Marine heatwaves drive recurrent mass mortalities in the Mediterranean Sea

Climate change is causing an increase in the frequency and intensity of marine heatwaves (MHWs) and mass mortality events (MMEs) of marine organisms are one of their main ecological impacts. Here, we show that during the 2015–2019 period, the Mediterranean Sea has experienced exceptional thermal conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m, across a range of marine habitats and taxa (50 taxa across 8 phyla). Significant relationships were found between the incidence of MMEs and the heat exposure associated with MHWs observed both at the surface and across depths. Our findings reveal that the Mediterranean Sea is experiencing an acceleration of the ecological impacts of MHWs which poses an unprecedented threat to its ecosystems' health and functioning. Overall, we show that increasing the resolution of empirical observation is critical to enhancing our ability to more effectively understand and manage the consequences of climate change.

Centro de Excelencia Severo Ochoa CEX2019-000928-S

Ministerio de Ciencia e Innovación RTI2018- 095346-B-I00, RTI2018-095441-B-C21

Interreg-Med Programme 1MED15_3.2_ M2_337

Ministry of Development and Investments of Greece MIS 5047038

Marie Sklodowska-Curie 801370

French National Research Agency ANR-17-MPGA-0001

H2020 Environment SEP-210597628

Ministerio de Economía y Competitividad CGL2015-71809-P, CTM2012-32603

National Geographic Society EC-176R-18

Italian Ministry of Education, University and Research AIM 1807508–1, PON 2014–2020

Ministerio de Transición Ecológica y Reto Demográfico CTM2016-77027-R

Foundation for Science and Technology UIDP/04423/2020, UIDB/04423/2020

Regione Autonoma Sardegna CUP 87G17000070002

Interdisciplinary Centre of Marine and Environmental Research UID/Multi/04423/2019