Environmental drivers of freshwater diatom assemblages in island streams: insights from the Canary Archipelago

Freshwater island streams are isolated systems often characterised by dynamic and fluctuating hydrological regimes with a great potential to host unique aquatic biodiversity. However, the processes structuring benthic diatom communities in these habitats remain poorly understood. Diatom samples and in situ water parameters were collected from 38 permanent and temporary streams located in Tenerife, La Palma, and La Gomera islands (Canaries archipelago) over three sampling campaigns. Multivariate ordination methods were used to assess community responses to environmental gradients and variance partitioning for evaluating the relative contribution of environmental and spatial drivers; the diatom-based Specific Pollution Sensitivity Index (IPS) was used to assess the ecological status of the studied streams. Our findings revealed wide variation in species richness among islands. Three distinct diatom communities were identified, each associated with specific geo-climatic and water chemistry conditions and each tending to be associated with a particular island, though with important exceptions. Application of the IPS indicated good ecological status when non-typology-specific thresholds were applied. These results highlight the main drivers of diatom community organisation in these streams and offers a first step towards informing water management policies and conservation strategies for these and similar island freshwater ecosystem communities.