The effect of three tidal levels- ebb, mid and flood tides- on the composition, abundance, distribution, and diversity of zooplankton species in the Great kwa River, a major tributary of Cross River, Nigeria were investigated every forthright beginning from July to September 2019 and compared to 1997 study. A total of 59 zooplankton species belonging to 41 taxa (genera) and 16 classes were identified and recorded during the present study. The zooplankters comprised 199 individuals of which 49 were recorded in low tide, 95 at mid tide and 55 during high tide. Generally, the class Rhizopoda (37.19%) were dominant, followed by Copepods (25.13%) while invertebrate, Lepidoptera and Malacostracan were each less than 1%. While the Copepoda dominated at low tide, the Rhizopoda was dominant at both mid-tide and high tide. Shannon Weiner index (H) showed that zooplankton species were high at low tide (3.95), followed by high tide (2.95) and least at mid tide (2.22). The absence of some zooplankton species at mid-tide and high tide suggest that zooplankton species had migrated vertically downwards prior to the onset of mid tide and high tide. Despite the highest number of individuals recorded at mid-tide, an evenness value of 0.49 compared to 0.74 (high-tide) and 0.85 (low-tide), suggests that the numerical abundance was less evenly distributed among species. Results are compared with 1997 findings.

Keywords : Tides, Zooplankton, Abundance, Vertical Migration, Succession