Microhabitat distribution of aquatic oligochaete communities in the Western Balkans peat bog

Peat bog pools are rare and fragmented in the Western Balkans. Thus, aquatic macroinvertebrate diversity and the implications for microhabitat loss in these ecosystems are poorly known. Aquatic oligochaetes, widely used as indicators, were sampled using a benthos net in the largest and oldest Croatian bog, in four main water body types: a pond, a deep pool, a shallow pool and a ditch. As these microhabitats lack spatial replication both in the studied bog and in the region, we applied a nested study design with replicates sampled over time. We found a species‐rich aquatic oligochaete fauna, with 11 taxa recorded. Oligochaete communities were strongly affected by vegetation complexity and the morphology of bog water bodies, namely, their size and depth. As revealed by generalised linear mixed models (GLMMs), taxon richness and abundance were significantly higher in the ditch than in other water body types. This could be attributed to the vegetation complexity, supporting many different niches and providing allochthonous food supplies for oligochaetes. The various bog pools contribute to regional biodiversity and promote distinct patterns in the spatial distribution of oligochaetes. However, the predominance of ubiquitous oligochaetes, with high taxon richness, might indicate the degradation of the studied peat bog. This was further confirmed by the spread of vascular plants to the bog area and higher pH water values. All these warning signals suggest that hydro‐ecological conditions should be urgently improved in order to preserve communities in the bog studied.