Zooplankton inoculation into large river systems - approaches through the examination of clonal diversity in rotifers, and the study of resting egg banks

Small-bodied metazoan zooplankton can prosper even in flowing waters. However, unidirectional flow is a unique characteristic of these environments, antagonistic to the persistence of plankton in the ecosystem. The repeated observation of organisms at any given point along a river implies, under the current state of our knowledge, that new individuals are constantly recruited from a variety of 'sources' intuitively located upstream. Even if many types of aquatic environments have been suggested as potential sources of inocula, their identity and location remains largely unknown, particularly in river systems like the Meuse in Belgium, whose floodplain has been largely modified by human activities.
The first aim of this study is to locate the major source(s) of zooplankton along the course of the Meuse. We use a method based on the examination of clonal structure in populations of two rotifers abundant in the river, Brachionus calyciflorus and Keratella cochlearis. Our work hypothesis is that populations originating from distinct sources could belong to different clonal lines, and that various clones could co-exist once inoculated. The analysis of allozyme patterns is our primary laboratory tool, given its versatility. The use of nuclear markers such as microsatellite DNA is envisaged.

A still poorly understood aspect of plankton inoculation into river systems is the speedy recovery of populations following periods of unfavourable hydrological conditions such as spates. It is unlikely that growth resumes only from 'relictual' populations spared by the flow. Our hypothesis is that dormant stages characteristic of the life cycle of small zooplankton, could play a role in this quick recruitment, and contribute largely to the global dynamics of inoculation.
Our second aim is to evaluate the existence of such 'seed banks' in the sediment of the Meuse and its associated water bodies, quantify them, examine their hatching potential and the species producing them