Tidal Flats

A tidal flat is a broad and flat land caused by the rising tide and exposed at its ebb. They can be divided into sand flat and mud flat based on the components of sediments, and into the coastal tidal flat and the estuary tidal flat based on the location. The components of sediments are decided by the physical characteristics of individual area, and subsequently, greatly influence both the biological diversity and productivity of the habitat. The bottom of a sand flat consists of sands of average size 0.2~0.7mm. The average sand flat width is 1 km, usually forming where the seawater flows quickly. The content of the organic matter is only 1% to 2%. In contrast, a mud flat is formed where the stream of the seawater is gentle. The width of a mud flat averages over 5 km and is composed of particles of the average diameter of 0.031mm. This tightly compacted sediment makes it harder for the seawater with oxygen and food to penetrate the flat. Tidal wetlands are one of the most productive ecosystems known. They produce large amounts of plant material, which are broken down into detritus by the myriad of animals and micro-organisms which live in the sediments of wetlands.

Subsequently, the creatures of the mud flat, such as crabs, snails and clams, make the seawater flow in by making holes and pipes. Bacteria, also abundant in the mud, play and essential role in the mud flat ecosystem, decomposing dead plant and animals and making nutrient-rich detritus. A tremendous number of burrowing animals exploit this productive food source. Most are deposit-feeding worms that swallow the sediments, digest the edible material and excrete the indigestible mud and sand. The mud protects them from would-be predators stalking the waters above, and also buffers them from changes in both temperature and water conditions that occur during the daily tidal changes. These and other creatures of the tidal flat, in turn, serve as the food base for predatory animals, primarily fishes and birds. Seasonally, many tidal flats serve as essential stopovers for migrating birds to rest, feed and breed.

Tidal flats additionally play a role in purifying pollutants discharged from the land into the sea, through the assimilation of excess nutrients and the removal of impurities such as heavy metals. All the creatures living in the tidal flat are involved in this purification process either directly or indirectly. Thus, the greater the biological diversity of the tidal flat habitat, the greater the stability of the ecosystem and the greater the potential service provided.