Marine algal flora of Graciosa Island, Azores

Abstract Background The macroalgal flora of Graciosa (central group of Azores archipelago) is poorly known, with only 116 species recorded so far (authors personal data). The published information reflects 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 around the Island. 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 algal flora of the Island.


Introduction
Around 400 species of marine macroalgae have been recorded in the isolated mid-Atlantic Azores archipelago so far (Freitas et al. 2019). The Azorean algal flora is cosmopolitan with species shared with Macaronesia sensu lacto, North Africa, the Mediterranean Sea, Atlantic Europe and America. Overall, it shares more species with the east Atlantic flora than with the west Neto 2006, Wallenstein et al. 2009).
Based on extensive analysis encompassing widely-dispersing phyla (as coastal fishes, echinoderms and macroalgae) and less-dispersing phyla (as brachyurans, polychaetes and gastropods), Freitas et al. (2019) suggested that the Azores should be a biogeographical entity of its own and proposed a re-definition of the Lusitanian biogeographical province, in which they consider four ecoregions: the South European Atlantic Shelf, the Saharan Upwelling, the Azores ecoregion and a new ecoregion herein named Webbnesia, which comprises the archipelagos of Madeira, Selvagens and the Canary Islands. In their paper, when comparing the Azorean algal flora to that of the new Webbnesia region, they reported that the Canary Islands, with 689 species, are by far the most diverse archipelago, followed by the Azores (405), Madeira (396) and Cabo Verde (333). The Selvagens are the least diverse one (295 species). 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 also be considered relatively rich (Tittley 2003, Tittley and Neto 2006).
From all Azorean Islands, São Miguel is by far the one with the largest amount of research dedicated to the study of the algal flora. The total number of algal species is at the moment 260, a number that is likely to increase due to ongoing research by authors of the present paper. Most of the remaining Islands have received less attention. To overcome this and to improve the understanding of the archipelago's macroalgal flora, research has been conducted over the past three decades in all the Islands. Data on the Islands of Pico and Terceira are already available on the recently-published papers by Neto et al. (2020a), Neto et al. (2020b). The present 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 (Link: https://ce3c.ciencias.ulisboa.pt/sub-team/island-aquatic-ecology), the MARBE, Marine Biodiversity and Environment Research Group of CIBIO-Açores at the University of the Azores (Link: http://cibio.uac.pt/en/research-groups/marbe-marinebiodiversity-and-environment) and the OKEANOS Centre of the University of the Azores (Link: http://www.okeanos.uac.pt). 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 organisations and the general public.

General description
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 Cardoso et al. 2011, Hortal et al. 2015, namely, the need to catalogue the Azorean macroalgae (Linnean shortfall) and to 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). Table 1.
Number of macroalgal species on the Azorean Islands (Neto et al. 2020b, c and authors' unpublished data).

Study area description:
The Azores archipelago, located in the North Atlantic, roughly at 38°43′49″N 27°19′10″W ( Fig. 1) comprises nine Islands and several Islets spread over 500 km in a WNW direction. The climate is temperate oceanic, with persistent winds, regular and abundant rainfall and high levels of relative humidity mainly during winter and autumn (Morton et al. 1998). The Islands have a restricted coastal extension due to the lack of a continental shelf and deep waters occur within a few kilometres offshore. The tidal range is small (< 2 m, see Hidrográfico 1981) and coasts are subjected to swell and surge most of the year. Shore geomorphology alternates between high cliffs and rocky cobble/boulder beaches (Borges 2004). Fig. 1) is the second smallest Island of the Azores archipelago. Located in the central group, roughly at 39°0′38″N, 27°59′1″W, about 37 km north of São Jorge and 58 km north-west of Terceira, it has an area of about 62 km and a maximum altitude of 402 m at the summit of the Caldeira, located at the south-western tip of the Island ).

Graciosa (in black in
With the exception of Serra Branca, bordered by cliffs higher than 200 m and the area between Lagoa and Barra, where the coastline consists of steep cliffs, the remaining coastline of the Island is low (below 50 m), with long stretches of cobble beaches interspaced with lava flows (forming irregular extensions of bedrock), boulder areas and the single sandy beach near the small village of Praia. Between Ponta Branca and Carapacho, there are several bays, of which the bay of Filipe is the largest in size and 2 easily accessible by land. Rock pools are common on the bedrock shores around the Island, creating a shallow subtidal habitat with a rich diversity of marine life ).
As on the remaining Azores Islands, the intertidal and shallow subtidal rocky-shore communities of Graciosa are dominated by macroalgae . The high intertidal level communities are characterised by a patchy mosaic of algae (principally Fucus spiralis Linnaeus, Gelidium microdon Kützing and Gymnogongrus spp.) and a few animals (mainly chthamalid barnacles) (Fig. 2). Lower, the shore is covered by algal turfs (growth forms of either diminutive algae or diminutive forms of larger species that create a dense, compact mat 20-30 mm thick), either monospecific or composed of several species, for example, calcareous algae (e.g. Ellisolandia and Jania) or by soft algae (e.g. Centroceras clavulatum (C.Agardh) Montagne, Chondracanthus and Laurencia) (Fig. 3). At this level, a few limpets may be seen. The erect, corticated macrophytes Ellisolandia elongata (J.Ellis & Solander) K.R.Hind & G.W.Saunders, Pterocladiella capillacea (S.G.Gmelin) Santelices & Hommersand (Fig. 4) and Treptacantha abies-marina (S.G.Gmelin) Kützing are common in the transition zone to the subtidal, which is usually dominated by large foliose species ). Subtidally, algal communities are characterised by associations of two or three frondose macrophytes (Fig. 5), predominantly the brown seaweeds, for example, Dictyota spp., Halopteris spp. and Zonaria tournefortii (J.V.Lamouroux) Montagne ).

Design description:
The algae, referred to in this paper, were collected during field studies at littoral and sublittoral levels down to approximately 40 m on the Island of Graciosa. Each sampling location was visited several times. On each occasion, a careful and extensive survey was undertaken to provide good coverage of the area. Both presence recording and physical collections were made by walking over the shores or by scuba diving. The specimens collected were taken to the laboratory for identification and preservation and the resulting vouchers were deposited at the AZB Herbarium Ruy Telles Palhinha and the Molecular Systematics Laboratory at the Faculty of Sciences and Technology of the University of the Azores.
Funding: This study was mainly financed by the following projects/scientific expeditions:     Collecting macroalgae at the rocky intertidal (by the Island Aquatic Ecology Subgroup of cE3c-ABG) .

Sampling description:
Intertidal collections were made during low tide by walking over the shores. Subtidal collections were made by scuba diving around the area. Sampling involved specimen collecting and species-presence recording. For the former, at each location, samples were obtained by scraping (Fig. 7) one or two specimens of all different species found into labelled bags. Species-recording data were gathered by registering all species present in the sampled locations visited (Fig. 8). Complementary data, for example, shore level (high, mid, low), orientation and type of substrate (bedrock, boulders, cobbles, mixed), habitat (tide pool, open rock, gully, crevice, cave) were also recorded.
Quality control: Each sampled taxon was identified by trained taxonomists and involved morphological and anatomical observations of whole specimens by eye or of slide preparations under the microscope for the diagnostic features described in literature.
Step description: Specimens were brought back to the laboratory, sorted and studied following standard procedures used in macroalgae identification.
Species identification was based on morphological and anatomical characters and reproductive structures. For small and simple thalli, this required the observation of the entire thallus with the naked eye and/or using dissecting and compound microscopes. For larger and more complex algae, investigation of the thallus anatomy required histological preparations (longitudinal and transverse sections) for the observation of cells, reproductive structures and other diagnostic characters. As the Azorean algal flora has representatives from several geographical regions, often causing difficulty in identification, floras and keys for the North Atlantic, Tropical Atlantic and Western Mediterranean were used (e.g. Schmidt 1931, Taylor 1967, Taylor 1978, Levring 1974, Dixon and Irvine 1977, Lawson and John 1982, Irvine 1983, Gayral and Cosson 1986, Fletcher 1987, Afonso-Carrillo and Sansón 1989, Burrows 1991, Boudouresque et al. 1992, Cabioc'h et al. 1992, Maggs and Hommersand 1993, Irvine and Chamberlain 1994, Brodie et al. 2007, Lloréns et al. 2012and Rodríguez-Prieto et al. 2013. For more critical and taxonomically-difficult taxa, specimens were taken to the Natural History Museum (London) for comparison with collections there.
A reference collection was made for all collected specimens by assigning them a herbarium code number and depositing them at the AZB Herbarium Ruy Telles Palhinha and the Molecular Systematics Laboratory, University of Azores. Depending on the species and on planned further research, different types of collections were made, namely (i) liquid collections using 5% buffered formaldehyde seawater and then replacing it by the fixing agent Kew (Bridsen and Forman 1999); (ii) dried collections, either by pressing the algae (most species) as described by Gayral and Cosson (1986) or by letting them air-dry (calcareous species); and (iii) silica gel collections for molecular study.
Nomenclatural and taxonomic status used here follow Algaebase (Guiry and Guiry 2020). The database was organised on FileMaker Pro.

Taxonomic coverage
Description: All macroalgae were identified to genus or species level. In total, 250 taxa were identified belonging to 31 orders and 66 families, distributed by the phyla Rhodophyta (17 orders and 41 families), Chlorophyta (4 orders and 9 families) and Ochrophyta (10 orders and 16 families).   Description: This data paper presents both physical and occurrence data from macroalgal surveys undertaken on Graciosa Island between 2004 and 2017 (Neto et al. 2020c. The dataset submitted to GBIF is structured as a sample event dataset, with two tables: event (as core) and occurrences. The data in this sampling event resource have been published as a Darwin Core Archive (DwCA), which is a standardised format for sharing biodiversity data as a set of one or more data tables. The core data table contains 50 records (eventID). The extension data table has 1692 occurrences. An extension record supplies extra information about a core record. The number of records in each extension data table is illustrated in the IPT link. This IPT archives the data and thus serves as the data repository. The data and resource metadata are available for downloading in the downloads section.  Many species were only sporadically recorded around the Island, but 12 were commonly found, namely: the Rhodophyta Ceramium virgatum Roth, Chondria dasyphylla A mismatch regarding the GBIF backbone taxonomy of some of the macroalgae species names was identified as detailed in Suppl. material 1.