Ilona B. Muskó

Qualitative and quantitative relationships of Amphipoda (Crustacea) living on macrophytes in Lake Balaton (Hungary)

Analysis was made of the species composition, egg number per female and the size-frequency of Amphipoda living on the dominating submerged macrophytes (Potamogeton perfoliatus and Myriophyllum spicatum) at 10 sampling stations of the northern and southern shoreline of Lake Balaton. The dominating Amphipoda at each sampling station was Corophium curvispinum (85.9–99.8%, mean: 96.6%). Besides this, two other species — Dikerogammarus haemobaphes and D. villosus — were also found in the samples. The two Dikerogammarus species were found in highest percentage near Keszthely (14.1 %); at the other places studied they were under 5%. The number of Amphipoda individuals per g macrophyte dry weight ranged from 5 to 574; the lowest value was found near Keszthely, the highest near B. Maria. The developmental stages of the C. curvispinum population differ in different parts of Lake Balaton: the adult (male and female) specimens occurred in highest percentage near Keszthely. The mean number of eggs per C. curvispinum female ranged from 2.4 to 6.3, showing differences at the different sampling stations. Regarding the two Dikerogammarus species, there were many more D. haemobaphes than D. villosus individuals at almost every station (mean: 75%). The mean number of eggs per egg-carrying female of D. haemobaphes was 11.7, being 19.1 for D. villosus.

Occurrence of Amphipoda in Hungary Since 18531)

Since the first finding in 1853 (Frivaldszky, 1865), 27 Amphipoda have been reported from Hungary, half of them being Niphargus species. The other amphipod species belong to the genera Gammarus, Dikerogammarus, Echinogammarus, Corophium, Synurella, Orchestia, and Talitrus. The most detailed data are available from Lake Balaton where altogether 8 species were found in different habitats, only a few species occurring together. In the 1930s Corophium curvispinum invaded Lake Balaton. This species was reported from Hungary for the first time in 1916 (from the Danube). In the 1950s Dikerogammarus species replaced Gammarus roeselii in the lake. We investigated the ecology of the Amphipoda fauna in Lake Balaton from 1983 to 1987. Both on the submerged macrophytes and in the stony littoral zone of Lake Balaton Corophium curvispinum, Dikerogammarus haemobaphes, and Dikerogammarus villosus occur, with dominancy of Corophium curvispinum. C. curvispinum and D. haemobaphes, living on the submerged macrophyte Myriophyllum spicatum near Tihany peninsula, reproduce in late spring, summer, and early autumn. They produce two generations a year. The biomass of C. curvispinum and D. haemobaphes was roughly 11 and 0.1 g animal dry wt.m -2 , respectively, in mid-July 1986, in areas covered by Myriophyllum spicatum.

Life history of Corophium curvispinum G. O. Sars (Crustacea, Amphipoda) living on macrophytes in Lake Balaton

Samples of the amphipod Corophium curvispinum were collected from Myriophyllum spicatum twice a month during the vegetation period. The animals were sexed, their length measured and the eggs of females were counted. Length frequency histograms served to follow the life history of C. curvispinum.

Differential response of invasive malacostracan species to lake level fluctuations

The water level of Lake Balaton (a large, shallow lake) was extremely low in 2003, after a dry period of several years. Due to the intensive precipitation in 2004, a regeneration period commenced. Stones of the littoral zone were sampled near the water surface and from the lake bottom four times in both years at four sampling stations. Malacostraca in the encrustation of the stones were represented by Ponto-Caspian immigrants: the invasive amphipods Chelicorophium curvispinum and Dikerogammarus spp. (D. haemobaphes and D. villosus), the mysid Limnomysis benedeni and the isopod Jaera istri. The amphipods dominated in both years. Species of the amphipod genus Dikerogammarus were relatively less abundant than the amphipod C. curvispinum in the regeneration period as compared to the drought period of 2003. Maximal density of Malacostraca (ind. m−2 stone surface) was 69,953 in 2003 and 82,465 in 2004. Vertical stratification of animal numbers and specific taxa occurred in May 2003 and throughout the year in 2004, with some exceptions. Many more Malacostraca individuals were recorded at the lake bottom than near the water surface.

Population dynamics and food of bleak (Alburnus alburnus L.) in the littoral zone of Lake Balaton, Hungary

Intra- and interspecific effects together with changing environmental conditions regulate the dynamics of the fragile bleak populations in Lake Balaton. Size- and age-structures, length-weight relationships and mortality were studied on 1493 individuals and growth history were determined using scales from 703 specimens. The population growth rate was slow and the basic population parameters showed area variations along the longitudinal axis of the lake. Gut contents were analyzed in 224 individuals. The bleak stocks are trophically strongly related to the littoral zooplankton and benthos; and they play a significant energy-mediating role in the food-webs between the periphytic communities and fish assemblages in the littoral zone of Lake Balaton.

Oxygen consumption of Limnomysis benedeni Czerniavsky, 1882 (Crustacea: Mysidacea), a pontocaspian species in Lake Balaton, Hungary

Limnomysis benedeni Czern. was artificially introduced into Lake Balaton in 1950 in order to increase the food source of young (1+, 2+) pike perch (Stizostedion lucioperca L.). L. benedeni successfully adapted to the alkaline water of the lake (pH = 8.4–8.8) and recently is a frequent crustacean of the littoral zone. We determined the relationship between body size and dry body mass and measured the oxygen consumption of L. benedeni at 0, 5, 10, 15, 20 and 23 °C, and at different pH (5.4 and 8.4). We obtained a significant relationship between the body length and the dry body mass of y=0.0101e0.8592x. The specific oxygen consumption decreased with the body length according to a power function. Treatment with low pH caused significant increase of the oxygen consumption of the animals at 23 °C, which reflects some acid-stress and enhanced energy demand. Below 23 °C only juveniles (smaller than 5 mm in size) consumed more oxygen at pH 5.4 than at pH 8.4. The oxygen consumption of the animals ranged from 1 to 30 μg O2 mg-1 dry mass h-1 depending on the body length and the temperature. The functional relationships of oxygen consumption obtained make it further possible to estimate the organic carbon flux of the populations of L. benedeni in Lake Balaton.

THE STRUCTURE OF THE ALIMENTARY CANAL OF TWO FRESHWATER COPEPODS OF DIFFERENT FEEDING HABITS STUDIED BY LIGHT MICROSCOPE

[Der Darmkanal des filtrierenden Eudiaptomus gracilis G. O. Sars (Calanoida) und des rauberischen Cyclops vicinus vicinus Ulianine (Cyclopoida) ist vergleichend lichtmikroskopisch nach Farbung mit Hamatoxylin/Eosin untersucht worden. Es konnen drei Abschnitte unterschieden werden: Vorder-, Mittel- und Enddarm. Der Vorderdarm besteht aus dem stark mukulosen Osophagus und bei C. vicinus der sich anschliesenden Erweiterung. Nur bei dieser Art findet sich am Ubergang zum Mitteldarm eine ringformige Membran, die in der Literatur noch nicht beschrieben worden ist. Das Mitteldarmepithel beider Arten besteht aus drei Zelltypen: Zylinder-, Cuboidal- und Drusenzellen. Entsprechend lassen sich drei Zonen unterscheiden. Die Zone I des Mitteldarms ist bei C. vicinus im Gegensatz zu den Verhaltnissen bei E. gracilis extrem variabel. In der Zone II sind die Zylinder- und Drusenzellen bei C. vicinus niedriger. In der Zone III fallt bei beiden Arten eine Verengung auf, die bei C. vicinus sehr viel ausgepragter ist. Die Struktur des hinteren Teils des Mitteldarms und die des Enddarms ist bei beiden Arten ahnlich. Arten der Calanoida haben fast stets einen Mitteldarmdivertikel, der aber in der hier untersuchten Art, E. gracilis, nicht vorhanden ist., Der Darmkanal des filtrierenden Eudiaptomus gracilis G. O. Sars (Calanoida) und des rauberischen Cyclops vicinus vicinus Ulianine (Cyclopoida) ist vergleichend lichtmikroskopisch nach Farbung mit Hamatoxylin/Eosin untersucht worden. Es konnen drei Abschnitte unterschieden werden: Vorder-, Mittel- und Enddarm. Der Vorderdarm besteht aus dem stark mukulosen Osophagus und bei C. vicinus der sich anschliesenden Erweiterung. Nur bei dieser Art findet sich am Ubergang zum Mitteldarm eine ringformige Membran, die in der Literatur noch nicht beschrieben worden ist. Das Mitteldarmepithel beider Arten besteht aus drei Zelltypen: Zylinder-, Cuboidal- und Drusenzellen. Entsprechend lassen sich drei Zonen unterscheiden. Die Zone I des Mitteldarms ist bei C. vicinus im Gegensatz zu den Verhaltnissen bei E. gracilis extrem variabel. In der Zone II sind die Zylinder- und Drusenzellen bei C. vicinus niedriger. In der Zone III fallt bei beiden Arten eine Verengung auf, die bei C. vicinus sehr viel ausgepragter ist. Die Struktur des hinteren Teils des Mitteldarms und die des Enddarms ist bei beiden Arten ahnlich. Arten der Calanoida haben fast stets einen Mitteldarmdivertikel, der aber in der hier untersuchten Art, E. gracilis, nicht vorhanden ist.]