From frustules to medusae: A new culture system for the study of the invasive hydrozoan Craspedacusta sowerbii in the laboratory

The invasive freshwater jellyfish Craspedacusta sowerbii, native from East Asia (Yangzi Jiang River), was introduced in Europe for the first time in the basins of the Royal Botanic Garden in London. From the beginning of the 20th century, worldwide reports of the presence of C. sowerbii have been increasing (USA, Canada, Europe, Australia, Russia). Despite its now worldwide distribution, C. sowerbii has rarely been the subject of recent studies. Moreover, C. sowerbii is difficult to rear in the laboratory, and individuals generally from the wild have only been reared for short periods. Many aspects of laboratory cultures have proven to be problematic for all stages of the life cycle (from frustule to medusae): lack of optimal growing system (circular current or not), water quality (physical and chemical conditions), diet (the type of food), and temperature. In this article, we present a technique for culturing all life stages of C. sowerbii, from polyps to medusae, to study its life history in the laboratory. To demonstrate the success of our culture protocol, the growth of polyps was measured for 80 days at 19 and 29 degrees C. Colony growth increased at both temperatures in our culture system, and data were similar to those presented in the literature, illustrating the success of this protocol. Medusae were cultured for 70 days, and their bell diameter increased from 0.60 +/- 0.08 mm (Day 0) to 9.0 +/- 2.1 mm (Day 32). We developed a closed culture system that allowed specimens (i.e., polyps and medusae) to be maintained for more than 2 months (80 days for polyps, 72 days for medusae). This culture system will allow researchers in the future to study more precisely the metabolism (growth, ingestion, longevity) of polyps and medusae to understand life-history characteristics important to this species' ecology (periods of medusae production, predation, and diet).