Marine algal flora of Flores and Corvo Islands, Azores

Abstract Background The algal flora of the western group of the Azores archipelago (Islands of Flores and Corvo) has attracted the interest of many researchers on numerous past occasions (such as Drouet 1866, Trelease 1897, Gain 1914, Schmidt 1929, Schmidt 1931, Azevedo et al. 1990, Fralick and Hehre 1990, Neto and Azevedo 1990, Neto and Baldwin 1990, Neto 1996, Neto 1997, Neto 1999, Tittley and Neto 1996, Tittley and Neto 2000, Tittley and Neto 2005, Tittley and Neto 2006, Azevedo 1998, Azevedo 1999, Tittley et al. 1998, Dionísio et al. 2008, Neto et al. 2008). Despite this interest, the macroalgal flora of the Islands cannot be described as well-known with the published information reflecting limited collections preformed in short-term visits by scientists. To overcome this, a thorough investigation, encompassing collections and presence data recording, has been undertaken for both the littoral and sublittoral regions, down to a depth of approximately 40 m, covering a relatively large area on both Islands (approximately 143 km2 for Flores and 17 km2 for Corvo). This paper lists the resultant taxonomic records and provides information on species ecology and occurrence around both these Islands, thereby improving the knowledge of the Azorean macroalgal flora at both local and regional scales. New information For the Island of Flores, a total of 1687 specimens (including some taxa identified only to genus level) belonging to 196 taxa of macroalgae are registered, comprising 120 Rhodophyta, 35 Chlorophyta and 41 Ochrophyta (Phaeophyceae). Of these taxa, 128 were identified to species level (80 Rhodophyta, 22 Chlorophyta and 26 Ochrophyta), encompassing 37 new records for the Island (20 Rhodophyta, 6 Chlorophyta and 11 Ochrophyta); two Macaronesian endemics (Laurencia viridis Gil-Rodríguez & Haroun and Millerella tinerfensis (Seoane-Camba) S.M.Boo & J.M.Rico); six introduced (the Rhodophyta Asparagopsis armata Harvey, Neoizziella divaricata (C.K.Tseng) S.-M.Lin, S.-Y.Yang & Huisman and Symphyocladia marchantioides (Harvey) Falkenberg; the Chlorophyta Codium fragile subsp. fragile (Suringar) Hariot; and the Ochrophyta Hydroclathrus tilesii (Endlicher) Santiañez & M.J.Wynne and Papenfussiella kuromo (Yendo) Inagaki); and 14 species of uncertain status (10 Rhodophyta, two Chlorophyta and two Ochrophyta). For the Island of Corvo, a total of 390 specimens distributed in 56 taxa of macroalgae are registered, comprising 30 Rhodophyta, nine Chlorophyta and 17 Ochrophyta (Phaeophyceae). Whilst a number of taxa were identified only to the genus level, 43 were identified to species level (22 Rhodophyta, eight Chlorophyta and 13 Ochrophyta), comprising 22 new records for the Island (nine Rhodophyta, four Chlorophyta and nine Ochrophyta), two introduced species (the Rhodophyta Asparagopsis armata and the Chlorophyta Codium fragile subsp. fragile and seven species of uncertain status (five Rhodophyta and two Ochrophyta).


Introduction
The Azorean algal flora, considered cosmopolitan, with species shared with Macaronesia, North Africa, the Mediterranean Sea, Atlantic Europe and America (Tittley 2003, Tittley and Neto 2006, Wallenstein et al. 2009), is relatively rich when compared to that of other remote oceanic Islands , Wallenstein et al. 2009). Around 400 species of marine macroalgae have, to date, been recorded for the isolated mid-Atlantic Azores archipelago (Freitas et al. 2019). These authors, based on extensive analysis encompassing data on brachyurans, polychaetes, gastropods, echinoderms, coastal fishes and macroalgae, suggested that the Azores should be a biogeographical entity of its own and proposed a redefinition of the Lusitanian biogeographical province, in which they recognised 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 comparing the Azorean algal flora to that of the new Webbnesia region, they reported that the Canary Islands, with 689 species of marine macroalgae, 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). It is worth mentioning that the published information reflects data from only a few of the nine Azorean Islands, since not all of them have been adequately investigated. In the Azores archipelago, São Miguel is by far the Island with the largest amount of research dedicated to the study of its 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 improve the understanding of the archipelago's macroalgal flora, research has been conducted over the past three decades on all the Islands. Data on the Islands of Pico, Graciosa and Terceira is already available on the recently-published papers (Neto et al. 2020a, Neto et al. 2020b, Neto et al. 2020c To provide a better understanding of the archipelago's seaweed flora, a long term research programme of study has been undertaken, mainly by local investigators into the marine macroalgae flora on several of the less studied Azorean Islands. The present paper presents both physical and occurrence data and information gathered from surveys Table 1.

Study area description:
The Azores archipelago (38°43′49″N, 27°19′10″W, Fig. 1), comprising nine Islands and several islets, is spread over 500 km, in a WNW direction. The Islands emerged from what is called the Azores Plateau and are located above an active triple junction between three of the world's largest tectonic plates (the North American Plate, the Eurasian Plate and the African Plate, Hildenbrand et al. 2018). Flores and Corvo (in black in Fig. 1), the westernmost Islands of the archipelago, are located in the North American Plate, whereas the remaining Islands are located around the boundary that divides the Eurasian and African Plates (Hildenbrand et al. 2018).
The Islands of Flores and Corvo are sub-aerial domains of a large volcanic formation, mostly submarine, implanted on an oceanic crust and aged between 9.0 and 10.0 million years (Ma). Each of these Islands has unique geomorphological characteristics: Flores (39°31'27″N, -31°15'31"W, Fig. 2), of approximately 141 km , is composed of two units, the central massif located in the central plain and the coastal periphery; Corvo, its neighbour (39°43'37"N, -31°7'44"W, Fig. 3), of approximately 17 km , is a crater of a major Plinian eruption and the smallest Island of the Azores archipelago (Azevedo 1999). The climate, as in the remaining Islands, is characterised by regular and abundant rainfall, high levels of 2 2 Figure 1.
The Azores, its location in the Atlantic and Flores and Corvo Islands highlighted in black (by Nuno V. Álvaro).
relative humidity and persistent winds, mainly during the winter and autumn seasons (Morton et al. 1998). Fog is common and almost permanent at the higher elevations.
Marine action is responsible for the predominance of erosive morphologies in the coastal areas of both Islands, examples of which on Flores (Neto et al. 2008) are: the valleys associated with fluvial erosion (Vales das Lajes and da Fazenda); the coastal or back cliffs (Fajãzinha -Ponta da Fajã); the large marine abrasion platforms (Fajãzinha -Fajã Grande); and the coastal platforms associated with landslides and collapses (Ponta da Fajã).
Owing to the lack of a continental shelf that characterises most volcanic Islands, coastal extension is restricted and deep waters occur within a few kilometres offshore. The tidal  range is small (< 2 m, Hidrogrográfico 1981) and coasts are subjected to swell and surge for most of the year.
The Islands' coastline, approximately 72.209 km long on Flores and 19.045 km long on Corvo, is predominantly rocky, subject to strong maritime erosion and presents an irregular slope with extensive and high cliffs cut by waterfalls and streams, alternating with a complex system of bays, rocky beaches and natural terraces (Azevedo 1999). The bottom is mostly made up of irregular rocky bedrock, containing, in some places, pockets of sediment of coarse sand and gravel, alternating with places covered by blocks that rest on either the rocky bed or the sediment. Submerged or semi-submerged caves, arches and tunnels of small amplitude and reduced length are common. As depth increases, the slope decreases, although the bottom is still rocky and uneven. This feature is interrupted by valleys and other structures of smooth to rough relief. The sediment floor in the deepest areas is stable, generally composed of medium and/or coarse sand. From this floor arise small islets with normally vertical walls and low irregular crowns, marked by ridges and valleys (Neto et al. 2008). Along the coastline and islets, natural sheltered habitats (arches and semi-submerged caves, tide pools) create favourable conditions for the growth of juveniles and adults of coastal fish. The constant recycling of nutrients caused by the wave-exposed coasts of these Islands, provides suitable conditions for the occurrence of considerable diversity and abundance of macroinvertebrates and pelagic and benthic fish (Neto et al. 2008). At the foot of the cliffs, the rocky intertidal zone is, as elsewhere in the Azores, dominated by algal communities that form mosaic and/or horizontal bands relative to tide level and are made up of multispecific algal turfs (growth forms of either diminutive algae or diminutive forms of larger species) that carpet the rocks. In the intertidal, a distinct zonation pattern is evident. The higher zone, dominated by invertebrates (littorinids and chthamalid barnacles, Fig. 4), gives rise below to a mid-shore zone covered by algal turfs that create a dense, compact mat 20-30 mm in thickness, Fig. 5). The turf can be monospecific (of either Caulacanthus ustulatus (Turner) Kützing, Centroceras clavulatum (C. Agardh) Montagne or Gymnogongrus) or multispecific and composed by soft algae (e.g. Centroceras clavulatum, Ceramium and Chondracanthus) usually growing as epiphytes over articulate calcareous forms (e.g. Ellisolandia and Jania). The low-shore zone is mainly dominated by calcareous crusts (first/basal strata), covered by corticated macrophytes, for example, Ellisolandia elongata (J.Ellis & Solander) K.R.Hind & G.W.Saunders (Fig. 6) and Pterocladiella capillacea (S.G.Gmelin) Santelices & Hommersand ( Fig. 7) and, in more exposed locations, Tenarea tortuosa (Esper) Me Lemoine (Neto et al. 2008). Seasonally and mainly in spring and summer, the introduced red alga Asparagopsis armata occurs often abundantly at this lower intertidal level. Important features and habitats at this shore level are rock pools, occurring in different shapes and sizes and often recreating a shallow subtidal habitat, which contains a rich diversity of marine life. A few shores consist of irregularly rounded boulders or cobbles between which coarse sand or gravel may be retained. Sandy shores are rare (Neto, pers. observ.). The rocky bottoms in the submerged zone are covered by more frondose macrophytes, such as Pterocladiella capillacea, Halopteris filicina (Grateloup) Kützing, Dictyota spp. or Zonaria tournefortii (J.V.Lamouroux) Montagne (Fig. 8). At this level, the edible barnacles Megabalanus azoricus (Pilsbry, 1916) and/or the limpets Patella aspera Röding, 1798 are concentrated in the first few metres, while the slipper lobsters Scyllarides latus (Latreille, 1803) or the spiny lobsters Palinurus elephas (Fabricius, 1787) are found at greater depths. Several species of fish, such as the blue wrasse Symphodus caeruleus (Azevedo, 1999)    Algal turfs at the low-shore intertidal level (by the Island Aquatic Ecology Subgroup of cE3c-ABG).
In 2007, both Flores and Corvo Islands were recognised by UNESCO as a Biosphere Reserve and thus integrated into the programme "The Man and the Biosphere". The programme focuses on the ecological, social and economic dimensions of biodiversity loss and uses the World Network of Biosphere Reserves as a vehicle for knowledge sharing, research and monitoring, education and training and participatory decision-making with local communities. The proposed area for the Biosphere Reserve includes the entire emerged land area of the Islands and a surrounding marine zone, covering a total area of 58,619 hectares in Flores and 25,853 hectares in Corvo and incorporating an important diversity of habitats of regional, national and international importance, which includes, for example, areas integrated in the Natura 2000 Network. The inclusion of a vast marine area promotes explicitly, along with conservation, an integrated management practice between terrestrial, coastal and marine environments (Neto et al. 2008).  The red agarophyte Pterocladiella capillacea, a common species at the low intertidal level (by the Island Aquatic Ecology Subgroup of cE3c-ABG).

Design description:
The algae referred to in this paper were collected during field surveys from both the littoral and sublittoral regions down to approximately 40 m on the Islands of Flores and Corvo. 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 in 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: • Projects: • IASTFC-"Impact Assessment Study for the construction of the Transport Infrastructures of the Islands of Flores and Corvo, Azores -natural environment", funded by the Azores Regional Government -Regional Secretariat for Tourism and Environment / Regional Environment Directorate, 1990; • LFFC-"Littoral flora of the islands of Flores and Corvo: Inventory, ecology and biogeographic affinities", Government of the Azores -Regional Secretariat for Tourism and Environment / Regional Environment Directorate (GRA-SRTA / DRA), 1995-1999;  ERDF funds through the Operational Programme for Competitiveness Factors -COMPETE; • Portuguese Regional Funds, through DRCT -Regional Directorate for Science and Technology, within several projects, 2019 and 2020 and SRMCT / DRAM -Regional Secretariat for the Sea, Science and Technology, 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 from the surface one or two specimens of all the observed species and then placing them into labelled bags (Fig. 9). Species recording data was gathered by registering all species present in the sampled locations visited (Fig. 10).
Quality control: Each sampled taxon was identified by trained taxonomists and involved morphological and anatomical observations of whole specimens by eye and/or of Table 3.
Information and location of the sampling sites on Corvo Island.
histological preparations under microscopes to determine the main diagnostic features of each species, as described in literature.
Step description: Specimens were sorted and studied in the laboratory, following standard procedures used in macroalgae identification.
Species identification was usually based on a combination of morphological, anatomical and reproductive features. For small and simple thalli, this required observing the entire thallus with the unaided eye and/or using dissecting and compound microscopes. For larger and more complex algae, investigation of the thallus anatomy required histological procedures (longitudinal and transverse sections) or squashed preparations of mucilaginous thalli, sometimes after staining, to observe vegetative and reproductive structures and other diagnostic features.
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 Collecting macroalgae at the rocky intertidal (by the Island Aquatic Ecology Subgroup of cE3c-ABG).
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 studies.
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. For Flores, a total of 196 taxa were identified belonging to 24 orders and 54 families, distributed in the phyla Rhodophyta (14 orders and 33 families), Chlorophyta (three orders and nine families) and Ochrophyta (seven orders and 12 families). For Corvo, a total of 56 taxa were identified belonging to 16 orders and 29 families, distributed in the phyla Rhodophyta (seven orders and 16 families), Chlorophyta (three orders and four families) and Ochrophyta (six orders and nine families).

Temporal coverage
Notes: The sampling was performed on several occasions between 1989 and 2018. Description: This data paper presents physical and occurrence data from macroalgal surveys undertaken on Flores and Corvo Islands between 1989 and 2018 (Neto et al. 2020d). 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 90 records (eventID). The extension data table has 2077 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.

Additional information
This paper accommodates the 1687 specimens of macroalgae recorded from Flores Island in 196 taxa comprising 128 confirmed species and 68 taxa identified only to generic level. The confirmed species (Tables 4, 5 Table 5.
Summary of the macroalgal flora of Flores Island, with information on the species origins and status.