Scientists confirm the "accelerated decline" of Posidonia meadows

PalmaOceanic seagrass meadows are experiencing an "accelerated decline". This is determined by a study carried out by the Institute of Interdisciplinary Physics and Complex Systems (IFISC-CSIC-UIB), the Center for Advanced Studies of Blanes (CEAB-CSIC), and King Abdullah University of Science and Technology (Saudi Arabia). The research has shown that prolonged warming degrades oceanic seagrass meadows even when temperatures remain below lethal limits.

The study takes advantage of artificial intelligence and high-resolution satellite imagery to link, for the first time, chronic thermal exposure with loss of cover and structural disassembly. Until now, most quantitative studies assessed the impact of climate change according to exceeding temperature thresholds, but this study demonstrates that chronic and accumulated thermal stress can “deteriorate and fragment” seagrass meadows, even when thermometers remain below critical survival limits.

Seagrass is the endemic marine phanerogam species that constitutes the backbone of the Mediterranean coastal ecosystems.

New index

To capture the subtle yet potentially destructive effects of prolonged and fluctuating conditions that do not reach critical thresholds, the research team has introduced a new, physiologically-based index called Stress Degree Days (SDD). Unlike traditional threshold-based approaches that focus exclusively on discrete heat peaks, this conceptual framework explicitly accounts for how thermal stress affects the organism over time under dynamic field conditions, explained CEAB-CSIC researcher Àlex Giménez-Romero.

By analyzing historical daily sea surface temperature data between 2000 and 2020 with experimentally derived mortality rate functions, scientists quantified the accumulated thermal exposure across the entire Mediterranean basin over the last two decades. After mapping over 30 satellite images in various Mediterranean regions, scientists determined seagrass coverage and fragmentation indices. The results revealed that areas of high accumulated thermal stress, concentrated along the southern and eastern coasts of the basin, exhibit a reduction.