Pinnularia austroshetlandica Cleve-Euler 1948

Pinnularia austroshetlandica (Carlson 1913: 16, pl. 1, fig. 25) (Figs 181–188)

Synonymy:— Pinnularia kolbei Manguin (in Bourrelly & Manguin 1954: 35) non P. kolbei Mölder (1952: 27), P. parakolbei Fukushima, Ko-Bayashi & Yoshitake (Fukushima et al. 2001: 108), P. bottnica Krammer (2000: 78) sensu Van de Vijver et al. (2002), Navicula nivorum Peragallo (1921: 20), Navicula nivorum var. elongata Peragallo (1921: 20).

Valves broadly elliptic-lanceolate with clearly convex margins and protracted, rostrate ends. Valve dimensions (n = 25): length 32–42 µ m, width 9.7–11.3 µm. Axial area linear to linear-lanceolate, narrow, slightly widening towards the central area. Central area a large, bow-tie-shaped fascia. Raphe filiform with weakly curved branches. Central raphe endings deflected to the secondary side with large, almost triangular-shaped, central pores. Terminal fissures bent to one side, opposite to the central endings. Striae geniculate, radiate near the centre, becoming convergent near the valve ends, 13–15 in 10 µm. Longitudinal lines absent.

Habitat:— The species is rather rare on Livingston Island. On Hurd Peninsula, it was found relatively abundantly in only one sample taken from a Sanionia georgico-uncinata vegetation, growing around a periodically drying shallow brook close to the sea. On Byers Peninsula, the species was more common. The largest population was found on wet soil close to the sea with a clear presence of elephant seal input (Van de Vijver, pers. obs.). The species seems to prefer more aerial circumstances influenced by biogenic input such as penguin rookeries and elephant seal wallows (Van de Vijver et al. 2002).

Observations:— There is much confusion about the correct taxonomic identity of Pinnularia austroshetlandica. In 1954, Manguin (in Bourrelly & Manguin 1954) described a new species of Pinnularia he named P. kolbei. The name kolbei had already been used by Mölder (1952: 27; see Fukushima et al. 2001: 107) making a new name for Manguin’s species necessary; Fukushima et al. proposed P. parakolbei Fukushima, Ko-Bayashi & Yoshitake (Fukushima et al. 2001: 108) as a substitute name. However, populations observed from the Falkland Islands did not entirely conform to Manguin’s original description as they lacked the typical rostrate apices, a feature clearly stated (‘ étirées rostrées aux extrémités ’) and illustrated by Manguin (in Bourrelly & Manguin 1954: fig. 52). Van de Vijver et al. (2002) separated the non-rostrate forms from P.kolbei identifying them as P. bottnica. Examination of type material of P. kolbei (Van de Vijver, unpubl. res., slide number AD9087). both rostrate and non-rostrate specimens present in the same population; no other morphological or biometrical differences could be found. Additionally, detailed analysis of some large populations from other southern Indian Ocean islands yielded the same result (Van de Vijver, unpubl. res.). Therefore, it can be concluded that the P. bottnica populations of Ile de la Possession (Van de Vijver et al. 2002) and the P. parakolbei population from the Falkland Islands (Fukushima et al. 2001) are conspecific and the name parakolbei should be used for both the rostrate and the non-rostrate specimens.

Fukushima et al. (2001) considered Pinnularia austroshetlandica to be similar to but distinct enough from P. parakolbei since the strongly protruding ends and the almost straight raphe distinguished the former. Type material of Navicula austroshetlandica (the basionym of Pinnularia austroshetlandica) has not yet been located. A careful examination of the description and drawing in Carlson (1913) and its comparison with specimens from different parakolbei -populations from the entire (sub-)Antarctic Region did not reveal any significant differences between P. austroshetlandica and P. parakolbei. Thus, P. austroshetlandica, P. parakolbei and P. kolbei sensu Manguin are considered synonyms and P. austroshetlandica should therefore be given priority. Another name that may need adding is Navicula nivorum and its variety elongata. Although the original material is apparently no longer available, the descriptions and drawings match clearly P. austroshetlandica.