Much of present-day coastal infrastructure offers perspectives not only to protect the coast, but also to create suitable habitats for certain ecosystems. This can be beneficial, as natural ecosystems can contribute significantly to coastal protection and provide other services. Moreover, most ecosystems, as opposed to traditional hard structures, are able to adapt to (relative) sea-level rise. ‘Ecosystem engineers’, i.e. species that influence their own habitat, form complex structures in the subtidal and intertidal zone and can provide sustainable shoreline or shoal edge protection. To successfully include ecosystem engineers in coastal protection, certain requirements have to be met for establishment and sustainable growth. Examples are requirements on hydrodynamic conditions, water quality, soil characteristics, light availability, etc., but also biological preconditions (e.g. connectivity to other or similar ecosystems). Parts of these requirements can be engineered or fostered through human intervention, while others cannot.
Ecosystem engineers are organisms (plants or animals) whose presence or activity alters its physical surroundings or changes the flow of resources, thereby creating or modifying habitats and influencing all associated species (Jones et al. 1994, 1997). Many ecosystems are greatly affected by ecosystem engineering species. Given the highly physical nature of the estuarine and coastal environment, organisms that affect the physical structure of these ecosystems can have significant influences on functions and services (e.g., Barbier et al. 2011). A diversity of organisms physically engineer estuarine and coastal ecosystems, including salt marshes, willow tidal forests, mangroves, seagrass beds, coral reefs and bivalve reefs, kelps.
There is growing recognition that the ecosystem engineering concept can contribute to ecological applications such as restoration and ecosystem management (Byers, Cuddington et al. 2006; Crain and Bertness, 2006). In recent years the interest in using them in coastal defense has grown. Especially the ecosystem engineering properties of reducing wave energy and trapping sediments make species such as reef building bivalves, mangroves and salt marsh plants interesting target species. All these species have in common that they can alter an otherwise bare soft sediment environment into a complex, three-dimensional structure. These structures influence abiotic conditions and interact with kinetic energy and materials within the abiotic environment, e.g. alter tidal flows, attenuate wave action and trap sediments. As a consequence, the abiotic change induced by an ecosystem engineer will cause biological change. The challenge is to determine how, when, where, and which organisms engineer habitats with important outcomes for ecosystem and community processes.
It is believed that the use of ecosystem engineers in coastal management can contribute to a more sustainable, cost-effective way of protecting our coasts, especially in the light of climate change and sea level rise. Secondly, there is also a need for methods of coastal protection that incorporates the natural dynamics and processes of the ecosystem, allowing a more resilient and robust future coastline (Day, Psuty et al. 2000). Only in this way many ecosystem services coastal habitats in general and ecosystem engineers in particular provide can be safeguarded.
Ecosystem engineers can be used to stabilize and protect shorelines and intertidal habitats against erosion and to minimize wave attack on the coast (e.g. Borsje et al. 2011). Furthermore. ecosystem engineers can induce positive facilitation cascades in which a certain engineer (e.g. an oyster reef) can have positive effects on the growing and survival conditions of another ecosystem engineer (e.g. sea grass). Also ecosystem engineers possibly can help to extend sustainability (i.e. lifetime) of sand nourishment sites by reducing erosion of the nourished sediment. By creating the right preconditions for settlement and growth a specific ecosystem engineer can develop and persist over time. The additional advantage is that several of these structural ecosystem engineers that inhabit intertidal habitats can grow to keep up with sea level rise (e.g. salt marshes).
Shellfish reefs can change the near-bed flow and
dissipate wave energy on intertidal flats, therebyinfluencing sediment transport, erosion and deposition.
Mangrove forests that dissipate wave energy
in the intertidal zone and influence erosion
Coral reefs can acts as natural shoreline protection,
but the health of coral communities depend on a
range of highly-linked environmental variables.
|Habitat requirements for seagrass||Habitat requirements for salt marshes|
Seagrass meadows that change the near-bed flow
and dissipate wave energy in shallow water, thereby
influencing sediment transport, erosion and deposition.
Salt marshes form natural barriers for coastal
defence due to wave reduction and can adapt
to sea level rise.