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What Is This Indicator, and Why Is It Important?
This indicator describes the condition of worms, clams, snails,
and shrimplike animals in bottom sediments (“benthic
communities”) by reporting the percentage of area in
which these communities are in “undegraded,” “moderate,”
and “degraded” condition. The indicator is calculated
by comparing the number and kinds of animals found in a sampling
site with those that would be expected in an undisturbed area
of similar character (a reference site). The indicator would
be reported for estuaries and for ocean areas within 25 miles
of the coast. Benthic communities reflect the influence of
contaminants, oxygen levels, physical changes in habitat (such
as from trawling), and shifts in temperature or salinity.
They are a good indicator because contaminants accumulate
in bottom sediments and hypoxia (lack of oxygen) is most severe
there. Also, these animals live several years, so their response
reflects exposure to these stresses over a long period, and
they are fairly immobile, so their condition strongly reflects
conditions at the site where they were collected (see the
depleted oxygen and sediment
contamination indicators).
Why Can't This Entire Indicator Be Reported at This
Time? Data are not
available from
estuaries in Alaska
or Hawaii. Only limited data are available
for ocean waters out to 25 miles.
What Do the Data Show? For the 1999-2000
time period, about three-fourths of the estuary area on the
Atlantic and Pacific coasts was “undegraded”. About
half the estuary area in the Gulf of Mexico and about one-third
of the estuary area in Puerto Rico (not shown in graphs)
were “undegraded”. About a quarter of the estuary
area in the North and Mid-Atlantic regions and a third of
the estuary area in Puerto Rico was “degraded”,
whereas in other regions, only about 10-20% was degraded.
Changes from 1990-1997 to the 1999-2000 time period, other
than those caused by reclassification of Mid-Atlantic data
that had been identified as "moderate", were not dramatic.
Trends, if any, will become apparent only as additional data
are collected in the future.
Discussion “Undegraded” means
that the benthic animals found at a site are similar in number
and type of species to those expected in an undisturbed site
in that region. “Degraded” means that the animals
found are quite different from those at a reference site,
reflecting one or more negative influences.
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