Gelatinous zooplankton – a potential threat to the ecosystem of the Puck Bay (the southern Baltic Sea, Poland)

Renata Kozak

Gelatinous zooplankton is a group of organisms, which in recent decades has become one of the most important elements to shape the marine ecosystem. Their growing numbers and spreading to the new marine regions, in combination with the high feeding rate, causes significant changes in the flow of energy in the food webs. The only regularly-occurring gelatinous zooplankton species in the Puck Bay area is scyphozoan Aurelia aurita, most abundant in the summer and fall seasons. As shown in Barz and Hirche’s (2005), Möller’s (1980a), Schneider’s (1989), and Schneider and Behrends’ (1994) studies, the abundance of jellyfish in Bornholm Basin and Kiel Bight was several times lower than that in Puck Bay. Nevertheless, the authors of these studies concluded that the population of A. aurita can significantly reduce mesozooplankton and fish resources by preying on their larvae and eggs. Taking this into account, it is possible that the impact of A. aurita medusae on the Puck Bay ecosystem is even higher than in other parts of the Baltic Sea. Verification of this thesis requires detailed investigation; the scope of which should include investigation of: A. aurita food selectivity and long-term mesozooplankton, and A. aurita medusae abundance. The aim of this study, based on the few data in the literature, is to estimate if the gelatinous zooplankton is also an important element of the marine ecosystem the Puck Bay