The intersection of human health and the ocean occurs overwhelmingly in the coastal zone. The coastal zone extends from the upland penetration of tidal rivers to the edge of the continental shelf, which can extend 100 miles or more beyond the coast itself. The world's coastlines, including temperate, tropical, and polar coasts, have been estimated to total about 372,000 miles (Smithsonian Institution 2002). The coastal ocean, the most biologically productive part of the marine environment, supports a dazzling level of biological diversity, including coral reefs, marine mammals, and economically important fisheries.
Major portions of marine resources harvested are from the coastal zone. These resources include food as well as material resources used in industrial and biomedical applications. One example of the latter is the production of Limulus amoebocyte lysate, proteins from the blood of horseshoe crabs, used clinically to detect endotoxins in intravenous fluids. The value of all marine ecologic resources and services from the coastal zone has been estimated to be $21 trillion (McGinn 2002).
The recently convened Presidential Ocean Commission (U.S. Commission on Ocean Policy 2002) has received reports that there are serious threats to the coastal environment from coastal population growth, pollution, and over-fishing. Approximately 50% of the world's population lives within 200 km of the coast, and this percentage is expected to increase in the future. This large and growing population affects the coastal ocean in a number of ways, including nutrient loading, toxic contamination, and habitat alteration. Each of these has effects on coastal ecosystems and on the health and economic well-being of human populations living near the coast.
A variety of human activities contribute nitrogen, phosphorus, and other nutrients to the coastal ocean: for example, the agricultural and residential use of fertilizer, the disposal of human and animal waste, and the burning of fossil fuels. These nutrients are carried to the ocean by groundwater and surface water, as well as through atmospheric deposition. Nutrient loading to the coastal ocean has also increased with the loss of wetlands that can intercept and utilize nutrients before they reach the ocean.
In the coastal ocean, nutrients stimulate the growth of phytoplankton or algae, marine plants that form the base of the marine food web. This can have benign or even beneficial effects; it is no coincidence that some of the most productive fisheries in the world are near the mouths of rivers that carry nutrients to the ocean. However, nutrient loading can cause serious problems. Thus, many species of algae produce toxins that threaten both human health and the health of marine organisms. The frequency and geographic distribution of these so-called harmful algal blooms appear to have increased over recent decades, and this increase may be due to increased nutrient-loading.
Excess growth of phytoplankton can also cause clogging of corals and other coastal environments that serve as habitat for fish, seabirds, and other animals. Another serious problem can occur when large quantities of phytoplankton die and sink to the bottom, where they decay through the action of aerobic bacteria. If the quantity of phytoplankton is large, then, under certain oceanographic conditions, oxygen in the bottom waters is depleted leading to environmental hypoxia. In the United States, the best-known hypoxic area is off the coast of Louisiana; this so-called Dead Zone is caused by the discharge of nutrients to the Gulf of Mexico by the Mississippi River. Since its discovery, the Dead Zone has grown to the size of New Jersey. Hypoxia can result in the loss of commercial species and large-scale changes in the biological communities that inhabit the seafloor.
As with nutrients, toxic pollution in the …