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'Estuaries are...rich in the nutrients of the continent itself, stirred by the forces of Nature like the soup of a French chef...the nursery, resting place and refuge of countless species." —Stanley A. Cain, ecologist
 | Alewife. R. Mickens / AMNH |
Coastal river deltas, lagoons and bays can all form parts of estuaries. Together with surrounding coastal regions, estuaries provide nearly half of the world's commercial fish harvest. They also act as buffers between land and sea by filtering pollutants, trapping nutrients and fending off floods. But decades of pollution, overfishing, alien species introductions and unchecked development have made many estuaries unhealthy. This trend is slowly reversing in some regions, but more protection measures are needed.
Introducing an alien species into an estuary, whether by accident or on purpose, can mean trouble for native inhabitants. In the 1940s, researchers tried to boost the failing eastern oyster harvest in the Chesapeake Bay estuary by adding Pacific oysters to the ecosystem. But they carried a parasite, which killed up to 95 percent of the native oyster population. A fishery that had produced over 3 million bushels of oysters in 1880 plummeted to 50,000 bushels by 1960. This disaster is a prime example of the unintended consequences of changing a complex ecosystem.
 | Toxic chemicals, including PCBs, entered the Hudson River from factories and contaminated a valuable resource and breeding ground for many fishes, especially striped bass and shad. Researchers first detected PCBs in the 1970s, but it took decades of lawsuits to start clean-up efforts. © Steve Stanne/Hudson River Sloop Clearwater |
Estuaries are so bountiful that many major cities and industries have developed along their shores. Some of these once-productive habitats have endured years of pollution running off the land into their rich waters.
Oil from drilling and shipping seeps into the sediment and damages bottom dwellers. Biological agents from sewage cause disease in plants and animals. And excess nutrients from fertilizer runoff destroy the water quality. Better management of the land surrounding estuaries may stave off further ruin and help these ecosystems recover.
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