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.