Stressors

Pollution is arguably the greatest stressor on all ecosystems. The U.S. has made great strides over the past three decades in controlling water pollution from what are called “point source discharges,” e.g., those with a clearly discernible source, such as an effluent discharge pipe. More problematic, however, is non-point source pollution. This type of pollution includes runoff from cities, roads and highways, and agricultural fields. Excess nitrogen runoff from agricultural and air pollution emissions continues to place substantial stress on fragile marine ecosystems.

Land and resource use associated with population concentrations and development pressures pose disproportionate risks to the nation’s coastal ecosystems, in part because those areas are among the most heavily populated. Urbanization, dredging, and commercial and residential construction can lead to increased sediment runoff and depleted fish populations, and can damage habitats that are critical to ecosystem vitality.

Invasive species, e.g., plants and animals brought to the U.S. from other countries or those relocated within U.S. borders, can threaten economically and environmentally important native plants and animals. They compete for finite ecosystem resources and change the general community structure.

Climate change and climate variability influence sea level, water temperature and currents, and stratification (layering) of water bodies. These effects, in turn, influence delivery of freshwater, sediments, and pollution to an ecosystem. This can lead to changes in salinity, tidal patterns, erosion, and coastal flooding, rendering coastal ecosystems and communities more susceptible to many adverse impacts.

Extreme natural events, such as hurricanes, algal blooms, coastal storms, floods, and droughts, profoundly affect coastal ecosystems. Storms can cause major geographic changes and lead to increased pollution in coastal ecosystems. The increased frequency, severity, or extent of harmful algal blooms can lead to costly closures of shell fisheries and to curtailed recreational opportunities. Advances in forecasting the effects of these events is helping both emergency responders and planners lessen the costly impacts.