Waterfalls as a reservoir for caddisfly larvae (Insecta, Trichoptera): exploring a poorly known habitat

Waterfalls have not been thoroughly studied as a habitat for freshwater macroinvertebrates, although they appear to be an exclusive environment for taxa with traits suited to these unique physical habitat conditions. To better understand the role of waterfalls as aquatic habitats in Costa Rica, macroinvertebrates were collected within the flow and spray zones of 38 waterfalls across the country, spanning an altitudinal range of 55 to 2,660 m above sea level, either by climbing up from the base or using rappel techniques from above. Additionally, in 11 of the waterfalls, corresponding river samples were taken to compare the associated assemblages. Caddisfly larvae were found at all waterfalls sampled, with a total of 10,642 individuals collected from 10 families and 24 identified genera. The family Hydroptilidae, with 12 genera, accounted for half of the individuals collected and was present in 37 of the 38 waterfalls. Metrichia (Hydroptilidae) and Calosopsyche (Hydropsychidae) were the most abundant genera, in terms of the highest number of individuals, and were most frequently collected, indicating a strong preference for this habitat. Larvae of Atanatolica (Leptoceridae) and Xiphocentronidae were quite common in spray zones. In contrast, Wormaldia (Philopotamidae), Contulma (Anomalopsychidae), Cerasmatrichia, and Alisotrichia (Hydroptilidae), although uncommon in rivers throughout the country, were also found abundantly in waterfalls, particularly the latter, which were especially abundant in intermittent and karstic waterfalls. Assemblages of Trichoptera in waterfalls were generally similar, with some differences associated with specific site characteristics, such as elevation or rock composition, and chemical factors like conductivity. This research constitutes the first systematic study of caddisfly larvae associated with waterfalls in the Neotropics. The results provide an important baseline for identifying new collection sites of adult caddisflies and for generating associations and descriptions of their larval stages, which may be unknown due to the understudied nature of this habitat.