Diel activity of Niphargus amphipods in spring habitats

In: Crustaceana
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  • 1 Department of Environmental Science and Policy, Univeristy of Milan, Via Celoria, 26, I-20133 Milan, Italy
  • | 2 Laboratory of Subterranean Biology “Enrico Pezzoli”, Regional Park of Mount Barro, I-23851 Galbiate, Italy
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Among crustaceans, numerous aquatic species are obligate groundwater-dwellers, i.e., stygobionts; their most common adaptations are the absence of eyes and a general depigmentation. Among the most widespread Eurasian stygobionts are the amphipods of the genus Niphargus. They are reported not only from groundwaters but also from groundwater-fed springs, where the abundance of food is higher, but where they also experience the constraint of UV radiation during the day. The aim of this study was to assess if in spring habitats Niphargus amphipods show diel activity, in particular if they are able to exploit the resources during the night. During two consecutive years, we evaluated, with both day and night surveys, the abundance of Niphargus sp. individuals at four springs in NW-Italy. We performed surveys both visually and with dip-nets and we evaluated the relationship between Niphargus sp. abundance and the number of potential predators. We detected a significant difference between day and night in the abundance of Niphargus sp.: during the night the number of individuals was substantially higher. No significant relationship was observed between Niphargus sp. abundance and the abundance of potential invertebrate predators. The broad implication of this study is that the number of active detectable Niphargus in springs is higher at night than during daytime, regardless of the number of potential predator species occurring. This suggests that one of the major constraints for the exploitation of spring habitats by Niphargus amphipods is the UV radiation, and that specific adaptations favouring diel activity in border habitats, like springs, may have evolved in these basically stygobiont species.

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