Zooplankton and salinity in the Rufiji River delta,Tanzania

A comparative analysis of the zooplankton from different salinities was carried out in the Rufiji River delta system, located on the mid Tanzanian coastline opposite Mafia Island (7° 45 S, 39° 20 W).Zooplankton samples were collected by vertical, oblique and horizontal surface tows (250 µm mesh) at three sites, namely at the river mouth (salinity = 20–25), in the estuary (salinity = 12–14), and in the upper reaches of the river (salinity = 0). Samples taken in the river mouth and estuary were collected at two times of the day, which coincided approximately with midday and sunset.A comparison of zooplankton diversity and abundance at the three sites showed that a much richer, more diverse fauna existed at the river mouth and estuary compared to the upper reaches. The zooplankton collected both at the mouth and in the estuary were very abundant at certain times of the day, although differences in faunal composition were found between the two sites.