Detect coastal disturbances and climate change effects in coralligenous community through sentinel stations

Finally, the proposed methodology could be extended to the entire geographical area over which the target species of this study are representative of the rocky bottom benthic communities that occur at similar depths and share similar biotic structures. This methodology could also be applied in other areas in which target species can be established and selected by employing the aforementioned implementation criteria. Additionally, the SBPQ method involves minimal imple- mentation difficulty both in terms of cost and installation. The a priori selection of the target spe- cies simplifies the taxonomic difficulty of visual identification. Therefore, this environmental warning and surveillance system is not only oriented toward the scientific and technical communi- ties of the relevant coastal countries but also toward environmental volunteers associated with div- ing centres and clubs. This methodology ultimately entails the aim of setting up geographical networks in regions with sufficiently high levels of homogeneity (e.g., the Alboran Sea or, on a larger scale, the western Mediterranean). Citizen science initiatives focusing on the mapping and monitoring of coralligenous assemblages have recently been implemented [148]. In the future, these networks could provide early warnings of changes to structured and unpolluted systems, par- ticularly those in littoral zones close to places subjected to strong anthropogenic pressure, which could be applied to the detection of local or general environmental alterations (i.e., climate change).

In contrast, the nature of the method, which is designed to monitor a group of taxa with respect to the total taxa of the community, implies that it is not useful as such in the ecological study of these habitats because the analysed information is biased. However, the generated databases (i.e., stored photographs) will allow for the performance of in-depth studies of the dynamics of the species within the communities over time, assuming that significant changes can be detected, and could aid parallel projects that aim to increase our knowledge of coralligenous assemblages. Conclusions The study assessed the Sessile Bioindicators in Permanent Quadrats (SBPQ) underwater environ- mental alert method in relation to the monitoring of pre-selected sensitive and sessile benthic spe- cies (P. clavata and A. calycularis) associated with rocky coralligenous habitats (which exhibit high stability and biodiversity) via the use of permanent quadrats fixed on rocky shores in under- water SBPQ sentinel stations. The obtained results have allowed for assessing the part of the method based on the initial hypothesis that, over a long temporal duration (a ten-year period in this study) and in a highly structured and biodiverse coralligenous assemblage, the cover of sensi- tive sessile species does not change over time if the environmental stability characterising the habi- tat is not altered. This stability of the cover of the sensitive sessile species is a key aspect for confirming the reliability and robustness of the SBPQ method. Given that, as in the present study,

the selected species are very sensitive to increases in temperature and deterioration of the environ- mental quality of the water column, the SBQP method is useful as an underwater environmental alert system because it should be solely sensitive to changes in the coverages of such species that result from physico-chemical changes in the system. Such changes include gradual increases in temperature due to global warming and changes due to the introduction of exotic species. A future usefulness would be to implement the SBPQ methodology in well-conserved areas so those areas can act as “SBPQ sentinel stations” in the event of possible disturbances. The method has been developed as a simple management tool for use by scientists and specialised technicians in addition to diving clubs that frequent certain areas. Supporting information S1 Table. Coverage of each species through the monitoring period. Time: 1 corresponding to 2005 and 10 to 2014. Slope: H, horizontal; V, vertical. (XLS) PLOS ONE Detect coastal disturbances in coralligenous PLOS ONE | https://doi.org/10.1371/journal.pone.0231641 May 5, 2020 15 / 23