Population and Environment Linkages: Oceans

By Gale Mead Hey

[Short Introduction also available]

Seen from afar, Earth is a water planet. The world's oceans cover 77% of the Earth's surface, comprise 99% of the planet's biosphere, and contain far greater diversity of life than is found on land (3). Even the most biologically rich tropical rain forests cannot match the biodiversity found in a coral reef community (based on the number of major categories of life represented). The oceans are so vast, and so full of life, that it has always seemed impossible that humans could have any appreciable impact on their functioning, or on the species that live in the deep. Many people assume that if land-based resources are ever depleted, the oceans will remain a virtually limitless resource which can feed humanity and meet the needs of a growing population.

But especially within the last 30 years, increases in human population, combined with improved technology, increased demand for seafood, use of products that directly or indirectly contribute to pollution, and a host of other factors, have led to impacts on marine ecosystems that could not have been imagined 100 years ago. As the Earth's human population approaches six billion, scientists, economists, policy makers, and the general public have begun to observe increasing evidence of the pressure humanity is placing on the ocean's natural systems and resources (23).

Human activity has influenced the nature of ocean resources and the functioning of the sea for centuries, but only in recent decades has an understanding of the complicated relationship between human population and oceans begun to come into focus. While much more needs to be done to assess the long-term impact of human activity on the ocean --- globally, regionally, and locally --- marine scientists have identified the following five areas of concern (9):

  1. Direct physical alteration of ocean environments

  2. Extraction of living and non-living resources

  3. Pollution of ocean environments

  4. Introduction of alien species

  5. Global climate change

Each of these topics is considered here with special reference to the role of human population levels. However, the effects of human population are inextricably linked with the impact of political, cultural, economic, and other factors, and effects of population must be considered in the context of these other factors.

Physical Alteration

Human activities physically alter the seabed directly in a variety of ways, including dredging, trawling, and boat groundings, and indirectly by deforestation, damming, erection of sea walls, and other activities that increase sedimentation and/or cut off the natural exchanges between land and sea. Alteration of the coastal landscape can be profound, as major urban centers, resorts, hotels, golf courses, ports, and factories replace natural coastal ecosystems.

Approximately 60% of the world's population currently lives within 60 km (37 miles) of coastal waters, and the coastal population is expected to double within the next 30 years (1). Cultural trends and economic pressures are driving many people from rural areas towards the major urban centers, most of which are located in coastal areas. Fully 2/3 of the world's urban centers (cities with populations over 2.5 million) are near tidal estuaries, and six of the world's eight megacities (cities with a population over 10 million) are coastal (11). Paradoxically, the shift to coastal regions is driven both by poverty and affluence, as poor people move to urban centers seeking a livelihood, and wealthier people spur new development along the shoreline, such as coastal resort hotels, and homes with a view of the sea.

Coastal zones are acknowledged to be among the most biologically productive habitats on earth, and with the increased rate of human population growth in coastal areas greatly outpacing overall population expansion, they are also among the most impacted. The World Resources Institute estimates that roughly half of the world's coastal ecosystems are threatened by development, with most of those threatened located in northern temperate and northern equatorial regions, including most of the coastal zones of Europe, Asia, the United States, and Central America (24).

As coastal areas are developed for human use, critical habitat for seabirds, marine mammals, and other marine species is reduced or eliminated. Shallow harbors are dredged to make them navigable. Sea walls cut off the natural exchange between land and sea. Rivers are dammed, cutting off critical migration routes for species such as salmon and blue crab, which need both fresh and salt water habitats to survive.

Physical changes along the coastline can also impact species and systems in the open ocean, particularly among species that spend part of their life cycle nearshore, onshore, or inland. Definition of the nature and extent of these effects has only just begun, and much more study will be necessary to develop a better understanding of these issues.

A less visible, but more widespread source of physical alteration of the marine environment is caused by the fishing method of bottom trawling. Bottom trawling involves dragging weighted nets across the sea floor, disturbing whatever rocks, coral, and organisms are in their path. Fish that rely upon hiding places among rocks and coral reefs find themselves homeless; coral which requires clear, clean water to survive becomes choked with silt; and ecosystems that support the very fishery behind the trawling are substantially altered (8).

The ecological effect of bottom trawling is often compared to clear-cutting of forests, but while a forest is clear-cut once, a given area of sea floor may be bottom-trawled 100 times in a single year. It is estimated that an area equivalent to the world's continental shelf is trawled every two years. Scientists estimate that 60 to 95% of the organisms scooped up by bottom trawlers are bycatch: Non-target species taken incidentally and usually discarded (8).

Other sources of physical disturbance of the seabed include: undersea mining operations, offshore oil exploration, and other types of resource extraction activity, ship groundings, and anchorage. The impact of these sources of disturbance on marine life has received very little study.

Physical damage to coral reefs and other ecosystems from boat anchorage and groundings may appear to be small and localized, but there is evidence that the cumulative effects, particularly in light of substantially increased frequency in recent decades, can be significant. For example, the Florida Keys National Marine Sanctuary receives reports of over 40 boat groundings per month within the sanctuary's boundaries. Based on observation of damaged reefs and seagrass beds, there are numerous additional groundings which go unreported. The damage to highly sensitive coral reef ecosystems from such frequent groundings can be profound (a).

Dynamite fishing is another form of physical alteration that devastates coral reefs and reef communities. Fishers explode dynamite on coral reefs to kill and stun fish, which can then be scooped from the water with nets. The explosions kill everything near the blast, including corals. Another technique, called muro ami, involves pounding reefs with heavy weights to scare fish out of their hiding places, destroying the coral heads in the process. To capture fish for the aquarium trade, and for the growing seafood market for live fish, reefs are deliberately poisoned with sodium cyanide, rotenone, or sodium hypochlorite bleach killing or injuring corals, fish, and other reef inhabitants (12).

These techniques are especially common in developing countries where regulations are often weak and poorly enforced, and the acute need to put food on the table often outweighs concerns about the effects those methods will have on the reef's ability to continue to provide sustenance in the future, let alone concerns about biodiversity and the health of the oceans (17).

Extraction of Living and Non-Living Resources

Overexploitation of marine resources includes overfishing, extraction of mineral resources, and exploitation of marine mammals. Potential effects of these activities are not limited to the removal of quantities of that resource, but also to possible side-consequences, such as accidental release of crude oil during the extraction process, and physical alteration of the sea floor with deep sea mining operations and bottom trawling. As with most issues involving the interactions among the human population and the marine environment, there are multiple causes and effects that are interrelated. Each issue therefore requires investigation in the context of the larger picture.

Few would question the importance of living marine resources to humans. Fish and shellfish provide a valuable source of food protein to our diets, and a livelihood to fishermen and others in the seafood industry. Other marine resources similarly meet the needs of the general population, and provide jobs. The issue at hand is the extent to which we can realistically expect the oceans to continue to meet those needs, and it is that issue which drives a pressing need for scientific study, and implementation of management principles based upon the results of such research.

Fish protein constitutes 19% of humans' animal protein intake (1), and per capita, humans consume an average of 13 kg of fish per year (21). The amount is higher in impoverished coastal populations which rely heavily on local catches, and in affluent societies with the means to import fish to meet local demand. In Hong Kong, per capita fish consumption is 100 pounds per year, mostly imported from elsewhere in Asia and beyond (17). The Food and Agriculture Organization of the United Nations (FAO) predicts that the global demand for fish will continue to increase with population growth.

Modern approaches to fishing and transportation make it possible to catch fish anywhere in the world, and transport them fresh to wherever there is demand. It can be confusing for consumers to hear that swordfish or grouper are in trouble when those species still appear on restaurant menus and in grocery stores. The globalization of the fish market tends to insulate residents of industrialized countries from the effects of overfishing, and helps to perpetuate the myth of the "bountiful, endless potential of the sea to feed us all." Substantial evidence in recent years has demonstrated that we can no longer continue making such assumptions about the world's oceans (2).

Global fishery landings increased fivefold from 1950 to 1989, peaked at 86 million tons in 1989, and subsequently declined, in spite of increased demand, an expanding fishing fleet, and more powerful technology (3). Increases in total fish landings since 1995 are largely a result of increased aquaculture, which now accounts for 15.5% of all fishery landings (21), and continuing increases in the exploitation of species which were previously regarded to be of little or no commercial value. While landings of 91 million tons in 1995 suggest the world's fisheries are doing well, there have been substantial qualitative changes. Populations of many of the larger species, larger specimens within a given species, and those higher on the food chain have continued to decline, and in many cases have ceased to be commercially viable (21).

Many commercial fisheries have collapsed; in 1993 the FAO estimated that more than 2/3 of the world's commercially valuable fish populations are overexploited or "fully exploited (21)." The 1991 National Fisherman Yearbook noted: "At present, 45 of the 190 fish stocks that provide 90% of the world's fish production are overexploited." Technological advances, management issues, economic forces, and cultural factors contribute to overfishing. All of these factors interact with one another, and with what is possibly the most influential factor: The increasing demand for living resources driven by a growing population.

Atlantic swordfish are old enough to reproduce only after they have grown to approximately 100 pounds in size. Yet they can be taken legally at only 33 pounds. Humans are eating the juveniles, while landings of adult swordfish have become increasingly rare (b). Landings of Atlantic cod declined from their 1970 high of 3.1 million tons to only 1.1 million tons in 1993, despite increased effort and improved technology (14). In 1991, an assessment of western Atlantic bluefin tuna showed that the adult breeding population had been reduced by 90% in the 20 years since their take had begun to be regulated. The regulations had been intended to ensure healthy populations of bluefin tuna, but gave every appearance of having had the opposite effect, as quotas had been set too high, and there was evidence of poaching which further depleted the population of bluefin (3).

In some cases, the decline in fishery catches for a particular population may be attributable to causes other than overfishing, such as natural cyclic variations in population, ocean currents, algal blooms, oil spills, or decline in that species' food supply. For example, the Black Sea anchovy population, already weakened by overfishing, was decimated by the introduction of a non-native species of comb jelly which competes with anchovies and feeds on their young. However, for the vast majority of those commercial species which have substantially declined in recent years, overfishing can be clearly demonstrated to be the main causal factor (21).

Hunting of marine mammal populations provides a clear illustration of the effects of overexploitation by humans. European whalers in the 12th through the 16th centuries depleted the northern right whale populations which could be found in Atlantic coastal zones. Subsequent advances in boat and harpoon design during the 1700's and 1800's enabled whalers to exploit the most remote reaches of the whales' ranges, and by the time right whales were given protection from hunting, in 1932, scientists estimated that only 100 right whales remained in all of the North Atlantic Ocean, a population reduction of over 99% (4).

After 65 years of protection, the northern right whale population is now estimated at approximately 350, reflecting a much slower recovery than was anticipated. Moreover, DNA studies of over 100 northern right whales revealed evidence that all of the individuals tested were descended from only three females. Such extreme loss of genetic diversity can substantially weaken a species' adaptability and long-term viability (4).

The white abalone provides another example of similar rates of population depletion due to overexploitation in much more recent times. In southern California, as supplies of popular pink and red abalones were depleted in the early 1970s, divers explored deeper reefs for the even more valuable white abalone. The commercial white abalone fishery reported landings of 60 metric tons in 1972 alone. Over the next seven years, landings swiftly declined to near zero. In the early 1970's, surveys documented more than 4,000 white abalone per acre on reefs at depths of 80 to130 feet around the Channel Islands. Surveys in 1996 revealed only an average of 0.4 per acre. Thus, white abalone populations have decreased 99.99% in the last 25 years, with an estimated remaining population of less than 600 individuals. A captive breeding program currently being developed may be the species only chance for survival (1).

Aquaculture would appear to present a promising means of meeting the global demand for seafood, as well as cultivating organisms to restore depleted natural populations. However, the industry comes with its own set of problems, including destruction of mangrove forests for shrimp farms, introduction of alien species, disease, and contaminants, and other forms of damage to local ecosystems. In addition, some farm-raised species, such as salmon, are carnivorous, requiring a fish-protein-based diet which is almost always supplied by wild-caught fish (21).

Fisheries in many regions of the world's oceans remain unregulated and inadequately studied, and even where research has been done, political and economic pressures have been known to override scientists' recommendations. For example, the New Zealand orange roughy fishery, which started in the 1970's, began to show signs of significant decline less than 10 years after fishers started pursuing that species. In 1986, scientists in New Zealand warned that the without an 84% reduction in the take of orange roughy, the fishery was at risk of crashing within five years. Policy makers instead chose not to cut quotas at all for two years, and implemented only a 20% reduction for 1989. Eventually, the New Zealand orange roughy fishery did collapse, and because orange roughy take 25 to 30 years to reach maturity, populations will be very slow to recover. To meet the demand for orange roughy, other populations, in unregulated waters, are now being exploited at rates that are similarly unsustainable (12).

Incidental taking and killing of non-target species, including fish, marine mammals, and sea birds, has impacted ocean ecosystems. FAO estimates for 1988 through 1990 indicate an average of 27 million metric tons of fish per year was discarded as bycatch by commercial fishermen, an amount equal to 1/3 of the total global landings for each of those years. This figure does not include the incidental killing of several hundred thousand sea turtles, marine mammals, and seabirds each year (12). Fishing methods such as bottom trawling, gill netting, and longlining are especially prone to bycatch. Shrimp trawlers catch and discard an estimated nine pounds of non-target species for every pound of shrimp caught (21).

Modern fishery management sometimes succeeds in preventing overexploitation of the magnitude seen with the right whale, bluefin tuna, and white abalone. Scientific study can assist policy makers in determining levels of taking which can be sustained on a long-term basis. However, much more research is needed in order to ensure the accuracy of those estimates, and to direct management efforts.


As the human population has increased, so have the following: The amount of sewage produced; the amount of fertilizers, herbicides, and pesticides used to raise crops and groom yards, golf courses, and parks; the amount of fossil fuels extracted and burned; the amount of land deforested and developed; and the various by-products of manufacturing and shipping generated. Cultural, political, and socioeconomic forces influence the kind and amount of waste and toxics produced, and affect how they are dealt with. Thus, increased population is clearly just one factor that contributes to pollution. As with other ways in which humans impact the environment, the causes and effects are complex.

Pollution of marine ecosystems includes runoff from land, rivers, and streams, direct sewage discharge, air pollution, and discharge from manufacturing, oil operations, shipping, and mining (5). As discussed earlier, the human coastal population already comprises 60% of the world's population. The number of people living within 50 miles of the sea is expected to double within 3 decades (11). Many cities and towns have found their infrastructure inadequate to the increased demands placed on them. Sewage treatment facilities that were adequate a decade ago may literally overflow, discharging untreated sewage into rivers and oceans.

Although coastal populations have the greatest per capita impact on ocean ecosystems, pollution from runoff is not limited to coastal cities. Runoff from over 90% of the Earth's land surface, inland as well as coastal, eventually drains into the sea, carrying with it sewage, fertilizers, and toxic chemicals. Similarly, air pollution from inland as well as coastal cities, including by-products of fossil fuel consumption, PCBs, metals, pesticides, and dioxins, eventually finds its way into the oceans after rain or snow. Effects include water quality degradation, sediment contamination, and human health risks from contaminated fish and shellfish (c).

Increased demand for oil has resulted in increased offshore oil extraction operations, and transport of oil, which in turn has led to more frequent oil spills. The frequency of oil spills in and near US waters increased from 371,000 spills in 1970 to 921,000 incidents in 1986, with a total of 321.5 million gallons of oil spilled in and near US waters during that period. However, spills account for only 10% of marine oil pollution. At least 50% of the oil pollution in marine waters comes from low-level chronic sources such as leaks at marine terminals, disposal of drilling muds from offshore oil operations, runoff from land, and atmospheric pollution from incompletely burned fuels (15).

The cumulative effects of pollution on ocean ecosystems can be profound. For example, in the Gulf of Mexico, the occurrence of what scientists call "dead zones" in once highly productive waters can be traced to the introduction of excessive nutrients from farms, lawns, and inadequately treated sewage, which stimulates brisk growth of plankton that ultimately leads to depletion of oxygen in the water. Similarly, dumping of 9 million metric tons of sewage sludge annually off the New York/New Jersey shore has resulted in deoxygenation of 4,700 square miles of formerly productive offshore bottom communities (12).

Blooms of toxic phytoplanktons and red tides have increased in frequency over the last two decades, and may be linked to coastal pollution. For example, a recent study traced stormwater runoff from the drainage into Santa Monica Bay, California which carried with it suspended particulates, nutrients, heavy metals, and toxics. The researchers concluded that effects of the stormwater runoff often resulted in dinoflagellate (red tide) blooms following storms. Such events not only cause mass mortality among some fish species, but can result in marine mammal deaths and pose a threat to human health (11).

Water treatment technology has advanced in recent years, leading to substantial improvements in those areas where the new technology is applied. However, many developing countries cannot afford to implement these new technologies, and population growth in coastal cities has continued to overwhelm existing waste treatment systems.

Worldwide, substantially more study is needed on the effects of pollution on the marine environment, which will facilitate understanding of the complex problems, their myriad potential causes, and ways in which damaged ecosystems can be restored.

Introduction of Alien Species

Alien species are plants and animals that naturally occur in one part of the world, where their natural predators, diseases, and interactions within the ecosystem keep their populations in balance, but that are artificially introduced into a new ecosystem where those controls may not exist. In many instances, the new environment is not hospitable to the introduced species, and it fails to thrive there. However, in many cases, the new species has thrived, outcompeting the naturally occurring species, upsetting, and in some instances devastating, the local ecosystem.

On land, some of the most devastating alien species introductions have occurred by accidental air transport of the non-native species. In the ocean, the primary mechanism of alien species introduction has been in the ballast water of shipping vessels. Ships fill and empty their ballast tanks in order to maintain stability in the water. Anything living in that water can easily get sucked in, and discharged elsewhere when the ship's ballast tanks are emptied. Scientists estimate that as many as 3,000 alien species per day are transported in ships around the world (23).

Alien species are more of a concern in coastal waters than in the open ocean, as coastal zones are more likely to be biologically and ecologically distinctive and disconnected. Alien species are also more likely to be problematic where bodies of water are not naturally connected to one another. For example, transport of a species from the Indian Ocean to the Pacific is unlikely to have significant impact, as the two oceans are already connected. Transport of a species from tropical regions of the Atlantic to the Pacific would be more likely to have a disruptive influence, because there is little naturally occurring exchange between them (c).

The impact of alien species has increased dramatically in recent decades because of a global increase in shipping. Depletion of local resources (including grain, wood, fuels, materials for consumer goods, etc.) in many areas of the world has outstripped global population growth rates. Places that were formerly self-reliant now depend on imports to meet their requirements. Driven in some cases by local depletion and in others by affluence, the needs of Earth's current human population are largely met by moving products and resources around the globe (23).

This increase in shipping has resulted in a corresponding increase in development of port facilities and risk of oil spills, as discussed in previous sections. But it has also brought with it a huge increase in the introduction of marine alien species into ecosystems incapable of coping with them, as ships pick up species from one part of the world in their ballast water, and release them in new areas, where those species had never previously occurred.

For example, Mnemiopsis leidyi, a comb jellyfish native to temperate and tropical western Atlantic bays and coastal waters, was first observed in the Black Sea in 1982, and is believed to have been introduced in ships' ballast water. Since it feeds on zooplankton including eggs and larvae of commercial fishes, it has been linked to a decline of Black Sea sprat and anchovy. Some have proposed introduction of another alien species, butterfish, into the Black Sea to control the mnemiopsis population. However, many scientists fear that such a plan would create new and potentially more severe problems (c).

The Green crab, Carcinus maenas, is a European native which was introduced and became established on the Atlantic Coast of North America more than a century ago, and now ranges from Nova Scotia to New Jersey. In recent years, the green crab has been introduced to the waters off South Africa, southern Australia and (starting in 1989 or '90) the US Pacific Coast.

Green crabs are voracious predators of invertebrates such as clams, mussels, oysters and smaller crabs. They threaten the large and important fisheries for mollusks and Dungeness crabs, as well as large numbers of noncommercial invertebrate species, but are too small to be themselves of commercial interest as seafood for humans. There is active discussion of releasing biocontrols, ranging from parasitic barnacles to microorganisms, to slow or stop the advance and proliferation of the green crab. However, there is concern regarding the possible hazards of introducing yet another alien species into those waters (c).

San Francisco Bay offers one example of an ecosystem that has been overwhelmed by numerous alien species introductions. Today, there are more that 200 different alien species living in San Francisco Bay, severely impacting on native species, and the overall functioning of the ecosystem. Although the alien species have not completely eliminated native species, the character and natural processes of the Bay have been substantially altered (d).

In addition to changing the functioning of marine ecosystems, alien species can also affect human health. Zebra mussels, an introduced species which has thrived in the Great Lakes, have caused problems ranging from disrupting native species to clogging pipes, but have also had the positive effect of filtering toxins and various pollutants from the water. More recently, another alien species, the round goby, has arrived, and has proved a voracious consumer of zebra mussels. The problem is that popular game fish eat the gobies, thereby ingesting highly concentrated amounts of the toxic substances that the gobies accumulated from the zebra mussels, and passing them on to the humans that eat them (d). Failure to understand the complex relationships between species can have serious consequences not just for natural systems, but human health as well.

Global Climate Change

As the world's human population has increased, so has use of fossil fuels and other pollutants that are known to contribute to global climate change. Between 1950 and 1987, annual global carbon dioxide emissions from anthropogenic sources increased from 1,638 million metric tons to 5,650 million metric tons (12). Although significant climate changes have occurred naturally throughout the Earth's history, most climate scientists agree humans' activities have accelerated the rate at which climate change is now occurring. The concern expressed by some ecological scientists is that species and ecosystems that may be capable of adapting to slow climate change may be unable to adapt quickly enough to survive. The implications for humankind are profound.

Effects of climate change on marine ecosystems have already been observed, and these effects appear to be accelerating. Melting of glaciers and polar ice caps, and increased water temperature, is causing the sea level to rise, threatening coral reefs, coastal mangroves, salt marshes, and other coastal and marine ecosystems. Estimates of projected sea level rise by the year 2100 range from four inches to eleven feet. The Intergovernmental Panel on Climate Change predicts a 26 inch rise in sea level by 2100, which suggests rates three to six times higher than those seen over the past century. Some experts believe these projections may be too conservative. Rising sea levels threaten humans as well as wildlife. Based on the above projections, Bangladesh would lose 12 to 28% of its total land area within the next century, and the island nation of Maldives would be entirely submerged (12).

While climate change affects water temperature and warm-water currents, melting of polar ice and changes in rain patterns which accompany climate change also affect the levels and patterns of salinity in marine waters. Many scientists believe that rather than a slow gradual shift in ocean systems and associated atmospheric patterns, a sudden, global reorganization of ocean-atmospheric patterns is likely to occur once some threshold point has been crossed. It is difficult to predict what the effects on marine ecosystems and species will be. Some could benefit, others perish. Changes in growth, migratory behavior, competition, and other interactions between species would likely be profound (12).

Global climate change can have profound effects on the oceans. But the reverse is also true. The ocean plays a vital role in regulating weather patterns, generating oxygen, and removing carbon dioxide from the atmosphere. Thus, the health of the oceans can have a profound impact on the nature and extent of climate change.

Microscopic life in the oceans helps reduce greenhouse gasses responsible for climate change by controlling the amount of carbon dioxide in the atmosphere. Phytoplankton living in the upper 100 meters of the water column take carbon out of solution, and when they die, they sink to the bottom, carrying the carbon with them. Photosynthesis and decay essentially pump carbon from the surface into the deep ocean. Without this biological process, the carbon dioxide in the deep sea would begin to rise to the surface and enter the atmosphere, potentially doubling or tripling the level of carbon dioxide in the atmosphere within only a few centuries. Human activities that reduce the effectiveness of this process could therefore contribute further to global climate change (12).


Population growth affects the health of the world's oceans via complex pathways. A multitude of factors which interact with one another appear to be contributing to degradation of marine ecosystems and loss of biodiversity. There is much scientists still need to learn about the causes and effects at work, and what can be done to reverse damage which has already occurred. Human population contributes to the amount and frequency of activities which may have long-term negative effects on the marine environment, and drives ever-increasing pressure on the Earth's finite resources.

Many scientists worry that changes in ocean ecosystems brought about by overexploitation, physical alteration, pollution, introduction of alien species, and global climate change, are outpacing efforts even to study them, let alone ameliorate their effects. The concern within the scientific community that the oceans are in trouble has led more than 1000 marine scientists and conservation biologists to sign the Troubled Waters Statement (9). The statement, a project of the Marine Conservation Biology Institute, was developed to demonstrate to policy makers and the general public that there is a strong scientific basis for concerns about the health of the oceans, and that those who are in the best position to know objectively what the facts are believe the oceans are in trouble.

Although population plays a role in the problems discussed here, it may be the factor least amenable to change in the short term. While efforts to slow or reverse population growth through political and social change are essential, the impact humans are currently having on the oceans can be addressed in other ways. Steps that can be taken to slow the effects of human activities on marine systems include:

  • Policies to support sustainable taking of living resources and to discourage unsustainable practices.

  • Policies and new methods to limit pollution.

  • Creation and management of marine protected areas.

  • Communication to facilitate understanding of how preserving the health of the oceans is in humankind's best interests.

  • Development of an ocean ethic which emphasizes long-term health and benefit to humankind over short-term profits.

Even if all of these are effectively implemented, however, the problem of overpopulation will remain, and will continue to be reflected in human effects on marine life and systems.

Recommended Reading

1. American Association for the Advancement of Science, 1997: Science Magazine, Vol 277 (magazine issue devoted to human dominated ecosystems).

2. American Oceans Campaign, 1997: Fisheries in Decline. Internet: http://www.americanoceans.org/issues/fshrs.htm

3. Earle, S. A., 1995: Sea Change: A Message of the Oceans. New York: G.P. Putnam's Sons.

4. Gray's Reef and Stellwagen Bank National Marine Sanctuaries, 1996: The Northern Right Whale: From Whaling to Watching. Savannah, GA: National Oceanic and Atmospheric Administration.

5. Hinrichson, D., 1996. Coasts in Crisis. Issues in Science and Technology, Summer, 1996, pp. 39-47.

6. Jackson, D. Z., 1997. A fish story that's dead serious. August 15, 1997, The Boston Globe.

7. Linden, Eugene, 1993: Megacities. January 11, 1993, Time, pp. 28-38.

8. Marine Conservation Biology Institute, 1996. Bottom Trawling: The Unseen Worldwide Plowing of the Seabed. Internet: http:www.mcbi.org/emerg.html

9. Marine Conservation Biology Institute, 1997. Troubled Waters: A Call for Action. Internet: http:www.mcbi.org/trouble1.html

10. Mooney-Seus, M. L. & Stone, G. S., 1996: The Forgotten Giants. Joint publication of the New England Aquarium and the Ocean Wildlife Campaign.

11. Miller, M.C. & Cogan, J. Eds., 1996: Coastal Zone 97: The Next 25 Years. Washington D.C.: Coastal Zone 97.

12. Norse, E. A., Ed., 1993: Global Marine Biological Diversity: A Strategy for Building Conservation into Decision Making. Washington D.C.: Island Press.

13. The Oceanography Society, 1996: Oceanography: Serving Ocean Science and its Applications Vol 9, No 1(magazine issue devoted to marine biodiveristy).

14. Population & Environment Program: Population Action International, 1995: Catching the Limit: Population and the Decline of Fisheries (informational poster). Washington D.C.: Population Action International.

15. President's Council on Environmental Quality, 1990: Environmental Quality 1970-1995: Twenty-Fifth Annual Report. Washington D.C.: President's Council on Environmental Quality.

16. President's Council on Sustainable Development, 1996: Sustainable America: A new Consensus. Washington D.C.: The President's Council on Sustainable Development.

17. Safina, C., 1998: Song for the Blue Ocean. New York: Henry Holt & Company.

18. Starr, C., 1997: Fish dying out, expert warns. August 28, 1997, The Cincinnati Post.

19. Stevens, W. K., 1994: Feeding a Booming Population Without Destroying the Planet. April 5, 1994, New York Times.

20. World Resources Institute, 1993: World Resources: A guide to the Global Environment. New York: Oxford University Press.

21. World Resources Institute, 1997: Marine Fishing Trends: Troubled Waters Ahead. Internet: http://www.wri.org/wri/wr-96-97/wa_txt2.html

22. World Resources Institute, 1997: Marine Biodiversity. Internet: http://www.wri.org/wri/wr-96-97/bi_txt4.html

23. World Resources Institute, 1997: Pressures on Marine Biodiversity. Internet: http://www.wri.org/wri/wr-96-97/bi_txt5.html

24. World Resources Institute, 1997: Threats to Coastal Ecosystems. Internet: http://www.wri.org/wri/wr-96-97/bi_txt3.html

Other References

a) Personal Communication, Alyson Simmons, Educational Program Director, Florida Keys National Marine Sanctuary

b) Personal Communication, Dr. Sylvia A. Earle, CEO, Deep Ocean Exploration & Research

c) Personal Communication, Dr. Elliott Norse, President, Marine Conservation Biology Institute

d) The Ocean Report, a SeaWeb project of the Pew Charitable Trusts. National Public Radio broadcasts of 4/16/97 and 7/8/97.

Definitions of Selected Terms

Anthropogenic: Caused by humans, whether intentionally or unintentionally.

Aquaculture: The farming of marine organisms for human use.

Biocontrols: Use of a living organism, whether plant, animal, or microorganism to control the population of an undesired species.

Biodiversity: The variety of different species in an ecosystem, genetic variation within a population of a species, and variety of kinds of ecosystems. Greater biodiversity makes species and systems more resilient, while loss of biodiversity weakens them, making them more vulnerable to extinction.

Biosphere: All of the combined regions of the planet which support self-sustaining ecosystems. The biosphere extends above and below the surface of the Earth, wherever there are living ecosystems.

Bottom Trawling: A fishing technique involving dragging heavy nets across the sea floor to catch bottom-dwelling fish. Results in severe changes to the sea floor, a high rate of bycatch, and loss of biodiversity.

Bycatch: Living organisms caught and/or killed by fishermen which are not what they intended to catch. Bycatch includes other species of fish or shellfish, marine mammals, birds, turtles, and specimens of the target species which are below the legal size or otherwise prohibited.

Coastal Zone: The area of land within 100 km the ocean and the area of ocean near the land. Coastal waters support critical habitat and nurseries for a vast number of important marine species.

Continental Shelf: A relatively shallow, submerged portion of a continent, extending to a point of steep descent to the ocean floor.

Coral Reef: A marine ridge or mound comprised primarily of coral, together with algal and mineral components, which forms the foundation for a biologically rich and diverse ecosystem.

Critical Habitat: Living areas that are crucial for a species' survival based upon their unique needs. Some species are less able to adapt than others to changes in their habitat, and thus more vulnerable to the effects of human activity.

Dinoflagellate: Microscopic marine organisms which have whirling whiplike appendages, and which form one of the chief constituents of plankton.

Dredging: Digging up the sea floor for such purposes as extending beaches or making harbors deeper.

Ecosystem: An ecological community, including the biological inhabitants, and the environment in which they live, and encompassing the interactions among them which permit the system to function and to sustain life.

Estuary: The area where a river meets the ocean, which may be a widening of the river where its current is met by the tides, or an arm of the sea which extends inland.

Genetic Diversity: The total number of genes for a given breeding population makes up its gene pool. A large gene pool is genetically diverse, and therefore more likely to be healthy and robust.

Greenhouse Gasses: Certain gases, such as carbon dioxide, which serve to hold heat in closer to the Earth's surface. Without any greenhouse gases, the Earth's surface would be about 33 degrees centigrade colder than it is. However, with an increase in greenhouse gases in the atmosphere, the temperatures increase.

Mangrove Forest: Dense coastal thickets of tropical evergreen trees and shrubs of the genus Rhizophora, or Avicennia, or similar species, which grow along tidal shores throughout tropical regions of the world, and which provide the foundation for a biologically diverse and ecologically important ecosystem.

Phytoplankton: Minute floating aquatic plants.

Sustainable/Unsustainable: When an activity can be done indefinitely without any increase in it's effects, it can be considered sustainable. If the activity is done at a rate or level which is faster or greater than nature's capacity to recover from it, the activity is unsustainable. Unsustainable practices are like squandering the capital in your savings account instead of living on the interest and keeping the capital intact, killing the proverbial "goose that laid the golden egg."

National Council for Science and the Environment
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