Cassiopea jellyfish (ntotal = 37, size: 5 to 8 cm in diameter) were collected from directly in front of the MSS jetty at water depths of 5 to 16 m using SCUBA. Cassiopea sp. specimens were collected by carefully lifting them from the seafloor and transferring them into seawater filled polyethylene zip-locked plastic bags (ca. 500 ml volume). Both, jellyfish exhibiting an association with I. tsurnamali and jellyfish without mysid-association, were collected, whereby associated mysids were removed. Cassiopea specimens were subsequently transported to two 40 L flow-through tanks supplied with in-situ seawater at exchange rates of approximately 1.5 L min− 1, providing in-situ water temperatures of 20.8 to 21.3 °C in February/March (23 Feb–08 Mar 2008) and 21.8 to 24.5 °C in May (10 May–30 May 2008). All Cassiopea specimens were kept in the flow-through tanks for 2 to 14 days, with jellyfish that exhibited mysid-association in-situ being kept separately from those that did not.