Content provided by Wynne Parry, LiveScience
Though some reports suggest jellyfish are taking over the world's oceans, long-term records of these gelatinous animals fail to show a global increase in jellyfish blooms likely caused by pollution, warming, coastal development and other human influences.
While the analysis of a team of researchers who have pulled together records of jellyfish presence going back to the 19th century don't support a rising gelatinous menace, the team did find a surprise: roughly 20-year cycles in the abundance of jellies.
Part of a recent rise-and-fall cycle may have prompted the perception of a global swell in jellyfish, according to the international team, whose researchers are part of the Global Jellyfish Group. They point specifically to the rising phase that began in 1993 and peaked in 2004.
Blamed for stinging swimmers, clogging fishing nets, overrunning ecosystems
and wreaking other havoc, jellyfish blooms - when these animals appear in massive numbers - have caught the attention of the media and scientists alike. A number of research papers have suggested that not only are blooms increasing on a global scale, but humans are likely responsible, because humans alter the oceans in ways that favor jellyfish. (See Stunning Photos of Jellyfish Blooms)