Ariadna spider as a good candidate bioindicator of heavy metal contamination in the Namib Desert

Human activities are strongly affecting natural ecosystems and native species have been proposed as bioindicators for pollution monitoring and assessment. The present study is the first attempt to use Ariadna spiders as indicators of trace metals contamination in the Central region of the Namib Desert. Mining activity is the biggest contributor to Namibia’s economy in terms of revenue and several trace elements as well as semi-precious gemstones and minerals are main products. Therefore, their released and potential contamination of specific Namib mining areas cannot be excluded. Various spider populations belonging to undescribed Ariadna species are widespread in gravel plains within the Central Namib Desert. Being sit-and-wait predators, Ariadna spiders spend their life in individual tunnels dug in the soil, so resembling the behaviour of ground-dwelling spiders known to be strong metal accumulators in terrestrial ecosystems. In the present study, we collected 60 specimens of three Ariadna populations (20 spiders from each site) in austral summer 2016, along a N/S and W/E transect at various distances from main mining areas of the Namib Desert. Depth and diameter of entrance burrow and body weight of each spider were recorded. Trace metals analysis were conducted in spider’s whole body as well as in soils samples collected around spider’s burrow. Oxidative stress parameters, CAT, GST and MDA were analysed in soft tissue of spiders and neurotoxicity assessed by measuring cholinesterases activity (ChE). Entrance diameter and depth of burrow seems to be affected by the distance from mining areas. Levels of Zn, Cd, As and Cu resulted higher in Ariadna body compared to levels found in soils around their burrows. On the opposite levels of Pb, V, Cr, Co and Ni were 1 or 2 order of magnitude lower in spiders than in soils. Similar trends in such levels and biological responses as CAT, GST and ChE were observed among sites and based on various distance from the mining area. Such preliminary results support the recognition of Ariadna spider as a good candidate as bioindicator of trace metals contamination in Namib Desert.