Global warming, over-fishing, invasive species, habitat destruction, acidification and agricultural runoff are creating oceans crammed with algae and jellyfish - a process one prominent scientist has dubbed "the rise of slime". And when algae blooms die, their decay starves the seas of oxygen, creating "dead zones" devoid of marine life.
Dead zones are being discovered everywhere researchers look: from massive areas of the Baltic Sea and Gulf of Mexico to small ones appearing episodically in river estuaries. It is estimated that the number and size of such zones has doubled every decade since the 1960s; a study released last month counts over 400 world-wide, collectively covering over 245,000 square kilometres of coastal seabed.
"We have utterly failed to appreciate the magnitude of the problem," said professor Jeremy Jackson of the Scripps Institution of Oceanography, (credited with coining the term "rise of slime"). "The oceans are out of sight and out of mind."
Too true. The major problem with devastation of the sea is that most humans cannot see it. We look out and see sparkling blue water and imagine everything is fine. It's only when we go beneath the waves that we realise there is a problem - a big one.
We already know that finfish stocks - the sort of sea-life generally caught by the world's fishing fleets and eaten by consumers - are in severe jeopardy. Some 30% of the commercial species are now in a state of collapse; that is, their numbers have fallen to below sustainable levels. Another 50% are "fully exploited" and in danger of collapse. And at the present rate of decline, none of the fish we currently like to eat will exist in the wild in anything like commercial quantities by 2050.
The dangers of over-fishing have been evident for fifty years or more, certainly since the America's Grand Banks cod fishery collapsed. But the major fishers are only just beginning to appreciate their responsibility for the stock loss and, hesitantly, start to try to redress it. The European Union, whose collective fishing fleet is second only to China's, has finally this month begun to look seriously at ways to cut the size of its fleet and the days it spends at sea - but still doles out generous subsidies to fishers to offset fuel prices to allow them to continue to overfish!
Meanwhile quota systems intended to maintain stocks at sustainable levels can instead lead to acts of criminal waste: it is estimated Scotland's fishing fleet alone dumps 100,000 tonnes of otherwise perfectly saleable commercial finfish back into the sea each year because if they are over quota they cannot land them. This makes little sense in the midst of a growing food crisis - especially as the fish are already dead.
Moreover rich nations' fishing fleets now habitually work the waters of some of the poorest countries of the world, depriving the locals not only of food but of a centuries-old way of life. Recent attention on illegal fishing off the West African coast is typical of the problem.
But fishing alone is not responsible for the accelerating spread of the dead zones, even though dragnet trawling, described as akin to pulling a bulldozer blade over the sea floor, continues to wantonly destroy benthic habitats by thousands of square kilometres per day - at increasingly deeper depths. No, the main culprit is agriculture and pollution - or more precisely, the nitrogen content from agricultural runoff and car exhaust/industrial smog.
Increased nitrogen in the sea promotes algal growth, particularly in coastal waters in summer. In a feast then famine cycle, the algae bloom, then die and sink to the bottom, where their decay robs the bottom waters of oxygen. Hypoxia, or low oxygen content, causes a general dying-off of marine life in the vicinity. When hypoxia is severe, it creates a dead zone.
Dead zones have existed for decades in some areas - such as Chesapeake Bay, Long Island Sound, Lake Erie and the Gulf of Mexico - but the new study identifies new zones in the Florida Keys, Puget Sound, and the tidal creeks of the Carolinas, to quote some of just the American examples. Indeed, the newest dead areas are being found in the Southern Hemisphere - South America, Africa, parts of Asia.
"These zones are popping up all over," said professor Robert Diaz of the Virginia Institute of Marine Science, who co-authored the study with Rutger Rosenberg of the University of Goteborg in Sweden. "We're saying that hypoxia is now everywhere, it seems," Diaz said. "Human activities have really screwed up oxygen conditions in our coastal areas."
Naturally, the effects reduce the productivity of commercial fisheries. The "biomass" missing because of depleted oxygen in the Chesapeake Bay, Diaz estimated, is enough to feed half the number of crabs that are commercially harvested in a typical year.
And while some hypoxic ecosystems have been improved recently by better management of pollutants - zones in New York's Hudson River and East River have actually disappeared - world-wide only 4% of dead zones are improving.
Nor is that the end of the problem. Douglas N. Rader, chief ocean scientist for the Environmental Defense Fund, said the chaos in the planet's nitrogen cycle is not only creating dead zones but also inciting the spread of toxic organisms, such as the pfiesteria that has appeared in recent years in the Chesapeake.
"The next big challenge, after global warming, is going to be addressing the massive upset of the world's nitrogen cycle," Rader said.
Part of Jackson's "slime" analysis involved constructing a chart of marine ecosystems and their "endangered" status. Coral reefs, Jackson's primary area of research, are "critically endangered" and among the most threatened ecosystems; also critically endangered are estuaries and coastal seas, threatened by over-fishing and runoff; continental shelves are "endangered" due to, among other things, losses of fishes and sharks; and the open ocean ecosystem is listed as "threatened" mainly through losses at the hands of over-fishing.
"Just as we say that leatherback turtles are critically endangered, I looked at entire ecosystems as if they were a species," said Jackson. "All of the different kinds of data and methods of analysis point in the same direction of drastic and increasingly rapid degradation of marine ecosystems. The challenges of bringing these threats under control are enormously complex and will require fundamental changes in fisheries, agricultural practices and the ways we obtain energy for everything we do."
Also this month the Proceedings of the National Academy of Sciences published online a study warning of "mass extinction in the oceans with unknown ecological and evolutionary consequences."
It would be difficult to state the breadth and import of the problem more clearly. Yet still the world simply gazes at the water and wonders very little about what's happening beneath it.
- The Future of Fish
- Kept Afloat on a Tide of Money
- No Reprieve for Eastern Pacific Tuna
- Nitrogen: Another Environmental Threat
- U.N. Biodiversity Conference Part I: Highlighting Wildlife Loss Around the World
- A Farmed Fish with a Hefty Price Tag
- Ocean Acidification Part II: Tipping a Planet Already in Peril
- Ocean Acidification Part 1: What's Happening to our Oceans and Why
- CO2 Pushed Deeper Into Oceans Than Previously Thought