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Cover story in Science reveals historical overkill of marine Megafauna triggered current ocean crises

SeaWeb

Leading marine scientists call for bold measures to restore oceans

While recent reports suggest Stone Age hunters drove dozens of species of huge land creatures to extinction, the cover story of the July 27 edition of Science describes the ecological extinctions of marine megafauna--vast populations of whales, manatees, dugongs, monk seals, sea turtles, swordfish, sharks, giant codfish and rays--from overfishing at a global scale never before realized.

Recognition of what has been lost, however, also shows what could be gained. The scientists claim this revolutionary historical perspective is essential to management because historic data provide a framework for remediation and restoration that is otherwise invisible.

"Comparing the magnitude of the mass ecological extinctions in the ocean to those on land may not be enough," states study co-author Dr. Roger Bradbury of the Australian National University in Canberra Australia. "On the land, as we killed off the giant mammals and destroyed the ancient forests, we replaced them with a new suite of farmed species. In the coastal seas, we took out animals and replaced them with nothing."

"Every marine ecosystem I have ever studied during my entire 30 year career looks unrecognizably different from the way it used to be, and I wanted to know why," says Dr. Jeremy Jackson of Scripps Institution of Oceanography in San Diego. Jackson, a renowned marine ecologist, instigated the two-year study of human impacts on oceans over time.

Jackson convened an international team of 19 leading marine researchers at the National Center for Ecological Analysis and Synthesis (NCEAS) in Santa Barbara, California. Drawing on paleoecological, archeological and historical data, the scientists uncovered past evidence of seas teeming with large animals as well as abundances of oysters and shellfish so vast they posed hazards to navigation. The new data also show that historical overkill of this marine life triggered current ecological collapses -many of which have been mistakenly attributed to pollution.

"We started out to study everything that people had ever done to oceans historically and were astounded to discover that in each case we examined, overfishing was the primary driver of ecosystem collapse," states Jackson.

The data demonstrate that overfishing triggered changes in ecosystem structure and function as early as the late aboriginal and early colonial stages. Even more chilling, the scientists show that grinding down marine food webs is responsible for many of the problems we face today. Removal of key predators and entire layers of the food chain set off sequences of events that are now culminating in toxic algal blooms, dead zones, outbreaks of diseases and other symptoms of ecological instability.

Water so clear you can see a cannon 30 feet down Examples of the negative chain reaction brought on by overfishing include:

* Chesapeake Bay, the ocean birthplace of the U.S.A. is a bacterially dominated, impoverished ecosystem. Historically oysters filtered the entire water column every three days. Records describe a lost cannon, "clearly visible in over 30 feet of water." Eutrophication commonly ascribed to increased run-off and nutrient loading began instead with the mechanized extraction of the vast oyster reefs. Overfishing the oysters removed the top down control of phytoplankton. Grey whales, (now extinct in the Atlantic), dolphins, manatees, river otters, sea turtles, alligators, giant sturgeon, and hammerhead sharks were all once abundant inhabitants of Chesapeake Bay but are now virtually eliminated.

* Overfishing of large fish has led to overgrowth of algae on coral reefs, which has smothered the reefs and jeopardized the approximately 3 million species they harbor.

* The recent die-off of turtlegrass beds in Florida Bay can be attributed to the ecological extinction of green sea turtles. Overkill of the green sea turtle and other seagrass grazers such as dugongs and manatees has contributed to outbreaks of disease and die-offs in seagrasses. This has undermined the habitat's ability to serve as a food source, breeding and nursery ground, erosion protector and more.

* Many scientists have long suspected that overfishing has caused the well-publicized collapse of sea lion and sea otter populations in the Bering Sea. But new work related to this study by Alan Springer (University of Alaska) and co-author James Estes at UC Santa Cruz and several others, suggests that vast depletion of the great whales by humans has contributed to this collapse in a heretofore unrecognized manner. Whaling and overfishing forced killer whales to switch prey from the great whales to sea lions and most recently to sea otters - ultimately causing sea urchin barrens and the loss of kelp forests.

Responding only to current events on a case-by-case basis cannot solve the ocean's problems because impacts of human disturbance are synergistic and have deep historical roots. Ecological extinctions make ecosystems more vulnerable to other natural and human disturbances such as nutrient loading, eutrophication, anoxia, disease, and climate change. Meanwhile various forms of human disturbance have increased and accelerated.

Instead the scientists say, problems need to be addressed by a series of bold experiments to test the success of integrated management on the scale of entire ecosystems. With few exceptions, such as the Steller's sea cow, and Caribbean monk seal, most species that are ecologically extinct probably still survive in sufficient numbers for successful restoration with proper management. This optimism is in stark contrast with many terrestrial ecosystems where many or most large animals are already extinct. Correcting History - Integrated Ecosystem Management to Restore Oceans

The scientists advocate major changes to management practices, such as calling for massive restoration of the once vast oyster reefs of Chesapeake Bay. This would result not only in cleaner water but in an economic mainstay. Current plans for remediation of eutrophication of estuaries are still based on the belief that it is caused only by increased nutrients without regard to overfishing of suspension feeders such as shellfish.

"Clearly we have allowed too much fertilizer to enter bay waters, but we have also removed the major biological filters in the bay to only 1 percent of historical levels in the Chesapeake Bay and North Carolina's Pamlico Sound system," states Charles Peterson of the University of North Carolina. "Oysters filter and clarify bay waters. Oyster reefs provide habitat for blue crabs, rockfish and many other valued fishery resources."

Other recommendations include the restoration of coral reefs and seagrass beds by protection of fishes, sharks, turtles and sirenians in very large reserves on the scale of all of Florida Bay and the Florida Keys. The potential for reducing diseases of corals and turtlegrass by restoring natural levels of grazing is unproven but consistent with historical evidence.

Historical data not only help clarify underlying cause and rates of ecological change, but they also demonstrate achievable goals for restoration, management and exploitation of coastal ecosystems that far exceed what we contemplate today. Scientific expectations for the recovery of marine ecosystems are too low because they are based on fisheries data that long postdate the decimation of fisheries.

"The many tens of millions of seaturtles in the Caribbean before Columbus easily exceeded the abundance and biomass of large animals in East Africa," states Jackson. "All we do today is micromanage remnants of once vast populations."

The scientists state that fisheries regulators and marine managers need to move beyond their fixation on quotas and boundaries and devise ways to restore the productivity and function of coastal seas. "We need to change the way we think about our coastal seas: not pristine, but damaged, and equally not hopeless, but salvageable," states Bradbury. "Our research points the way."

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Other authors of the study include: Wolfgang Berger, Michael Kirby and Carina Lange, Scripps Institution of Oceanography; Karen Bjorndal, University of Florida; Louis Botsford, University of California, Davis; Bruce Bourque, Bates College, Maine; Richard Cooke, Smithsonian Tropical Research Institute, Washington; Jon Erlandson, University of Oregon; Terrence Hughes, James Cook University, Townsville, Australia; Susan Kidwell, University of Chicago; Hunter Lenihan, Hatfield Marine Centre, Newport, Oregon; John Pandolfi, Smithsonian Institution, Washington, D.C.; Robert Steneck, Darling Marine Centre, University of Maine; and Robert Warner at University of California, Santa Barbara.

For more information, including scientists' contact information, please contact Dana Topousis at Fenton Communications: dtopousis@fenton.com/ 202-822-5200 ext. 238 or Jeremy Jackson at cell # 858-518-7613. (Direct connect to France.). Upon lift of the embargo, scientists' contact information, graphics, and additional information will be available at http://www. seaweb.org/ScienceJuly27.html For a copy of the study please call 202-326-6440 or contact scipak@aaas.org

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