Fluctuations in jellyfish abundance can impact aquatic food webs severely and have been proposed as an important indicator for changing conditions in marine ecosystems. Of particular interest is how environmental conditions affect jellyfish populations, especially in semi-enclosed and sensitive habitats such as the Baltic Sea. The distribution of sessile polyp stages in this region is likely to play a key role for the development and population dynamics of its two most abundant medusa species Aurelia aurita and Cyanea capillata (Scyphozoa, Cnidaria). The Baltic Sea is a brackish ecosystem connected to the North Sea, notably characterized by a steep salinity gradient from about 26 in the western Kattegat to extremely low salinity of 3-4 in the north-eastern Gulf of Bothnia. We conducted laboratory experiments and investigated the population dynamics (larval settlement, individual and population growth of polyps, asexual reproduction) of A. aurita under different levels of temperature, pH, and salinity commonly occurring in the Baltic Sea. Comparatively, we examined the effect of reduced salinity on similar ecophysiological responses of polyps of C. capillata and determined survival thresholds for both species. Polyps showed a high degree of tolerance to fluctuations in these environmental parameters. Low salinity was the only factor potentially restricting the distribution of scyphopolyps in the Baltic. Our results highlight the importance of short- versus long-term exposure to naturally fluctuating hydrological conditions and extend predicted distribution boundaries of C. capillata to salinity levels as low as 8.
|Status||Udgivet - 2012|