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Review the indicators
at a glance
- How much of the nation’s shoreline is composed of beach,
sand or mudflats, steep cliffs, wetlands and mangroves, and how
much has bulkheads or riprap? More than two-thirds of the
37,000 miles of shoreline mapped to date is coastal wetlands,
most of which are in the South Atlantic region. Sixteen percent,
or 6,000 miles, is beach. Steep shorelines and mud and sand flats
each make up about 8% of the total, and armored shorelines account
for about 11%. (Some areas, such as sandy beaches backed by steep
cliffs, may be counted twice.) These data are for the Pacific
and South Atlantic coasts; data for other regions have not yet
been analyzed.
Chemical and Physical Condition
Four quite varied indicators describe the chemical and physical
condition of the nation’s coasts and oceans. Oxygen and temperature
are two key determinants of the kinds of marine plants and animals
that can inhabit a region. Thus, we track the area of coastal waters
with abnormally low oxygen levels and changes in regional sea surface
temperature. Chemical contamination is also of concern, so we track
changes in harmful man-made chemicals that can accumulate in bottom
sediments. The fourth indicator will track the percentage of the
nation’s shoreline that is eroding.
- How extensive are areas with low dissolved oxygen levels?
Low-oxygen (hypoxic) and no-oxygen (anoxic) conditions can cause
mass mortalities among aquatic animals and disrupt migration patterns.
Data are not adequate to report on the extent of these areas.
- How contaminated are bottom sediments in estuaries and coastal
ocean waters? About 42% of the Nation's estuarty area
has levels of contaminants that might harm fish or
wildlife, and 7% has levels that probably will harm these
organisms. Neither trend data nor data on other regions are
available. Because previous data had significant gaps, it
is not possible to discern trends.
- How much of the nation’s coastline is eroding? Erosion
can damage coastal properties and decrease the recreational value
of beaches. Data are not adequate for national reporting on erosion
and the opposite process, accretion, for the U.S. coastline.
- What is the temperature of the ocean’s surface? Plants
and animals are accustomed to certain water temperature ranges,
and changes in temperature may cause species to disappear (or
appear) in certain areas. Data for a 14-year period show neither
warming nor cooling trends for waters within 25 miles of the U.S.
coast.
Biological Components
Six indicators describe biological conditions within coastal waters.
As in other ecosystems, one indicator tracks species that are at
risk of extinction. Another records unusual “mortality events”
among such marine animals as whales, sea turtles, seabirds, and
fish, and a third considers the condition of worms, snails, and
other bottom-dwelling animals. Three indicators, two still under
development, focus on undesirable species or conditions. One of
the indicators that needs further development would track the “blooms”
of several toxic algae harmful to people or marine animals; the
other would report on invasions of non-native species that can supplant
more desirable natives. The last of the indicators measures the
concentration of chlorophyll in coastal waters—chlorophyll
is a measure of the presence of algae, which in excess can be harmful
to fish and other animals and plants and interfere with swimming
and other recreation.
- How many native marine species are at different levels of
risk of extinction? The nation’s coastal waters are home
to a staggering diversity of plants and animals, from microscopic
organisms to the world’s largest animals. However, we know
the status of only a very few of these species; data are not adequate
for national reporting on marine species at risk of extinction.
- What is the extent of invasion by non-native species?
More work is needed to develop this indicator, which will consider
both the number of non-native species and what fraction of available
habitat they occupy.
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