Riparian ecosystems have received little attention from apidologists, but their study is essential to know the diversity and conservation status of bees as well as to evaluate and properly conserve the ecological value of these habitats. In this work, we sampled bees (Anthophila) from a 500 m stretch of the Algars River (municipalities of Arnes and Horta de Sant Joan, Tarragona province, Spain) during the peak flowering period in July and August, using plant-pollinator surveys. A total of 107 bee species were detected, representing approximately 10% of the diversity of the Iberian Peninsula, highlighting that this riparian ecosystem is a biodiversity hotspot and a refuge for bees in summer, when floral resources in adjacent terrestrial ecosystems are scarce. The bee community stands out for the presence of rare (Hylaeus nigrifacies) or very abundant (Ceratina spp.) taxa which are strongly associated with floral and nesting resources (e.g. reed beds) present in riparian ecosystems. New faunistic records are provided for the Iberian Peninsula (including the first record of Tetralonia alticincta) and, at the regional level, first records of eight species in Catalonia, NE Spain: Hylaeus dilatatus, H. kahri, H. lineolatus, H. pictipes, Nomiapis paulyi, Lasioglossum medinai, Sphecodes longulus, Tetralonia salicariae. Two habitats of community interest are present in the study area, and two potentially threatened bee species have been detected (Epeolus cruciger and Lasioglossum brevicorne). The present study highlights the ecological value of riparian ecosystems for wild bees, and due to the extraordinary results obtained, we propose the creation of a pollinator nature reserve in the studied section of the Algars River, following the recommendations of the European legislation as well as those from regional pollinator conservation plans.
Hernández-Castellano et al. (2025) studied this question.