Ecological effects of coastal armouring

The coastal zone has long been the focal point of major human settlements and, in Australia supports approximately 85% of the population. Coastal settlements are increasingly under threat from sea-level rise and storm surge... [ view full abstract ]

The coastal zone has long been the focal point of major human settlements and, in Australia supports approximately 85% of the population. Coastal settlements are increasingly under threat from sea-level rise and storm surge and coastal structures, such as seawalls, are being used to protect property, infrastructure and public amenity of the coastal zone. Seawalls, which are static structures that impede natural migration of the shoreline, produce a number of physico-chemical and morphological changes to the coastal environment.

Most studies have focused on the habitat seawalls provide to fouling organisms, and how their design may be modified to enhance the extent to which their habitat mimics that of natural rocky shores. Nevertheless, seawalls built in sedimentary environments can also modify sediment-dwelling organisms through direct and indirect effects. Seawalls may act as barriers to the transfer of materials between the land and sea and disrupt replenishment of the coastline by restricting the natural movement of sediments and organic material. Seawalls can reduce intertidal area and therefore beach and foraging area for shorebirds and other coastal predators. They may also shade adjacent sediments and through altering patterns of reflection change sediment grain size.

The ecological effects of seawalls may be tempered by the habitat to which the seawall is introduced, characteristics of the local environment, the tidal elevation of seawall placement, and small-scale morphological features of the seawall. However, there are relatively few comparative studies examining how environmental context influences seawall impacts.

This study investigates ecological consequences of seawalls constructed in sedimentary environments, at wave-exposed and sheltered estuarine locations. At five sites within Brisbane Waters, NSW, Australia, three wave-exposed and two sheltered locations, benthic invertebrates, sediment characteristics, and substrate cover are compared between adjacent stretches of shoreline with and without seawalls. By understanding the ecological consequences of seawalls in different environments, better management practices can emerge leading to more sustainable development and maintenance of local biodiversity. This will assist developers and managers in their efforts to maintain ecosystem services when planning for future population growth.