HOW ARE TIDAL FLATS
LINKED
TO OTHER HABITATS?
Tidal
flats are semi-terrestrial habitats that interact with both aquatic and
terrestrial environments. They
occupy the space that salt marshes fill in other areas.
Runoff from upland areas contributes fresh water, detritus, nutrients
and sediment and may be a source of pollutants such as herbicides, pesticides,
fertilizers, industrial wastes and chemical spills. In urban areas, direct discharges of domestic and industrial
wastes can constitute significant nutrient inputs into tidal flat systems.
Most of the sand that forms
tidal flats is carried via the wind from barrier island dunes. Coastal marshes and seagrass habitats contribute nutrients
to tidal flats in the form of detritus and
may provide a source of invertebrates to colonize tidal flats.
The open bay interacts with tidal flats by providing water, nutrients,
and invertebrates and by transporting nutrients and wastes away.
On a hemispheric scale, tidal flats in the Coastal Bend are linked
to northern breeding habitats by the shorebirds that winter in the area.
WHY ARE TIDAL FLATS VALUABLE?
The
primary function of tidal flats is the conversion of plant biomass (usually
in the form of detritus) to animal biomass
that can be used by organisms at higher trophic
levels. The presence
of tidal flats in the mosaic of the coastal
environment is very important to shorebirds and wading birds.
For migrating and wintering shorebirds, the tidal flats of the
Laguna Madre represent the largest continuous expanse of suitable habitat
between northern breeding grounds and more distant wintering grounds in
South America. Most shorebird mortality is thought to be due to a lack of
resources in wintering and migratory staging areas. The invertebrates of the flats provide an abundant food source
for shorebirds. Alternate
feeding sites are available on nearby beaches for shorebirds when flats
are completely flooded. Adjacent
upland and transitional habitats provide areas for nesting and roosting.
Tidal flats are also a source of “new” nitrogen to the ecosystem
since the blue-green algae that comprise the algal mat convert atmospheric
nitrogen into nitrogen that can be used by other plants and much of what
is converted leaks from the flat into surrounding shallow water.
HOW
ARE TIDAL FLATS THREATENED?
The
primary threat to tidal flats is a lack of understanding about their importance.
To most people “wetlands” means marshes not tidal flats.
Most people understand why marshes need to be preserved but are
not easily convinced that tidal flats deserve the same consideration.
Although the plight of the Piping
Plover has helped improve the status of tidal flats, the lack of a
readily understood component like cordgrass as a focal point means that
the value of tidal flats remains difficult to convey to people outside
the circle of scientists and resource agencies involved in their management.
Birders aside, most people just don’t understand why they should
care and this poses a distinct challenge in the conservation and protection
of tidal flats as important natural coastal habitats.
Wind-tidal
flats in Laguna Madre are the most important habitat for wintering
shorebirds at the northernmost extent of most species’ wintering range. The tidal flats in Laguna Madre are being impacted by a
variety of natural and human disturbances, some of which are serious and
long-lasting. Over the last
40 years there have been dramatic reductions in the extent of tidal flats,
largely due to global sea-level rises.
This means that remaining flats may be essential to shorebirds in
general and critical to populations of some species, like Piping Plover. Reduction of serious, long-lasting human disturbances like
commercial or residential development is necessary to ensure the integrity
of this vital habitat.
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