Jellyfish populations are increasing in numerous ecosystems around the globe. Not surprisingly, these increases are not uniform across time and space. So why are jellyfish increasing in some places and not others? What are the consequences for humans and ecosystems? And what, if anything, can we do to manage or prevent increasing jellyfish blooms?
Jellyfish population dynamics are complex, partly because of the unique life cycles of many species. Jellyfish may exist as pulsing medusae, sessile polyps, or cysts capable of resisting harsh environmental conditions. Reproductive strategies include sexual and asexual reproduction, as well as hermaphroditism. As such, jellyfish populations are influenced by a variety of anthropogenic and environmental factors at different, often cryptic, life stages.
Increasing jellyfish populations can impact humans in both negative and positive ways. Industries such as tourism, aquaculture, fishing, power generation, desalination, and shipping have all reported considerable economic losses due to jellyfish blooms. In contrast, fisheries that harvest jellyfish for food are expanding around the globe, and jellyfish are now a popular draw for public aquaria. As both human and jellyfish populations increase, new interactions are sure to emerge, as jellyfish get in our way and as we find new ways to exploit them.
Ironically, it appears that in some cases, humans may be responsible for the observed increases in jellyfish populations. While there is no single cause of increasing jellyfish populations, there is evidence that fishing, pollution, aquaculture, shipping, global warming, and coastal development can all create conditions that favour jellyfish over fish. Most of these links are only correlative, but the rise of jellyfish in coastal ecosystems worldwide should be cause for concern. We may need to decide now whether or not we want our children to be eating jellyfish burgers. If our behaviour doesn’t change, they might not have a choice.