Five-Year Monitoring of a Desert Burrow-Dwelling Spider Following an Environmental Disaster Indicates Long-Term Impacts

Abstract

Deserts are characterized by unpredictable precipitation and extreme temperatures. Their fauna and flora are sensitive to anthropogenic environmental changes, and often recover slowly from environmental disasters. The effects of oil spills on the biota of desert regions, however, have scarcely been studied. We predicted that terrestrial invertebrates suffer long-term negative effects from an oil spill, due to their close association with the substrate. Thus, we investigated the effects of two oil spills that occurred in 1975 and 2014 in the hyper-arid 'Arava desert (Israel), on a spider that constructs silk-lined nests in burrows in compact, sandy soil in this extreme desert habitat. The spider, Sahastata aravaensis sp. nov. (Filistatidae), is described herein. We assessed spider burrow abundance in plots located in oil-contaminated and nearby uncontaminated clean soil (control) areas over five consecutive years and measured habitat characteristics in these plots. In the laboratory, we determined the preference of individuals for clean vs. oil-contaminated soil as a resting substrate. Finally, as this species was previously undescribed, we added a new species description. The abundance of Sahastata was significantly lower in oil-contaminated plots, and this was the case in the 40-year-old oil spill (1975) as well as in the recent one (2014). In laboratory tests, spiders showed a significant preference for the clean soil substrate over the oil-contaminated substrate. In the field, soil crust hardness and vegetation density did not differ significantly between oil-contaminated and control plots, but these measures were highly variable. The burrows were significantly clustered, suggesting that the young disperse only short distances. In the laboratory adult spiders did not dig burrows, perhaps indicating that adults remain permanently in their natal burrows and that in the field they may use vacant burrows. We conclude that Sahastata populations were affected negatively by the oil spills and these effects were long-lasting. We propose that by monitoring their spatial distribution, burrow-dwelling spiders such as Sahastata can be used as effective bioindicators of soil pollution in desert habitats.

Keywords: Araneae; Filistatidae; Sahastata; bioindicator; hyper-arid; oil-spill; ‘Arava valley; ‘Avrona.

Figure 1

The study area with the 2014 and 1975 oil spill areas are marked in black. Rectangles designate monitoring plots: 2014 oil-contaminated plots in red, 2014 uncontaminated clean soil (control) plots in green, 1975 oil-contaminated plots in orange, 1975 uncontaminated clean soil (control) plots in turquoise. Dots and stars designate Sahastata burrows: burrows found in the first year of monitoring (2016) in white, burrows found after 2016 in blue, yellow stars designate burrows used for the quadrate survey.

Figure 2

‘Avrona nature reserve habitats. (A–C) 2014 area dominated by sand and loess soils, (D,E) 1975 area dominated by loess covered by stones (gravel). Pictures: (A,C–E) Assaf Uzan, (B) Ibrahim N. A. Salman.

Figure 3

Sahastata burrows. (A,C,F): ‘Avrona nature reserve 1975 area dominated by loess covered by stones (gravel), (B,D): ‘Avrona nature reserve 2014 area dominated by sand and loess soils, (E): Yotvata sand dune. Pictures: (A–D): Igor Armiach Steinpress, (E): Nitzan Segev, (F): Yoram Zvik.

Figure 4

Presence of Sahastata spiders in burrows indicated by the spider response to stimulating the silk in the burrow entrance with a twig. Pictures: (A): Assaf Uzan, (B): Yoram Zvik, (C,D): Igor Armiach Steinpress.

Figure 5

Quadrat survey. (A,B): Quadrats in ‘Avrona nature reserve 2014 oil-spill area, (C,D): Quadrats in ‘Avrona nature reserve 1975 oil-spill area. (A,C): Quadrats with Sahastata burrow (18 quadrats), (B,D) No-burrow quadrats (20 quadrats). Pictures: Assaf Uzan.

Figure 6

Laboratory spider keeping and experimental setup. (A): Plastic boxes with shredded cardboard and a cardboard cylinder used for keeping the spiders, (B): Spider feeding on an ant, (C,D): Arena used for experiments, half of the arena was filled with clean soil (control) and the other half with oil-contaminated soil. Two artificial burrows, 1 cm depth and 1 cm diameter, were dug 7 cm from the center of the arena and 7 cm from each other. The artificial burrows were lined with paper to prevent the sand from collapsing, the arrow (6D) points to the spider location in the arena during one of the replications. Pictures: (A,C,D): Yebin Byun, (B): Shlomi Aharon.

Figure 7

(A). Distribution of 139 Sahastata burrows observed in four plot types during the entire monitoring period. (B). Percentage of burrows with spiders (white), active burrows where spiders were not observed (grey), and with burrows that looks abandoned or where no spider was observed (black) in four plot types during the entire monitoring period. (C). Mean burrow opening diameter (centimeters) in the quadrat survey.

Figure 8

(A). The total number of spiders found in each soil type in the arena on the first night, last night, and last day of the five-day experiment. (B). The total number of spiders found in each soil type at the end of the 24-h experiment. Black—number of spiders found on the oil-contaminated soil side, white—on the clean soil side (control), and gray at the border between the two sides.

Figure 9

Sahastata aravaensis sp. nov. female endogyne. (A): paratype MACN-Ar 41837. (B): paratype SMF. Drawings: Ivan L. F. Magalhaes, Scale bars = 100 µm.

Figure 10

Sahastata aravaensis sp. nov. female endogyne. (A–C): Holotype HUJI-AR 20302, Pictures: Zeana Ganem, (D): paratype SMNH, Picture: Sergei Zonstein, (E,F): paratype MACN-Ar 41837, (G,H): paratype SMF. Pictures: Ivan L. F. Magalhaes.

Figure 11

Sahastata aravaensis sp. nov. habitus of live spiders in laboratory. (A,B): paratype MACN-Ar 41837, Pictures: Ivan L. F. Magalhaes, (C,D): paratype HUJI-AR 21001, Pictures: Shlomi Aharon.

Figure 12

Sahastata aravaensis sp. nov. (A–E): Holotype HUJI-AR 20302, G-C: Paratype HUJI-AR 21001. (A): Spinnerets, (B): left anterior lateral spinneret, (C): left posterior median spinneret, (D): left posterior lateral spinneret, (E,F): calamistrum, (G): cephalothorax dorsal, (H): sternum. Pictures: (A–E), (G,H): Zeana Ganem, (F): Efrat Gavish-Regev.

Figure 13

Sahastata aravaensis sp. nov. burrow excavated from ‘Avrona nature reserve. Pictures: (A,B,D): Igor Armiach Steinpress, (C): Ibrahim N. A. Salman.