Title: Spatial variability of aquatic organisms and phytoplankton preference diet by fish community lower Mara wetland, Tanzania

Author: Peter Otieno Omollo

Supervising Institution: IHE Delft  - Institute for Water Education

Year: 2023



Wetlands are essential ecosystems that support a diverse array of aquatic life and play a critical role in global biodiversity. However, human activities can harm these ecosystems, leading to a decline in biodiversity. This study aimed to investigate the diversity of macroinvertebrates and phytoplankton, as well as the diet and prey items of fish species in the lower Mara wetland. The study was conducted from December 2022 to January 2023, with physicochemical variables measured in situ using a multi-probe. Macroinvertebrates were collected using a D-frame aquatic kick-net with a mesh size of 500 μm or a grab-sample at each of the nine sampling sites. Fish samples were obtained using monofilament gill nets, and the stomach contents of 350 individuals from nine fish species were examined for prey items. Phytoplankton were also sampled using plankton during the study. The researchers used Non-Metric Multidimensional Scaling (NMDS) and Cluster Analysis to identify similarities and differences between different sampling sites based on macroinvertebrates and phytoplankton data. They also employed Canonical Correspondence Analysis (CCA) to investigate the relationship between macroinvertebrates or phytoplankton and water quality parameters at different sampling sites. The study found 8 orders of macroinvertebrate with Gastropoda order being the most abundant, and the Shannon-Wiener diversity index for aquatic insects ranged from 0.33 to 1.72. Further, the researchers identified nine classes of phytoplankton, with Chlorophyceae being the most dominant. The distribution of macroinvertebrates and phytoplankton was influenced by water quality variability. In terms of fish diet, the researchers identified eleven dietaries of phytoplankton taxa across nine different fish species, with Bacillariophyceae being the most common. The study also revealed dietary overlaps between Tilapia rendali and Synodontis afrofischeri, as well as Schilbe intemedius and Synodontis victoriae. This study emphasizes the importance of preserving wetland ecosystems and managing human activities to prevent a decline in biodiversity. The findings also highlight the complex interrelationships between different components of the ecosystem and the need for integrated management approaches.

Key words: Wetland, monofilament, fish, macroinvertebrates, phytoplankton