DIATOM RESEARCH – Determining geographical range and alien status in diatoms
by Jana Kulichová |
One of the papers recently published on the Diatom Research website that I find particularly interesting is David Mann’s study on the distribution of three well distinguishable species of marine benthic diatoms. David examined the morphology of the three ‘flagship species’ and critically evaluated taxonomic and identification issues that may have led to false negative or false positive occurrence records in the past. Based on a thorough review of available distribution records of the three species and a consideration of potential dispersal vectors, David proposed nine criteria for establishing whether the geographical range of a marine or freshwater species reflects their native range or an introduction outside its natural range.
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.
David G. Mann (2022) 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, Diatom Research, DOI: 10.1080/0269249X.2022.2078428