Assessing the environmental status of temperate mesophotic reefs: A new, integrated methodological approach.

Highlights • Temperate mesophotic reefs host animal forests vulnerableto fishing activities. • These habitats provide goods for society and their monitoring is of major interest. • A multiparametric index based on ROV footages is herein proposed and tested. • Results show five different environmental status levels for the investigated sites • The MACS index provides a valuable tool to monitor the health of mesophotic reefs. Abstract Temperate mesophotic reefs (circalittoral and offshore circalittoral hard/firm habitats), host complex three-dimensional animal forests and are vulnerable habitats protected by international agreements. In order to evaluate and monitor the environmental status of these ecosystems, the multi-parametric index Mesophotic Assemblages Conservation Status (MACS) was developed, including two independent components, namely Index of Status (I s) and Index of Impact (I i). The I s includes six metrics, targeting conspicuous species diversity, basal layer and canopy composition, whilst the I i is composed by six metrics targeting siltation level, canopy condition and marine litter occurrence. Underwater video transects recorded with a Remotely Operated Vehicle (ROV) along the Ligurian and Tyrrhenian Seas offered the chance to test the index on a large geographic scale and various ecological settings, for a total of 14 sites subjected to different human pressures. MACS index showed a high potentiality to distinguish among a wide range of environmental conditions, with local critical situations mainly related to high fishing pressure. With respect to other existing indices, MACS is based on a larger number of parameters, resulting in a higher ability to disentangle natural and anthropogenic factors, hence it leads to a better interpretation of local situations. This tool represents a contribution to the requirements for the monitoring of these marine environments, set by the EU Marine Strategy Framework Directive, the Habitats Directive, and the guidelines of the Integrated Monitoring and Assessment Programme of the Mediterranean Sea and Coast of the Barcelona Convention. [ABSTRACT FROM AUTHOR]