Monday, July 11, 2016

Floating Safehouse for Fish




Baby fish hide from predators under a jellyfish's translucent bell

earthtouchnews.com  By Sarah Keartes November 24 2015 

The beautiful Versuriga anadyomene jellyfish is a spectacle all on its own. And it's an even cooler sighting when you find dozens of tiny fish hiding beneath its tendrilled bell.

This short clip was captured on a dive in the waters off Thailand's coast by Earth Touch cameraman Stewart Whitfield – and you can probably guess what's going on here. The fish (which are juvenile shrimp scad, also known as slender yellowtail kingfish) are using the jelly for protection against the predatory trumpetfish lurking nearby.

But the jelly's billowing structures aren't what they seem. 

Versuriga jellies are part of the order Rhizostomae, a group of jellyfish with no tentacles at all. Instead, they have eight highly branched "oral arms" – masses of spongy tissue used for filter feeding – like the ones you see in the video. This jelly doesn't have one mouth, but rather many small ones, like some kind of ocean-dwelling Hydra. The mouths sit along the lengths of the arms, and gobble up plankton as they swim by.

"The arms aid the jelly in pulling the plankton in from the water," explains jellyfish biologist and Deep Sea News staffer Rebecca R. Helm.

The jelly also has stinging thread cells at its disposal, which the baby kingfish are careful to avoid. 

Their sting isn't harmful to humans, but it's enough to deter some species of fish from getting too close (apparently these trumpetfish are willing to take their chances for a quick meal). 


Helm explains that lots of critters, including crabs, sea spiders, molluscs, brittle stars and even turtles have been seen hitchhiking on various species of jellyfish. "Yet for many of these interactions it is not clear what role jellies may play. Are jellyfish permanent homes for some of these animals? A quick shelter? A mobile food source? Or even a form of transport between different habitats? As with many aspects of jelly biology, the questions far outnumber the answers," she says.   

As for the kingfish, they'll stay hidden amongst the stinging threads, feeding on the jelly's leftovers until they're big enough to venture into the open ocean. Just what (if anything) the jellyfish gets out of the situation remains a mystery. In captivity, these fish often turn to snacking on their gelatinous host – likely because they don't have enough plankton. 

"Citizen scientists documenting these interactions serve an invaluable role in advancing our knowledge of these puzzling and poorly known relationships,” says Helm.

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