L. Forró szerk.: Miscellanea Zoologica Hungarica 9. 1994 (Budapest, 1994)

Andrikovics, S.; Hadnagy, T.: Ecological evaluation of aquatic invertebrates distribution of Apátkút Creek (Visegrádi Mountain, Hungary) in winter

All of the eight species can be found on small and big stones, in the largest percentage Baetis rhodani can be found on both places, it is the most common species along the creek. Epeorus silvicola, Hydropsyche pellucidula, Rhithrogena semicolorata can be found among small stones, Ecdyonurus venosus group and Electrogena lateralis are among larger stones in great number. Table 4. Distribution of the more frequent taxa (%) on different substrates Taxa Substrate Stone Plants Detritus Sand Epeorus silvicola 100 Ecdyonurus venosus group 96 4 Electrogena lateralis group 99 1 Rhithrogena semicolorata group 98 2 Baetis rhodani 97 1 2 Nemoura sp. 89 8 3 Hydropsyche pellucidula 100 ' Halesus sp. 31 57 12 The typical species are among large stones. Electrogena lateralis is found in the upper part of the creek, but among small stones Rhithrogena semicolorata, Ecdyonurus venosus group on the lower part of the creek among large stones. Epeorus silvicola and Hydropsyche pellucidula can be found among small stones in greater number. Altogether 4 species live on detritus. Among them Baetis rhodani can be found in the greatest number, it does not require high level of dissolved oxygen and it changes its place from slow-flowing water to almost still-water. Halesus sp. and Nemoura sp. find their food in this substrate. The occurrence of Electrogena lateralis on detritus - even in small number - means that this species is able to live at low level of dissolved oxygen. Plant fragments are food for Halesus sp. and Nemoura sp., the previous species makes its case from these material. These are the dominant taxa of the fauna living on wood branches, leaves and submerged vegetation. All ecological factors, which have influence on the aquatic insect distribution (dissolved oxygen content, water discharge, water-depth, substrate, food type) are in very close connection with the mean velocity of water. Summary 1376 insect larvae and amphipods (7 Ephemeroptera , 6 Plecoptera, 4 Trichoptera, 1 Coleoptera, 1 Megaloptera, 3 Diptera and 1 Amphipoda taxa) were collected in 174 samples. The number of species and individuals of invertebrates is great in the creek even in winter. The reason is the low water-temperature and high dissolved O2 level, caused by high water velocity. The current of water is rather strong, in winter the average water velocity is about 1 m/sec, much stronger than the values of the creeks in Mátra and Bükk Mts estimated by Oláh (1967) and Kiss (1978, 1979). Distribution of larvae primarily depends on the mean velocity of water. The higher dissolved oxygen concentration allows the greater number of individuals of larvae. The number of