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Global warming facilitates the nesting of the loggerhead turtle on the Mediterranean coast of Spain

Photo: Female loggerhead turtle returning to the sea after spawning and camouflaged the nest. @UB

Environmental temperature is one of the main determinants of geographical distribution in animals, and due to intensifying global warming, the ranges of many species are shifting polewards. This process of displacement may be less intense in philopatric species, i.e. those that reproduce in the place where they were born.

The loggerhead turtle is a marine species found in tropical and temperate zones around the world. It nests on the coasts of Japan, Oman, Australia, Brazil, the Caribbean and the east coast of North America, as well as in Cape Verde and in the eastern Mediterranean (especially in Greece, Turkey, Cyprus, Libya, Lebanon and Israel). They also make long migrations to feeding grounds such as the western Mediterranean. The vulnerability of turtles to global warming is accentuated by a life history that combines delayed sexual maturity, temperature-dependent sex determination and low survival of embryos at high incubation temperatures.

In a climate change scenario, the future of loggerhead turtles may depend on their ability to colonise new areas. Despite their philopatric nature, some females do not always return to their original nesting grounds and may occasionally lay in new areas. The phenomenon of sporadic nesting, considered exceptional, has been increasing in recent years on the beaches of the western Mediterranean, so the protection of these regions may be decisive for the survival of the species in the future.

The detection of loggerhead turtle nesting events in the western Mediterranean has greatly increased during the first two decades of the 21st century, which could be a response to global warming or the result of increased sampling effort. Deployment of temperature data recorders on 52 beaches scattered along the Mediterranean coast of Spain showed that sand temperature is currently high enough to allow loggerhead turtle nesting on most Spanish beaches. However, reconstruction of sand temperature from 1950 to 2019 at El Prat de Llobregat beach revealed that thermal conditions suitable for regular loggerhead turtle nesting have only existed on Spanish beaches since 2010, although sporadic nesting was previously possible in exceptionally warm years.

Future establishment of a stable population would probably require an even greater increase in temperature to ensure female-biased offspring production, but the process could be compromised by increased erosion and beach flooding as a result of rising sea levels.

The research was led by Lluís Cardona, from the Large Marine Vertebrates research group of the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the UB. Researchers from the Doñana Biological Station (CSIC), the Cavanilles Institute of Biodiversity and Evolutionary Biology of the University of Valencia, the BETA Technology Centre of the University of Vic, the Department of Agriculture, Rural Development, Climate Emergency and Ecological Transition of the Generalitat Valenciana, Xaloc. Hermanos de Sal, and the Department of Climate Action, Food and Rural Agenda of the Generalitat de Catalunya.

Reference article:
L. Cardona, J. San Martín, L. Benito, J. Tomás, E. Abella, J. Eymar, M. Aguilera, J. A. Esteban, A. Tarragó & A. Marco "Global warming facilititas on the Mediterranean coast of Spain" Animal Conservation 2022 doi:10.1111/acv.12828