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Sardines

Sardines Photo Credit: TANAKA Juuyoh (田中十洋) [CC-BY-2.0], via Wikimedia Commons

Everyone likes an underdog story. So you'll want to hear how the humble sardine could save the lives of countless sea creatures.


Transcript

Turning sardines into superheroes. I'm Bob Hirshon and this is Science Update.

Off the coast of southwest Africa, toxic gas is bubbling up from the ocean floor, killing marine life across areas as large as New Jersey, and even worsening the greenhouse effect. What could stop this menace? Why, the lowly sardine.

Andrew Bakun is a professor of marine biology and fisheries at the University of Miami. He says the toxic gas comes from decaying microscopic plankton—microscopic plants that sardines normally eat.


Bakun:

They have very fine filters in their gill rakers, and they can actually filter these microscopic phytoplankton directly out of the water, and actually consume them directly.

With the local sardine population decimated by overfishing, Dr. Bakun says a rebound might stave off the toxic eruptions. And protecting other sardine populations could stop this from becoming a global problem. I'm Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

The area Bakun describes is commonly known as a "dead zone": a gigantic, cloudy, lifeless ghost town within the ocean. The killer here is a natural process, not a man-made pollutant. However, it's a natural process that wouldn't turn deadly if humans hadn't taken away a crucial piece of the ecosystem.

In this part of the ocean, powerful upwellings constantly churn plant nutrients to the surface. In this rich environment, microscopic plants called plankton bloom and thrive. Normally, sardines—strong swimmers that can buck the churning currents—would rush in and devour the plankton almost single-handedly. But over the past few decades, up to ten million tons of sardines have been lost to overfishing. So now there aren't nearly enough sardines to eat the plankton.

That's where the trouble starts. With no sardines to eat them, the plankton simply die off and sink to the bottom of the sea. As the plankton decompose, they starve the sea floor of oxygen, which leads to the release of gases, including methane (a greenhouse gas) and hydrogen sulfide (a toxic gas that kills brain cells and can rust a car). These gases form bubbles, which rise, expand, and then erupt, killing tons of marine creatures and driving others away.

Among the casualties of this "dead zone" are as much as two billion hake, an important food fish for the Namibian people. But the dead zone doesn't just disrupt the food chain. All that methane eventually escapes into the atmosphere, where it substantially worsens the greenhouse effect. According to Bakun, there's some evidence that the greenhouse effect may cause upwelling patterns in other seas. Do you see where this is going? More gas eruptions means a stronger greenhouse effect, which can cause more upwellings, which in turn can cause more dead zones and greenhouse gas eruptions—especially if the local sardine populations aren't protected. Eventually, this could lead to massive fish kills all over the world.

There's no hard proof yet that says restoring the sardine population will mitigate the problem. But logic suggests that it should. Bakun also notes that a small, recent rebound in the Namibian sardine population seemed to help matters. Furthermore, sardines often wind up in animal chow, where they're hardly the only option. So, hard as it may be to believe, simply thinking of other things to feed our cats could prevent a catastrophe across the world's oceans.

Now try and answer these questions:

  1. Why is toxic gas killing marine life off the coast of Namibia?
  2. Why are sardines a potential key to this problem?
  3. What might happen if this problem continues? Think one step at a time and see where it leads you.
  4. Can you think of other seemingly small human choices that have big environmental consequences?

For Educators

The University of Miami's Pew Institute for Ocean Science sponsored this research. Their sponsoring organization, the Pew Charitable Trusts' Ocean Science Division, is dedicated to the conservation and protection of oceans and marine life.

Creeping Dead Zones, by NASA's Goddard Space Flight Center, describes the growing worldwide problem of oxygen-starved oceans. The site includes color satellite images.


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