By Carlton, James T.; Butman, Cheryl Ann
Oceanus , Vol. 38, No. 2
The biological diversity of the world ocean is subject to unprecedented alterations that are largely due to potentially irreversible effects of human activities. What do we know about the pattern and scale of these changes, and how are they altering the structure and organization of marine communities? How can we improve our ability to predict the effects of a growing human population on the diversity of life in the sea? Answering these questions requires a substantially improved understanding of the fundamental mechanisms that create, maintain, and regulate diversity in the sea.
In 1993 the National Research Council's Ocean Studies Board and Board on Biology established the Committee on Biological Diversity in Marine Systems(*) to tackle the daunting task of laying the foundation for a national research agenda on marine biodiversity. The committee's principal tool was a 1994 biodiversity workshop (see "The Workshop Experience" on page 6). The workshop provided a vehicle for building consensus and gathering information, while for six months both before and after the workshop the committee assembled further important materials. The result is a book, Understanding Marine Biodiversity (National Academy Press, Washington, DC, 1995, 114 pages), that identifies the urgent need for a national research program and outlines a research agenda.
The work of the committee and the workshop identified five major critical environmental issues that affect or could potentially affect marine biodiversity. All are directly or indirectly linked to human activities, and have affected and may yet affect life from the tidal zone to the deep sea. The issues are:
* Fisheries operations, ubiquitous across marine habitats, include overexploitation to the extent that some of the world's greatest fisheries (such as the Grand Banks and Georges Bank) have now been closed. Significant indirect effects include high mortalities of by-catch species, habitat destruction (especially as a result of trawling and dragging), and food-web changes.
* Chemical pollution and eutrophication (nutrient enrichment from agricultural and urban sources) have severely impacted shallow seas and estuaries. In addition to effects on biodiversity, researchers find that increased incidence of tumors and diseases in fish is one of many associated consequences of marine contamination by a "cocktail" of pollutants.
* There have been profound physical alterations in coastal-zone habitats over the last 150 years. In many areas of the world, vast amounts of shoreline that once included marshes, lagoons, and mangroves have been dredged, diked, and filled. Mining, agriculture, deforestation, and dam construction are so ubiquitous that the patterns of sedimentation, erosion, and freshwater flow in some of our nation's largest estuaries are better described from the point of view of anthropogenic change than natural processes.
* Less widely known are the profound changes in biodiversity caused by invasions of exotic species. And yet on a typical day more than 3,000 species of marine animals and plants are in silent motion around the world, traveling in ships' ballast water. The results of releasing this water include the invasion of the Black and Azov Seas by the carnivorous American comb jellyfish Mnemiopsis (an event now correlated with a startling decline in these seas' anchovy fishery) and the invasion of Australia by Japanese species of red-tide-causing dinoflagellates (leading to the closure of shellfish beds).
* And finally atmospheric pollution has led to increased ultraviolet radiation and growing concentrations of gases that lead to rising temperatures. These global climate changes may result in new patterns of ocean circulation and thus of nutrient supply and distribution.
The list of human impacts on marine ecosystems includes, then, loss of fisheries; loss of species with important potential for biomedical products; altered aesthetic and recreational value of coral reefs, marshes, beaches, and bays; vast reductions in ecologically important animals and plants; and, indeed, profound changes in basic ecosystem functions, such as energy flow and chemical cycling. …