The rise of the jellyfish
Friday, October 25, 2013, 9:32
They're big, gooey, and they pack a punch.
Jellyfish have never been in short supply in the world's oceans, but experts say their numbers are growing.
Back in June, researchers were keeping a close eye on the Mediterranean, where a jellyfish population boom was threatening biodiversity and countless tourists.
Off the coast of Spain, stretches of sandbanks were observed containing up to 40 mauve stingers - one of the most poisonous species of jellyfish -- per square metre.
And earlier this month, Sweden's biggest nuclear reactor was forced to shut down after an army of the gelatinous creatures clogged the plant's cooling water intake pipes.
Sharyl Crossley, a senior aquarist at the Tennessee Aquarium, says the rise of the jellyfish can be attributed to a number of things.
"For each bloom there is a different combination of factors that can play into the cause," she says.
While jellyfish populations are naturally dense, Crossley says that population blooms appear to be happening more frequently -- and in larger numbers.
"Scientists studying the blooms have linked them to climate change, pollution, overfishing and the loss of predators, dead zones, invasive species, and so on. In general, what they discover is that a jellyfish bloom is an indicator that something is imbalanced in the ecosystem ... although we are paying more attention to jellyfish now than ... ever before ... so we may not exactly know what the 'normal' ... is regarding the frequency and size of jellyfish blooms."
Jellyfish are predators, and hungry ones at that.
Zooplankton, fish eggs and larvae are their favourite meals, but they've been known to dine on other things as well -- including other jellyfish.
Large blooms "can have a significant effect on local fish and invertebrate populations by causing a break in the 'food chain'," Crossley says, "either by consuming a common food source or by preying on eggs/larvae of various aquatic species."
There are economical impacts as well.
Tourists get stung, fishing lines get clogged and cruise ship thrusters get jammed.
In the Mediterranean, approximately 150,000 people are treated each year for jellyfish stings.
"There are now beaches on the island of Lampedusa, which receives 300,000 tourists a year, where people can only swim for a week in the summer," jellyfish researcher Piraino Josep María Gili told the Guardian back in June.
While they aren't inherently bad ("they aren't going to crawl out of the water and attack you," Crossley says), experts are trying to mitigate population blooms, although there are some benefits to the plastic-like puddles.
They're a tasty treat for turtles, birds and fish and in some countries -- like Japan and Korea -- jellyfish are considered a delicacy.
In Australia, scientists are using their venom to create new medicines.
Jellyfish populations are generally studied on a case-by-case basis, and many appear to be short-lived. Some scientists believe the current blooms will die off on their own, but others -- like jellyfish expert Lisa-Ann Gershwin -- believe that warming oceans, depleting oxygen levels in the sea and ocean acidification will only speed up the burgeoning jellyfish population.
Either way, many experts agree that the best way to restore balance to an "out-of-whack" ecosystem is to tackle the issues that caused that imbalance in the first place.