As recently as the 1950s, very smart people like Rachel Carson and Jacques Cousteau believed the oceans were so vast that fish stocks and the ocean's capacity to absorb human wastes were for all practical purposes unlimited. In reality, though, overfishing and degradation of water quality had long been apparent in places like the North Sea and New England. But no one took the problems seriously until the collapse of the legendarily abundant Newfoundland cod fisheries in 1992. The news has been unrelentingly bad ever since. Unfettered exploitation, pollution, and now climate change have brought entire ocean ecosystems to the brink of extinction, and we are left scrambling to figure out what to do.
Recent reports by the Pew Ocean Commission and the U. S. Ocean Commission, as well as innumerable National Research Council reports, clearly summarize the causes and consequences of ocean degradation. But they have failed to capture public attention. To do this we need to distill the seemingly endless litany of problems and threats into four basic questions: How and why are the oceans changing for the worse? What will happen to the oceans if degradation is allowed to continue? What can we do to stem the tide?
The answers to the how and why are all too clear. Most fishery species, including tunas, swordfish, and snappers, are fished to capacity or beyond, and once phenomenally abundant cod, bluefin tuna, and rockfish are severely overfished. Even Alaskan pollock stocks are in serious trouble. Pollock is comparatively well managed and certified as sustainable by the Marine Stewardship Council. Yet two of the four stocks are completely shut down, a third is just a fraction of its former size, and now the fourth and largest has declined by half since just last year. Foolish fishing practices, such as targeting spawning aggregations for their roe before the fish can spawn and the destruction of critical fish habitat by trawling, are major problems. But the bottom line, as for global fisheries generally, is that too many people are competing for too few fish, and the economic pressures to keep on fishing have overwhelmed common sense.
Besides overfishing, increased runoff of nitrogen and other nutrients from chemical fertilizers, industrial animal waste, and burning of fossil fuels has led to population explosions of planktonic algae and microbes beyond the capacity of their predators to keep them in check -- a process termed "eutrophication" that I call the Rise of Slime. Many of the species are toxic, as in the infamous red tides. Oxygen is reduced to fatally low levels due to the decomposition of unconsumed plankton, and massive fish kills occur. The number and extent of such coastal "dead zones" globally has increased exponentially from fewer than 100 to more than 400 since the 1960s.
Warming of the oceans due to increased atmospheric carbon dioxide from the burning of fossil fuels threatens all Arctic and Antarctic ecosystems that are being rapidly invaded by warmer-water species. And reef corals are dying en masse due to coral bleaching during increasingly frequent and severe warm spells. Bleaching is the breakdown in the symbiosis between corals and the microbes that live inside coral tissues and provide their food by photosynthesis. When temperatures rise too high, photosynthesis stops, the corals evict the microbes, rendering their tissues a ghostly white. If the symbiosis is not re-established, the corals eventually die. Increased carbon dioxide is also making the oceans more acidic, so that it is more difficult for animals and plants to make their shells.
The list of unwelcome changes goes on and on. The biggest problem, however, is that the different forms of human and natural disturbances act synergistically so that the net consequences are much greater than the sums of the different factors acting alone. Synergies are also complex and difficult to anticipate because of historical contingencies and chance, although they make sense in retrospect.
For example, estuaries throughout the world used to be packed with shellfish and other animals that fed on particles in suspension and kept populations of plankton in check. Oysters in the Chesapeake Bay were so abundant that they filtered the equivalent of all the water in the bay every few days. Virtual elimination of oysters by dredging killed the living filter, and water quality began to deteriorate because of agriculture and untreated sewage -- even before the massive use of chemical fertilizers exacerbated the problem. Huge increases in nutrient runoff are now the pre-eminent problem. But the question remains whether reduction in nutrients could restore water quality without the restoration of oysters, just as the Great Lakes initially failed to recover from eutrophication after nutrients were decreased.
Loss of biodiversity is perhaps the ultimate synergistic effect that reduces the resilience of ecosystems to overfishing, pollution, or climate change. The ecological role of the number of species in a community is extremely difficult to evaluate, as opposed to the role of specific predators or competitors. But increasing evidence suggests that more diverse communities are more productive, more difficult to invade by alien species, and recover more quickly from disturbances such as overfishing. We have no idea how many species may have gone extinct in the oceans due to human disturbance, but huge numbers of species are effectively extinct ecologically because their numbers are so reduced they no longer have any significant detectable effect. The rate of such ecological extinction is ever increasing so that resilience will almost certainly decline accordingly.
We can summarize all these changes that have already occurred by classifying entire ecosystems as if they were species by the criteria of the Endangered Species Act. Coral reefs, coastal seas, and estuaries are globally "critically endangered," with habitat-forming species like corals, oysters, kelps, sea grasses, marsh plants, and mangroves, as well as all large fishes, sharks, turtles, and marine mammals reduced by more than half to more than 99 percent of their former abundance. Continental shelf ecosystems are globally "endangered," with reductions often as great as coastal seas, and pelagic ecosystems are merely "threatened" because of their remoteness -- but perhaps also out of ignorance and lack of rigorous baselines for comparison.
Where will all this lead? Predictions are inevitably fraught with uncertainty, but we have sufficient understanding of the basic ecological processes involved to predict what will happen if we continue business as usual. Failure to stop overfishing will push increasing numbers of species to the brink of extinction, while more resistant species -- the future rats and cockroaches of the oceans -- will take their place. Runoff of nutrients and rising temperatures will increase dead zones to the point that they merge as a continuous band around the continents, and outbreaks of diseases will multiply. Even farmed seafood will be increasingly toxic from increased mercury from the burning of coal unless grown in isolation from the ocean. Increased carbon dioxide emissions will increase ocean temperatures and acidity. Warmer surface waters will inhibit the vertical mixing of the oceans, and bottom waters in the open ocean will become increasingly anoxic as in the Black Sea and the northern Gulf of Mexico.
All these changes are already happening and are routinely measured by oceanographers where I work. Even more frightening, albeit more poorly understood, is that biogeochemical cycles of carbon, oxygen, nitrogen, and sulfur will change in still uncertain ways, as they have in the past during the great mass extinctions and revolutions in the history of life.
How can we stop this runaway degradation of the oceans? The driving factors are obvious, and no new scientific research is required to know where to begin. But the implications for the ways we exploit the oceans, grow our food, and use energy for everything we do are vast.
Changes in fisheries should be the easiest to achieve in developed countries because wild fisheries are a dying industry due to diminishing stocks and rising fuel costs, and the tools for effective management are well established if widely ignored. Whatever we do, wild fisheries cannot possibly sustain increasing global demand so that industrial-scale aquaculture of species low on the food chain is the only viable alternative. Environmentalists have strongly opposed aquaculture because of irresponsible habitat destruction for shrimp farms, introduced species, and emphasis on species high on the food chain like salmon and tuna that require even more fish for food. But aquaculture is the way of the future, and we should focus on more effective regulation rather than on futile opposition. Subsistence overfishing is a vastly greater problem in developing countries where fishing whatever meager catch might be available is commonly a matter of survival. Rationalization of these fisheries will require subsidies to provide alternative sources of protein and employment.
The rise of slime is a vastly greater problem that will require a global revolution in agriculture. The agricultural establishment has made known its conservatism and environmental irresponsibility since its opposition to Rachel Carson's critique of pesticides in Silent Spring. This irresponsibility continues in the unregulated and subsidized overuse of chemical fertilizers and pesticides, unnecessary loss of soils, and lack of treatment of animal wastes that are released into the environment in staggering abundance. The harmful effects on terrestrial ecosystems are also severe. As for fishing, these issues are especially sensitive in developing countries where growing adequate food is a matter of survival. But in developed nations, removing subsidies for fertilizers and pesticides, and taxing their use, would significantly reduce nutrient loading and eutrophication with only modest reductions in production and increases in costs.
The most encouraging news about climate change is that more and more people understand that the rise of carbon dioxide in the atmosphere is due to the burning of fossil fuels and that the climate is warming and the oceans are becoming more acidic accordingly. Even more encouraging is that states like California are taking steps to reduce emissions through mandatory use of clean-energy technologies and conservation. But the challenges are enormous and societal inertia so great that it will be a very long time before emissions level off, much less decrease. Thus, the oceans will become warmer and more acidic for decades to come, and many scientists have already written off coral reefs and any marine creatures whose lives depend on their calcareous skeletons.
But hope for reefs still remains in the commonsense observation that ecosystems that are protected from overfishing and pollution appear to be more resistant to the effects of climate change than those that are not -- just the way being fit helps us to survive a catastrophic illness. The ecological mechanisms are obscure and the limits to the benefits of local protection unknown. Nevertheless, local conservation may buy precious time for alternative-energy practices to emerge.
So what will the oceans be like in 2025? It all depends on how rapidly we act. We could make enormous progress by instituting and enforcing more effective fishery regulation with responsible aquaculture to restore marine food webs. We could also reverse the increase in dead zones and outbreaks of disease to make places like the Chesapeake Bay and North Carolina's Pamlico Sound healthy again. The only thing standing in the way is profit at the margins of bad agricultural practice, unregulated waste disposal, and greed. As for warming and acidification, we can only hope that making progress with the rest will make a sufficient difference for a few more decades. At least we still have a choice about what our oceans will be like, a choice we may not have for long.
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