Ruppia-communities in the camargue, France. Distribution and structure in relation to salinity and salinity fluctuations

Abstract

The distribution and structure of communities dominated by representatives of the genus Ruppia in the Camargue, France, were investigated during May and June, 1974. With its many isolated “étangs”, “marais” and “baisses” having entirely different and markedly varied salinity conditions, the area is very suitable for the growth of Ruppia. Three taxa of Ruppia appeared to be present: Ruppia cirrhosa (Petagna) Grande, Ruppia maritima L. and Ruppia maritima var. brachypus (Gay) Marsson. The roughly determined distribution pattern of these taxa as well as the distribution of Potamogeton pectinatus L. and of the rarely encountered Althenia filiformis Petit, is presented in a map (Fig. 2). Comparison of this map with a detailed 1965 vegetation map shows some differences due mostly to human intervention. The floral and faunal compositions of the Ruppia communities were determined and related to available data on environmental conditions such as average salinity, annual salinity fluctuations, permanent or temporary existence of the water body, and temperature. The classification of Camarguan waters by Aguesse proved useful in this respect. Communities dominated by Ruppia species were found in waters with considerable salinity fluctuations. Ruppia maritima communities only occurred in oligohaline and mesohaline waters (average salinity 2–18‰ S), whereas R. cirrhosa communities were also present in polyhaline and hyperhaline waters (average salinity 2–40 ‰ S); Ruppia maritima was found in small temporary ponds drying out in summer, whereas R. cirrhosa was mainly found in large permanent “étangs”. The structures of four different kinds of Ruppia communities occurring in the Camargue is described in detail. In addition to important environmental factors, the structure of vegetation (zonation, growth forms, spatial patterns, periodicity) and aquatic fauna (position and behaviour) are described. Finally, some remarks are made on the significance of Ruppia vegetations as initial links of food chains.