Drought in small streams: a laboratory experiment with invertebrates

MARILUÁN, GUSTAVO; ALBARIÑO, RICARDO; DÍAZ VILLANUEVA, VERÓNICA

Bariloche

Congreso; Southern Connection Conference; 2010

We aimed to analise the survival of 3 species of invertebrates, common in headwaters of north andean Patagonia, when exposed to an experimentally recreated drought. Larval specimens of the leptophlebid mayfly Meridialaris chiloensis and the limnephilid caddisflies Monocosmoecus sp and Verger capillatus were placed in individual containers with clean fine substrate, food (M. chiloensis: stones with periphyton, both caddisflies: stones + decaying leaf litter) and filtered stream water, and maintained aerated at 13°C with a 14:10 day-night photoperiod. Every third day water, food and substrate from the containers were renewed and survival of insects and feeding signs were checked. The experiment consisted of a treatment with a 14% reduction in the water level per day (i. e. only wet sediment from day 15) and a control with a constant water level (70mm above substrate). In all cases, four replicates per treatment and species were set. Specimens of V. capillatus were alive in the four containers after 90 days of experiment, all M. chiloeensis and Monocosmoecus sp. died before 20 and 50 days respectively. In contrast, invertebrates in the controls were alive longer, and adult emergencies were also registered. This study provides a first approach to assess the vulnerability of aquatic biota to drought in small streams. Further field and laboratory investigations would allow us to understand the ecological effects of such disturbance.