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Ecological Indicators 122 (2021) 107296
E. Turicchia et al.
considered when interpreting the results. The main strengths of the
MedSens index are that the sensitivities of the selected species in a wide
range of taxonomic groups and biological and ecological features are
based on scientific evidence and that these sensitivities were assessed
according to the different pressure types. This can help discriminate
against local pressures that are likely to act in an area. Conversely, the
main weaknesses lie in the reduced number of considered species, which
could be increased in the future, and the need for large amounts of data
from many well-trained volunteers.
The success of a CS project stems from simple and effective protocols
(Bonney et al., 2009; Holt et al., 2013), developed by scientists to
include particular aims, proper training and skills assessment of the
participants, and timely feedbacks on the progress and efficacy of the
participants’ actions to keep high their involvement (Devictor et al.,
2010). The RCMed U-CEM protocol is a simple but effective visual
census, with easy-to-monitor species that encompass the key ecological
aspects of the Mediterranean subtidal habitats (Cerrano et al., 2017).
This protocol is easy to learn and may provide a large amount of timely,
up-to-date geo-referred data, from the Mediterranean Sea coasts. Data
quality is assured by rigours participant training (subject to learning
tests), numerous surveys by independent observers, and quality control
measures.

4.2. Future perspectives

The population of European divers is over 3 million people (data
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from the European Underwater Federation ), many of whom dive in the
Mediterranean Sea. The Mediterranean Sea has about 23,000 km of
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rocky coasts (Furlani et al., 2014) and more than 7000 km of subtidal
rocks and biogenic reefs in the scuba diving depth range (EMODnet
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broad-scale seabed habitat map for Europe, v2019 ). With the MedSens
index, volunteers applying the RCMed U-CEM protocol can support re-
searchers and managers to collect and interpret data over larger spatial
and temporal scales than would otherwise be possible.
Fig. 4. Temporal change in the MedSens index at: a) Gallinara Island from 2006 The MedSens index provides a free, complementary to professional
to 2018 and b) Secca del Papa, Tavolara Island before and after the 2008 mass investigations, and user-friendly tool to evaluate the ecological quality
mortality of Paramuricea clavata. of the Mediterranean subtidal rocky habitats according to the Habitat
Directive and the MSFD requirements. This will also help decision-
allowing the effective integration of a consolidated community-based makers as they plan and apply conservation strategies. The MedSens
environmental monitoring into ecosystem-based management policies. index offers a detailed picture of the vulnerability levels of different
It provides a proxy of the mean sensitivity of the rocky bottom assem- coasts, allowing tailored measures of conservation in an adaptive
blages to natural and anthropic pressures listed by MSFD. Higher management framework. Moreover, this index can enable more oppor-
average assemblage sensitivities are associated with lower levels of tunities for effective feedback to volunteers involved in the RCMed U-
disturbance, thereby indicating good environmental conditions. CEM protocol. The MedSens index application may represent a way to
The MedSens index was calibrated on a large dataset of wide-ranging raise public awareness and enhance the collaboration between coastal
conditions occurring along the Mediterranean Sea coasts. Case studies management authorities, stakeholders, and researchers. By directly
showed that the index responds well to the local pressures documented involving stakeholders, the MedSens index increases the acceptability of
by previous studies. The MedSens index may also be applied in a wide management decisions, including unpopular ones, as they may occur in
range of circumstances; it is particularly suitable for monitoring MPAs MPAs where fragile sites and restoration areas are closed to the public.
and can aid spatial gradients analysis, time series analysis, and before/ The RCMed U-CEM protocol and MedSens index may also comple-
after-control/impact studies. Moreover, the newly developed QGIS ment ocean observation systems and oceanographic forecast models,
plugin provides an easy freeware tool to calculate the index whenever helping to develop an early-warning system for mass mortality events in
data are available. benthic species along the Mediterranean Sea coasts (Turicchia et al.,
MedSens is a biotic index based on the sensitivities and tolerances of 2018). Thus, their combined application provides an effective strategy
the species to pollution and/or other disturbance sources (for a review to achieve the habitat and species conservation objectives set by the
see Ponti et al., 2009). Other indices based on a similar approach for the European Union (Borja et al., 2010) and the Mediterranean Regional
Mediterranean benthic communities include the AZTI’ Marine Biotic Activity Centre for Specially Protected Areas (UNEP-MAP-SPA/RAC,
Index, AMBI (Borja et al., 2000), for soft bottoms, and the Ecological 2017).
Status of Coralligenous Assemblages index, ESCA (Piazzi et al., 2017), The MedSens index was designed for the Mediterranean subtidal
for rocky bottoms. These indices are based on the assumption that rocky bottoms, but its approach may be applied to other habitats, from
sensitive species decrease in abundance and number as the pressures temperate to tropical reefs, by including the relevant local species, with
increase, leaving space for the more tolerant species (Hilsenhoff, 1987). appropriate calibration and validation.
While the high abundance of a sensitive species is likely witness of
reduced pressures, the high abundance of tolerant species is not neces-
sarily related to poor environmental conditions – this should be 5 https://www.euf.eu
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https://www.emodnet-seabedhabitats.eu
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