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Toxic effect of cyanobacterial blooms on the grazing activity of Daphnia magna Straus

100%

Lotocka M.

nr 4

The investigations aimed to determine the impact of cyanobacteria Microcystis aeruginosa (K¨utz.) K¨utz. and Aphanizomenon flos-aquae (L.) Ralfs ex Bornet et Flah., both toxic algae, on the grazing intensity of Daphnia magna Straus. In order to determine the parameter permitting the quantitative determination of the grazing intensity of herbivorous organisms, methods based on the following techniques were applied: microscopy, to determine the degree of gut fullness; spectrophotometry, to determine the levels of chlorophyll a and its degradation products in the food composition; high-performance liquid chromatography (HPLC) to determine the content of exogenous and endogenous carotenoids. Each of these methods confirmed that the tested algae species inhibited grazing intensity in D. magna Straus. The most obvious effects were obtained when M. aeruginosa (K¨utz.) K¨utz. was used as food. With these cyanobacteria, the gut fullness indicator did not exceed 58%, and the chlorophyll a content in the digestive system of the tested D. magna was three times lower than that in the control organisms. It seems that the defensive reaction of organisms was a reversible process. However, the possibility of a long-term, sublethal influence of cyanobacteria on the physiology and internal processes of this species cannot be ruled out.

The effect of temperature and humidity on the grazing activity of Deroceras reticulatum (O. F. Muller, 1774) and the damage to rape plants

80%

Kozlowski J. , Jaskulska M. , Kaluski T. , Kozlowska M.

nr 4

Winter rape is susceptible to damage caused by D. reticulatum (O. F. Müller) mainly in the early phases of the plants’ development. The degree of damage and the size of yield losses depend on the slug population and the grazing activity, which are governed by many environmental factors. Laboratory studies were performed to analyse the rate and amount of damage to rape plants (2–3 leaf stage) caused by D. reticulatum, and the effect of temperature and soil humidity on the slug’s grazing activity. With increasing air temperature (up to 16°C) the amount of damage increased, but the effect was not lasting. The slugs were also active at low temperatures (+1°C), and although their grazing was less intense, the amount of damage after seven days could reach an average of 34%. In laboratory tests, the soil humidity had no marked effect on the amount of damage done by the slugs.

Grazing effects of alien amphipods on macroalgae in the littoral zone of the Neva Estuary [Eastern Gulf of Finland, Baltic Sea]

80%

Berezina N. , Golubkov S. , Gubelit J.

nr Suppl.1