Due to climate change, more and more streams are drying up periodically, while other pressures, such as pollution or channel modification, mean that many streams are no longer suitable for their natural wildlife. A new study reveals how these unfavourable conditions – both separately and in combination – affect the composition and survival abilities of aquatic macroinvertebrates.
The research found that when a stream experiences intermittent flow, it makes life far more difficult for its inhabitants than poor water quality does. This is because flow intermittency completely removes the habitat, whereas polluted but still present water still offers at least some opportunities for life. Both types of stress reduce the number of species present and significantly alter community composition, leaving only those species that can withstand these challenging conditions.
One key finding is that not all physical or behavioural characteristics (so-called “traits”) respond in the same way to environmental stressors. Some “neutral” traits occur in almost all environments, meaning they are not particularly sensitive to drying or to water quality decline. Examples include small body size, producing many eggs, or strong flying ability. Such traits generally promote survival – for instance, small-bodied animals can hide more easily in moist sediments after drying, while species with large wings can quickly recolonise when water returns.
Other traits, however, are highly sensitive to environmental change. Some species disappear as water quality deteriorates – especially those that filter or collect fine organic matter. In the case of drying, species are most at risk if they are short-lived or have movement restricted to the water. Interestingly, predators also respond differently: in permanent, good-quality streams they may be outcompeted, while in intermittent streams – where there are fewer competitors – they may thrive.
These findings improve our understanding of what aquatic life needs to survive and how streams can be better protected in the future from drying and habitat degradation. The study also makes it clear that it is not the amount of stress that matters most, but its type: drying acts as a much stronger environmental filter than water quality deterioration. This is why conservation measures must give priority to maintaining streamflow regimes – a fundamental prerequisite for sustaining diverse and resilient aquatic communities.
Publication:
Szeles, J., B-Béres, V., Bozóki, T., Fekete, J., Ficsór, M., Boda, P., & Várbiró, G. (2025). Exploring macroinvertebrate community assembly rules: unraveling the effects of flow intermittency and poor ecological potential on environmental filtering and limiting similarity through functional traits. Hydrobiologia, 852(7), 1825-1846.
