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Sharks Hide in Corals to Escape Ocean Acidification

Oct 16, 2014 10:42 AM EDT
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A certain species of shark is hiding out in corals in an attempt to escape ocean acidification, according to a new study.

The epaulette shark (Hemiscyllium ocellatum) was already known for being able to tolerate low oxygen levels - described as hypoxia - in short bursts, and now researchers suggest that they can withstand short periods of elevated carbon dioxide (CO2) levels as well.

The findings were described in the journal Conservation Physiology.

Atmospheric CO2 levels have increased by almost 40 percent in the last 250 years, and the world's oceans have had to take on this heavy burden, absorbing more than 30 percent of the extra CO2 in the air. What's more, the ocean is acidifying at a rate 10 times faster than it did during a similar upheaval 56 million years ago.

So what does this mean for sharks? Well, first of all, a recent study has found that at the very least ocean acidification is robbing sharks of their predatory senses - a necessary skill if they want to sniff out their prey.

But taking to the corals may be one way of escaping ocean acidification and all its harmful effects for the epaulette shark. A team of researchers mainly based at James Cook University in Queensland, Australia decided to expose these longtailed carpet sharks to various conditions while adjusting CO2 levels. For a period of 60-90 days, these reef-dwellers swam in either control (390 µatm), medium (600 µatm), or high (880 µatm) CO2 treatments. Meanwhile, research team measured resting oxygen consumption rates, sensitivity to low oxygen levels, delivery of oxygen, and the presence of a metabolic enzyme responsible for energy production.

Even after being exposed to CO2 levels equivalent to those that are predicted for their natural habitats in the near future, these resilient sharks displayed noticeable physiological tolerance to the abundant greenhouse gas.

"Our findings suggest this reef-inhabiting animal is indeed making some physiological adjustments to cope with elevated CO2, and these may be linked to maintaining oxygen transport, energy, and balancing ions and pH, but at no obvious cost to the animal," Dr. Jodie Rummer, corresponding author of the study, said in a statement.

Epaulette sharks, Aquarium of the Pacific says, can be found at depths of 164 feet (50 meters), but they prefer to spend most of their time in the warm, relatively shallow waters of coral reefs, usually at the sandy bottom. This may be good news, considering it's these very areas they may help them survive in an increasingly acidic environment. These bottom feeders, which inhabit waters off New Guinea and Australia, are known for "walking" with its fins over coral reefs.

However, despite the good news that epaulette sharks may have found a safe haven, their protective corals may themselves be in danger. Corals in the Great Barrier Reef, for example, are diminishing, and have in fact plummeted 40 percent since the mid-1970s.

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