Delicatophycus liuweii sp. nov., a new cymbelloid diatom (Bacillariophyceae) from an upper tributary of the Liujiang River, Guangxi, China

During a survey of freshwater diatoms from streams in the upper reaches of the Liujiang River, Guangxi, China, a new Delicatophycus species, Delicatophycus liuweii sp. nov. was discovered and is presented here based on light and scanning electron microscopy. The main features of D. liuweii include strongly dorsiventral valves with slightly truncate and obtusely rounded ends and 3–6 stigmata positioned on ventral striae adjacent to the middle. The new species is compared with Delicatophycus williamsii, D. pouemboutensis, D. nepouianaus and Cymbella parvulissima, all of which show similarities to the new species, but differ in size, valve shape, striae density, puncta density and number of stigmata.

Using metabarcoding and « Diat.Barcode » database to perfom molecular identification on marine biofilms

Marine benthic diatoms highly contribute to biofilms formation, playing a crucial role on both living and artificial surfaces ‘colonization (Briand 2017, Salta 2013). However, their microscopic morphological identification is time consuming and requires a high expertise in taxonomy. We therefore decided to look toward molecular analyses and especially metabarcoding. In this study, we determine : (i) if the use of the “Diat.barcode” database, mostly developed for freshwater diatoms (Rimet 2019), is relevant to characterize marine biofilm communities, (ii) if the amplification of degenerated primers targeting the rbcL gene (Vasselon et al. 2017) could improve the diversity of marine diatom biofilms, and (iii) if molecular and morphological analyses could be correlated.A large majority of OTUs (>95%) was affiliated using the “Diat.barcode” database and the pipeline FROGS, with coverage and affinity values above 80%. OTUs tables contained 75% of diatom species already reported from marine environment, with 82% belonging to the pennates group. The use of degenerated primers significantly improved richness and diversity. Moreover, it allowed us to identify taxa that were not present before, as Iconella, Sellaphora and Coronia. Finally, we showed higher richness and diversity, but also a higher repeatability (replicates closeness) leading to a better clustering with metabarcoding. We found differences in terms of biomarkers, but more broadly, we were able to correlate significantly (r = 0,404; p<0.0001) diatom assemblages.While the latest version of “Diat.barcode” database contains only 12.4% species referenced as marine, it appears to be a powerful tool, even on biofilm samples from the Mediterranean, Baltic seas and Indian Ocean. Furthermore, we confirmed the relevance of degenerated primers to amplify a higher diversity of diatoms. Finally, beta-diversity similarity using molecular and microscopic analysis appeared positive, leading to the conclusion that the two methods should be used in a complementary way.

Diatom diversity and distribution in Madeira Island streams (Portugal)

Here, we present the data obtained from the samples collected in a field campaign during the spring of 2015 which aims for a better understanding of the diversity and distribution patterns of freshwater diatoms in Madeira Island. Following European and Portuguese standards and recommendations for routine diatom sampling and analysis, we collected samples in 40 sites, distributed in 27 permanent streams and identified the diatom species present, using general diatom floras and studies in Portuguese freshwater diatoms. Little is known about the diversity and distribution of freshwater diatom assemblages from Madeira Archipelago. This study reports a survey in 40 sites in Madeira Island distributed in 27 permanent streams. A total of 965 diatom (Bacillariophyta) occurrences were recorded, belonging to 130 different taxa from 44 genera and 27 families. The families with the highest number of occurrences were Bacillariaceae (176), Achnanthidiaceae (135) and Naviculaceae (133). The two diatom endemisms, described previously in Madeira Island (Lange-Bertalot 1993), Nitzschia macaronesica Lange-Bertalot and Navicula madeirensis Lange-Bertalot, were only observed in a small number of sites, located mostly at Laurissilva forest. Sixty species are new records, not only to Madeira Island, but also to the Madeira Archipelago.

Morphological investigation and description of two new Gomphonema Ehrenberg (Bacillariophyta) species from India and Vietnam with biogeographical comments

Two new species of Gomphonema Ehrenberg are described based on light and scanning electron microscopical observations. These are Gomphonema kallarense sp. nov. found in India and G. kezlyae sp. nov. found in India and Vietnam. We also report and document the morphology and variability of G. doonense from Vietnam, a species previously described from India based on a limited number of valves. Both G. doonense and G. kallarense have striae composed of doubly-punctate striae that are without occlusions, while G. kezlyae has striae with single rows of areolae that have external occlusions giving the impression of C-shaped openings. Our investigation shows that India and Vietnam share some species in common, adding additional evidence that the biogeography of freshwater diatoms from the tropics warrants future investigation.

Continental diatom biodiversity discovery and description in China: 1848 through 2019

In this paper we inventory the continental diatom taxa described from inland waters in China, from the first species descriptions dating back to 1848 through 2019. China’s geography and hydrography are complex, including the world’s highest mountains, many large rivers, salty lakes, and large karst regions. From this area, a total of 1128 taxa have been described from China over this time period. We examine the number of taxa described in ca. 20-year intervals and note the periods of time of no to few descriptions, versus time intervals with many taxon descriptions. Early on, taxon descriptions of freshwater diatoms from China were done by mostly by Europeans working alone, and the time frame of 1948 to 1967 had few descriptions, as a devasting famine and the cultural revolution impacted scientific work and productivity. B.V. Skvortzov produced a large number of taxon descriptions, during his time in residence in Harbin, later while in Sao Paulo, Brazil, and even posthumously. More recently, a wide range of labs and collaborations across China, and with a diverse array of international partners, is ushering in a new, robust era of research on the biodiversity of continental diatoms. A few areas of research and work for the future are discussed.

Kurtkrammeria tiancaiensis sp. nov. a new cymbelloid species (Bacillariophyceae) from Lijiang Laojunshan National Park in Yunnan Province, China

During a survey of freshwater diatoms from a mountain lake, Lake Tiancai, Laojunshan National Park, Hengduan Mountain Range, Lijiang City, Yunnan Province, China, a new Kurtkrammeria species, Kurtkrammeria tiancaiensis sp. nov. was recorded. A detailed morphological description of K. tiancaiensis is presented, based on light and scanning electron microscopy. The main features of K. tiancaiensis include slightly dorsiventral valves with narrowly rounded, or slightly protracted ends, a wide central area, apical pore fields at both poles and lack of stigmata. The new species is compared with K. treinishii, K. weilandii, K. lacusglacialis and K. eileencoxiae (≡ Gomphonema eileencoxiae), all of which show similar valve outlines to K. tiancaiensis, but differ in details of size, striae density, puncta density, number of apical pore fields, shape of the central area and/or presence of stigmata.