Asellus aquaticus is a freshwater isopod found throughout much of Europe and is one of only two freshwater isopod species native to the British Isles. A. aquaticus is widespread, abundant and considered to be tolerant to various freshwater pollutants, both organic and inorganic, and, perhaps most notably, heavy metals. The species has been proposed as an indicator species for poor ambient water quality, and has been proven to bioaccumulate trace metals. While a number of studies have examined this species’ tolerance to polluted environments, the mechanisms by which A. aquaticus is able to survive a polluted environment are not fully understood. In particular, it remains unclear to what extent adsorption contributes to the uptake of environmental pollutants. To date, there has been no comprehensive study carried out which examines the micro-topography of this species, and, therefore, the connection between surface features and adsorption. Notably, several types of micro-structures are present on the surface of A. aquaticus which are clearly visible through the utilization of Scanning Electron Microscopy (SEM). The aim of this study is to use SEM to describe the micro-structures present and gain a further understanding of pollutant adsorption through the carapace.
Results/Conclusions
Here, we characterize the various micro-structures found on Asellus aquaticus. We use electron microscopy to study the surface topography and structure. We conduct elemental analysis of the carapace using Energy-Dispersive X-Ray Spectroscopy (EDS). We also examine the sub-cutaneous physiology and layout of these micro-structures, and consider whether metal pollutants accumulate in relation to these micro-structures. We find that the micro-structures can be categorized into several groups, including setae and microtrichia. Additionally, we note a variety of other structures, often co-located with a small depression in the carapace. We qualitatively map the relative distributions and size ratios of the observed micro-structures. We propose that the pores associated with these micro-structures could form a potential pathway for cuticular adsorption of nanomaterials and trace metals in A. aquaticus, and, therefore, their properties could affect the rates of adsorption of these contaminants. A greater understanding of the micro-topography of A. aquaticus could be a significant advantage in modeling the bioaccumulation of metals by the species, and understanding its potential for use as an indicator species.