Recurring cryptic mass mortalities—Lessons from bioturbating echinoids under combined climatic and anthropogenic stress

Marine mass mortality events (MMEs) are a growing source of concern globally. Affecting diverse marine ecosystems, they frequently cause significant ecological disruptions, often leading to large-scale ecological shifts. However, in contrast to terrestrial MMEs, most marine mortalities likely occur undetected, particularly in cryptic and infaunal taxa. Here, we present the first documented reports of irregular echinoid mass mortalities from the Eastern Mediterranean Sea—a region at the forefront of ocean warming and anthropogenic pressure. Compiling ecological, morphometric, molecular, and remote-sensed environmental data, we reconstruct a 14-yr history (2011–2024) of MMEs involving the key infaunal bioturbating echinoids of the genus Echinocardium. We analyzed environmental parameters, namely sea surface temperatures, chlorophyll a concentrations, river discharge, and wave intensity, in the weeks preceding five MMEs and analyzed skeletal remains to explore the potential drivers of mortalities. We show that these events are neither rare nor stochastic but rather recurring and spatially structured—spanning hundreds of meters and positioned at the outlet of major rivers, likely driven by cumulative environmental and human stressors. By revealing patterns in taxa often overlooked in marine monitoring, this work highlights the urgency of assessing ecological stability in sedimentary ecosystems. We highlight the need for implementing long-term monitoring and improved environmental assessments, at both national and regional scales, to include benthic infaunal communities—particularly in rapidly warming regions like the Eastern Mediterranean.