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    Background The macroalgal flora of Graciosa (central group of Azores archipelago) is poorly known, the published information reflecting occasional collections from sporadic field visits to the island. To overcome this, a thorough investigation under the Expedition “GRACIOSA/2004”, the Campaigns “PADEL/2006”, “MACROBIOLMOL/2014” and “PIMA-BALA/2017” involving sample collecting and presence data recording, was undertaken over an area of 19 km2 encompassing littoral and sublittoral levels down to about 40 m. This paper lists the taxonomic records and provides information on species ecology and occurrence around the island improving the knowledge of the Azorean macroalgal flora at both local and regional scales. New information A total of 1692 specimens belonging to 250 taxa of macroalgae (and including 55 taxa identified only at the genus level) are registered, comprising 166 Rhodophyta, 36 Chlorophyta and 48 Ochrophyta (Phaeophyceae). From these, 195 are identified to the species level (126 Rhodophyta, 31 Chlorophyta and 38 Ochrophyta) and comprise 156 native, 20 of uncertain origin and 14 introductions to the island. Predaea feldmannii subsp. azorica Gabriel is an Azorean endemic, whereas Codium elisabethiae O.C. Schmidt, Botryocladia macaronesica Afonso-Carrillo, Sobrino, Tittley & Neto, Phyllophora gelidioides P.Crouan & H.Crouan ex Karsakoff and Laurencia viridis Gil-Rodríguez & Haroun represent Macaronesian endemics. Seventy-nine species are newly recorded to the island. Introduction Around 400 species have been recorded in the isolated mid-Atlantic Azores archipelago so far (Freitas et al. 2019). When compared to that of other remote oceanic islands (e.g. the Shetlands and Faroes in the colder North Atlantic, and Ascension and Tristan da Cunha in the Southern Atlantic), the algal flora of the Azores can be considered relatively rich (Tittley 2003, Neto et al. 2005; Tittley & Neto 2005; Tittley & Neto 2006, Wallenstein et al. 2009). It is a cosmopolitan flora with species shared with Macaronesia, North Africa, the Mediterranean Sea, Atlantic Europe and America. Overall, it shares more species with the east Atlantic flora than with the west (Tittley & Neto 2006, Wallenstein et al. 2009). Although São Miguel has been thoroughly investigated, most of the Azorean islands have received little attention, there algal flora being scarcely studied. To overcome this, and improve the understanding of the archipelago’s seaweed flora, research has been conducted over the past three decades. This paper presents both physical and occurrence data, and information gathered from macroalgae surveys undertaken on Graciosa (central group of the archipelago) by the Island Aquatic Research Group of the Azorean Biodiversity Centre of the University of the Azores ( the MARBE, Marine Biodiversity and Environment Research Group of CIBIO-Açores at the University of the Azores (, and the OKEANOS Centre of the University of the Azores ( In these surveys particular attention was given to the small filamentous and thin sheet like forms that are often short-lived and fast-growing species, very difficult to identify in the wild, requiring the aid of a microscope. The paper aims to provide a practical resource for biological studies, such as systematics, diversity and conservation, biological monitoring, climate change and ecology, and also for academics, students, government, private organizations, and the general public. Purpose In this contribution we list taxonomic records for Graciosa and present general information for the occurrence of each taxon around the island. By doing this, we are contributing to address several biodiversity shortfalls (see Hortal et al. 2015), namely the need to catalogue the Azorean macroalgae (Linnean shortfall) and improve the current information on their local and regional geographic distribution (Wallacean shortfall), as well as on species abundances and dynamics in space (Prestonian shortfall).