Top predator absence enhances leaf breakdown in an intermittent stream

• Published in: The Science of the total environment 2016-12, Vol.572, p.1123-1131
• Main Authors: Rodríguez-Lozano, Pablo, Rieradevall, Maria, Prat, Narcís
• Format: Article
• Language: English
• Subjects: Animals; Barbus meridionalis; Biodiversity; Biomass; Cyprinidae - physiology; Food Chain; Food web; Freshwater fish; Fungal biomass; Fungi - metabolism; Invertebrates - physiology; Macroinvertebrate communities; Mediterranean stream; Plant Leaves - microbiology; Predatory Behavior; Rivers; Spain; Species extinction
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2016.08.021

Current biodiversity loss is characterized by the extinction of top predators, but small-bodied freshwater fish are often overlooked in research and conservation management even when threatened because they usually lack commercial value. Therefore, the ecosystem impacts of their possible loss remain mostly unknown. We assessed whether the presence/absence of an endangered predatory fish (Barbus meridionalis (A. Risso, 1827)) in an intermittent stream affects leaf fungal biomass and leaf quality (i.e. leaf carbon:nitrogen ratio and leaf toughness), macroinvertebrate assemblages colonizing leaf packs, and leaf breakdown rates. We conducted a leaf bag experiment comparing a control reach with a population of B. meridionalis with an adjacent upstream fishless reach. In the fishless reach, leaf fungal biomass and microbially mediated breakdown rate were lower compared to the control reach. This was probably caused by the lack of the bottom-up stimulation through nutrient recycling by fish. Shredders and scrapers were found at higher abundance and biomass in the fishless compared to the control reach, and the whole macroinvertebrate community composition changed with fish absence. Consequently, macroinvertebrate mediated leaf breakdown was faster in the fishless than in the control reach, not only compensating for the lower microbially mediated leaf breakdown in the fishless reach, but accelerating the overall leaf breakdown rate. Our study contributes to understand the potential cascading effects produced by the extirpation of endangered small-bodied fish. [Display omitted] •Current Mass Extinction is characterized by the loss of top predators.•There is a knowledge gap regarding the ecosystem consequences of fish loss in intermittent streams.•We assessed if the presence/absence of an endangered fish affects leaf breakdown.•Fish absence affected macroinvertebrate communities, leaf fungal biomass, and breakdown rates.•Small-bodied fish can have a key role in ecosystem processes in intermittent streams.