Jellyfish Spread

Sprawling man-made structures are creating a gelatinous future

If you build it, they will come. The flood of jellyfish in ocean waters may be due in part to the expansion of man-made structures, according to a new study. The ocean-wide sprawl of docks, moorings, and rigs provides a strong foundation for jellyfish nurseries, which bud and inundate the water with medusas.

Thousands of jellyfish begin life as single, tiny polyps cemented to a rocky surface. Although researchers have evaluated the impact of climate change and later life stages on jelly proliferation, little attention has been paid to the beginning stages of their lifecycle and the conditions that foster large-scale blooms.

jellyfish graph Jellyfish SpreadTo assess the impact of different structures, the research team surveyed sites worldwide for polyp infiltration and created their own underwater scaffolds to assess which man-made and natural surfaces best supported jelly nurseries.

The team found that young polyps infiltrated a variety of man-made habitats and preferred many of these surfaces to natural rock or oyster beds. From discarded plastic bags to wind-turbine supports, opportunities abound for jellyfish to get their start—and new construction expands ocean sprawl each year.

“Artificial structures provide ideal conditions for settlement by jellyfish polyps. Floating docks and crevices within riprap increase the amount of shaded surfaces of the type that polyps prefer,” the study authors write. “Indeed, medusa densities have been shown to decline when artificial substrate is removed.”

To thwart the continued spread of jellies, new structures will have to implement design elements that discourage polyp growth. Together with environmental measures to control other favorable conditions such as high nutrient density and low oxygen levels, proper planning could help jelly blooms go bust.

—Caitlin Stier

Duarte, C. M. et al. 2012. Is global ocean sprawl a cause of jellyfish blooms? Frontiers in Ecology and the Environment doi: 10.1890/110246.

Photo ©Planctonvideo/Dreamstime.com

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