Processing samples of benthic marine diatoms from Mediterranean oligotrophic areas

Abstract

The processing of benthic diatoms is tedious and involves several potentially damaging steps for cells. Although the preservation of siliceous frustules is of paramount importance in the implementation of biotic indices, only few studies quantified treatment-induced cell losses. We assumed that commonly used treatments may lead to mechanical (centrifugation, sedimentation, boiling, sonication and mounting in Naphrax) and chemical (cold H 2 O 2 digestion) damages on diatoms. We analysed the potential adverse effects of these treatments and the cleaning efficiency of H 2 O 2 and incineration in order to find out the most suitable technique to process lightly silicified Mediterranean populations. Results showed that successive resuspensions of material after each concentration treatment (sedimentation and centrifugation) and low speed centrifugation did not alter the physical integrity of frustules. In contrast, boiling and sonication exhibited adverse effects especially on the preservation of large frustules and Naphrax mounting proved to be the most damaging step whatever the size of diatoms. For cleaning treatments, incineration provided the most satisfactory results and acted on a non-selective way as opposed to hydrogen peroxide which led to either a large number of non-cleaned frustules or dissolved valves. Our recommendations for processing samples of lightly silicified Mediterranean benthic diatoms include the use of low speed centrifugations, dehydration at room temperature, incineration and dry mounting.

Taxonomic survey of benthic diatoms in Neum Bay, southeastern Adriatic

“…Other authors obtained quite different results due to differences in the size of the studied areas, environmental conditions and seasons. In addition, special attention must be paid to the use of different cleaning and processing treatments of benthic marine diatom samples from Mediterranean oligotrophic areas (Vermeulen et al, 2012);marine diatoms are likely to be very sensitive to common treatments used in studies of freshwater populations because of the lower availability of silicic acid and of the interference of salinity in silica fixation (Conley et al, 1989).…”

Multiproxy analyses of Lake Allos reveal synchronicity and divergence in geosystem dynamics during the Lateglacial/Holocene in the Alps

“…This step prevents underestimation of large-sized diatoms, which are typically fragmented during treatment and slide mounting (Petit-Maire et al, 1983). The remaining samples were incinerated at 500 C in a muffle furnace for 30 min to remove organic matter (Vermeulen et al, 2012), then treated using standard procedures (rinsing in 10% HCl and 30% H 2 O 2 : water mixture, repeated rinsing with water), and the treatment was completed by high liquid-density separation (ZnBr 2 at a density of 2.0; Quesada et al, 2015). Slides were made using Naphrax as the mounting medium.…”

Diatom frustules as a biomaterial: effects of chemical treatment on organic material removal and mechanical properties in cleaned frustules from two Coscinodiscus species

“…acids, bleaching, oxidising or denaturation functions from different chemicals, and thermal treatment. There are few systematic studies with comparisons of different cleaning methods [30] , [31] , [32] , [33] , [34] . Here, a comparative study of two frustule cleaning methods is presented, using carefully described cleaning protocols based on established cleaning principles [35] .…”