Mixing it up, jellyfish style

With the advent of overfishing of the worlds oceans and climate change, jellyfish are slowly beginning to dominate oceanic ‘deadzones’ (see the ‘never-ending jellyfish joyride‘ for more details). Now, researchers are coming around to the idea that in such high numbers, jellyfish might just be able to stir up the oceans in a similar way to the tides and winds, according to a recent paper published in Nature. Sounds  crazy? Take a look at this video footage of the researchers squirting fluorescent dye into the water column infront of the Mastigias jellyfish. As the jellyfish swims through the watercolumn, the dyed water travels along with the jellyfish rather than being displaced – a mechanism apparently first described by Charles Darwin’s grandson that is enhanced by the viscosity of seawater. Read more at Live Science and over at Wired Magazine, and watch the video footage below:

“As a body moves in a fluid, a high-pressure field is created in front of the body, and a low-pressure field behind. Because fluid moves from high to low pressure, the fluid that’s adjacent to the rear of the body moves along with it,” said Katija. “You get a permanent displacement of the water.”

Katija and CalTech bioengineer John Dabiri have provided the first direct observation of this phenomenon. Using fluorescent dyes and underwater video cameras, they’ve made visible the invisible, producing videos of swimming jellyfish trailed by the water they came from.

If swimming generates tide-scale forces, then “it has an impact on global climate. This is a rather novel twist to the whole climate story,” said William Dewar, a Florida State University oceanographer. “How one would extend existing models to include a biosphere mixing input is not clear, largely because no-one has spent much time thinking about it.”


The never-ending jellyfish joyride


Whilst the media have run with a series of entertaining headlines (“Sea of deadly jelly lurks, scientist warns“, second only to “jellyfish joyride threatens oceans“), University of Queensland scientist Dr Anthony Richardson issued a grave warning as to the future of the worlds oceans (co-inciding with World Oceans Day). Dr Richardson’s research shows convincing evidence that jellyfish aggregations, associated with overfishing of their main predators and increases in nutrient run-off from fertilisers and sewage, are likely to take over large parts of the worlds oceans in the decades to come.

“Small pelagic fish like sardines and pilchards are being fished out in many places and they eat plankton, which is partly made up of juvenile jellyfish,”

“Nutrient run-off on land causes phytoplankton blooms which produce water with low oxygen which jellyfish can survive but fish can’t.

“As well, a warming ocean associated with climate change sees increasing numbers of tiny flagellates in surface waters, and they are a favourite food of some jellyfish.” (Read More)

Amongst the more impressive of these are the giant Nomura jellyfish (over 2m in diameter, weighing over 200kg), which is already causing problems for fisherman in Japan by clogging nets (click through the image above for a higher resolution photograph). Despite the serious topic, I think Dr Richardson is a definite contender for the best paper title of the year (“The jellyfish joyride: causes, consequences and management responses to a more gelatinous future“, with a subsection entitled “Self-enhancing feedback: the never-ending jellyfish joyride“).