Zooplankton of the open Baltic: Extended Atlas - IOW

A B
Figure 5.1.1. Cnidaria, Scyphomedusae: A, Aurelia aurita (modified
from Hayward & Ryland, 2005); B, Cyanea capillata (after Russel, 1970).
The moon jelly, a scyphomedusae Aurelia aurita is the most dominant
species of the Baltic Sea. Barz et al. (2006) characterise it as a species, which
can reduce the stocks of mesozooplankton communities considerably in years
of high abundance (e.g. Möller, 1980; Matsakis & Conover, 1991; Purcell,
1992; Olesen, 1995; Omori et al., 1995; Lucas et al., 1997; Schneider &
Behrends, 1998). These medusae compete for zooplankton with commercially
important planktivorous fish species and ctenophores, but they may also prey
on fish eggs and larvae and thus directly affect their recruitment (Barz et al.,
2006). The Belt Sea, the western Baltic Sea and also the Archipelago Sea are
known as strobilation areas for A. aurita. However, ephyra are not regularly
found in the Baltic Proper. Some authors concluded that A. aurita does not
strobilate in this area (Janas & Witek, 1993; Barz & Hirche, 2005). However,
the occurrence of the other larger Scyphomedusae, Cyanea capillata in the
western Baltic Sea and in the Baltic Proper is always a sign for salt water
influx from the Kattegat area. An indication for strong salt water influxes is
the occurrence of the hydromedusae Euphysa aurata in the western Baltic Sea
(Wasmund et al., 2004).
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