Baseline study of the plankton productivity of Ibeno Atlantic coastline, South south Nigeria was carried out every second week of the month for 13H/day beginning from 0600 to 1800 hours at both surface and interstitial waters from November 1996 to June 1998. Physicho-chemical parameters and major elements were analyzed. Moderate acidity during the dry season and alkaline medium during the wet season were observed. Wet season turbidity, D.O., colour, NO3, PO4, Silicate decreased sharply from those of the dry season while pH and NH4 did not vary significantly between seasons. Peak phytoplankton production of five classes, 35 genera and 42 species occurred in October 1997 with Bacillariophyceae dominance while peak zooplankton species (28) belonging to 21 genera, 19 of which was from the class Copepoda were observed. High plankton densities were identified between 0600 and 0800 and 1300 to 1600 hours. At interstitial water depths of 0cm, 10cm, 20cm and 30cm, plankton densities decreased with depth. Plankton productivity took a sinusoidal curve and was not unconnected with the tidal changes. Chlorophyll-a values ranged from 0.000

Keywords : Physico-Chemical, Plankton, Productivity, Grazing, Interstitial.