Measuring and managing changes in estuaries and lagoons: morphological and eco-toxicological aspects.

Just like any other ecosystem, coastal and estuarine ecosystems are complex and dynamic in terms of their species structure and functioning. The resilience of the different types of coastal ecosystem to change depends on the structural complexity of the different trophic relationships within the local food web, the connectivity between habitats and larger (eco)system units, and the ecological and biological strategies of the species they contain. There is evidence that changes in living systems may be irreversible and that the course of change is asymmetrical (Scheffer & Carpenter 2003). The path to structural complexity, maturity and climax for coastal systems is assumed to be long and slow, while the reverse is usually faster (Margalef, 1997). In this context, natural perturbations play a role in maintaining spatio-temporal heterogeneity in ecosystems, introducing more or less local and rapid fluctuations, which may either prevent the system from reaching steady state (Scheffer et al. 2003) or stimulate backward steps in the ecological succession, thus maintaining a certain level of youngness in the ecosystem. Transitional waters (TW), including part of the coastal waters, estuaries, coastal lagoons and brackish coastal inland waters, have the added difficulty of being naturally stressed – thanks to their strong spatiotemporal variability – and exposed to frequent environmental disturbances and fluctuations (Barnes, 1980; UNESCO, 1980, 1981; Kjerfve, 1994).