Zooplankton Associations in the Middle Niger‐Sokoto Basin (Nigeria: West Africa)

Abstract

The species richness of the crustacean zooplankton (Cladocera and Copepoda) and Rotifera in the Middle Niger-Sokoto Basin is characterised from 35 1 samples collected from 109 localities. 26(4) Cladocera, 18(8) Copepoda and 38(8) Rotifera are recorded. Figures in brackets indicate first records of species for Nigeria. Zooplancton associations of the Middle Niger are compared with one of its major tributaries, River Sokoto, and seven of its minor tributaries using similarity indices of S~rensen and Pearsons Product Moment Cluster Coefficients. The Rivers Sokoto and Shagari consistently had the highest similarity of zooplankton associations, for all combinations of rivers studied with r = 0.54 (Cladocera), r = 0.91 (Copepoda) and r = 0.54 (Rotifera). Zooplankton associations of the Middle Niger are weakly correlated with all tributaries studied (r < 0.1). Species composition and hydrology of the River Sokoto Basin are also compared with previous studies in Nigeria. A Principal Component Analysis of species abundance accounted for 54 % of the total variance. It again confirmed the similarity of the branches Sokoto and Shagari. Two groups of species assemblages were identified. The occurrence of Asplanchna sp., Testudinelta patina and Microcyclops varicans in one group appears related to microhabitat selection. The other group made up of Brachionus calyciflorus calyciflorus, Macrothrix spinosa, Lecane h a , Thermocyclops decipiens and Metacyclops minutus is suspected to be linked to physico-chemistry. Further studjes on the hydrology and physico-chemistry are required for definitive identification of both factors.

The response of phytoplankton and zooplankton to river damming in three cascading reservoirs of the Tana River, Kenya

“…The observed dominance by copepods in the reservoirs was not surprising. However, this study only reported high abundance and dominance of copepods and cladocerans, a finding different from documented works on other African water bodies, including Lake Cubhu (Martin & Cyrus ), Ogun and Ona rivers (Akin‐Oriola ) and Niger‐Sokoto River (Jeje & Fernando ), which also reported a high abundance of rotifers, in addition to copepods and cladocerans.…”

Zooplankton assemblage of Oyun Reservoir, Offa, Nigeria

“…Kirk & Gilbert (1990) have noted this type of scenario in a tropical reservoir. The low genera abundance of cladocerans and copepods have also been documented in other water bodies like Lake Cubhu, South Africa (Martin & Cyrus 1994), Ogun and Ona rivers (Akin-Oriola 2003) and Niger-Sokoto River (Jeje & Fernando 1992). The predominance of Daphnia among the cladocerans could have arisen due to its large bodied size which enables it to graze on large quantities and diverse forms of phytoplankton.…”

On the diversity of the Cladocera in the tropics

“…In contrast, Korinek (1984) surveyed c. 50 localities (in all, c. 100 samples) in the Upper Zaire Valley, Central Africa, and recorded 53 species of Cladocera here, only three of which were Daphnia. Not only are the tropics therefore probably richer on a unit areal basis than the non-tropics, but studies like Jeje & Fernando (1992), wherein a remarkably low number of crustaceans was reported from a large area and numerous samples in Nigeria, indicate that their material was not exhaustively studied.…”