Marine strategy framework for detecting mass mortality: From local surveys to monitoring improvements in the coralligenous habitat

Mediterranean coralligenous assemblages are threatened by the effects of climate change and human activities that have led to mass mortality events (MMEs) in recent decades. The ecological roles of this habitat and the possible consequences of its loss have necessitated the scientific analysis of MMEs on a Mediterranean regional scale, highlighting the need of new standardized monitoring and data collection tools across the basin. In September 2021, during the monitoring activities of the Marine Strategy Framework Directive (MSFD) for the coralligenous habitat of the Egadi Islands Marine Protected Area (MPA), an MME of the red gorgonian Paramuricea clavata was recorded. Five of the six surveyed sites revealed a high degree of impact, with mortality values ranging from 46.9% in the least affected site to 100% in the most affected. The observed MME occurred during a prolonged period of anomalous warmer sea temperatures down to 60 m in depth. By enhancing the MSFD protocols for coralligenous habitat with the addition of a series of biotic/abiotic variables (e.g., temperature, pH and mucilaginous bloom) and methodologies (e.g., scuba survey and citizen science activities) to evaluate and monitor Good Environment Status (GES), we propose to implement a monitoring and data collection system which is able to provide essential information about MMEs. This multiple shared surveillance tool would allow the tracking of MME events in the Mediterranean region, as well as the planning of mitigation and/or restoration strategies for these vulnerable habitats on an inter-regional scale.