Flooding Induced Occurrence of Terrestrial Nematode Species and Genera in the Benthos of River Nun, Niger Delta

Abstract

Aims: To investigate; the effects of flooding and dredging on the nematode community composition in River Nun, Niger Delta, Nigeria. Study Design: The study is a survey using River Nun as a case study. Place and Duration of Study: Study area is a section of River Nun in Bayelsa State, Niger Delta, Nigeria, Samples were collected for 30 days. Methodology: Eckmann’s grab was used in collecting samples at depths; 0-10cm and 10-20cm from nine designated collection points (Ax – Gx) along the river course. Nematodes were extracted from the sediment by the use of the modified Baermann’s extraction method. Identification was by the use of the binocular light microscope and standard guides. Physicochemical parameters were determined using handheld water checkers. Data was analysed using Measures of Central Tendency, ANOVA and Species Diversity Index (SDI). Results: The study revealed that the physicochemical parameters considered in the study did not deviate from the standard permissible in freshwater ecosystems despite the persistent flooding and dredging of the water way. Species abundance and diversity revealed seven (7) nematode species and genera from six (6) families amounting to a total of 46 nematodes. There was variability in vertical distribution and speciation in the study. Data showed the following speciation and abundance; Tylenchus filiformis, 14 (31.0%); Ditylenchus spp., 2 (4.0%), Pratylenchus pratensis 18 (39.0%), Longidorus spp., 2 (4.0%); Tylenchorhynchus dubius, 2 (4.0%); Criconema spp., 2 (4.0%) and Meloidogyne spp., 6 (13.0%). Depth related prevalence indicated a preference of nematodes to the top trophic level with the 0-10cm having the highest number (30 individuals) of nematode and the 10-20cm depth having a total of (16) nematodes. There was no statistical difference (P≤0.3) in nematode occurrence between the two depths. SDI showed that the nematode species diversity in River Nun was relatively high (0.76). Also data showed that sediment soil typology influenced the occurrence of nematodes in the study with all the recorded nematodes occurring in the sandy sediment in contrast to clayey and silty sediment where no nematodes were recorded. Conclusion: The study revealed a colonization of the sediment by terrestrial nematode species and genera due to the persistent flooding experienced in the area which has converted the freshwater ecosystem to a depository of debris and other suspended particles that come in with the run-off water from the hinterlands. The absence of aquatic species of nematodes in the studied samples is also attributed to the aggressive dredging in the habitat that may have altered the bottom substrate, washed away the native nematode fauna making re-establishment of new aquatic nematode community difficult as a result of increased current. The study concludes that the affiliation of nematodes to sandy sediment is due to increased aeration and availability of food which guarantees the survival of other organisms.