New evidence indicates that jellyfish blooms are associated with over-fishing and excess nutrients from fertilisers and sewage. Dense jellyfish aggregations can be a natural feature of healthy ocean ecosystems, but a clear picture is now emerging of more severe and frequent jellyfish outbreaks worldwide.
“Fish normally keep jellyfish in check through competition and predation but overfishing can destroy that balance. For example, off Namibia, intense fishing has decimated sardine stocks and jellyfish have replaced them as the dominant species,” says University of Queensland scientist, Dr Anthony Richardson.
Climate change may favour some jellyfish species by increasing the availability of flagellates in surface waters—a key jellyfish food source. Warmer oceans could also extend the distribution of many jellyfish species.
“Mounting evidence suggests that open-ocean ecosystems can flip from being dominated by fish, to being dominated by jellyfish,” Dr Richardson says. “This would have lasting ecological, economic and social consequences. We need to start managing the marine environment in a holistic and precautionary way to prevent more examples of what could be termed a jellyfish joyride.”