Jellyfish blooms linked to offshore gas platforms and wind farms – New Scientist

Invasion of the sea jellies

Jeff Wildermuth/NGS/Getty

By Kate Ravilious

Jellymageddon is upon us and we might be partly responsible. Vast blooms of moon jellyfish and other related species are being reported with increasing frequency in the media. Evidence now suggests that our offshore constructions, including oil and gas platforms and wind farms, may be aiding these gelatinous invasions.

Jellyfish form an important part of the oceans ecosystem, but create problems when they appear in large numbers. Such groups shut down beaches for swimmers, clog fishing nets, cause the closure of power plants and desalination facilities by blocking their water intakes, and alter the marine food chain by gobbling fish larvae and food for plankton feeders.

Many jellyfish, including the harmless purple moon jellyfish, start life as polyps that need to attach themselves to a surface often preferring overhanging ones. Such surfaces are fairly rare in nature, but some researchers think the increase in number of marine constructions may have inadvertently helped jellyfish to thrive by providing polyps with the ideal home (see Jellyfish takeover).

Moon jellyfish have become increasingly common in the Adriatic Sea in recent decades. They were first observed there in 1834, but tended to be a rare occurrence. Between the 1950s and 70s they appeared once or twice per decade, and by the 80s and 90s were present around eight years in every 10. In the last two decades, they have been present every year. This surge in numbers has coincided with a rise in gas platforms in the Adriatic, from its first in 1968 to around 140 now.

Martin Vodopivec from the National Institute of Biology in Piran, Slovenia, and his colleagues investigated the influence of these platforms on moon jellyfish, using a computer model to simulate their life cycle and dispersal patterns over the course of five years. The model included accurate representations of the ocean currents and positions of gas platforms in the area.

The model results suggest there is a link between the platforms and the rise of the jellies. The platforms have increased connectivity between gatherings of moon jellyfish in the Adriatic, helping to sustain populations that might otherwise be wiped out during times of hardship when one area of the sea becomes heavily polluted, for instance.

More specifically, the results indicate that platforms close to prominent ocean currents have had the greatest influence on jellyfish numbers. Our simulation shows that jellyfish can travel up to 1000 kilometres in a strong current like the western Adriatic current, says Vodopivec.

Lisa-ann Gershwin, a jellyfish researcher for CSIRO in Hobart, Australia, thinks Vodopivecs findings present a strong argument, but are not the only explanation for the increase. Right now, we are seeing multiple factors creating the ideal conditions for jellyfish, including overfishing [reducing jellyfish predators], increased nutrient run-off and more offshore constructions, she says.

Offshore construction is booming worldwide. For example, the power capacity of European offshore wind installations has more than doubled in the past three years, and right now there are over 500 offshore turbines under construction in UK waters. Vodopivec is concerned that this boom could result in a rising tendency for jellyfish plagues to occur in some areas, though he thinks that careful positioning of platforms may help to minimise the effect.

But Gershwin is sceptical that adjusting the location of platforms will make that much difference. I suspect that platform position wont make that much difference because jellyfish larvae can drift over long distances and jellyfish live a long time.

The Chinese construction boom may be partially responsible for the massive increase in Nemopilema nomurai, one of the world's largest jellyfish. This 2-metre-wide, 200-kilogram beast, which lives and breeds in the South and East China seas, used to bloom very rarely (only three times during the 20th century). But since 2000 it has bloomed almost every year, resulting in plagues in which half a billion or more of these monsters drift into the Sea of Japan each day.

We think that the polyps have benefited from the coastal construction around China, plus the nutrients entering from Chinese cities and the overfishing of jellyfish predators, says Lisa-ann Gershwin, a jellyfish researcher for CSIRO in Hobart, Australia. They are now such a problem that the Japanese government has been looking for ways to use the jellyfish, she says even seeking good recipes involving N. nomurai.

Journal reference: Environmental Research Letters, DOI: 10.1088/1748-9326/aa75d9

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Jellyfish blooms linked to offshore gas platforms and wind farms - New Scientist