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Something fishy: How climate change reaches into the ocean

Researchers examined the effects of rising global temperatures on a variety of fish.

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Box fish. Cocos Island, 300 miles off the Pacific coast, is an isolated ocean oasis that lures divers with some of the best big-animal scuba diving in the world.

Melanie Stetson Freeman/The Christian Science Monitor/File

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Climate change could have devastating consequences for the world’s fish.

As global temperatures rise, the resulting ocean acidification and warming may hurt the diversity and population of fish species across the globe, say researchers.

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“This ‘simplification’ of our oceans will have profound consequences for our current way of life, particularly for coastal populations and those that rely on oceans for food and trade,” said Ivan Nagelkerken, Australian Research Council (ARC) Future Fellow with the University of Adelaide’s Environment Institute in a news release.

Professor Nagelkerken and his colleagues published their findings in a paper Tuesday in the journal Proceedings of the National Academy of Sciences

Although researchers predict diversity and population among fish to decrease, that may not be true across all species.

Tiny plankton may increase production in the warmer water. But an increase of these creatures low on the food chain may not translate up to larger animals.

“With higher metabolic rates in the warmer water, and therefore a greater demand for food, there is a mismatch with less food available for carnivores ─ the bigger fish that fisheries industries are based around,” said Nagelkerken. “There will be a species collapse from the top of the food chain down.”

Using data from 632 published experiments across a range of marine environments, the researchers looked at the impact of warming water and acidification on the underwater ecosystems.

The researchers found that either condition exacerbated by climate change could impact coral, oysters, mussels, and other habitat-forming species. 

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Coral, for example, might become bleached by warmer ocean temperatures. Just in the past couple of years scientists have seen significant bleaching events across the globe

When coral becomes stressed by the warmth it releases the algae that it typically co-exists with and that gives the reef-forming organism its color. When coral bleaching occurs, it is difficult for the reef to recover and many of the corals die.  

Habitat-forming species, like coral, shape the reefs that other fish live in, magnifying the impact of such marine changes throughout the ecosystem. 

Other marine life has been shifting its range in response to warmer water temperatures. Some tropical species have been spotted a ways from the tropics, like some black sea bass, unique squid, and blue crabs that have been eyed by fishermen in the Gulf of Maine.

King crabs are on the verge of moving into ecosystems that haven’t seen such shell-crushing predators in tens of millions of years. The royal crustaceans seek out warmer waters, and the Antarctic shelf has now reached suitable temperatures for the king crabs.

“We know relatively little about how climate change will affect the marine environment,” said University of Adelaide marine ecologist Sean Connell, a fellow author on the current study.

“We need to know what we are doing to our world,” Richard Aronson, lead author of the study on king crabs in Antarctica and head of the department of biological sciences at Florida Institute of Technology told The Christian Science Monitor. “We need to know the full extent of climate change effects.”