Introduction
Cockburn Island, a small island that is part of the James Ross Archipelago, is located 5 km north of Marambio (Seymour) Island (64°13' S, 56°50' W), in the east of the Antarctic Peninsula. Cockburn Island was formed by volcanic activity and was one of the first places in Antarctica to be explored during the first half of the nineteenth century. It consists of an area of ~4 km2 and measures 2.8 × 1.8 km (Stilwell Reference Stilwell2002). The archipelago to which the island belongs represents a transitional region between marine and continental Antarctica. Bryophytes and lichens are the two main floral components of the island. There are three lineages of bryophytes: hornworts, liverworts and mosses, with only the latter of which being represented on the island.
The moss flora of Antarctica has a relatively short history compared to in other parts of the world, especially tropical and temperate regions (Putzke et al. Reference Putzke, Athanásio, Pereira de Albuquerque, Victoria and Pereira2015). The earliest data on the study of mosses on Cockburn Island date from Hooker's expeditions, from which five species were documented and mentioned by Lewis Smith (Reference Lewis Smith1993). This author also presented a survey of vegetal diversity at different levels on the island (coast, plateau and cone) and an inventory of the moss flora. More recently, Ochyra et al. (Reference Ochyra, Bednarek-Ochyra and Smith2008) reported six moss species on Cockburn Island. The present study aimed to survey the moss flora of Cockburn Island.
Knowledge of the moss flora present on Cockburn Island will provide a baseline for monitoring vegetation in the region. From this foundation, it will be possible to assess the impacts of climate change and establish mechanisms for biodiversity conservation of Antarctic moss flora. The present study aimed to survey the moss flora of the Cockburn Island plateau.
Materials and methods
As part of the 2021–2022 summer Antarctic campaign, the Instituto Antártico Argentino (IAA), Dirección Nacional del Antártico (DNA), Argentina, carried out plant collections on Cockburn Island. Sampling was only carried out on the depressed side of the plateau (north-east), which is the most favourable area for the presence of vegetation due to the humid conditions caused by the accumulation of snowdrifts (Roman et al. Reference Roman, Nedbalová, Kohler, Lirio, Coria and Kopácek2019), solar radiation and the fact that it is relatively protected from the wind (mainly from the south-west; Fig. 1).
Location of the study area. a. Map of a portion of Antarctica showing the location of the northern Antarctic Peninsula and James Ross Archipelago (black box). b. Map of the James Ross Island group. The black box highlights Cockburn Island. c. Cockburn Island. White points show sampling sites. 1) 64°12'11,052" S; 56°50'28,607" W: Bryoerythrophyllum antarcticum, Ceratodon purpureus, Syntrichia magellanica. 2) 64°12'6,228" S; 56°50'35,016" W: Bryoerythrophyllum antarcticum, Bryum argenteum, Syntrichia magellanica. 3) 64°11'58,2" S; 56°50'31,343" W: Bryum argenteum, Bryum pseudotriquetrum, Syntrichia magellanica. 4) 64°11'57,804" S; 56°50'20,112" W: Schistidium lewis-smithii. 5) 64°12'16,92" S; 56°50'16,26" W: Bryum argenteum, Pohlia wilsonii.
For the identification of the moss species present in each sample, the morphology and anatomy of the different structures, of the gametophyte (e.g. leaf or cells) and, when present, of the sporophyte (e.g. capsule, operculum or calyptra) were observed (Gradstein et al. Reference Gradstein, Churchill and Salazar-Allen2001). The observations on general aspects were made using a stereoscopic microscope (Olympus BX50) in both dry and hydrated states. The cuts for anatomical study were made under a magnifying glass and free-handed using razor blades. Water was used for mounting fresh mounts (Frahm Reference Frahm2003). For the identification and distribution of the taxa, the following bibliography was used: Lewis Smith (Reference Lewis Smith1993), Sharp et al. (Reference Sharp, Crum and Eckel1994), Ochyra & Zander (Reference Ochyra and Zander2002), Ochyra et al. (Reference Ochyra, Bednarek-Ochyra and Smith2008) and Sollman (Reference Sollman2015). The identified specimens were deposited in the repository of the IAA and duplicates were deposited at the Herbarium of the Centro Regional Universitario Bariloche (BCRU). Specific names have been updated according to the Missouri Botanical Garden database (Tropicos.org). The maps (Fig. 1) were made using Antarctic Reference Elevation Model of Antarctica (REMA) Explorer (https://livingatlas2.arcgis.com/antarcticdemexplorer/). The location maps in Fig. 1 were made using Quantarctica (Matsuoka et al. Reference Matsuoka, Skoglund, Roth, de Pomereu, Griffiths and Headland2021). The detailed map of Cockburn Island is based upon REMA (Howat et al. Reference Howat, Porter, Smith, Noh and Morin2022) with 50 m contour intervals extracted and digitalized in Quantum GIS (QGIS Development Team 2020).
Results
The collections resulted in 22 specimens belonging to seven species, all of which were georeferenced (Fig. 1). Based on the specimens examined, the list by Lewis Smith (Reference Lewis Smith1993) and the descriptions in Ochyra et al. (Reference Ochyra, Bednarek-Ochyra and Smith2008), an updated list of the species registered on Cockburn Island was produced. The species are presented with updated and valid names.
The following is the updated species list (asterisks mark new records for the Cockburn Island plateau):
1) Bryoerythrophyllum antarcticum (L.I. Savicz & Smirnova) P. Sollman [Pottiaceae]*
2) Bryum argenteum Hedw. [Bryaceae]
3) Bryum pseudotriquetrum (Hedw.) Gaertn., Meyer et Scherb. [Bryaceae]
4) Ceratodon purpureus (Hedw.) Brid. [Ditrichaceae]*
5) Didymodon brachyphyllus (Sull.) R.H. Zander [Pottiaceae]
6) Encalypta rhaptocarpa Schwägr. [Encalyptaceae]
7) Hennediella heimii (Hedw.) R.H. Zander [Pottiaceae]
8) Pohlia wilsonii (Mitt.) Ochyra [Bryaceae]*
9) Schistidium antarctici (Cardot) L.I. Savicz & Smirnova [Grimmiaceae]
10) Schistidium lewis-smithii Ochyra [Grimmiaceae]*
11) Syntrichia magellanica (Mont.) R.H. Zander [Pottiaceae]
12) Syntrichia sarconeurum Ochyra & R.H. Zander [Pottiaceae]
An alphabetically annotated list of all 12 species recorded on the Cockburn Island plateau is presented in the Supplementary Appendix, with citations of descriptions and iconography, habitat and distribution, comments and examined material. The following species are reported for the first time for the plateau: B. antarcticum, C. purpureus, P. wilsonii and S. lewis-smithii.
Discussion
Since Lewis Smith's last visit to the island plateau in 1989 (Lewis Smith Reference Lewis Smith1993), Cockburn Island has remained unvisited, mainly because of the difficulty of accessing the island. The studies carried out since then up to the present work are based on valuable collections held in various repositories. Our work contributes to knowledge of the island's diversity with the discovery of four new species present there. B. antarcticum has been reported at James Ross Island (Sollman Reference Sollman2015), so its presence at Cockburn Island is unsurprising. However, the presence of P. wilsonii was unexpected. This species was first reported from Antarctica in Enderby Land by Ochyra et al. (Reference Ochyra, Bednarek-Ochyra and Smith2008), and our finding at Cockburn Island is novel because this is the first mention of this species in the Antarctic Peninsula region. The morphological, anatomical and ecological features observed in the examined specimens of P. wilsonii are consistent with those described by Ochyra et al. (Reference Ochyra, Bednarek-Ochyra and Smith2008).
The finding on the plateau of S. antarctici, which is the most representative species of the genus, was predictable (Biersma et al. Reference Biersma, Jackson, Stech, Griffiths, Linse and Convey2018), but S. lewis-smithii was not. The geographical range of S. lewis-smithii is currently restricted to the South Shetland Islands: 25 de Mayo Island (King George Island; Ochyra Reference Ochyra2003), Livingston Island (Ochyra et al. Reference Ochyra, Bednarek-Ochyra and Smith2008) and Ostrov Geologov Island (Câmara et al. Reference Câmara, Carvalho-Silva and Stech2021). In this paper, we present the first record of this species from the eastern Antarctic Peninsula. This species could be confused with Schistidium falcatum (Hook.f. & Wilson) B.Bremer due to the absence of a gymnosomal capsule (Ochyra et al. Reference Ochyra, Bednarek-Ochyra and Smith2008), but the morphological differences of its leaves allow no room for confusion with the latter. They are certainly very similar, and molecular phylogenetic reconstructions show that the species are closely related. However, these reconstructions are based on a single specimen (Biersma et al. Reference Biersma, Jackson, Stech, Griffiths, Linse and Convey2018), and so further studies are needed. On the other hand, the specimen reported by Lewis Smith (Reference Lewis Smith1993) as Schistidium cf. chrysoneurum is in fact S. lewis-smithii, and we consider it to be so.
The location of the mosses near the base of the cone, in the plateau (Fig. 1), can be explained by several factors: the protection it provides from the highly erosive south wind, the high degree of radiation that allows the snow to melt and the impermeability of the volcanic terrain that provides the necessary moisture for vegetation growth. According to Ochyra (Reference Ochyra, Bednarek-Ochyra and Smith2008), C. purpureus is rare on the coast of the Antarctic Peninsula, but it was mentioned as being present on James Ross Island. D. brachyphyllus, H. heimii and S. sarconeurum were found on the northern side of the island, above the Adélie penguin colony and between the base of the cliff and the Adélie penguin colony at 15–150 m (Ochyra et al. Reference Ochyra, Bednarek-Ochyra and Smith2008). Nevertheless, these three species have not been registered on the Cockburn Island plateau area. These are the first records of them. B. argenteum and B. pseudotriquetrum had been previously reported in the plateau (Lewis Smith Reference Lewis Smith1993). According to Ochyra et al. (Reference Ochyra, Bednarek-Ochyra and Smith2008), these two species were found together with E. rhaptocarpa, S. magellanica and S. antarctici at an altitude of 400 m. However, the plateau is at 250 m, so it is not clear exactly where they were found.
As mosses in Antarctica rarely produce sporophytes, their absence from our samples was unsurprising. However, Casanova-Katny et al. (Reference Casanova-Katny, Torres-Mellado and Eppley2016) suggest that the production of fully mature sporophytes might be related to environmental conditions, such as elevated temperature, rather than being a physiological limitation or adaptive response. Their studies were conducted on 25 de Mayo Island (King George Island), within the 0°C isotherm. Cockburn Island's location at the -7°C isotherm, which, together with cold winds blowing from the Filchner-Ronne Ice Shelf, the ice-covered Weddell Sea and the mountains of the Antarctic Peninsula (Van Wessem et al. Reference Van Wessem, Reijmer, Van de Berg and Broeke2015), creates an environment that does not allow for sporophyte development in moss species.
Despite the scarce and sporadic reports, slow colonization events could occur with the establishment of new species from spores transported long distances by the wind from more northerly latitudes (Lewis Smith Reference Lewis Smith2005). This observation is also supported by the absence of birds in the area. Most floristic studies of the archipelago have focused on James Ross and Vega islands (Ochyra Reference Ochyra1999, Barták et al. Reference Barták, Váczi, Stachoň and Kubešová2015, Goga et al. Reference Goga, Sabovljević, Lang and Bačkor2018). This underscores the necessity of continued monitoring on this difficult-to-access volcanic island.
The increase in the number of moss species on Cockburn Island highlights the ongoing need to study the dynamics of the flora at this site, as these plants are potentially good proxies of Antarctic climate change (Singh et al. Reference Singh, Singh and Khare2018).
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/S0954102024000014.
Acknowledgements
All of the authors thank the crew of Marambio Station and the logistical support provided by Instituto Antártico Argentino. A.C. Cottet and M.I. Messuti thank Consejo Nacional de Investigaciones Científicas y Técnicas and Universidad Nacional del Comahue for funding their research. We thank C.R. Amenabar and A. Zakrajsek, who helped with the preparation of the maps, and J.M. Lirio for his advice on Cockburn Island's topography. This work was wholly funded by Instituto Antártico Argentino (PICTA 0091). L.P. Dopchiz and M. Ansaldo are the managers of the project to which the present work belongs.
Author contributions
The material was collected by A.C. Cottet and L.P. Dopchiz. The identifications were made by A.C. Cottet. All authors commented on and edited previous versions of the manuscript. All authors approved the final version for publication.
Competing interests
The authors declare none.
