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.


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.



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.