Sharks Key To Climate, Thanks To Seagrass Sequestration Of Marine CO2
Another one of those moments of "Oops! I had no idea!"
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In Shark Bay, we have worked not only on sharks, but on their prey — including dolphins, sea turtles and sea cows — as well as the wider ecosystem. Our findings demonstrate that tiger sharks are critical to the Shark Bay ecosystem. But not in the way you might think. It turns out that the fear of sharks – by the sea cows and sea turtles that eat the seagrass – helps protect the seagrass from being over-grazed.
Here is how it works: Tiger sharks like to hunt in shallow waters in the bay; a perfect place for seagrass to grow. To avoid becoming a shark snack, turtles and sea cows generally avoid these areas. The seagrass can grow into a lush habitat that provides shelter for small fish and shellfish that will grow up into species people want to catch. In areas that sharks don’t frequent, seagrass is heavily grazed and does not support big populations of fish and shellfish. That means that if we were to lose tiger sharks from the bay, the seagrass likely would be grazed down all over.
The loss of seagrass would be bad news for fish and fishermen – and maybe even for turtles and sea cows! It also could result in the loss of a large amount of carbon dioxide back into the atmosphere that would no longer be stored by seagrasses. There is evidence that the loss of sharks is hurting seagrass in some places.
In Bermuda and the Indian Ocean, where shark populations have declined, increasing populations of sea turtles are causing entire seagrass beds to virtually disappear. And it isn’t just in seagrass ecosystems where sharks are important. Recent studies point to the possibility that healthy coral reefs need sharks, too.
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http://www.scientificamerican.com/article.cfm?id=threats-to-sharks-destabilize-entire-ecosystems