Living in Tidal Sediments

Abstract

Tidal flats are subject to the extremes of terrestrial climate: heating, frost, desiccation, and rain. Day and night differences and seasonal fluctuations are more pronounced than in the adjacent subtidal zone. Arid climates cause more extreme low tide conditions than do humid climates. Diurnal tides are likely to impose more stress than semi-diurnal tides. The chemical properties of the sediment change with each tidal cycle (Fig. 3.2). However, tidal flats are not semi-terrestrial. They remain primarily a marine habitat. Most sediments are moist if not saturated with marine interstitial water throughout the low tide periods. Frequently also puddles are present at low tide. It is important to realize that the physical extremes of low tides are predictable and interrupted by the next flood. Organisms only have to adapt to these short-term perturbations. This is in contrast to shallow nontidal lagoons where extremes of temperature, salinity, and water level must be endured for prolonged periods of time. The tidal exchange of water masses may be viewed as a buffer system for the tidal flats. The tides mitigate physical extremes, prevent local deviations of water chemistry, and mediate wide dispersal of tidal flat organisms.