Marine algal flora of Pico Island, Azores

Abstract Background The seaweed flora of Pico Island (central group of the Azores archipelago) has attracted interest of researchers on past occasions. Despite this, the macroalgal flora of the island cannot be considered well-known as published information reflects only occasional collections. To overcome this, a thorough investigation encompassing collections and presence data recording was undertaken. Research under the Campaigns “AÇORES/89”, “PICO/91”, “PICOBEL/2007” and “LAUMACAT/2011” covered a relatively large area (approximately 39 km2) around the island, encompassing the littoral and sublittoral levels down to about 40 m around the Island. This paper improves the knowledge of the Azorean macroalgal flora at local and regional scales by listing taxonomic records and providing information on the ecology and occurrence of each species present on the Island’s littoral. New information A total of 4043 specimens (including taxa identified only to genus level) belonging to 303 taxa of macroalgae are registered, comprising 197 Rhodophyta, 53 Chlorophyta and 53 Ochrophyta (Phaeophyceae). From these, 225 were identified to species level (142 Rhodophyta, 41 Chlorophyta and 42 Ochrophyta), encompassing 110 new records for the island (69 Rhodophyta, 20 Chlorophyta and 21 Ochrophyta), three Macaronesian endemisms (Botryocladia macaronesica Afonso-Carillo, Sobrino, Tittley & Neto; Laurencia viridis Gil-Rodríguez & Haroun; Codium elisabethiae O. C. Schmidt), 14 introduced and 25 species with an uncertain status.


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 2006Wallenstein et al. 2009), has been considered relatively rich when compared to that of other remote oceanic islands , Wallenstein et al. 2009). Even so, it is worth mentioning that the published information (approximately 400 species, Freitas et al. 2019) reflects data from only a few of the nine islands, since not all of them have been thoroughly investigated. To overcome this and improve the understanding of the archipelago's seaweed flora, an effort has been made by local investigators over the past three decades and research on the marine macroalgae flora has been conducted on several of the less-studied Azorean islands. This paper comprises both physical and occurrence data and compiles the gathered information from macroalgae surveys developed in Pico Island mainly by the Island Aquatic Research Group of the University of the Azores (https://ce3c.ciencias.ulisboa.pt/sub-team/island-aquatic-ecology). It aims to constitute 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: By listing taxonomic records for Pico and presenting general information for each taxon occurrence on the Island's littoral, this paper addresses several biodiversity shortfalls (see Cardoso et al. 2011, 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).

Study area description:
Located in the North Atlantic, roughly at 38°43′49″N, 27°19′10″W, the Azores comprise nine islands and several islets spread over 500 km, in a WNW direction (Fig. 1). The climate is temperate oceanic, with regular and abundant rainfall, high levels of relative humidity and persistent winds, mainly during the winter and autumn seasons (Morton et al. 1998). The islands lack a continental shelf, thus presenting a restricted coastal extension and deep waters occur within a few kilometres offshore. Shore geomorphology varies considerably with high cliffs in some places and rocky cobble/ boulder beaches elsewhere (Borges 2004), the tidal range is small (< 2 m, see Hidrográfico 1981) and coasts are subjected to swell and surge most of the year.
Pico (in black in Fig. 1), of approximately 447 km and dominated by its 2351 m tall mountain, is the second largest and the youngest island of the Azores archipelago, composed of basaltic volcanic deposits less than 300,000 years old (Cruz and Oliveira 2001). The Island's coastline is approximately 126 km long, generally devoid of high cliffs and consists mainly of irregular extensions of bedrock, presenting a variety of stack, arch and gully formations due to its recent volcanic origin. Intertidal platforms, occasionally dissected by channels and gullies, are mostly easily accessible by land and exhibit considerable variation in width (Wallenstein et al. 2009). Important features and habitats at this shore level are rock pools. These differ in shape and size and are a stressful environment due to the changes in salinity caused by either evaporation or dilution during low tides. They often recreate a shallow subtidal habitat and contain a rich diversity of marine life. A few shores consist of irregularly rounded boulders or cobles between which coarse sand or gravel may be retained. Sandy shores are rare (Neto pers. observ.). 2 The rocky-shore communities of Pico, like all over in the Azores, are dominated by macroalgae at both intertidal and shallow subtidal levels . At intertidal levels, a distinct zonation pattern is evident with a higher zone dominated by invertebrates (littorinids and chthamalid barnacles, in which patches or fringes of the algae Fucus spiralis Linnaeus and Gelidium microdon Kützing can occur (Fig. 2). This is followed by a midshore zone 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, Fig. 3). Depending on the shore, turf can be monospecific (of either Caulacanthus ustulatus (Mertens ex Turner) Kützing, Centroceras clavulatum (C. Agardh) Montagne or Gymnogongrus) or multispecific and composed of soft algae (e.g. Centroceras clavulatum, Chondracanthus and Laurencia) usually growing as epiphytes over articulate calcareous forms (e.g. Ellisolandia and Jania). The lower zone is mainly dominated by calcareous crusts (first strata), covered by corticated macrophytes (e.g. Ellisolandia elongata (Fig. 4), Pterocladiella capillacea, Treptacantha abies-marina (S.G.Gmelin) Kützing). Mainly during spring and summer, considerable amounts of the introduced Asparagopsis armata Harvey can be seen at this level. Subtidally, algal communities are mainly characterised associations of two or three frondose macrophytes, for example, Dictyota, Halopteris and Zonaria tournefortii (J.V.Lamouroux) Montagne (Fig. 5).  Littorinids, chthamalid barnacles and the algae Fucus spiralis and Gelidium microdon at the high intertidal (by the Island Aquatic Ecology Subgroup of cE3c-ABG).   Frondose macrophytes (Halopteris spp., Zonaria tournefortii and Dictyota spp.) at the subtidal level (by the Island Aquatic Ecology Subgroup of cE3c-ABG).

Design description:
The algae referred to in this paper were collected during field studies at littoral and sublittoral levels down to approximately 40 m around Pico Island. Each sampling location was visited several times and, on each occasion, a careful survey was made covering much of the area. Presence/absence data were recorded for all known species and whenever an unknown or potential new species was found, it was collected, assigned an individual registration number and vouchers were deposited at the AZB Herbarium Ruy Telles Palhinha, based 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: Sampling description: Intertidal collections were made at low tide by walking over the shores. Subtidal collections were made by scuba diving around the area. Sampling encompassed both physical collections and species presence recordings. For the former, in each sampling location, collections were made manually by scraping one or two specimens of species found into previously labelled bags (Fig. 7). 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.

Figure 7.
Collecting macroalgae at the rocky intertidal (by the Island Aquatic Ecology Subgroup of cE3c-ABG).

Figure 8.
Subtidal species recording data (by the Island Aquatic Ecology Subgroup of cE3c-ABG).
Quality control: Each sampled taxon was investigated by trained taxonomists with the help of keys and floras. This involved morphological and anatomical examination by eye or under dissecting and compound microscopes of an entire specimen or slide preparation. In difficult cases, specimens were sent to experts for identification.
Step description: In the laboratory, the specimens were 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 by eye and/or under dissecting or compound microscopes. For larger and more complex algae, the investigation of the thallus anatomy required histological work to obtain longitudinal and transverse sections needed for the observation of cells, reproductive structures and other diagnosing characters.
For more critical and taxonomically-difficult taxa, specimens were taken to the Natural History Museum (London) for comparison with collections there or sent to appropriate specialists.
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, 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); (iii) silica 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. In total, 303 taxa were identified belonging to 30 orders and 67 families, distributed by the phyla Rhodophyta (15 orders and 39 families), Chlorophyta (3 orders and 10 families) and Ochrophyta (12 orders and 18 families). Collection identifier: 4ea1e09c-13c8-4b8e-a28a-72c55bde8f66; 0f2368fa-0a53-43c5-9f19-b126260e4e83; 6163248c-236b-4778-99cf-39dbf28a9784; b4ed4e44-3e8f-42d4-a44b-d78585a8f8f0; acc4fc70-0cb6-496e-982c-9207d09b856a; 468e613d-1ce9-4a32-a5f9-c5a8b58545c1; a8405f3e-fdc6-452d-9dc9-ca1fd3abdf2c; 84ff06f5-8c7c-4c3c-9296-38ad24b347bd. Description: This data paper presents physical and occurrence data from macroalgal surveys undertaken on Pico Island between 1989 and 2018. The dataset submitted to GBIF is structured as a sample event dataset, with two tables: event (as core) and occurrences (Neto et al. 2020). 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 74 records (eventID). The extension data table has 4043 occurrences. An extension record supplies extra information about a core record. The number of records in each extension data table is given 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.   A mismatch regarding the GBIF backbone taxonomy of some of the macroalgae species names was identified as detailed in Suppl. material 1. Figure 9.

Column label Column description
Laurencia pyramidalis, a new record for Pico Island (by the Island Aquatic Ecology Subgroup of cE3c-ABG).