Introduction

Marine benthic flora of the Atlantic coasts of the Iberian Peninsula has been studied for over 250 years (e.g., Clemente y Rubio 1807; Colmeiro 1867, 1889; Lázaro e Ibiza 1889); Sauvageau 1897; Chalon 1905; Miranda 1931; Dizerbo 1956, etc.) and, currently, many species are catalogued in various checklists or compilations (e.g. Miranda 1943a, b, c, 1944; Ardré 1970; Cremades et al. 2002; Gorostiaga et al. 2004; Araújo et al. 2003, 2009; Bárbara et al. 2003, 2005; Cires and Cuesta 2010, 2019). In recent years, new floristic contributions have increased our knowledge of the algae in the north of the Iberian Peninsula, and new research at the molecular level has been developed, enriching the traditional systematics.

However, within the Iberian coast, Cantabrian marine benthic flora is scarcely known to the point that no detailed checklist of the region has been developed. Some lists focused on the Western and Eastern stretches of the coast were published (Fernández-Montero et al. 1998; Menoyo et al. 1998) and later expanded (Martínez-Gil et al. 2007), which verse around the benthic marine algae from Noja (Cantabria). Although these works add up a total of 252 species to the marine flora of the province, a much higher value is found in neighboring territories (Fig. 1).

Fig. 1
figure 1

Map showing the location of Cantabria and the regions with which its flora is compared. (A) Study area of the present work. (B) Map showing the location of Atlantic provinces. Red: publication year of the checklist or compilation - North of Portugal (Araújo et al. 2009), Galicia (Bárbara et al. 2005), Asturias (Cires and Cuesta 2010, 2019); Basque Country (Gorostiaga et al. 2004). Black: number of algae listed

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Thus, the present work aims to expand the knowledge on the marine algae flora of the coast of Cantabria for the first time. It is worth highlighting that a thorough knowledge of natural resources of a territory is always required, not only for a proper evaluation and conservation management, but also as it constitutes an exceptionally valuable source of scientific information. Therefore, this inventory does not attempt to be a definitive catalogue, as new records appear continuously, but to contribute to increase our understanding of the biogeographical characteristics of this area in the Atlantic coast and the knowledge of its marine biodiversity, which altogether may be useful for the sustainable management of the future marine protected area.

Materials and methods

Description of study area and applied methodology

The coast of the Cantabria region, between 43º 21’ N, 3º 09’ W and 43º 23’ N, 4º 30’ W covers about 220 km (Fig. 1). It borders Asturias to the west at Tina Mayor, a small estuary formed by the mouth of Deva river, while to the east it borders the Basque Country. It is characterized by extensive cliffs (approximately 136 km are occupied by cliffs). In short, it is a steep coast with many geographical features (e.g., wave-cut platformer beach, estuaries, bays, headlands and beaches). The climate is temperate, oceanic, with moderate winters and warm summers.

This catalogue compiles an intensive search of scientific information related to benthic marine algae from the Cantabrian coast. The checklist is based on a compilation of data from literature references and herbarium data. For the literature survey, international publications on macroalgae where Cantabria is cited were retrieved from four different search engines, i.e., the Web of Science (https://clarivate.com/webofsciencegroup/), ScienceDirect (https://www.sciencedirect.com/), Scopus (https://www.scopus.com) and Google Scholar (https://scholar.google.com/). Subsequently, inquiries were made regarding papers that were published locally in journals of different local universities and in final reports of national and international projects. The last step was to obtain unpublished works such as M. Phil. Thesis, Ph.D. Doctoral Thesis and Technical Reports from universities and scientific institutions. The herbarium specimens checked belong to University of Oviedo (FCO-Algae), Royal Botanic Garden of Madrid (MA-Algae), University of Barcelona (BCN-Phycophyta), Complutense University of Madrid (MACB-Algae), University of Valencia (VAL-Algae), University of País Vasco (BIO-Algae), University of Santiago de Compostela (SANT-Algae) and The French National Museum of Natural History (Muséum National d’Histoire Naturelle, PC-cryptogamy) (see GBIF 2021; https://www.gbif.org/).

The current taxonomic status and nomenclatural changes of the taxa of interest have been considered following Algaebase (https://www.algaebase.org/; Guiry and Guiry 2021). Phyla, class, orders, families, genera and species are alphabetically arranged. To classify the Cantabrian algae flora, we have applied Feldmann’s ratio [R/O] (number of species of Rhodophyta / number of species of Ochrophyta) and Cheney’s ratio [(R+C)/O] in a similar manner to Feldmann’s but including green algae (Feldmann 1937 and Cheney 1977 respectively). These ratios indicate the position of a flora in relation to cold and warm waters.

Results

Table 1 presents the checklist of the seaweeds of Cantabria in taxonomic order. It includes most synonyms used in literature, bibliographic references and herbarium sheets. The list includes 425 species: 25 Cyanobacteria, 55 Chlorophyta, 81 Ochrophyta, and 264 Rhodophyta. The number of specific, infraspecific taxa, and stages is 437: 25 Cyanobacteria, 57 Chlorophyta, 89 Ochrophyta, and 266 Rhodophyta. We have also excluded 7 species from the coast of Cantabria due to misidentifications, and considered doubtful the presence of 6 further taxa. The confirmed species (Table 2) comprise 7 classes, 37 orders and 84 families of macroalgae (excluding cyanophytes). Additionally, 9 fossil algae were registered.

Table 1 Catalogue of the benthic marine algae of Cantabria (Eastern Cantabrian, Spain)
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Table 2 Main taxonomic figures of the macroalgal flora of Cantabria (Spain)
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Discussion

Previous studies conducted in Cantabria (see Fernández-Montero et al. 1998; Menoyo et al. 1998; Martínez-Gil et al. 2007) reported the presence of 252 seaweeds. The 437 taxa reported here increase the total of marine benthic algae recorded in this region by 58%, revealing that seaweed diversity from the Atlantic coast of Southern Europe remains partially unknown. This study reveals the presence of alien species such as Anotrichium furcellatum, Antithamnionella ternifolia, Bonnemaisonia hamifera, Caulacanthus okamurae, Centroceras clavulatum, Ceramium secundatum, Codium fragile, Colpomenia peregrina, Falkenbergia rufolanosa (tetrasporophytic phase of Asparagopsis armata), Grateloupia filicina, Grateloupia subpectinata, Hypnea musciformis, Melanothamnus collabens (= Neosiphonia collabens), Melanothamnus harveyi (= Neosiphonia harveyi), Polysiphonia morrowii, Phycocalidia suborbiculata (= Porphyra suborbiculata), Sargassum muticum, Ulva australis, Umbraulva dangeardii and Undaria pinnatifida, all of which are also present in other nearby Cantabrian regions.

It is worth mentioning that considering Cheney´s ratio ([Rhodophyta+Chlorophyta]/Ochrophyta), all values fell within the range of 3.42 to 4.15 (Table 3). A closer look to this ratio showed that nearby regions such as Basque Country, Asturias and Galicia present ratios of 4.09 (Gorostiaga et al. 2004), 2.91 (Cires and Cuesta 2010) and 2.94 (Bárbara et al. 2005), respectively. Based on this, the flora of Cantabria (3.93) appears to be closer to the one of Basque Country, possibly indicating its warm-water character.

Table 3 Number of species and percentages of each algae group in the Cantabrian coast, including Cheney´s ratio
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Our data indicates that the coast of Cantabria sustains a relatively rich marine macroalgal flora and confirms that the Atlantic coast is a suitable geographic location for the settlement of macroalgae with different biogeographical affinities. Despite this richness, specific habitats and locations remain fully or partially overlooked (e.g., subtidal environments or certain groups that required detailed studies such as Cyanobacteria). The present study aims to contribute to fill those gaps, ultimately deepening the knowledge of the macroalgal flora of Cantabria, as well as its connections with other bordering territories.