coral populations. These reefs have attracted 137 different species, of which 55% are of fisheries interest and 47% are key species. Over 4,700 colonies have been transplanted, achieving a 93% survival rate and 84% total recovery (with colonies expected to reproduce after two years), among other successful indicators. Additionally, more than 4,000 larvae have been seeded, resulting in the establishment of 73 incipient colonies.