Dr. Fűköh Levente szerk.: Malakológiai Tájékoztató 9. (Eger, 1990.)

Szabó Sándor: Malakológiai megfigyelések a Háromszögi-tóban (1978-1989 között)

In 1978 the water fauna gave a picture characteristic of sodic lakes. In shalloewr parts of the water with a higher pH-value (9,5) only Lymnaea (Radix) peregra and Physa fontinalis existed. In the western, deeper part of the lake with a lower pH-value (8,2) Planorbarius corneus and Lymnaea stagnales were also observed. In the summer of 1979 I, put by 25 Planorbarius corneus from the eastern part of the lake in two close jnets (50x50 cm each) to the western part in order to study nutrition and growing. Within a month B individuals, in 2 month only one survived

.This is a clear evidence of the limit of tolerance for Planorbarius corneus being 9 pH. (RICHNOVSZKY

, 1978). The same year during a distribution research in the eastern part of the lake cumulative distribution was shown by Anisus spirorbis

, insular by Lymnaea (Radix) peregra

, and inequal by Lymnaea stagnalis and Flanorbarius corneus

. (SZABÛ, 1983 /1986/). An average square of biomass gave the following result : plants + other being - 1.150 grs

.:gasteropoda : 22,5 grs. (1,95 \)

. By the autumn of 1979 the lake had completely dried out. Individuals of four species were found in the wet silt. At the depth of 5 to 7 cms 2 % of individuals of 2 species Lymnaea (Radix) peregra and Physa fontinalis

) were still alive. The bed of the Háromszögi-tó was not refilled by water because of the extremely dry period. There was only some water in the east, in the pit at the dam and next to the sluice. Four species existed in that water, but no Physa fontinalis were observed. The next years showed the same. After nearly 10 years of dryness the lake was refilled in a year with relatively more rains (19B9). A water depth of 70 cms was observed even in September. I made a detailed analysis of the whole lake. I found individuals of 12 species in the soil and silt samples taken from the lake. At higher spots individuals from 6 terrastrilal species were found at a contancy value, of 10..30 S. Pupilla muscurum took the largest quantity of findings on dry sand. Some samples of Helicopsis striata were found completaly fossilesed. 5 aquatic species were in fossil and subfossil state near the water, at deeper part of the soil. Samples of Planorbarius corneus and Anisus spirorbis in the wet silt of the pit were alive. Coenological researches on the Háromszögi-tó and the channels conected with it produced the following results: Recently 6 species exist in the lake, with the largest quantity of Physa fontinalis (70 \ of constancy value). Lymnaea (Radix) peregra exist in nearly the same quantity, but having only 30 \ of constancy value. A relatyvely great number of Lymnaea stagnalis has also been observed (50 % of constancy). Many samples of this latter species were dark greyish-brownish. 30...40 S of all samples are young. A remarkable fact is that Anisus spirorbis now show a 10 \ of constancy and only 3,5 \ of dominance, while nine years ago they showed a cumulative dispersion. Position of the species in the lake significantly varies. In the south living individuals can be found rarely, aHid are ' samples of species with a larger body (

Planorbarius corneus and Lymnaea stagnalis

). Most of the species and their individuals can be found in the east of the lake. Anisus spirorbis and Acroloxus lacustris exist only in the west of the lake. It seems that the species had survived during the long and uncongenial period in the wet silt, from which the migration started again. In channel XXXIII being in close connection with the lake 4 specien exist. No Planorbarius corneus and Acroloxus lacustris were found that exist in the lake. The farther channel XXXIII/a is free of water, but in its wet bed species similar to those dserged nine years ago were found. j(2...5 \ of Anisus spirorbis and Lymnaea (Radix) peregra were alive.) (SZABŐ, ,1980.) The appearing of Segmentina nitida that didn't exist here earlier, is a remarkable fact. This species lives in a dhannel called Baker (Ramrill), in a distance of 5 kms from the lake. After putting the silt samples of lake in a Jfishtank, and filling it with 15 cms of tip water, I observed the following |facts: within 2,5 days 4 or 5 individuals of Anisus spirorbis apperared. The pH-value increased to 8,2 from 7. In a ^eek^s time 15-20 individuals were moving, and this quantity didn't increase* Malakológiai megfigyelések á Háromszögi-tóban (1978-1989) A szikes vizű Háromszögi-tó eddigi malakológiai vizsgálata során 21 faj került lelő. Jelenleg 12 faj él itt. A tó hosszú, kiszáradt időszaka után újra benépesül. Úgy tűnik, hogy a kedvezőtlen időszakot a fajok a nedves iszapban ívészelik át.