Determining geographical range and alien status in diatoms: three instructive case histories of species newly recorded in the British Isles, including a non-native marine species from the Pacific, Diademoides luxuriosa

Abstract

Three benthic diatom species – Diademoides luxuriosa, Navicula entoleia and Nitzschia ocellata – have been discovered for the first time in Scottish coastal waters. All are highly distinctive but rarely recorded, with less than 100 mentions found worldwide in an exhaustive search of the literature, even after taking into account possible synonyms. Even so, one of the three, D. luxuriosa, can be argued to be non-native in the British Isles, being a recent introduction from the Pacific rim (with a distribution from New Zealand, Australia, Indonesia, China and Japan to W North America). Plausible vectors are via ship hulls or co-transport with Pacific oysters. The distributions of the other two species show no clear pattern, Navicula entoleia having been found in Europe and NW USA, while Nitzschia ocellata, or at least a lineage of similar species containing N. ocellata, occurs in Europe, S America and E Asia. The three case histories are used to define a series of criteria for establishing geographical range and alien status in diatoms and other microalgae. Diademoides luxuriosa may be the first example anywhere of an alien marine diatom, since previous claims of such status, e.g. for Coscinodiscus wailesii and Trieres (Odontella) sinensis, fail to satisfy the criteria outlined. The morphological characteristics of D. luxuriosa and N. entoleia, including cellular detail, are used to comment briefly on their systematic position.

Keywords:

• aliens
• biogeography
• endemism
• introductions
• marine diatoms
• new records
• taxonomy

Acknowledgements

I am very grateful to Olivier De Clerck for comments on Pacific seaweed distributions; Ioanna Louvrou and the late Daniel Danielidis for the unpublished record of N. ocellata from Milos; Helen Jones and her subaqua team for collection of the Toscaig and other UK material, which was done in the early 1990s as part of the British Marine Diatom Flora under NERC grant GR3/7923 project (co-principal investigators: the late Prof. F.E. Round and Drs R.M. Crawford, E.J. Cox and D.G. Mann); Alan Stickle for sampling Edinburgh and Lothian shores between 1984 and 1986 (funded by Science and Engineering Research Council grant C/68484); former colleague Stephen Droop for considerable assistance with the collection and processing of marine epipelic diatom samples from many UK sites in the 1990s; the late Klaus Kemp for his cooperation and helpful correspondence over many years and for sending a slide of picked Diademoides luxuriosa from Sulawesi, prepared by the late Frithjof Sterrenburg; Bart Van de Vijver and the late (and much-missed) Luc Ector for helping with literature, especially when I was separated from RBGE literature resources by Covid-19; an anonymous reviewer for useful cautionary remarks; and the late Dr R.F.O. Kemp for identifying the subfossil Paludella I found in cores from a bog near Edinburgh, where it is now extinct. Eoina Rodgers (then Marine Policy and Advice Officer – Marine Ecology, Scottish Natural Heritage) replied very helpfully to my enquiry about possible routes of introduction of D. luxuriosa and gave valuable information about Pacific oyster cultivation in the Forth. Fiona Doherty, then Port Manager for the Forth ports, very kindly answered a query about shipping movements in and out of the Firth of Forth. And David Williams was chivalrous in handling a manuscript that departed in several places from his own views and in checking aspects of the history of Diademoides luxuriosa, for which I am most grateful.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental data

Supplemental data for this article can be accessed here https://doi.org/10.1080/0269249X.2022.2078428

Supplementary Information. Further discussion on the systematic position of Diademoides.

Supplementary Table 1. Voucher material for Firth of Forth sites sampled 2013–2019. In the case of the lens tissue samples, the vouchers comprise unmounted cleaned material in 70% ethanol together with two or more microscope slide preparations.

Supplementary Table 2. Records of Cocconeis placentula varieties found by Google searches in October 2006 and on 1 July 2021.

Supplementary Fig. 1. Greville's (1863) original illustrations of Navicula luxuriosa from Port Stephens, New South Wales, Australia. Scale bar = 10 µm (see main text for details).

Supplementary Fig. 2. Three picked specimens of Diademoides luxuriosa in a preparation by F. Sterrenburg from Sulawesi, Indonesia. A–C show different focuses of a medium-long valve, while D and E show later stages in size reduction- Scale bar = 10 µm.

Supplementary Fig. 3. Cleve's (1896) original illustration of Navicula entoleia, from the Kattegat (A), and Heiden & Kolbe's original illustration of Navicula tripartita from Antarctica (B). Scale bar = 10 µm.

Supplementary Fig. 4. Living cells of ‘Navicula entoleia’ from the sublittoral of Loch Goil, collected in 1988 and 1989. A–C. Three focuses of a single cell, showing the valve and chloroplast lobes (A), peripheral focus of chloroplast bridge with droplets of reserve material (B) and mid focus (C) with nucleus (n) and volutin granules (e.g. v). D. Short specimen in mid focus: note the triangular profile of the pyrenoid (arrow: compare Figs 3 and 7). Figs E–H. A single cell, focused on a valve, upper plastid lobes, midsection, and lower plastid lobes, respectively, with nucleus (n) and triangular pyrenoid profile (arrow). Scale bar = 10 µm.

Supplementary Fig. 5. The drawings of Nitzschia ocellata provided by Cleve (1881, pl. 4, fig. 47a, b), showing a valve (A) and a frustule (B). Scale bar = 10 µm.

Supplementary Fig. 6. Valve identified as Nitzschia ocellata on Academy of Natural Sciences of Philadelphia slide GC90577, drawn by D.G. Mann in 1981. Note the absence of an orderly row of smaller fibulae close to the raphe. Scale bars = 10 µm.