Spatial Fluctuations in Zooplankton Biotypes of the Imo River in a Niger Delta Area of Nigeria

Abstract

The study identified zooplankton biotypes of the increasingly in-stream sand-mined Imo River in Etche, a Delta area of Nigeria, as indicators of the health of the aquatic ecosystem. Plankton samples were collected with a 55µm mesh size plankton net that was hauled horizontally along the river course for 5 minutes at 7 sampling locations once monthly for 24 months (March 2007-February 2009. Samples were fixed/preserved in 4% formalin solution in labelled plastic containers. In the laboratory, a wide-mouthed pipette was used to withdraw 1ml of the plankton subsample and to place it on a Sedge-wick rafter-counting chamber. Standard keys were used for species identifications and counts made through direct microscopy. The ANOVA, post-hoc plots of group means, hierarchical cluster analysis (HCA), and the Margalef's species diversity index were used to analyze data. Zooplankton had low diversity index (0.926 ± 0.100) and was made up of 7 taxa and a mean density of 433 organisms/ml; with order of dominance as Cladocera (25.87%)> Copepoda (20.55%)> Protozoans (19.17%)> Rotifera (18.71%)> fish eggs and larvae (9.24%)> Crab larvae (4.62%)> Beetle larvae (0.69%). Plankton abundance peaked in sampling location 1 (140 organisms/ml; 32.41%) and was least in location 3 (21 organisms/ml; 4.86%), even as there was marked spatial heterogeneity in the taxa composition [F (11.94) >F crit(3.94) ] at P<0.05. The HCA revealed that crab larvae, fish eggs and larvae, beetle larvae, and copepods formed the first and richest cluster, while the rotifers, cladocerans and protozoans formed the sparse 2 nd , 3 rd and 4 th clusters, respectively. The low biotic diversity recorded could be attributed to growth-limiting perturbations created by ongoing in-stream sand mining in water columns.

Morphological, Electrical and Thermal Performances for Rubber High Voltage Applications

“…In terms of number of species and number of cells per litre, the most abundant zooplankton was the taxonomic group Cladocera. Similar results have been reported in Nigerian freshwater ecosystems: Ezekiel et al [17] in Sombreiro River, Ude et al [34] in Echara River, Ogbuagu and Ayoade [18] in Imo River, Dimowo [1] in Ogun River. However, the finding in this present work is at variance with the observation of Kennie et al [11] in the Jebba Upper Basin in which the dominant taxonomic group was Cladocera.…”

Despoilation of Mangrove Wetland through Illegal Sand Mining Activity and its Effect on Phytoplankton Abundance in the Niger Delta, Nigeria

“…Generally, the investigation discovered that there were no significant variations in some physicochemical parameters in Abuloma, Ogbogoro and Eagle Island except for TDS and salinity contents [83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102]. Some parameters analyzed such as DO, BOD, EC and TDS were found to be above the approved limits based on WHO standards, hence implying that water quality on these studied areas have been impacted negatively by continuous in-stream sand mining activities alongside other anthropogenic perturbations.…”

Influence of Environmental Variables on the Abundance and Distribution of Phytoplankton: A case Study of Lekki Lagoon, Sub-Saharan Africa

“…Plankton samples were obtained in 150ml labeled plastic bottles using plankton net of 55μm mesh size that was slowly hauled horizontally at about 30 cm depth against the water current in each sampling station for 5 minutes. Samples were then preserved in 4% formalin as described by Ogbuagu and Ayoade (2012) and Sharma et al (2015). Samples were obtained during daylight between 11am and 2pm so as to minimize variations as a result of the diurnal migration of plankton (Adesalu, 2012).…”