Population dynamics, growth and predation impact of the common jellyfish Aurelia aurita and two hydromedusae, Sarsia tubulosa, and Aequorea vitrina in Limfjorden (Denmark)

Gelatinous plankton: irregularities rule the world (sometimes)

“…Opposed to the almost regular occurrence of blooms of crustacean plankton, the pulses of gelatinous zooplankton are paradigmatic in this respect: they may last for rather short times, may occur over vast scales and are not recurrent on a regular basis (CIESM 2001, Kawahara et al 2006). Despite such constraints, studies in the last 2 decades focusing on gelatinous zooplankton taxa revealed an underestimation of jellyfish importance in the pelagic food webs (Möller 1984, Båmstedt 1990, Schneider & Behrends 1994, Behrends & Schneider 1995, Olesen 1995, Boero & Mills 1997, Purcell 1997, Mills 2001, Hansson et al 2005, Møller & Riisgård 2007.…”

“…Gelatinous herbivores usually contribute to marine snow and their dead bodies sink to the bottom, directly fuelling the benthic compartment. Gelatinous carnivores (medusae, siphonophores and ctenophores) can affect nekton in the pelagic web, both by competition (by feeding on the potential prey of fish: the crustaceans) and by direct predation on nekton (feeding on fish eggs and larvae) (Sanvicente-Añorve et al 2006, Titelman & Hansson 2006, Møller & Riisgård 2007. Both phytoplankton and grazing zooplankton are the energetic basis for the peaks of medusan abundance (Figs.…”

Feeding, bioenergetics and growth in the common jellyfish Aurelia aurita and two hydromedusae, Sarsia tubulosa and Aequorea vitrina

“…In Limfjorden (Denmark), S. tubulosa is present in the plankton during early spring together with A. aurita ephyrae. During summer, medusae of A. aurita make up the vast majority of the plankton (Hansson et al 2005, Møller & Riisgård 2007b. Before 2004, the hydromedusa A. vitrina was unknown in Limfjorden, where it later became very abundant during August and September (Møller & Riisgård 2007b).…”

“…Thus, in a companion paper we use the maximum growth rates obtained in the present work to evaluate whether the jellyfish realize their growth potential in Limfjorden. Further, we use the present data on minimum concentrations of prey organisms needed for sustaining maximum growth for comparison with the actual prey concentrations in Limfjorden to evaluate jellyfish-predation impact (Møller & Riisgård 2007b). The medusae were brought to the laboratory and kept in aquaria (15°C, 20 psu) until experiments could be performed.…”

New contributions to the jellyfish fauna of the Marmara Sea

“…Comparably, the introduction of a novel predator "guild" into the Marmara Sea habitats, such as formed by the newly recorded jellyfish species, may affect the vulnerable food network assembled by native species. Under certain environmental conditions, jellyfish can attain very high local abundances, not only severely depleting and altering the structure of zooplankton communities, but also feeding directly on larval and juvenile stages of commercially valuable fish (Titelman & Hansson 2006;Møller & Riisgård 2007). In conclusion, it will be worth investigating the non-indigenous jellyfish species throughout the Marmara Sea by intensive surveys in order (a) to quantify and potentially predict effects of introduced species on valuable fisheries resources, and (b) to plan future strategies to limit further aquatic introductions.…”