Davidovich N.A., Davidovich O.I., Polyakova S.L., Eker-Develi E., Nikulin V.Yu., Nikulin A.Yu.
Regional Studies in Marine Science 2026; 102: 105360
Diatoms morphologically resembling the toxigenic species Nitzschia navis-varingica have been reported in the Sea of Marmara and the Mediterranean Sea, questioning its global spread. Using integrative taxonomy (biometrics, phylogenetics of rbcL, SSU and LSU rDNA, and mating experiments), we reassessed clones from populations from these basins and new isolates from the Black Sea. All clones belong to the "Nitzschia traheaformis" lineage. Our integrative approach not only provides the first confirmed record of N. traheaformis in the Black Sea—where it was likely overlooked due to its recent description and historical misidentification—but, more importantly, corrects the previous misidentification of N. navis-varingica in the Sea of Marmara, a finding with direct implications for regional biotoxin risk assessment and harmful algal bloom monitoring. Reproductive experiments revealed that Black Sea and Sea of Marmara populations are reproductively compatible, suggesting they belong to the same biological species. Mediterranean clones exhibited only rare homothallic reproduction, preventing a conclusive assessment of their relationship to other populations. Thus, our results demonstrate that the isolates examined from the Black Sea, the Sea of Marmara, and, based on our molecular data, the Mediterranean basin belong to the N. traheaformis lineage—for which no toxicity has been reported to date—rather than the hazardous N. navis-varingica. This study underscores the critical importance of integrative taxonomy in uncovering easily misidentified or taxonomically challenging diatom species that require high-level morphological expertise for reliable discrimination, with direct implications for the accurate assessment of biotoxin risks and biodiversity trends.
