In the Okavango Delta wetland, in northern Botswana, plant and animal communities switch every year from terrestrial to aquatic species when the floodplains and connected waterbodies are inundated by the flood pulse. This phenomenon fosters a rapid growth of populations of aquatic organisms, which evidences the connection between terrestrial and aquatic ecosystems. Aquatic macroinvertebrates, the target group of this thesis, are organisms without a backbone and bigger than 0.25 mm. They provide many direct and indirect benefits to local people in the region, representing a high percentage in the diet of fish and contributing to water purification (e.g., freshwater mussels). However, the knowledge about community composition at species level and their distribution across the Delta is scarce and the chironomids have never been studied. Therefore, the main aim of this thesis is to provide further taxonomical knowledge about aquatic macroinvertebrates in the region, focusing on Chironomidae. For that, a comprehensive literature review of all the freshwater species recorded in the Delta and Lake Ngami was conducted (Chapter 3), resulting in 2,204 species in total, of which 482 are macroinvertebrates and only one chironomid (Chironomus formosipennis Kieffer, 1908). This was complemented with a review on traits and adaptations of chironomids to droughts and floods (Chapter 4) and the collection of 50 macroinvertebrate bulk samples taken in 24 sites during recession and peak phase across four major areas of the Delta (Upper and Lower Panhandle, Boro/ORI Camp and Maun), in three different types of waterbodies (lagoons, channels, pans) and one floodplain. Additionally, 33 UV-trap samples and 3 adult chironomid samples were taken during the peak phase in some sites. This resulted in 258 morphospecies of macroinvertebrates (Chapter 5) and 73 morphospecies of chironomids (Chapter 6), giving some insights into their ecology and temporospatial variation across the hydroperiod gradient. Further information is given in Chapter 5, through the metabarcoding of 60 eDNA samples collected in the same sites and seasons, which resulted in 56 new taxa not found with traditional taxonomy. The efficiency of molecular methods in the region is also discussed. The main conclusion of this thesis is that the regional freshwater biodiversity is considerably higher than previously thought, with the inclusion of 87 new national records, including 70 morphospecies of Chironomidae and two very rare species of Bryozoa: Lophopodella stuhlmanni Kraepelin, 1914 (pending confirmation) and Lophopodella thomasi Rousselet, 1904 (confirmed).
Characterising freshwater macroinvertebrate diversity in the Okavango Delta (Botswana) using taxonomic and molecular techniques
Moliner Cachazo, L. (Author). 1 Sept 2024
Student thesis: Doctoral Thesis › Doctor of Philosophy