Mediterranean warming cuts Posidonia seagrass coverage by up to 40%

A study by IFISC‑CSIC‑UIB, CEAB‑CSIC and King Abdullah University of Science and Technology (Saudi Arabia) used artificial‑intelligence analysis of high‑resolution satellite imagery to link chronic thermal stress in the Mediterranean Sea to substantial loss and fragmentation of Posidonia oceanica meadows. The researchers mapped sea‑surface temperature data from 2000‑2020 and introduced a new “Stress Degree Days” (SDD) index that quantifies cumulative heat exposure. Areas with high SDD, especially along the southern and eastern coasts, showed a reduction of seagrass coverage exceeding 40% and severe structural breakup.

The findings highlight that prolonged, sub‑lethal warming can degrade these vital marine forests even when temperature thresholds for acute mortality are not breached. The study calls for climate‑impact assessments that consider the duration and intensity of heat stress, not only extreme temperature spikes, to better protect Mediterranean coastal ecosystems.