LAUSR

Regulatory instruments concerning invasive alien species rely on national and regional inventories and reviews of alien species. The data on the origin, pathway/vector, and impacts of alien species are essential for developing effective policies for their prevention and control. Since reviews such as published by Marampouti et al. (2021) have scientific, political, commercial, and social relevance, their accuracy and reliability is paramount. Marampouti et al. (2021, abstract) declare that their aim is “...to explore the origins... of HABs caused by nonnative algal species in the Mediterranean Sea” (the term “nonnative” is exchanged in the article for “alien/ invasive” and “introduced”). Yet the authors fail to provide evidence for the “alien”/“introduced” status of the “introduced harmful algal species” in their article, nor discuss findings that contradict that status. Marampouti et al. (2021) offer a “final list of introduced harmful algal species” encompassing fifteen species of dinoflagellates, four diatoms, and one raphidophyte. The authors list the “origin” (Supplementary Material), presumably the natural range of the species, according to their definition of invasive alien species. Incongruently, the authors chose to illustrate the process of the “tropicalization” of the Mediterranean Sea using Alexandrium ostenfeldii introduced from subarctic waters; A. andersonii from Cape Cod, USA; Lingulodinium polyedra from the Baltic Sea; Coolia monotis from the North Sea; and Dinophysis acuminata from a Norwegian fjord. As the authors adhere to the notion that the type locality is the species’ natural population origin, these examples fit better with ‘borealization’ of theMediterranean Sea. Yet, type locality is just the site where the type specimen of the original species description was collected. It is well established that the study of microscopic marine biota began in northern Europe. Consequently, species first described from the Baltic or North Seas are considered to have wide, even cosmopolitan, distributions. In commercially important marine shellfish farming regions, attention was understandably paid to identification of potentially harmful species of phytoplankton, associated with diarrhetic or paralytic shellfish poisonings. In the early 1990s, Alexandrium andersonii and Gessnerium (=Alexandrium) taylorii were described from the historically important marine farming regions of Cape Cod and Arcachon, respectively. Yet, until the late 1990s, they were pooled as Gonyaulax tamarensis or G. catenella in the Mediterranean Sea due to taxonomic difficulties, though Gessnerium taylorii is more common in the Mediterranean Sea than in its type locality. Epiphytic dinoflagellates (Coolia, Gambierdicus, Ostreopsis, Prorocentrum, Sinophysis) have received full scientific attention in the late 1970s, once some warm water species were identified as associated with Ciguatera fish poisoning. As in the case of Alexandrium, the first monitoring surveys in the Mediterranean Sea began when many of the epiphytic dinoflagellate species were already described from other regions. It is entirely possible that species categorized as alien are native biota. Intense research effort following a toxigenic event in late 1980s, attributed to the domoic acid produced by species of the diatom genus Pseudo-nitzschia, resulted in the description of numerous new taxa. Again, when the first detailed studies on the diversity of Pseudo-nitzschia began in the Mediterranean Sea, species already described in other locations were identified (i.e., P. multistriata in Japan) and categorized as aliens. The use of molecular tools in aiding robust identification has revealed that Mediterranean populations are genetically distinct from their supposed natural populations (see details in the Appendix S1 as Supplementary Material): Alexandrium ostenfeldii, Protogonyaulax catenella (=Alexandrium pacificum) or Ostreopsis ovata Mediterranean populations are genetically Responsible editor: Philippe Garrigues