Rhodolith occurrences in the Azores (central north Atlantic) between 1998 and 2018

Rhodoliths is a general term used to designate non-geniculate coralline red algae (Rhodophyta) that live unattached (Riosmena-Rodríguez, 2017). The term is used here to encompass (i) branched free-living coralline algae devoid of an evident nucleus, but also (ii) nucleated nodules where the biogenic calcium carbonate deposit around the core represents >50%, as well as (iii) “coated grains” where the core is larger than the algal carbonate component.
In some sublittoral sites with favourable environmental conditions, rhodoliths form dense beds which are integrated in the EUNIS classification as ‘Maerl beds’ (code: A5.51). The complex microhabitats found above and within these beds typically harbour high levels of biodiversity and sustain various organisms of commercial interest at different life stages. Because of their vulnerability, rhodolith beds (=‘Maerl beds’) have been listed as threatened and/or declining under the OSPAR convention.
Knowledge on the rhodolith assemblages occurring  around the Azores archipelago (central North Atlantic) remains scarce and their distribution and ecological niche remains poorly investigated. The first rhodolith records in the region were made in shallow environments, including a sheltered but well-mixed flooded crater off São Miguel Island (Hawkins et al., 1990) and infralittoral rockpools on the southern coast of Pico Island (Rosas-Alquicira et al., 2009). More recently, deep rhodoliths have been identified on open shelf sectors near the infralittoral to circalittoral transition in more than 60-meter depths (Rebelo et al., 2018). Four rhodolith-forming species have been so far identified in the Azores: Neogoniolithon brassica-florida, Lithophyllum crouaniorum (as 'crouanii') and Phymatolithon calcareum (Rosas-Alquicira et al., 2009), which occur in shallow water; and Lithophyllum incrustans, which has been reported to form the deep rhodoliths (Tempera et al., 2013; Rebelo et al., 2018).
This dataset compiles sublittoral rhodolith occurrences from surveys conducted across the Azores archipelago between 1998 and 2018. Sampling was made using: (i) van Veen grabs, (ii) a box corer, (iii) two small remotely-operated vehicles (a VideoRay Explorer micro-ROV and a SeaBotix LBV300S-6 mini-ROV); (iv) two custom-made drop-down cameras (built from Tritech MD4000, GoPro Hero3+ and GitUp Git 2 cameras); and (v) SCUBA divers using conventional open-circuit systems.
The compilation comprises 363 presences and absences identified between 2 m and 264 m depth. Information on taxonomy and rhodolith nucleation is provided where available. A few literature-based records are included for the sake of completion.	

"Acknowledgements:
To the Portuguese Foundation for Science and Technology for grants and individual contracts awarded to F. Tempera (refs: SFRH/BD/12885/2003, SFRH/BPD/79801/2011), A.C. Rebelo (SFRH/ BPD/117810/2016) and Pedro Afonso (IF/01640/2015) and for funding the Okeanos Strategic Programme. To the Azores Regional Government for the Estagiar-L grant awarded to A.L. Sinde-Mano and funding surveys conducted under the BALA and MoniZec-ARP (DRAM) monitoring programmes. To projects MONICO and Mission Atlantic (EC H2020-LC-BG-08-2018) for funding this data compilation. To EC project MARFOR (BIODIVERSA/004/2015) for D. Milla-Figueras contract and fieldwork funding. To project PLATMAR (FCT PTDC/GEO-GEO/0051/2014) for funding fieldwork in 2018. To the projects GEMAS (SRA-Açores), MARINOVA (FEDER INTERREG III-B MAC/4.2/M11), MAROV (PDCTM/P/MAR/15249/1999) and MESH-Atlantic (AA-10/1218525/BF) for funding sediment sampling around the Faial and Pico islands. To the Oceano Azul Foundation and the Waitt Foundation for funding the Blue Azores 2018 expedition. To the University of St. Andrews (Scotland) for providing the Video Ray micro-ROV and the Tritech camera used in 2004 and 2005. To the crews of the vessels R/L Águas Vivas, and R/V Arquipélago and Nossa Senhora dos Milagres for all their help in the preparation and execution of the sampling surveys. To Renato Martins (IMAR-DOP/UAz) for the mini-ROV SP operation, troubleshooting and 2016 sediment collection. To Ricardo Serrão Santos and Frederico Cardigos for their general support and organisation of the early BANCOS expeditions promoted by IMAR/DOP-UAç."