Toxic effect of cyanobacterial blooms on the grazing activity of <i>Daphnia magna</i> Straus

• Main Author: Maria £otocka
• Format: Article
• Language: English
• Published: Elsevier 2001-12-01
• Series: Oceanologia
• Subjects: <i>Daphnia magna</i> Straus; Cyanobacterial blooms; Grazing activity
• Online Access: http://www.iopan.gda.pl/oceanologia/43_4.html#A5

The investigations aimed to determine the impact of cyanobacteria <i>Microcystis aeruginosa</i> (Kütz.) Kütz. and <i>Aphanizomenon flos-aquae</i> (L.) Ralfs ex Bornet et Flah., both toxic algae, on the grazing intensity of <i>Daphnia magna</i> 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 <i>a</i> 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 <i>D. magna</i> Straus. The most obvious effects were obtained when <i> M. aeruginosa</i> (Kütz.) Kütz. was used as food. With these cyanobacteria, the gut fullness indicator did not exceed 58%, and the chlorophyll <i>a</i> content in the digestive system of the tested <i>D. magna</i> 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.