THE CAUSES OF OCEAN CHANGE
1. Chemical pollution and marine debris
The dumping or discharge of oil, nuclear waste, plastics and other debris, and a vast
variety of chemical contaminants causes a wide range of impacts. For example,
contaminants directly poison marine life or cause chronic disease, reproductive failure, or
deformities. The sources of marine pollution include commercial, military and
recreational shipping and boating; run-off from urban streets and agricultural fields; oil
drilling installations; and industries and sewage treatment plants.
Destructive or non-existent fisheries policies and the development of oversized, overcapitalized,
over-mechanized and highly subsidized fleets have led to the depletion of
numerous fish populations and the collapse of various fisheries. Many commercial
fisheries are also responsible for adverse impacts on non-target species and on marine
habitats. The incidental catch and mortality of marine mammals, seabirds, sea turtles and
unwanted fish species or age-groups by various fishery-types, and the destruction of
habitat and benthic communities by bottom-dragging fishing gear, are altering food
chains and sea-life communities.
3. Nutrient pollution
The discharge or release of nutrients and other substances - for example, in human wastes
in sewage; in fertilizers and animal waste from farm runoff; and in air emissions from
coal- and oil-burning electric utilities, industries and gas-burning vehicles - is polluting
coastal waters with excess nutrients. Effects include oxygen depletion of near shore
waters, promotion of harmful algal blooms, and dramatic reductions in the richness of
sea-life communities in affected environments.
4. Coastal development
Urbanization, road construction, port and marina activities, boating, dredging and
dumping; mining; and coastal agriculture, forestry, and aquaculture, among other
activities, continue to reduce, fragment, or degrade coastal habitats and cause reductions
in plant and wildlife populations and local and regional extinctions of species.
5. Exotic species introductions
The introduction of exotic species and their pathogens, often inadvertently, is causing the
disruption of natural systems on a global scale. The major cause of marine environment
introductions is the transport and subsequent discharge of species via ships ballast water
into environments where they did not previously occur. Other vectors include those
aquaculture practices where exotic species are purposefully introduced or can escape into
local waters. Introduced or exotic species can prey on or outcompete native species and
have caused fundamental and irreversible alterations in natural communities.
6. Damming rivers
The damming or diversion of rivers for power generation, flood control or irrigation
purposes has resulted in, among other things, significant reductions and/or changes in the
timing of freshwater flow to the sea, reduced sediment flow into deltas and wetlands, and
obliteration of fish spawning habitat. Impacts have been widespread and include fisheries
reductions, loss of biodiversity, increased concentrations of pollutants, the salinization
and subsidence of surrounding coastal lowlands, and the overall alteration of estuaries.
7. Destruction of the ozone layer
The human-induced reduction in the stratospheric ozone layer has allowed increased
ultraviolet-B radiation to reach the earth's surface. It has been shown that this radiation
can seriously affect human health and damages or kills fish eggs and larvae and tiny
planktonic animals and plants which live in the surface waters of the ocean.
8. Global climate change
Human-induced global climate change -- with concomitant sea-level rise, increased air
and water temperatures, and changes in precipitation patterns -- is predicted to alter
coastal and oceanic environments through a variety of direct and indirect impacts.