The Cladocora caespitosa, or Mediterranean pillow coral, is a species of coral endemic to the Mediterranean Sea, the only one in this area capable of forming coral reefs, similar to those found in tropical seas.

It is a protected species at different levels; it is listed as an endangered species on the IUCN Red List and included in Annex I of the Habitats Directive. At the national level, the pillow coral is included in the LESPRE (List of Wild Species under Special Protection Regime), and within Catalonia, it is included in the Catalogue of Endangered Native Wildlife of Catalonia. Despite this, and despite its uniqueness and importance, there is very little information available about its status and distribution.

The Fauna and Flora Service of the Government of Catalonia has commissioned SUBMON to prepare a document that will establish the preliminary foundations for developing a conservation plan that can address the needs of this species. As part of the work carried out, a campaign to locate populations of Mediterranean pillow coral has been conducted, specifically in the Cap de Creus area, and available information about this species has been compiled.

The biology of the Mediterranean pillow coral itself makes it particularly sensitive to multiple impacts, many of them directly or indirectly related to human activity. Being a sessile species (living attached to a firm structure) with great longevity and slow growth, it is highly vulnerable to impacts such as the effects of climate change, the presence of invasive species, or pollution, all of which pose a threat to its survival.

Climate change, the main threat to Mediterranean corals

The effects of climate change, which already affect human health in many ways, are the main threat to the Mediterranean pillow coral. The progressive warming of the Mediterranean Sea, along with increasingly frequent and prolonged heat waves, has led to mass mortality episodes within populations of this species.

One of the effects that can be easily observed, caused by this increase in sea temperatures, is the bleaching of Mediterranean pillow coral colonies, similar to what happens with tropical corals. This bleaching occurs because, due to thermal stress, the pillow coral colony drives out symbiotic algae (zooxanthellae), which coexist in its reefs, exposing its calcium carbonate skeleton.

Obtaining more data on Cladocora caespitosa and its distribution is crucial to understanding its environmental status, an essential step in implementing the most appropriate conservation actions to preserve this jewel of the Mediterranean.