The zooplankton communities of the Thames estuary

Abstract

Zooplankton comprises those animals which live suspended in the water column with limited powers of movement such that they drift with water currents. Some spend their entire lives in suspension (holozooplankton) whereas others only inhabit the water column for part of their life cycle (merozooplankton). Estuarine zooplankton has an autochthonous component, which develops and remains in the estuary, and an allochthonous component comprising freshwater organisms washed downstream by the river and marine organisms that have penetrated the estuary from the coastal waters. The presence of allochthonous zooplankton typically results in estuaries possessing high species diversity in the upper and outer ends and having a species-depauperate fauna in the middle reaches, a pattern similar to that recorded for benthic invertebrates (Chapter 6).