engleski

Surviving the dry phase: Water mite (Acari: Hydrachnidia) adaptations to flow intermittency in karst rivers

Water mites have complex life cycles, synchronizing five life stages according to host, prey and habitat availability and, in intermittent rivers, to dry periods as well. Six karst intermittent rivers, ranging from zero (sporadically intermittent) to more than 200 days per year with no flow, were analysed in order to assess water mite occurrence along a flow intermittency gradient. In total: 18 water mite species (10 new to Croatia) were recorded. Most intermittent rivers showed that water mite abundances decline with the increased duration of the dry phase. One river showed high abundances despite its relatively long dry period (75 days/year). However, this river dries up only at its middle reach, making water mite recolonization effective from both upper and lower river reaches. Water mites found at sites with highest flow intermittency showed morphological features (swimming setae) typical for lentic habitats (surviving dry phases in separated pools), while rheophilous “hard bodied” mites were found in rivers with least flow intermittency most likely surviving the dry period dormant, buried in the sediment. Different water mite survival strategies in overcoming the dry phase resulted in relatively high species richness, while harsh environmental conditions, caused by flow intermittency, resulted in their low abundances.

water mites, Hydrachnidia, karst rivers, IRES

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