Using expert-elicitation to deliver biodiversity monitoring priorities on a Mediterranean island

Introduction The earth’s climate and habitats are changing at unprecedented rates, with species and ecosys- tems increasingly threatened by multiple, often interacting, anthropogenic pressures [1]. Five main threats to biodiversity were identified by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES): changes in land and sea use; direct exploita- tion of organisms; climate change; pollution; and, invasive alien species (IAS) [1]. The Medi- terranean basin is one of the 34 global biodiversity hotspots, including a large number of endemic species, where, due to increased anthropogenic pressure, there is an urgent need for species and habitat conservation [2]. Mediterranean-climate areas are predicted to be likely to experience the highest levels of biodiversity change by 2100 [3]. The most conspicuous threats that affect the greatest number of taxonomic groups in the Mediterranean are habitat loss and degradation, followed by the unsustainable exploitation of species, pollution, climate change, eutrophication and species invasions [4]. Increased tourism and urbanisation in this region also adversely affect biodiversity through habitat loss, disturbance, use of pesticides and herbi- cides and increased pollution [5–7]. In addition, over-exploitation of natural resources is spe- cifically an issue for fisheries of the Mediterranean Sea [8]. To attempt to halt and, where possible, reverse species population declines and habitat deg- radation, policy-makers need to use scientifically robust biodiversity data [9, 10]. Monitoring

is therefore needed to provide evidence on biodiversity status and trends [11]. Hochkirch and others [12] suggest an eight-point strategy for reducing gaps in available biodiversity data. At the local level, the most relevant of these are: increasing explorative field surveys; increasing monitoring of less well-studied taxa; building capacity in areas where there is high species- richness or levels of endemism; providing mechanisms of funding in order to fill knowledge gaps; and the use of global online data repositories such as the Global Biodiversity Information Facility (GBIF; https://www.gbif.org/) for hosting high quality, open data. Open data can be an important mechanism to enable the effective use of biological monitoring information [13]. The increasing use of technologies for biological recording has resulted in many millions of records being made freely available through global platforms such as GBIF. However, open data repositories may also contain important biases in the records uploaded [12, 14]. The other elements of Hochkirch and others [12] strategy: linking information on taxonomy to information on conservation; the mapping of spatial threat data; and automating pre-assess- ments, could also be relevant locally, although they are further removed from the basic task of documenting what biodiversity occurs where. Information on species distributions and identification [15] is essential for supporting con- servation [16], but funding and support for taxonomic training may also be limited [17], with

numbers of taxonomists decreasing globally [18, 19]. Initiatives such as the Distributed Euro- pean School of Taxonomy, which offers education and training opportunities (https://cetaf. org/dest/about-dest/), are one mechanism for bridging these gaps between data needs and data availability; however, limited support for both taxonomic training and the availability of employment still present challenges for conservation [20, 21]. Indeed, the “provision of fund- ing mechanisms” was another strategy highlighted by Hochkirch and others [12] as important for increasing the availability of biodiversity data. Technology is also increasingly being used to fill knowledge gaps, as it can assist with the surveying of large or difficult to reach areas more rapidly and cheaply than on-the-ground surveys. For example through remote sensing [22], the use of habitat suitability maps [2], and environmental DNA [23]. In some areas, e.g. the UK, reduced governmental funding for the collection and curation of records within statutory organisations has led to a diversification in mechanisms for biologi- cal data gathering [24]. In this situation, citizen science, the involvement of volunteers in PLOS ONE Expert-elicitation to prioritise biodiversity monitoring PLOS ONE | https://doi.org/10.1371/journal.pone.0256777 March 24, 2022 2 / 20 National Capability. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors declare the following financial interests/personal relationships

which may be considered as potential competing interests: All authors are involved in various aspects of biodiversity conservation, and they may benefit from increased investment in this area. This does not alter our adherence to PLOS ONE policies on sharing data and materials.