Quantitative plankton samples were collected from the nearshore waters of Porto Novo and from three stations in Vallar Estuary. The environmental factors which influenced the zooplankton biomass in the coastal zone have been discussed. The total zooplankton biomass (by number) was between 1950 and 739l90/m' during the two years of study. The invertebrate larval contribution ranged from 455 to 373070/m'. In the nearshore waters, in the two years, an average of 23.84% of the zooplankton were of invertebrate larvae and the maximum recorded was 75.95 %. In the Vellar Estuary, the contribution of invertebrate larvae was higher than in the nearshore waters. The average contributions ranged from 29.07 to 37.23 % in the different locations of the estuary and the maximum was 93.08%. The reasons for higher production of invertebrate larvae in the estuary are traced and the larval resource utilisation in the natural systems are discussed.