Recent Research

Could jellyfish blooms be attributed to “ocean sprawl”?

Photo of Jellyfish by Ole Kils

Image by Ole Kils

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.

Map of population change in US coastal watersheds

Why Urban Marine Ecology?

Despite all my hype about urban marine ecology, it’s a field that really doesn’t exist yet. At least not in any standardized or formal way. It’s a discipline in the making, inspired by the explosion of research in terrestrial urban ecology and a void of comparable knowledge when it comes to the marine environment in cities.

You may have seen the statistics about coastal population growth. Overall, it’s estimated that we will reach a population of 8 billion in ten years. Currently about 50% of people live in coastal areas, but by 2025, it’s expected that that percentage will increase to 75%. That an estimated 6 million people living within 100km of a coastline!

The movement of people to coastal areas is not uniform. Check out this graphic from the National Oceanic and Atmospheric Administration (NOAA) of population change in coastal watersheds (link). From this, you can see that population in more rural coastal areas is actually decreasing. People aren’t just moving to the coasts. They’re moving to coastal cities.

What will be the effect of population growth on marine ecosystems?  We have no idea.  Not only are we limited in our understanding of what these will look like in the future – we know almost nothing about the characteristics of urban marine ecosystems today.  Much work is needed to characterize the biodiversity of these systems, understand their ecological processes and identify how they differ from their natural, more rural ecological counterparts.  In many respects, these are systems of our own making. Don’t you want to know what we’ve created?  I certainly do.  There’s much work ahead!