You may have heard that jellyfish are taking over the world’s oceans, proliferating at a rate that is unfounded by historical standards. Is it possible that this has been facilitated by the urbanization of coastal ecosystems?
This is the question posed by Carlos Duarte and colleagues in a recent a paper published in Frontiers in Ecology and the Environment (link). Many jellyfish have two life stages: the pelagic, medusoid phase that probably comes to mind when you think of jellyfish, and a juvenile stage in which they are attached to the bottom as tiny polyps. Most previous studies that have tried to explain recent increases in jellyfish abundance have focused on the pelagic stage. Tiny polyps are hard to find, and have thus not been a central focus for research.
That is until now… Duarte and colleagues searched far and wide for the tiny creatures. Where did they eventually find them? On the underside of floating docks, buoys, riprap and other artificial structures. They suggest that the proliferation of artificial structures (which they identify as “ocean sprawl”) is precisely what has allowed jellyfish populations to explode.
Many questions remain, of course, and much more must be done to see if their theory holds water. While Duarte et al. found that jellyfish polyps of some species favor shaded habitats, has the increase in shaded habitat associated with “ocean sprawl” really been sufficient to facilitate the types of increases we’ve seen in adult jellyfish populations? Does the trend extend to species they have yet to test experimentally? And can we actually find these polyps on our local floating docks prior to jellyfish blooms? All of this remains to be seen.