Cristina Cejudo-Figueiras

Are diatom diversity indices reliable monitoring metrics

A biological survey was carried out in 640 stations spread over the Loire-Bretagne National Network (France) between 1996 and 2000. Epilithic diatom inventories were obtained following standard methods. A total of 934 diatom taxa were identified. Common diversity indices (species richness, Shannon’s diversity, equitability, dominance, etc.) were calculated and compared against abiotic factors verify their reliability as biomonitoring metrics. Sampling stations were classified according to their trophic status (TP concentration). Several theoretical predictions about the relationship between community structural parameters and limnological variables were tested. In general, diversity indices exhibited poor linear correlations with environmental factors indicating ecological status. No clear patterns were found concerning species accumulation curves, occurrence-abundance, frequency-abundance and frequency distribution of diatom taxa between different trophic levels, although assemblages from stations with lower TP levels were characterized by relatively high dominances of certain taxa, mainly Achnanthidium minutissimum. In the light of these findings, the use of diatom diversity indices in biological quality surveillance protocols in continental waters is discouraged. Results are compared and discussed with similar studies.

Analysis of the type of Fragilaria construens var. subsalina (Bacillariophyceae) and description of two morphologically related taxa from Europe and the United States

Cejudo-Figueiras C., Morales E.A., Wetzel C.E., Blanco S., Hoffmann L. and Ector L. 2011. Analysis of the type of Fragilaria construens var. subsalina (Bacillariophyceae) and description of two morphologically related taxa from Europe and the United States. Phycologia 50: 67–77. DOI: 10.2216/09-40.1 Fragilaria construens var. subsalina is a common diatom found in a wide variety of aquatic systems worldwide. It was described by Hustedt (1925) from brackish waters in Oldesloe, Germany; a lectotype specimen was established by Simonsen (1987). We analysed the ultrastructure of specimens from the lectotype material by means of light (LM) and scanning electron microscopy (SEM) and show that this taxon should be placed at the species level within the genus Pseudostaurosira (as Pseudostaurosira subsalina). A similar but distinct taxon from the United States, found in waters with low electrolyte content, is proposed as a new species of Pseudostaurosira, namely Pseudostaurosira americana sp. nov. We also describe a second new species from Spain (Pseudostaurosira alvareziae sp. nov.), found in waters with moderate conductivity, which was misidentified as P. subsalina in the past. A morphometric analysis of the valve shape supports the morphological separation between the three species. The present study clarifies the taxonomy, ecology and systematic position of these three taxa and provides a comparison with other, similar taxa.

Spatiotemporal changes in diatom ecological profiles: implications for biomonitoring

Diatom indices developed in certain geographic regions are frequently used elsewhere, despite the strong evidence that such metrics are less useful when applied in regions other than that where species–environment relationships were originally assessed, showing that species have particular autoecological requirements in different geographic areas. In this study, we define the ecological profiles for selected environmental variables in three common epilithic diatom species in the Duero Basin (NW Spain), comparing our results with data gathered from different geographic regions. We assess differences in autoecological parameters obtained from the northern and southern subbasins, and from different years, in order to observe whether significant small-scale, spatiotemporal changes exist. Our results show that there are variations in species’ autoecological parameters between different regions. Furthermore, there are significant changes comparing northern and southern Duero subbasins for certain species and physiochemical variables. Additionally, different autoecologies have been observed for certain diatoms and environmental factors comparing two different years. It can be concluded that freshwater diatom autoecologies can vary between different geographic areas. This implies that, in order to improve water-quality bioassessments, autoecology-based diatom metrics should be developed by quantifying species distributions along environmental gradients, using datasets representative of the areas or river types where the metrics will be applied.

New diatom taxa from high-altitude Andean saline lakes

During a biological survey carried out in five shallow, high-altitude saline lakes of the Bolivian Altiplano in 2009, six unknown diatom taxa were found in various lake populations. Detailed light and scanning electron microscopy observations allowed the description of the following new taxa: Navicula venetoides (distinguished from N. veneta Kützing by having coarser lineate striae), Pinnularia boliviana (similar to P. rhombarea var. halophila Krammer but with coarser striae and a narrower central area), Nitzschia sansimoni (morphologically close to N. supralitorea Lange-Bertalot, the latter having denser striae), Surirella striatula var. halophila (differing from the nominate and other varieties in a distinctly heteropolar outline and the presence of denser fibulae) and S. moralesii (with large, strictly isopolar valves and a deep pervalvar depression). Differential diagnostic criteria with respect to similar taxa, together with ecological and biogeographical implications of these findings, are briefly discussed.

Contribution to the diatom flora of Cambodia: Five new recent freshwater taxa

Abstract  Cambodian aquatic ecosystems are extremely diversified and constitute major preservation targets. However, the species composition, diversity, and distribution of the inhabiting algal communities are largely unknown. During a sample collection carried out in the Angkor and Banteay Srei monuments area in 2010, several unknown diatom taxa were found in various population densities in the artificial lakes surrounding these temples. Detailed light and scanning electron microscopy observations allowed the description of five of them (Pinnularia cambodiana, P. shivae, Gomphonema angkoricum, G. paradaphnoides, and Frustulia lacus‐templi) as taxa new to science. Differential diagnostic criteria with respect to similar taxa, together with the ecological and environmental implications of these findings, are briefly discussed.

Recovery of the algae and macroinvertebrate benthic community after Didymosphenia geminata mass growths in Spanish rivers

This study aims to assess the ecological profile of the invasive alga Didymosphenia geminata in NW Spain, analysing the biotic and abiotic factors related to the presence of massive colonies and their effect on river benthos. Physical and chemical parameters were measured in three infested rivers during 2009 and 2010, and biological samples of benthic community were taken according to standard protocols. Collected data was compared with that of control stations located in the same rivers but presenting no evident infestations. The autoecology shown by D. geminata in this study supports former observations reporting the expansion of its ecological niche, with current velocity and nutrients concentrations the environmental variables that best explain the establishment and development of mats in the studied rivers. Regarding its impact, it was observed that the mass growths of this diatom produced a dramatic change in the composition of the algae and macroinvertebrate benthic community which persisted after their disappearance. These results led to the development of a geostatistical predictive model to identify potential risk of dispersion of this diatom in Spanish rivers. The expected distribution of this algae according to this model agreed in general with the actual observed infestations, thus validating it as a tool to prevent and manage future infestations.