Arlette Cazaubon

Methodical approach to distribution of epilithic and drifting algae communities in a French subalpine river: Inferences on water quality assessment

In a sub-alpine river, the Asse, with an unpredictable discharge regime, chlorophyll, density and taxonomic diversity of both drifting and periphytic communities were studied from a methodical approach. The investigations based on stamping two close cross-sections to know their spatial distributions in a heterogeneous bed substrate showed a heterogeneous pattern of colonization mainly influenced by hydrological variables as the current velocity, the size of the substrata (gravel-pebble-boulder). For the drifting algae, mainly composed with benthic species temporarily unhooked to the substrata, the heterogeneity of the distribution was reduced in fast flow which induced a mixing of the whole mass of water.For the periphyton, some results indicated that the greatest diversity and the highest chlorophyll concentration were found on pebble substratum where the current velocity was moderate. These results have also shown that the classical methods used to day for investigations were inadequate for most Mediterranean rivers.It was really difficult to estimate the water quality from classical index created for use in regular large plain rivers.

Heterogeneity of periphyton in French Mediterranean rivers

The ecological niche of periphytic algae can be characterized by a long list of environmental variables: hydrology, substratum, light, water chemistry, temperature, other biota (Rott, 1991). In the french mediterranean area, all the watercourse types are represented; we investigated permanent or intermittent, natural or perturbed streams, large rivers or brooks and tricklets flowing out on limestone or crystalline massifs. Most of studies are based on samples of periphyton from natural substrata (e.g. pebbles, cobbles, sand, silt and clay and macrophytes), but also some from artificial substrata. We also sampled simultaneously measurements of water quality and other relevant environmental variables. All investigations in mediterranean area show the high sensibility of periphyton reacting quickly to environmental parameters; it is shown by a heterogeneous pattern of colonization at different levels.

Morphology and ecology of Oblea rotunda (Diplopsalidaceae, Dinophyceae) from a new habitat: a brackish and hypertrophic ecosystem, the Étang de Bolmon (South of France).

A small thecate dinoflagellate was encountered during winter and spring in the phytoplankton community of a shallow, brackish and hypertrophic pond in the South of France. The abundance of material permitted its identification, using scanning electron microscopy, as Oblea rotunda Balech ex Sournia. However, morphological features showed some discrepancies with the typical characteristics of O. rotunda. Environmental hydrographic parameters in the pond were very different from marine ecosystems where O. rotunda is usually reported. In this polluted and alkaline pond, salinity was low, ranging from 1.1 to 6.2 p.s.u.; the maximum densities of O. rotunda (greater than 1 × 105 cells l − 1) were observed at temperatures around 13°C, after a Cylindrotheca closterium – Heterocapsa rotundata bloom in early spring. These two species and other abundant taxa of the phytoplankton had seasonal patterns that could explain the presence of O. rotunda, since they could have been a food for this heterotrophic species. As this population showed most of the morphological criteria of O. rotunda, but with some variability and a different ecology, it is better considered as a variant of the marine species, rather than as a new species. This study provides additional data on the ecological and morphological features of this poorly known small peridinioid species, previously only reported from open seas and oceans.

Epizootic algae and Protozoa on fresh water branchiopods (Anostraca, Notostraca and Spinicaudata) in Moroccan temporary ponds

Epizootic algae and Protozoa occur on the exoskeleton of fresh water branchiopods in temporary ponds in Morocco. Algal colonization seemed linked with turbid waters and access by the epibionts to the nutritive and oxygenated flows created by the rhythmical beat of the thoracic legs of the branchiopods. It also seemed linked to the mode of life (planktonic or benthic) of the host, and to their exposition to light. Appendages of anostracans, which swim ventral side up, bear a rich community of Chlorophytes, while in conchostracans, where body and appendages are protected by a bivalve carapace, and which swim ventral side down, epibionts colonize the valves, particularly near the hinge and umbo. The lack of algae on notostracans may result from their habit of living in the deeper part of ponds. Protozoans fixed on notostracan shields and on conchostracan valves or appendages, seem to benefit principally from the flow of nutrient- and oxygen-rich water created by the host.

Pearsoniella variabilis Fritsch et Rich (Chlorophyta) en France: description et données autoécologiques

Abstract Pearsoniella variabilis Fritsch et Rich (Chlorophyta) in France: description and autoecology data. The genus Pearsoniella (Ulvophyceae, Ulotrichales, Ulotrichaceae) described by Fritsch & Rich (1924) from South Africa includes one known species: P. variabilis. It is herein recorded for the first time in France, in a part of Durance river. The ring-shaped morphology of chloroplasts is a characteristic feature of the genus and justifies its distinction from other genera of the Ulotrichaceae such as Ulothrix.