Oral Presentation Freshwater Sciences 2023

Does low shredder diversity compromise functional indices and litter decomposition metrics as indicators of ecological conditions in Afrotropical headwater streams? (#412)

Augustine Sitati 1 2 , Mourine J Yegon 3 , ELIZABETH WAMBUI 1 , Frank O Masese 1 4 , Steve Thomas 5
  1. Fisheries and Aquatic Science, University of Eldoret, Eldoret, Kenya
  2. Biological Sciences, University of Alabama, Tuscaloosa, Alabama, USA
  3. Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria
  4. Aquatic Science and Ecosystems Group, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa
  5. Biological Sciences, University of Alabama, Tuscaloosa, Alabama, USA

In the Afrotropics, land-use change associated with agriculture and urbanization is rapidly replacing natural forests with croplands, grazing lands and human settlements. These activities have severe consequences for biodiversity and ecosystem functioning. Studies in Afrotropical headwater streams report a low diversity of shredders dominated by omnivorous freshwater crabs. Thus, it is unclear whether the low shredder diversity compromises functional indices and organic matter processing rates that are frequently used as indicators of ecological integrity of headwater streams. This study investigated the composition of macroinvertebrate functional feeding groups (FFGs) in forested, agricultural and urban streams and, specifically, the role of shredders in leaf litter decomposition. The study also evaluated the performance of abundance- vs. biomass-based metrics of FFGs where shredders are used as indicators of ecosystem functioning. We conducted leaf litter decomposition experiments in both coarse- and fine-mesh litterbags using native and non-native leaf species in forested, agricultural and urban streams to determine the effect of land-use change on instream litter decomposition. We supplemented the results by data from literature review of similar studies in the region. Shredders were less abundant and had lower diversity than other FFGs in agricultural and urban streams compared to forested streams. Forested streams had higher leaf litter decomposition rates than agricultural and urban streams. Furthermore, the combined role of both shredders and microbiota (coarse-mesh litterbags) was greater than the sole role of microbiota, implying that shredders played a major role in the decomposition process.  Abundance-based metrics were better predictors of ecosystem attributes than biomass-based metrics.  Similarly, there was incongruence between abundance- and biomass-based shredder related metrics (P/R and CPOM/FPOM) in predicting ecosystem functioning. Despite the low abundance and diversity of shredders in Afrotropical headwater streams, this does not appear to limit their role in organic matter processing and their value as indicators of ecological condition.