Biodiversity and Conservation

, Volume 25, Issue 14, pp 2965–2986 | Cite as

Diatom flora in Mediterranean streams: flow intermittency threatens endangered species

Original Paper


In the context of global environmental changes, Mediterranean rivers are considered highly endangered. Temporal and spatial increases of the dry stretches during the summer lead to the loss of river tridimensional connectivity, which represents a major threat for freshwater biodiversity. In this study, we aimed at exploring the response of diatom communities to summer droughts by analyzing taxonomical composition, specific ecological requirements, ecological guilds and percentages of endangered species. The evolution of diatom communities was monitored under both intermediate and intermittent flows, with traditional and innovative sampling procedures, i.e. collecting diatoms from transects and microhabitats, respectively. Microhabitats differed in terms of water velocity, substrate, isolation and presence of macrophytes. Diatom flora was mainly composed of β-mesasoprobous taxa. We highlighted an increase of species considered as aerophilous and planktonic in sites characterized by intermittent flow. In general, ecological guilds did not respond to hydrological disturbance as expected. Statistical models identified the maintenance of a minimum of 0.20 m/s flow velocity as the main factor influencing the abundance of endangered species. Conversely, flow instability, lentification and habitat fragmentation represented the major threats for endangered species. In conclusion, diatoms can provide useful information to improve river management practices when faced with an increasing water scarcity scenario. Water stability and river habitat heterogeneity strongly favor the presence of endangered diatom species. In the absence of these conditions, isolated pools surrounded by dry riverbed are very important habitats to be preserved, representing the only refugia for benthic diatom communities during summer.


Red list Bacillariophyceae Hydrological instability Pools 



We would like to thank Marco Bodon and Anna Risso of ARPAL for providing useful data on Ligurian rivers and for their valuable help in scheduling the work. We also thank Sabrina Mossino, Marta Franchino, Alberto Doretto, Giacomo Bozzolino, Leonardo Manzari and Irene Conenna for their help in the fieldwork and in the laboratory analyses. We thank Dr. Radhika Srinivasan for language editing. We are grateful for the constructive criticisms of two anonymous referees, whose comments greatly improved this article. This work is part of the research fellowship won by Dr. Elisa Falasco in 2014 “Diatom communities and droughts in Mediterranean rivers”, cofounded by the University of Turin and by the Local Research Grant 60 % 2014 assigned to Francesca Bona.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflicts of interest.

Supplementary material

10531_2016_1213_MOESM1_ESM.pdf (102 kb)
Stream characterization in terms of hydroecoregion, main geological composition and percentage of urban land use. Further details on chemical-physical parameters (mean ± SD) detected during the sampling seasons (SPRING and SUMMER) are also displayed. (PDF 102 kb)
10531_2016_1213_MOESM2_ESM.xlsx (41 kb)
Complete checklist of all the taxa detected in the samples. CODE = taxon code from OMNIDIA 5.3 with database 2015. Ecological requirements include species preferences in terms of saprobity, salinity, moisture (Van dam et al. 1994) and current velocity (Denys 1991). Saprobity: 1 = oligosaprobous; 2 = β-mesosaprobous; 3 = α-mesosaprobous; 4 = α-meso/polysaprobous; 5 = polysaprobous. Salinity: 1 = fresh (Cl <100 mg/l); 2 = fresh-brackish (Cl <500 mg/l); 3 = brackish-fresh (Cl = 500–1000 mg/l); 4 = brackish (Cl = 1000–5000 mg/l). Moisture: 1 = never or very rarely occurring outside water bodies; 2 = mainly occurring in water bodies, sometimes on wet places; 3 = mainly occurring in water bodies, also rather regularly on wet and moist places; 4 = mainly occurring on wet and moist or temporarily dry places; 5 = nearly exclusively occurring outside water bodies. Current: 0 = unknown, 1 = irrelevant, 2 = rheobiontic, 3 = rheophilous, 4 = indifferent, 5 = limnophilous. Life forms and ecological guilds follow the classification proposed in Rimet and Bouchez (2012); for species not included in that list, we inferred data to the closest taxon in terms of taxonomy and ecology. Life forms, Planktonic: 0 = non planktonic; 1 = planktonic. Colonial: 0 = solitary; 1 = colonial. Mucous tubule colony: 0 = other type of colony; 1 = mucous tubule. Adnate: 0 = not adnate; 1 = adnate. Peduncolate: 0 = not peduncolate; 1 = peduncolate. Pioneer: 0 = not pioneer; 1 = pioneer. Ecological guilds, low profile: 0 = not low profile, 1 = low profile; high profile 0 = not high profile, 1 = high profile; motile: 0 = not motile, 1 = motile. Red List column refers to conservation status defined in (Lange-Bertalot and Steindorf 1996): 1 = threatened with extinction; 2 = severely endangered; 3 = endangered; D = data scarce; G = probably endangered; R = rare; V = decreasing; * = at present not considered threatened; ** = surely not threatened. In the last columns, we display the presence or absence of each taxon during SPRING and SUMMER and in upstream (UP) and downstream (DW) sites. (XLSX 41 kb)


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© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  1. 1.Department of Life Sciences and Systems BiologyUniversity of TurinTurinItaly

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