GARCIA (X.F.) & LAVILLE (H.). 2000 - Spatio-temporal distribution of the chironomid populations in the lower part of a large river : the Middle Loire (France). Verh. Internat. Verein. Limnol., 27(5) : 2524.

Abstract

The spatio-temporal distribution of the chironomid fauna has been studied in a potamal section of the river Loire (Tours region, Middle Loire, 6th order), in relation with the characteristic strong flow dynamics of the river.

Pupal exuviae of chironomids have been collected monthly, from March to December 1996, with drift nets, in the main channel and two waterbodies, on an one kilometre long site.

A former study of 9 000 specimens collected in the same section (1994-1995), had previously shown the faunistic richness and the originality of the Loire chironomid population with 99 taxa recorded, of which 13 were new records for France (GARCIA & LAVILLE 2000). The identification of 10 000 more specimens has allowed to record 34 added taxa, upgrading the faunistic list to 133 taxa in 62 genus found in this Middle Loire section.

On the whole, 22 taxa are new records for France, including three new genera : Hayesomyia, Robackia and Saetheria, and a new pupal exuviae : Chironomus Pupae 23 (LANGTON 1995).

The spatio-temporal distribution of the chironomid populations has been analysed with special reference on the seasonal changes in connectivity between the main channel and the hydraulic annex.

The chironomid distribution of the Middle Loire appears clearly bimodal, with a specific winter population equally distributed in space (December to March) and a pool of species present from April to November, but unequally distributed in space during spring (partial similarity of communities in main channel and hydraulic annex) and during summer (complete dissimilarity of communities in main channel and hydraulic annex).

The observed communities organisation correspond exactly with the three annual contrasting periods of flow : high winter discharge, periodic high spring discharge and low summer discharge.

The consequences of this spring connectivity pattern, in the hydraulic annex, are both, the periodic entry of species specific from the main channel and the persistence of mesologic conditions similar to those of the main channel, by contrast with the waterbodies summer stable conditions.

The spatio-temporal connectivity pattern between the waterbodies and the main channel appears consequently as one of the basic factor of the chironomid distribution by transfer of species through the different parts of the riverbed and by carrying along structural changes in local mesologic conditions, to which fauna reacts.

References

GARCIA (X.F.), LAVILLE (H.). 2000 - First inventory and faunistic particularities of the Chironomid population from a 6th order section of the sandy River Loire (France). Arch. Hydrobiol.,147(4) : 465-484.

LANGTON, (P.H.). 1995.- A key to pupal exuviae of West Palaearctic Chironomidae. Update on the genus Chironomus. Privately published Huntington, England, 14 pp.

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