The ocean has long been thought to have both a limitless bounty and ability to absorb human impacts. Its sheer volume supported the observation that "dilution is the solution" to point-source pollution, as tides and currents removed almost anything that entered the sea. However, increased pressures on the marine environment resulting from increases in human population, industry, and agriculture have led to concern that the ocean's health is being negatively affected by human activities.
The ability of scientists to monitor the ocean's health is hindered by the ocean's complexity. Although the basic chemistry of sea water has been stable for millions of years, components that directly affect plant and animal life (e.g., nutrients and dissolved oxygen) and the living populations themselves vary naturally due to interactions between oceanic and atmospheric processes. Evaluating the health of the oceans therefore requires that human impacts must be distinguished from a natural, changing background.
Methods for evaluating the ocean's health include estimates of commercial fishery stocks (populations) and localized studies of plant and animal species (including estimates of estuarine productivity and coral bleaching). Impacts from contaminants and adverse water quality ideally are monitored through long-term baseline studies. In the United States, this approach has been followed by the National Oceanic and Atmospheric Administration's Mussel Watch program, for example, that focuses on organic and inorganic contaminants in mussels and oysters in U.S. coastal waters. The success of this approach has led to similar studies on an international scale.
Historical trends of contaminant input have been evaluated through "dated core" programs in which contaminants are measured in marine sediment layers and compared with estimates of when they were deposited. Larger spatial scales are evaluated by remote sensing to measure such variables as temperature, plankton populations, and sediment load of surface waters.
At present, pollution, habitat alteration, and overfishing are considered the primary threats to the ocean's health. Pollutants includes chemicals (including compounds that may affect animal development during sensitive life stages), sewage, floating debris such as plastic and trash, and nutrient elements (nitrogen and phosphorus) that are largely released to coastal areas either directly, via rivers, or via the atmosphere.
Ocean margins are impacted almost everywhere by alteration or destruction of critical habitat. These changes include erosion and loss of salt marshes; drainage of wetlands; siltation of estuarine areas after deforestation and erosion; alteration of fresh-water inputs; and restriction of fish migration routes by dams. Dredging, boating, and pressure from tourism have affected coral reefs.
Overfishing target species (e.g., whales, sharks) and the accidental removal of nontarget species (as bycatch) have damaged overall ocean health. Many fishery stocks (populations) have declined dramatically as a result of overfishing, and the annual catch has remained high only as a result of switching to new target species. At present, the seventeen major ocean fishery areas are fished to capacity, overfished, or depleted.
In the future, although human population and development in coastal areas will continue to expand, releases of chemical contaminants and nutrients will continue to be regulated in developed countries. Lessons learned in developed countries will assist developing nations in improving their economies and infrastructure while preserving their natural environments.
Unfortunately, the popularity of coastal areas and their importance in trade will exert continued pressure on habitat. Difficult policy decisions will be required if habitat is to be conserved or restored to earlier conditions. Similarly, the dependence of expanding human populations on fisheries as protein sources, particularly in developing countries, coupled with the cultural importance of fishing as a lifestyle, will continue.
Economic considerations may ultimately provide the impetus for conserving and improving marine environmental conditions. Increasing costs per unit catch will ultimately restrict the expansion of fishing, especially if government subsidies are reconsidered. Appreciation of the economic importance of ocean-based tourism and coastal habitat for renewing valuable living resources will provide additional incentives to maintaining ocean health.
SEE ALSO Coastal Ocean ; Coastal Waters Management ; Corals and Coral Reefs ; Erosion and Sedimentation ; Estuaries ; Fisheries, Marine: Management and Policy ; Pollution of the Ocean by Plastic and Trash ; Pollution of the Ocean by Sewage, Nutrients, AND Chemicals ; Pollution Sources: Point and Nonpoint ; Salmon Decline and Recovery .
Robert J. Taylor
Thurman, Harold V., and Elizabeth A. Burton. Introductory Oceanography, 9th ed. Upper Saddle River, NJ: Prentice Hall, 2001.
"Chemical Contaminants in Oysters and Mussels." State of the Coastal Environment. National Oceanic and Atmospheric Administration. <http://state-of-coast.noaa.gov/bulletins/html/ccom_05/ccom.html> .
Global Coral Reef Monitoring Network. National Oceanic and Atmospheric Administration. <http://coral.aoml.noaa.gov/gcrmn/> .