Aquatic monitoring, II - invertebrate biology: summary of annual report for 1990 - 1991

t,: t.- ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST ECOLOGICAL GROUP Thirteenth session OCP/VCU/HYBIO/92.2 , Bobo-Dioulasso. 20-24 Januarv 1992 ORIGINAL: FRENCH AQUATIC MONITORING II - INVERTEBRATE BIOLOGY SUMMARY OF ANNUAL REPORT FOR 1990.1991 ,l (F. Konde and K. Nabe) For the period 1990-7991,, the monitoring of the non-target entomofauna in the rivers in Guinea was mainly carried out at three stations: the Niandan at Sassambaya; the Milo at Boussoule; the Dion at Tere; ,if eof ;J+i,::#ffi:hl,"lifr:xf":':#;3Jfi :H'L:Tffi f II*"J;'I,l:,g;1 .-, watercourse but disrupted by diamond searchers. The monitoring protocol is still the same: sampling once per month in Novenrber and December and twice per month in January, February, March and April. The principal activities undertaken by the Guinea Invertebrate Biology Team were: - Drift collection and the taking of five Surber samples at the above-mentionecl monitoring stations. - Analysis of the monitoring results. - Study on the duration of the larval life of the Tricorythidae (a report has been , prepared already and sent to the Aquatic Monitoring Coordinator in Ouagadougou). i-\ l\ 2 The Niandan }as for a long time been the only monitoring starion; this is rvhy rhcrehas been no disruption.in the application of the prbtocol at this station this ye1i. 'l'lre arralysis of the results will therefore concern only the Nianclan. MONITORING OF THE NIANDAN - For the day drift - 200-micron nets - the annual variations obtained in 1990 ancl 1991for the whole fauna are very different. This general pattern is followed by all the Chironomidae (Diptera). Among the Ephemera, the Baetidae show similar drift index variations for 1990 irncl 1991. The Diptera are mainly representecl by the chironomictae. - Day drift. 5O0-micron nets: The curve representing the annual faunal trencl is a bit different for 1990 and lt)91. The acrophase is at the end of March and due mainly to the Chironomirlae ancl Ephcrrrc'rir. A.s regards the Ephemera, the BaeticJae make up the greater part of the fauna arrcl the acrophase is at the end of March (Fig. 7). t The drift curves obtained in 1991 for the Orthocladiinae are similar to those of 1990. But the third peak observed in 1990 is not founcr in 1991 (Fig. 9). - Night drift. 200-micron nets The seasonal trend of the whole fauna is similar between 1990 ancl 1991. [ror rhe two periods, the index for the whole fauna increases from January to March encling. rhe p decreases in April, The acrophase is still at the end of March (Fig. 10). The curve for the Ephemera is similar to that of the whole fauna; the Caenidae ftrrrn the greater part of the Ephemera. The peak at the end of March is due to the Caeniclae. The Orthocladiinae-Chironomidae-Diptera show very different variations in 1 990 ancl 1991 (Fig. 12). The Orthocladiinae curves show two peaks (December encling and March ending). - Saxicolous fauna. The densities of all the saxicolous fauna are very different berrveen 1990 and 1991. However, a certain resemblance is noted as regards ihe in.reuse ol the curve from December ending to the beginning of March. Generally speaking, the reappearance of the Tricorythidae ancl the abuncJance of rhe Hydropsychidae at the end of January 1991 in the Surber samples suggesr a launal recolonization.