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How Baby Fish Could Lose Their Most Trusted Bodyguards

One of the oceans' most fascinating symbiotic relationships is being threatened.

For fish born in the open ocean, there’s really nowhere to hide. Without protective rocks or corals, baby fish stand out against the immeasurable blue like finger food on a platter for predators.

This is why some species of fish developed an ingenious relationship with some species of poisonous jellyfish, working out a deal where the little fish swim, protected, among the jelly’s tentacles. Think about it like clownfish in an anemone — except the anemone is moving.

It was a pretty foolproof strategy — until now. In a new study, scientists from the University of Adelaide found that fish are far less likely to strike up these symbiotic relationships in acidic waters.

They examined the behavior of juvenile fish in an aquarium that contained water high in CO2, discovering that the baby fish interacted with the jellyfish three times less than they would in normal waters. Moreover, only 63 percent of fish (compared to 86 percent) interacted with the jellyfish at all.


These interdependent, symbiotic relationships mean the difference between life and death for many ocean creatures, for whom survival just can’t happen on their own. And scientists still don’t know how climate change could wreak havoc on these important partnerships that have existed without a problem for generations. So these new findings aren’t good news.

“This is a the first study that demonstrates how climate change will disturb such a symbiotic relationship between two animals that interact closely for survival,” says study leader Ivan Nagelkerken, an associate professor at the university’s environment institute, in a press release provided by the university.

Around 80 species of fish — including pollock, jacks and trevallies — are known to form these symbiotic relationships with jellyfish. Though only one species of fish actually boasts known immunity to the jellies’ poison, the other species somehow avoid stinging even while swimming amid a curtain of tentacles.


And in some cases, the jellyfish will actually eat the baby fish that seek its shelter. Nevertheless, scientists have observed that the baby fish do significantly increase their odds of survival by shacking up with the jellyfish.

Only time will tell how much these changing ocean conditions could cripple these fish populations. But one thing’s for sure: It won’t be for the better.

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