The burrowing crayfish Parastacus pugnax (Decapoda: Parastacidae) in the Semiarid Region of Chile: findings of a naturalized or threatened population?

ABSTRACT Parastacus pugnax is an endemic burrowing crayfish from the basins of the Mediterranean and Temperate Wet regions of Chile. For the first time, specimens were found incidentally in the Semiarid Region of Chile (Choapa River Basin). In these regions, hydrological changes derived from global warming and the intensive use of water for irrigation have resulted in highly fragmented habitats, where the effects of the dry season are exacerbated by periods of permanent drought. Unfortunately, in the Semiarid Region there are not regulatory measures for the conservation of the native biota. The aims of this study were to determine the spatial distribution patterns of P. pugnax in the Choapa River Basin (⁓31°S) to expand and contribute with updated knowledge about the distribution and natural history of this species highlighting local environmental management issues. Seasonal occurrence surveys were carried out at eight sites stratified by elevation in the lower, middle, and upper zones of this basin. This was complemented by semi-structured interviews within local prawn´s fisher. Parastacus pugnax was distributed across ⁓25 km in the lower and middle zone of the basin, and it is present in lentic and lotic environments. The occurrence of this excavator species in lotic environments is somehow unusual according to its ecology, which suggests that it is a primary facultative excavator, so a re-evaluation of its current ecological category (category 1; primary excavator) is necessary. According to the interviewees, P. pugnax corresponds to a naturalized species introduced by humans ⁓25–30 years ago for artisanal aquaculture in ponds. The wide altitudinal distribution of P. pugnax in the Choapa River Basin indicates the need to re-evaluate its distribution limits, which traditionally placed the Parastacidae family to the south of Aconcagua River Basin (⁓33°S). To understand the origin of the species in the Choapa River Basin, is clue to specify the phylogenetic structure and determinate whether the presence in the Semiarid Region is constrained to the Choapa River Basin or extends to other basins within this region.