National Geographic's “Strange Days on Planet Earth”
April 23, 2008 - PBS
Every so often, off Africa’s remote Namibian coast, the ocean blanches white, releases a putrid stench of rotting eggs and coughs up multitudes of dying fish up and down the shoreline. What’s behind this strange case of oceanic indigestion? To crack the mystery, marine biologist Brownen Currie teamed up with satellite expert Scarla Weeks and oceanographer Andrew Bakun. Their first step involved delving deep into Namibia’s complex ocean dynamics.
Namibia is home to one of the most productive ocean systems in the world. Fueled by nearly constant winds that help draw up deep-water nutrients, these plankton-rich waters attract billions of hungry sardines. The sea is transformed into muscular silver. At least, that’s what used to happen. After foreign fishing fleets over-harvested these waters in the 1970s, the sardine populations never fully recovered despite Namibia’s best efforts. Working together, Currie, Weeks and Bakun revealed how the sardines may have been key to keeping those oceanic stench events in check. Here’s how their theory works.
Without sardines devouring plankton, mountains of the stuff sink to the bottom and decay producing a ticking time bomb of hydrogen sulfide and volatile methane on the seafloor. Under the right conditions, say when a rainy low-pressure weather system reduces pressure on the coastal ocean, the whole thing can blow. And the results can be explosive—like popping the tops off millions of rather stinky bottles of champagne. Once that hydrogen sulfide reacts with oxygen, the resulting elemental sulfur turns the ocean water white. Toxic gas suffocates nearby fish and an unmistakable rotten egg odor permeates the air. Along with the hydrogen sulfide comes methane, lots of it.
Methane packs a punch since this gas is 26 times more effective at trapping heat than carbon dioxide. And according to Andrew Bakun, global warming can lead to more winds, which can in turn lead to more nutrients, more plankton growth, more decay and more releasing of smelly gas. Bakun suggests that that this system could be creating a rather unfortunate positive feedback loop. Who would have thought loosing sardines could be linked to methane production or changes in Earth’s atmosphere?
Across the world scientists are discovering how the removal of one component of any ocean system can often have unsavory domino effects that scientists call trophic cascades. Take for example the recent collapse of the bay scallop fishery on the East Coast of the United States. Turns out, overfishing of sharks has led to huge increases in one of their prey: cow-nosed rays. All these hungry rays have subsequently devoured enormous amounts of scallops and essentially wiped out the fishery there. For every subtraction, there’s a reaction.
Thanks to burgeoning technologies and collaborations of the global scientific community however, we can now see how our actions fit into the overall matrix of living systems. Empowered with this new perspective, we can work to conserve not just ocean life but also the links that comprise the ocean’s diverse ecosystems. As renowned naturalist John Muir mused at the turn of the century, “When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” And we as citizens can “hitch” our efforts together to make a difference. Here’s how:
- Support policies for the protection of whole ocean regions through marine protected areas.
- Support fisheries measures that keep entire habitats, not just single species, in mind.
- Stay informed on ocean issues. Visit the World Ocean Observatory Forum.
- Make wise choices at the market and only purchase seafood that has undergone rigorous certification standards to ensure its sustainability, like those from Marine Stewardship Council—certified fisheries.
For more solutions see: What can we do? http://www.pbs.org/strangedays/episodes/dangerouscatch/do/index.html
Bakun, A. and Weeks, S. (2004). Greenhouse gas buildup, sardines, submarine eruptions and the possibility of abrupt degradation of intense marine upwelling ecosystems Ecology Letters 7: 1015-1023.
Weeks S. J., Currie B. and A. Bakun (2002). Satellite identification of massive hydrogen sulphide emissions in the southeastern Atlantic Ocean. Nature 415: 493-494.
Myers, R. A, J.K. Baum, T.D. Shepherd, S. P. Powers, C. H. Peterson (2007) Cascading effects of the loss of apex predatory sharks from a coastal ocean, Science 315(5820): 1846-1850.
For more solutions see: What can we do?