Incidental consumption of ephyrae of moon jellyfish Aurelia aurita s.l. by three filter-feeding sessile organisms: laboratory experiments

Abstract

Moon jellyfish Aurelia aurita s.l. has been suggested to have high mortality during the ephyra stage, which potentially affects the population size of the later medusa stage. However, the mechanism behind the high mortality rate has still not been clarified. Ephyrae of A. aurita are liberated from the sessile strobila, which are usually surrounded by filter-feeding sessile organisms. In the present study, we carried out a series of feeding trials at 10 °C, offering A. aurita ephyrae to three potential predatory filter-feeding sessile organisms: the mussel Mytilus galloprovincialis, the ascidian Styela plicata, and the barnacle Amphibalanus eburneus. From the experiments, the mussel was estimated to have the highest ability to consume ephyrae among the sessile organisms. Size-selective filtration experiments showed that the mussel consumed newly liberated ephyrae [3 mm total body diameter (TBD)] at a significantly higher efficiency than larger (5 and 7 mm TBD) ephyrae. Our results demonstrate that filter-feeding sessile organisms, especially the mussel, are potential consumers of the early ephyra stage.