Tropicalization of the Mediterranean Sea Reflected in Fish Diversity Changes: A Case Study from Spanish Waters

This article belongs to the Special Issue Adaptation to Global Change in Fisheries Resources and Associated Marine Ecosystems.

The Mediterranean Sea, a semi-enclosed basin at mid-latitudes, is experiencing significant environmental changes driven by global warming. This study examines recent shifts in fish species composition within Spanish Mediterranean waters, focusing on the potential tropicalization of marine communities. Using an updated dataset derived from the Spanish marine fishes checklist, we analyzed newly recorded species across two Spanish demarcations: the Levantine-Balearic (LEBA) and the Strait of Gibraltar and Alboran Sea (ESAL). A total of 25 new records (including 23 new species) were reported, with 15 new records in LEBA and 10 new records in ESAL and also including 2 new species recorded occurring in both demarcations. To assess changes in species’ thermal preferences, we compared the mean temperature of newly recorded species with that of previously established species in each demarcation using the Mann–Whitney U test. While no significant differences were found in LEBA, a marked increase of up to 6.08 °C in thermal preference was observed in ESAL. These findings suggest that tropicalization is occurring unevenly across the Spanish Mediterranean, with the Alboran Sea and Strait of Gibraltar being particularly affected. The complex oceanography of the Alboran Sea, coupled with extreme weather events and biological invasions, may exacerbate these shifts.

D. Torreblanca received support for the BIODIV project “Scientific and technical advice for monitoring marine biodiversity: marine protected areas and species under state jurisdiction (2022–2025)”. This project was funded by the European Union (NextGenerationEU) through the Recovery, Transformation, and Resilience Plan and promoted by the General Directorate of Biodiversity, Forests, and Desertification of the Ministry for Ecological Transition and the Demographic Challenge and the CSIC (Spanish National Council of Oceanologists), through the Spanish Institute of Oceanography (IEO). JC Báez was financially supported by the project ‘Plan complementario de I +D + i en el ‘area de Biodiversidad (PCBIO)’, funded by the European Union within the framework of the Recovery, formation and Resilience Plan—NextGenerationEU; by the Spanish Ministry of Science, Innovation and Universities; and by the Regional Government of Andalusia.

Peer reviewed