Population and Environment Linkages: Oceans

by Gale Mead Hey

[In-Depth Introduction also available]

The effects of human activity on marine ecosystems and life have become increasingly apparent in recent decades. The ways in which humans have affected the world's oceans include:

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 are described in detail in Troubled Waters, a statement signed by over 1,600 marine scientists and conservation biologists from 65 countries. For the purposes of this discussion, the question to be addressed is how human population contributes to these sources of ecological harm.

Population plays a role in direct physical alteration of ocean environments in terms of global population growth, but more importantly because 66% of the world's 5.8 billion humans live within 100 km of the ocean, and populations in coastal zones are increasing at a much faster rate than overall population growth. As more coastal areas are developed for human habitation, critical habitat and breeding grounds for marine species is degraded or destroyed. Dams, sea walls, golf courses, shrimp farms, homes, and shopping malls alter the ecology of coastal zones. Another form of physical alteration is bottom trawling, a fishing method with effects comparable to clear-cutting of forests. As discussed below, population growth fuels demand for seafood, including those species which are obtained by bottom trawling.

Overexploitation of marine resources includes commercial fishing, extraction of mineral resources, and exploitation of marine mammals. Demand for these resources is driven in part by cultural, economic, and political forces, but also by increased population. At the most basic level, it takes more resources to meet the needs of six billion people than to meet the needs of one billion. Humans currently consume 13 kg of fish per capita each year. Fish protein currently constitutes 19% of humans' animal protein intake, and the FAO predicts that as population increases, demand for seafood will increase accordingly. The FAO has stated that virtually all of the world's commercial fisheries are either overexploited or fully exploited.

Pollution of ocean environments is both direct and indirect. It is estimated that the runoff from 90% of the Earth's land mass ultimately makes its way into the ocean, including fertilizers, pesticides, herbicides, heavy metals, and sewage. Air pollution is eventually carried into the ocean with rain and snow, and marine waters are polluted directly via oil spills, ocean dumping, and release of sewage. While the contributing factors are diverse and complex, population growth plays a significant role. It would be too simplistic to state "more people equals more pollution," but the extent of the damage caused by marine pollution is largely a problem of scale brought about by the fact that there are 5.8 billion of us.

Introduction of alien species occurs when species from one part of the world are transported into a new environment, where their natural competitors, parasites, and predators do not exist. Most marine alien species are introduced by being sucked up into ships' ballast tanks, then expelled when the tanks are emptied, in distant waters. The relationship to population is that population growth has contributed to 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.

Global climate change is now acknowledged to be a significant problem, caused at least in part by human activities. As the world's human population has increased, so has use of fossil fuels and other pollutants which contribute to global climate change. While significant climate changes have occurred naturally throughout the Earth's history, humans' activities are accelerating the rate at which climate change is now occurring. Species and ecosystems which may be capable of adapting to slow climate change may be unable to adapt quickly enough to survive.

The relationship between human population and the negative effects of human activities on the oceans is largely a matter of scale. Marine ecosystems are capable of surviving a limited amount of fishing, pollution, and habitat destruction, but there is increasing documentation that they cannot sustain the amount of pressure currently being placed on them. Human activities are continuing to cause changes so quickly that scientists are hard-pressed even to study them, let alone ameliorate their effects.

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