Planothidum audax sp. nov. (Bacillariophyta, Achnanthidiaceae), a new diatom from temporary streams in southern Portugal

Abstract

Temporary streams represent ca. half of the river network at the worldwide level, and in regions such as southern Europe their dominance of the landscape is evident (Larned et al. 2010, McDonough et al. 2011, Barbosa et al. 2020). Currently, these streams are receiving increased attention due to their importance as high diversity spots for algae, arthropods, plants, etc., and due to the ecosystem services they provide (Acuña et al. 2014, Datry et al. 2018b). Because of their geographical position and the land use changes in their watersheds (increased urbanization, agriculture, etc.), climate change, contamination and habitat fragmentation constitute forces threatening their integrity and ecological characteristics (Datry et al. 2018a, Bonada et al. 2020). Conditions in temporary streams change dramatically from rainy to dry seasons (McDonough et al. 2011, Bonada et al. 2020). Diatoms adapt to these changes in different ways, thus producing communities that are spatially and temporarily varied (Sabater et al. 2016 , Várbíró et al. 2020, Novais et al. 2014). In southern Portugal, these communities have a high proportion of still undetermined species and we lack ecological preference information for them, which impairs their use as bioindicators (Novais et al. 2014, 2020). As shown by Novais et al. (2014), diatoms in Portuguese temporary streams include a high proportion of endangered species (ca. 12%), which together with the existence of dynamic and diverse assemblages point to the importance of conservation of these streams (Várbíró et al. 2020), and the urgency to taxonomically describe such a diversity. Several Planothidium species were found in samples from these streams, as part of an ongoing project to unravel the ecological features of their diatom communities (see methods in Novais et al. 2020). A small-valved Planothidium population called our attention due to its small size and the difficulty to see its features under light microscopy (LM). Upon scanning electron microscopy (SEM) analysis, it became evident that we had found the new taxon presented below.