Mosses of Cockburn Island plateau, Antarctica

Abstract

Located east of the Antarctic Peninsula, Cockburn Island is a small island in the James Ross Archipelago. Studies of mosses on the island are scarce. The oldest studies date from the first half of the nineteenth century to the most recent in 1993. The number of records of mosses is very small due to the difficulty of accessing the area. Here, we report an updated composition of the moss flora of the plateau, in which four new records have been found: Bryoerythrophyllum antarcticum, Ceratodon purpureus, Pohlia wilsonii and Schistidium lewis-smithii. The occurrence of these species on the plateau shows that the ranges of these species have expanded from the Antarctic Peninsula to the east. This collection highlights the need for further research into the dynamics of moss flora in the context of climate change.

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 2002). 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. 2015). 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 (1993). 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. (2008) 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. 2019), solar radiation and the fact that it is relatively protected from the wind (mainly from the south-west; Fig. 1).

Figure 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. 2001). 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 2003). For the identification and distribution of the taxa, the following bibliography was used: Lewis Smith (1993), Sharp et al. (1994), Ochyra & Zander (2002), Ochyra et al. (2008) and Sollman (2015). 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. 2021). The detailed map of Cockburn Island is based upon REMA (Howat et al. 2022) 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 (1993) and the descriptions in Ochyra et al. (2008), 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. 1) Bryoerythrophyllum antarcticum (L.I. Savicz & Smirnova) P. Sollman [Pottiaceae]*

2. 2) Bryum argenteum Hedw. [Bryaceae]

3. 3) Bryum pseudotriquetrum (Hedw.) Gaertn., Meyer et Scherb. [Bryaceae]

4. 4) Ceratodon purpureus (Hedw.) Brid. [Ditrichaceae]*

5. 5) Didymodon brachyphyllus (Sull.) R.H. Zander [Pottiaceae]

6. 6) Encalypta rhaptocarpa Schwägr. [Encalyptaceae]

7. 7) Hennediella heimii (Hedw.) R.H. Zander [Pottiaceae]

8. 8) Pohlia wilsonii (Mitt.) Ochyra [Bryaceae]*

9. 9) Schistidium antarctici (Cardot) L.I. Savicz & Smirnova [Grimmiaceae]

10. 10) Schistidium lewis-smithii Ochyra [Grimmiaceae]*

11. 11) Syntrichia magellanica (Mont.) R.H. Zander [Pottiaceae]

12. 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 1993), 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 2015), 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. (2008), 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. (2008).

The finding on the plateau of S. antarctici, which is the most representative species of the genus, was predictable (Biersma et al. 2018), 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 2003), Livingston Island (Ochyra et al. 2008) and Ostrov Geologov Island (Câmara et al. 2021). 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. 2008), 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. 2018), and so further studies are needed. On the other hand, the specimen reported by Lewis Smith (1993) 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 (2008), 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. 2008). 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 1993). According to Ochyra et al. (2008), 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. (2016) 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. 2015), 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 2005). 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 1999, Barták et al. 2015, Goga et al. 2018). 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. 2018).