Blooms, or proliferations, of jellyfish can show a substantial, visible impact on coastal populations—clogged nets for fishermen, stinging waters for tourists, even choked cooling intake pipes for power plants—and recent media reports have created a perception that the world’s oceans are experiencing trending increases in jellyfish. Now, a new multinational collaborative study, involving the University of Southampton, suggests these trends may be overstated, finding that there is no robust evidence for a global increase in jellyfish over the past two centuries.
The results of the study, which includes lead co-author Dr Cathy Lucas, a marine biologist at the University of Southampton, appear in the latest issue of Proceedings of the National Academy of Sciences.
The key finding of the study shows global jellyfish populations undergo concurrent fluctuations with successive decadal periods of rise and fall, including a rising phase in the 1990s and early 2000s that has contributed to the current perception of a global increase in jellyfish abundance. The previous period of high jellyfish numbers during the 1970s went unnoticed due to limited research on jellyfish at the time, less awareness of global-scale problems and a lower capacity for information sharing (e.g. no Internet).
While there has been no increase over the long-term, the authors detected a hint of a slight increase in jellyfish since 1970, although this trend was countered by the observation that there was no difference in the proportion of increasing vs. decreasing jellyfish populations over time.