This video from Italy is about a barrel jellyfish.
Giant jellyfish on Dutch coast because of mild winter
Friday, May 16, 2014
Barrel jellyfish half a meter in diameter, and eleven kilos! In recent days there have been several reports of unusually large jellyfish in the Wadden Sea, but also on the British coast. These barrel jellyfish are not only unusually large, but also appear at an odd time. Normally, you will find barrel jellyfish on the Dutch coast only in the late summer and autumn.
Grown in winter
The explanation for this phenomenon is simple: these giant jellyfish have survived the winter. Meanwhile, they have grown, and therefore they are so big. That happens occasionally, but only in a mild winter. In a cold winter the jellyfish all die, leaving only the polyps alive. These polyps produce jellyfish at the end of spring again; making the barrel jellyfish you see in summer much smaller.