ABSTRACT
Introduction Any one location offshore generally presents relatively little change in its physical and chemical conditions over a short time-scale. The same cannot be said of near-shore waters, estuaries, and coastal lagoons, which provide some of the more varied and unstable environments on Earth. The organisms inhabiting such areas may experience wave action to differing degrees, tidal change, salinity, temperature, and oxygen variations, high sediment loads, and tidal currents of varying velocities on a daily or seasonal basis. Locations such as saltmarsh pools (Figure 16.1), estuarine creeks (Figure 16.2), and shallow sloping beaches (Figure 16.3), can experience quite wide ranges in one or more of their physical characteristics. Tidal progression (Figure 16.4) may further compound the difficulties for colonisers by imposing rapidity in the changes of factors such as salinity and temperature. Add to
Figure 16.1 Estuarine raised marsh on the River Test, Hampshire, England, showing tidal creeks and saline pools. The creeks experience substantial salinity variation during the tidal cycle, while the pools are exposed to sudden changes when the surrounding grass is submerged on high spring tides.
