The ADRIREEF database: a comprehensive collection of natural/artificial reefs and wrecks in the Adriatic Sea

The paper presents a database of information on wrecks, natural and artificial reefs located in the Adriatic Sea, collected within the framework of the Interreg Italy–Croatia project ADRIREEF – Innovative exploitation of Adriatic Reefs in order to strengthen Blue Economy. The data collection lasted more than 1 year and included three surveys and a wide literature review. After being collected, data were harmonized and, where possible, made machine-readable. Moreover, data were widely metadated, published in a WebGIS (https://adrireef.github.io/sandbox3/, last access: 3 May 2021), and shared as open data in EMODnet (European Marine Observation and Data Network) Data Ingestion Portal through the SEANOE repository (Ferrà et al., 2020; https://doi.org/10.17882/74880). The database is composed of 285 three-dimensional records, each one described by 51 attributes. Parameters are clustered in four main groups: identification, reef description, site description, and management/exploitation information. Available literature (scientific and/or grey) was also included in the database and linked to the corresponding site. Published by Copernicus Publications. 1906 A. Minelli et al.: The ADRIREEF database


Introduction
In the Blue Innovation concept, the attractiveness and possible use of existing marine resources which are not yet properly exploited is relevant to promote sustainable economic development (Vogt, 1998;Orams, 2002;Cater and Cater, 2007;Kiper, 2013;Sakellariadou and Kostopoulou, 2015;Nurhayati et al., 2019) and redefine marine fisheries (Pauly, 2018;Stead, 2018).In this context, the recognition of less known and appreciated natural reefs (NRs), existing artificial structures (e.g.artificial reefs, rig-to-reefs; ARs), and wrecks could also be a successful way to pursue Blue Growth as all these sites might be suitable places for developing or improving sustainable activities such as fishing (both recreational and professional), nautical tourism, diving, and aquaculture (Wilhelmsson et al., 1998;Stolk et al., 2007;Uyarra et al., 2009;Needham, 2010;Edney, 2011;Spalding et al., 2017;Alempijević and Kovačić, 2019).Therefore, qualitative and quantitative information about the heritage presence and already existing human activities is fundamental to pursue an ecosystem-based sea use management according to the Maritime Spatial Planning (MSP) Directive (EU Directive 2014/89/EU, 2014; Douvere, 2008;Gilliland and Laffoley, 2008).As MSP is based on the three pillars for sustainable development -social, economic, and environmentalits implementation will in turn facilitate the enforcement of the Marine Strategy Framework Directive (MSFD, European Commission, 2008) and the achievement of Good Environmental Status (GES).
This work represents the joint effort of Italian and Croatian partners participating in the Interreg Italy-Croatia project ADRIREEF (Innovative exploitation of Adriatic Reefs in order to strengthen blue economy, https://www.italy-croatia.eu/web/adrireef, last access: 3 May 2021) aimed at assessing the potentiality of reefs in the Adriatic Sea, in order to strengthen the Blue Economy.Within the framework of the project, natural reefs are defined as either biogenic or geogenic formations protruding from the solid or soft seabed with distinctive living marine resources.An artificial reef is a submerged natural or manmade structure deliberately constructed or placed on the seabed to emulate some functions of a natural reef such as protecting, regenerating, concentrating, and/or enhancing populations of living marine resources, while doing "no harm".Accidentally sunken ships and planes are instead defined as wrecks.
Based on the above considerations, this paper presents a comprehensive collection of 285 natural reefs, artificial reefs, and wrecks located in the Adriatic Sea within Italian, Croatian, and international waters.
An analogous attempt of inventory was made on intentionally sunk shipwrecks to serve as ARs over six continents (Ilieva et al., 2019).Anyway, no structures of this type were signalled in the Adriatic Sea, whereas available literature (Pivetta and Spazzapan, 2012) and our search highlighted the occurrence of several accidentally sunken ships which, any-way, act as artificial habitats.Similar attempts to geolocalize ARs and wrecks were made along the national coasts and offshore waters of Florida and Alabama (USA), by querying municipalities about the deployment of the reefs (US Fish and Wildlife Service, Wildlife & Sport Fish Restoration Program, https://www.fws.gov/wsfrprograms/, last access: 3 May 2021), as well as in the Gulf of Mexico (Alabama Marine Resources Division, https://www.outdooralabama.com/saltwater-fishing/artificial-reefs, last access: 3 May 2021).The latter dataset reports all the submerged structures (including ARs, rig-to-reefs, and wrecks) in the Gulf of Mexico, but only name, type of reef, and coordinates are publicly available.Lastly, some efforts were made concerning NRs within the ReefBase project (http://www.reefbase.org/projects_partners/projects.aspx, last access: 3 May 2021), which helped localize and concisely qualify ∼ 10 000 reefs on a global scale (Oliver et al., 2002).
Another attempt made to identify aquaculture zones in the Adriatic Sea, also through a WebGIS application (http: //www.caps2.eu/caps2/,last access: 3 May 2021), reports zones of production, harvesting, and farms (Tora et al., 2017), but it does not include a few Italian reefs dedicated to this practice.
The collection work presented here is thus an ambitious attempt to gather in a single dataset the location, geometries, history, and detailed characteristics of natural reefs, artificial reefs, and wrecks existing in the Adriatic Sea.It required a deep knowledge on the overall status of the sites, their history, past and ongoing research and monitoring programmes carried out to characterize their ecological features, and on their current exploitation level.In this perspective, a key exercise in the ADRIREEF project was to obtain a classification of NRs, ARs, and wrecks occurring in the cooperation area and to provide a map of these sites from different perspectives: from the environmental to the economic point of view.
The result is an interactive map and an open-access detailed dataset (Ferrà et al., 2020) published on SEANOE whose contents are available for any user and purpose.

Data mining
Starting from an existing database, established in 2009 within the Italian Artificial Habitat Group of the Italian Society of Marine Biology (Fabi et al., 2011(Fabi et al., , 2015; http://www.habitatartificiali.irbim.cnr.it/wp, last access: 3 May 2021) carrying basic information about location and description of the artificial reefs, the National Research Council -Institute of Marine Biological Resources and Biotechnologies (CNR-IRBIM, http://www.irbim.cnr.it/it/index.php,last access: 3 May 2021) coordinated the data collection activity to improve it by developing and sharing among the ADRIREEF partners three online questionnaires on NRs, ARs, and wrecks (Appendices A, B, and C, respectively).
Earth Syst.Sci.Data, 13, 1905Data, 13, -1923Data, 13, , 2021 https://doi.org/10.5194/essd-13-1905-2021 An initial review of available literature and data was carried out to identify the necessary information on NRs and ARs and wrecks to be required.The questionnaires were structured in such a way to obtain a unique database for the two reef typologies and wrecks, including physical, ecological, and economic aspects, and allowing the classification of elements according to their characteristics.Given the importance of collecting answers quickly and having a structured and homogeneous database, it became essential to use easy online tools and to limit the possibility of free answers by proposing multiple-response questions (e.g.Google Forms application; https://www.google.com/forms/about/,last access: 3 May 2021).
The collected information was used to create the final ADRIREEF database which fed, in turn, a WebGIS application allowing the visualization of reefs and wrecks on an interactive map and their selection basing on running queries.
Projects' partners (PPs) were surveyed and answers were harmonized to obtain a consistent database.New features were defined and used as categories for the elements' classification and/or for the WebGIS application.Finally, all data properly checked and harmonized were assembled and used to populate the database.

Literature and data review
The review of existing literature took into account European environmental databases (https://www.eea.europa.eu/data-and-maps, last access: 3 May 2021, https://ec.europa.eu/environment/nature/natura2000/data/index_en.htm, last access: 3 May 2021), research projects carried out by CNR-IRBIM and other entities, scientific publications, and grey literature.Based on the results of the review and expert knowledge, existing gaps in the information of already known reef sites and wrecks were identified.
With regard to ARs, a large part of inputs came from the abovementioned CNR-IRBIM database on artificial habitats in Italy, containing more than 500 bibliographic references and information on 80 Italian artificial habitats such as harbours, breakwaters, fish aggregating devices (FADs), offshore platforms, and ARs since 1967.By checking this database, it was possible to obtain a list of 150 studies regarding the Adriatic ARs published between 1977 and 2017.Conversely, a similar literature heritage was not present for NRs and wrecks.

Questionnaire design
The analysis of the collected information highlighted the need of improving existing data, especially on NRs and wrecks.
As ARs and NRs have completely different features, it was decided to develop two distinct questionnaires.A third questionnaire was developed for wrecks as they have peculiar characteristics.All questionnaires were built in a systematic way with the aims of (i) investigating the reefs' and wrecks' suitability for Blue Economy purposes and identifying those answers that would help to achieve this target and (ii) facilitating experts' participation in the poll by ordering questions into a logical structure.
The identification of the person(s) filling in the questionnaires was considered relevant to collect consistent information and have a contact person in case of missing data.Moreover, numerical information (distances, measures, coordinates) were asked in specific measurement units to add collected data directly to the database and avoid transformations.

Natural and artificial reefs
Questions about reefs' characteristics that could influence their suitability for sustainable exploitation were divided into four main groups.
1. What is the reef and where is it located?
As a baseline, data regarding the identification of a reef are needed; therefore name and location (in the WGS84 coordinate reference system and decimal degrees) of the reef were required.
2. What are the main characteristics of the area where the reef is located?
The environmental characteristics of the area where a reef is located may influence its possible exploitation as well as its attractiveness to perform some activities; hence the following features were considered: minimum distance to the coast (km); typology of the surrounding seabed; presence of meadows; important biocoenoses, alien, and protected species (in case of NRs); and possible protection level applied to the area (in case of NRs).

What are the physical features of the reef?
The reef's physical features may also influence its potential use, especially for ARs, which are hand constructed and designed for specific scopes.To answer this fundamental question, multiple characteristics are needed: the typology of the reef, reef bottom depth (m), reef edge (in metres, for NRs), spatial extension of the reef (m 2 ), the origin of the reef (for NRs, if biogenic or geogenic), the material used for the reef construction (for ARs), and structural design of the reef (for ARs, where it is necessary to know the type and number of modules/structures put in place and their layout).
identify possible synergies and conflicts with additional potential users.At the same time, the original purpose of an artificial reef turns out to be key information for better understanding monitoring and surveillance programmes, management plans, and possible grants taking place in the area, as those could also limit or benefit future uses.Therefore, the following information was requested: scope(s) for which an AR was built; whether the reef is managed (for both NRs and ARs) and, if yes, who is the management entity; whether a monitoring programme is already in place (for both NRs and ARs) and, if yes, its duration and the investigations carried out; and whether the reef area is subjected to grant or surveillance service (only for ARs).Furthermore, questions regarding available data (scientific publications, grey literature, monitoring data) were added to the questionnaires, as they could help for future research purposes.

Wrecks
The questionnaire related to the category of wrecks required some information shared with reefs and some extra information about the physical features of structure.Shared information concerns (i) wreck identification (location and name), (ii) characterization of the surrounding area (distance from the coast, type of surrounding seabed, presence of meadows), (iii) physical features of the wreck (material, bottom depth, and wreck edge), and (iv) exploitation and protection of the wreck (exploitation, protection, and management of the site, if existing).
Extra information requested from the partners included weight of the wreck (tonnes), total area of the footprint (m 2 ), total volume of the shipwreck (m 3 ) and known dimensions (length, width, height in metres).

Harmonization and construction of the database
Firstly, all data collected from 270 questionnaires were screened to delete duplicates and identify incomplete entries and missing information, in order to make possible an evaluation of a reef/wreck for Blue Economy purposes.For these missing records, a data integration was requested from the contact person.
Data collected from questionnaires were then assembled together with those already contained in the CNR-IRBIM database and harmonized, as some answers were not in line with the requirements.Moreover, geolocations of reefs were inspected in a GIS environment, and, when those were inconsistent, clarifications were requested.
Once data control and harmonization were completed, a preliminary analysis and classification of the Adriatic reefswrecks were performed, and query filters of the WebGIS application were identified.Once criteria for reef/wreck classification and filters to be applied in the WebGIS applica-tion were definitely agreed upon with PPs, the ADRIREEF database was finalized.
The final database counted 51 columns, 48 of them derived by the questionnaires and 3 created by the database manager (type of reef, country, region).Of these fields, 10 were used as filters in the WebGIS application and/or for the reefs' classification, while the remaining 41 were used as part of technical information sheets.

Database structure and geographical coverage
The database counts 285 three-dimensional elements (latitude-longitude coordinate and bottom depth), described by 51 parameters and divided into 129 natural reefs, 47 artificial reefs, and 109 wrecks located in the Adriatic Sea falling into Italian, Croatian, and international waters (Table 1).
All artificial reefs and most wrecks fell within the Italian territorial waters, while the majority (79 %) of natural reefs were located within the Croatian ones.The presence of almost all the natural reefs on the eastern side of the studied area is mainly due to the geological morphology of the Adriatic basin (Stefanon, 1972), while the complete absence of artificial reefs on the same side is currently due to Croatian legal constraints.It is worth noting that the number of wrecks reported in the Croatian waters is somewhat underestimated.This fact is due to the lack of basic information about several wrecks (e.g.lack of exact position of the shipwreck, which did not allow placing it on the map), so it was decided to keep only those with adequately detailed information in the database.It is also worth noting that, given the great occurrence of rocky substrates along the Croatian coast, it was agreed within the ADRIREEF Consortium to identify homogeneous areas and map each of them as a single natural reef (Zec et al., 2019).
Location of reefs and wrecks is expressed in decimal degrees and the coordinate reference system WGS84.The database is available as a unique comma-separated value (CSV) file.
Table 2 summarizes the structure of the ADRIREEF database specifying the parameters required for each new element: parameter name, description, unit of measure, origin of the data (if they come directly from questionnaires or have been created by the database manager), and possible applicability restrictions.Table 2 also reports, for each parameter, the group it belongs to.As mentioned in Sect.2.2.1, Group no. 1 corresponds to reef identification and geolocation information, Group no. 2 contains parameters summarizing the characteristics of the area hosting the reef or wreck, Group no. 3 concerns aspects of the reef/wreck that may also have an effect on its usage, and Group no. 4 includes parameters about the present and/or possible future reef or wreck exploitation.

Data interrogation and visualization
With the purpose of easily exploiting, representing, and filtering data, a WebGIS was created enabling the contemporary filtering (where applicable) of more than one of the following selected attributes: type of element, country, minimum depth of the reef/wreck, distance from the coastline, usage of the reef/wreck, reef typology (for natural reefs), reef material (for artificial reefs).
The WebGIS main page is reachable at the following URL: https://adrireef.github.io/sandbox3/(last access: 3 May 2021), and it is composed of two user-friendly windows (Fig. 1), one reporting all available data filters (left side) and the other one (right side) showing the map where points, identifying elements, are divided by colour in NRs (green), ARs (blue), and wrecks (red).Hovering on an element with the mouse, its name and location appear in the left bottom corner of the map.
The total number of currently visualized elements is reported at the top right of the map.Moreover, when an element is clicked, a pop-up window appears showing the associated relevant information (Fig. 2).From this pop-up, it is possible to print out information regarding the selected element in PDF format.From the main page, it is also possible to access to the "list view" that shows, for the visualized elements, some common information throughout natural reefs, artificial reefs, and wrecks (Fig. 3).The number of visualized elements, in the top right corner of the map view, is updated accordingly to the output of data filtering operations.
From a technical point of view, data were entered in .csvformat and then transformed in JSON objects as "collection of features" class, with prototype (generic) and object (specific) capabilities.For each element, an integer and consecutive identification number were assigned by default.The interactive map has been published using the GitHub Pages extension (https://pages.github.com/,last access: 3 May 2021), which represents an easy and rapid way to make information quickly available online.The base map coming from the open-source cooperative geographical project OpenStreetMap (https://www.openstreetmap.org/,last access: 3 May 2021) and the Nominatim package for geocoding operations (https://nominatim.openstreetmap.org/,last access: 3 May 2021) were used.The whole infrastructure is based on Searchable Map Template -CSV project (https:// github.com/datamade/searchable-map-template-csv,last access: 3 May 2021).

Data analysis
Data contained in the database can be analysed in many different ways and for different purposes.For example, Fig. 4, representing the wrecks' sink and the artificial reefs' deployment on time (excluding missing information elements), shows that until the end of the 1990s the majority of artificial structures occurring on the seabed of the Adriatic Sea were represented by wrecks, most of which had accidentally sunk.Afterwards, almost all the manmade structures deployed on the seabed were purposely constructed artificial reefs.
Another interesting example of analysis that can be performed on the data is the evaluation of the number of natural reefs subjected to any form of protection.Again, after deduction of "no data", it is possible to identify 31 Natura 2000 sites, 12 protected areas, 4 natural reserves, and 11 national parks (Fig. 5) with overlapping at some sites.Figure 5 also shows how NRs are distributed in these categories through Italian and Croatian waters.Coupling this graph with the information contained in Table 1, it results that almost the totality of the Italian natural reefs are subjected to some form of protection, while only half of the Croatian ones are under preservation constraints.
Also, the 3D representation of the sites can be useful for dissemination purposes.For example, in Fig. 6a all reefs and wrecks are reported over a bathymetric map of the Adriatic Sea.A section of the Tremiti Islands (Apulia, Italy), connecting three observations of the database, is reported in the zoom (panel b). https://doi.org/10.5194/essd-13-1905-2021 Earth Syst.Sci.Data, 13, 1905Data, 13, -1923Data, 13, , 2021 , 2007) to unlock existing but fragmented and hidden marine data and make them freely accessible for a wide range of users (Calewaert et al., 2016), while respecting FAIR data management principles (Findable, Accessible, Interoperable, Reusable; Wilkinson et al., 2016).
In this way, an invaluable heritage of marine data were   Earth Syst.Sci.Data, 13, 1905Data, 13, -1923Data, 13, , 2021 of the art and some hints on possible future exploitation of reefs and wrecks in this geographical zone and a tool to implement the EUSAIR strategy (European Commission, 2014), aimed at promoting economic and social prosperity and growth in the Adriatic-Ionian region by creating synergies and fostering coordination in some thematic pillars: sustainable tourism, environmental quality, connecting the region, and, in wider terms, the Blue Growth (European Commission, 2017).Indeed, the collected information can be useful for different purposes, from spatial management, to the strengthening of some economic activities and/or development of new ones taking into account the local environmental features Knowing the environmental status and current exploitation level of reefs/wrecks located in a specific geographical area is in fact fundamental to identify potential additional ecosystem services they can provide and, consequently, develop sustainable economic activities with subsequent positive impacts on the local communities (Costanza et al., 2014).In addition, from the research point of view, a comprehensive database like the one presented here could be a starting point for the implementation of ecological studies where the information is still scarce or lacking as well as of monitoring programmes aimed at evaluating the impact of some economic activities (e.g.tourism, small-scale fisheries) on sensitive habitats.
Lastly, the interactive map represents a tool that allows, through the simultaneous usage of different filters, to highlight and quantify particularly interesting situations in a userfriendly and quick manner, so as to be also easily handled by the wider public.It could be, for example, used by tourists to identify suitable and less known sites for recreational activities such as snorkelling, diving, and sailing.
Overall, the provided collection can be helpful to increase visibility and attractiveness of reefs and wrecks existing in the Adriatic Sea while increasing awareness of both policy makers and citizens towards the need of managing and exploiting these sites in a sustainable way in order to assure their preservation over time.
The general perception derived from an overall evaluation of the collected data is that, in the Adriatic context, reefs and wrecks still represent an underestimated environmental heritage that, if adequately preserved and promoted, could provide new opportunities for developing activities in line with the Blue Economy in the near future.Data, 13, 1905Data, 13, -1923Data, 13, , 2021

Figure 1 .
Figure 1.The WebGIS interface.On the left side: the filter window.On the right side: the map window with hover function (bottom left) and the total number of identified elements (top right).Basemap credits: © OpenStreetMap contributors 2020.Distributed under a Creative Commons BY-SA License.

Figure 2 .
Figure 2. Example of the pop-up that appears once an element is clicked.Basemap credits: © OpenStreetMap contributors 2020.Distributed under a Creative Commons BY-SA License.

Figure 3 .
Figure3.List view.Once elements are selected, it is possible to obtain some common information by clicking the "List view" button (that turns into "Map view" when the list is visualized, evidenced in red).

Figure 4 .
Figure 4. Artificial reefs and wrecks by year of deployment at the decadal scale.

Figure 5 .
Figure 5. Protection measures applied to natural reefs in Croatia and in Italy.

Figure 6 .
Figure 6.A 3D visualization of the spatial distribution of natural reefs, artificial reefs, and wrecks in the Adriatic Sea (a).In the red square, the area concerning the zoom reported below.A view of Tremiti Islands and the vertical terrain section from left to right crossing three elements (b): Padre Giovanni and Lombardo wrecks (points no. 1 and 3) and Mediterranean mesophotic coral reef (point no.2).

Table 1 .
Adriatic reefs and wrecks by typology and country.

Table 2 .
Column name, the current name of the parameter, type of parameter, unit of measure, origin of the information, and eventual applicability restrictions.