Differences in physical properties of revetments determine various abiotic factors that influence settlement rates of aquatic species communities and their diversity. Physical properties of revetments can be observed in small scale (mm-dm) and large scale (dm-hm and hm-km). Examples of small scale physical properties are: used building materials, water retention capacity, substrate color, surface roughness, presence of small pools and pits and, if applicable, toxicity (caused by heavy metals and leaching).Large scale physical property examples are: the size of available substrate such as tiles, boulders and columns, their sorting (one uniform size or varied sizes), spatial orientation, the size of stone clusters and distance between them.
Small scale surface roughness (mm-cm scale)
Based on experimental setup rich revetment studies, revetment surface roughness determines the number of possible microhabitats and species richness. Increasing roughness of a concrete substrate on a mm scale has a positive effect on the colonization and settlement rate of seaweed, mussels and other sessile organisms. Significant organisms for sustaining biodiversity are mussels and bladder wrack (Fucus vesiculosus) as they create structures on the hard substrate, that provide food and shelter for small macrofaunal species, for instance, amphipods. These small prey species form the bulk of fish and shorebird diet.
However, while surface roughness in a mm scale does influence initial settlement of species, it does not determine the long-term development of the seaweed and macrofauna communities or their climax state. In a long-term scale (months/years) both rough and smooth surfaces exhibit mostly similar coverage and density of organisms. Case in point, while green seaweeds and acorn shell barnacles (Sessilia) favor rough substrate for settlement, in time they can be found on all concrete structures.
Small surface structures (cm-dm scale)
When observed on a cm to dm scale surface structures, such as small pools, holes and crevices, increase the survival rate of bladder wrack and periwinkles (Littorinidae), aid the settlement and survival of mussels, and create and increase in overall species richness. Bladder wrack, which prefers sheltered, mid-intertidal areas, also can benefit from revetments with a lava eco-topping. Such eco-topping not only provides additional surface roughness, but also retains water during low tide. It helps to retain the density of bladder wrack cover even after the summer season. Mussels, on the other hand, grow best in horizontal crevices situated in the low intertidal zone. Elastocoast covering provides porous surface on which mussel mats are able to form. While there are concerns, that the relatively smooth surface of Elastocoast would be detrimental to algae settlement, laboratory experiments suggest that Elastocoast does not hinder their colonization (Lock, 2009). However, Elastocoast has a reduced wave runup and may decrease the surface area of intertidal habitats. Effects such as these, could be mitigated by reducing the gradient of a revetment’s slope.
Increase of surface roughness on a cm-dm scale may also lead to enhanced colonization rates and greater species richness. Several international studies provide evidence of such interactions. For instance, organisms that especially benefit from small pools, holes and crevices include: algae, ascidians, barnacles, bivalves, hydroids, anemones, shrimps, annelids, crabs, ctenophores, sponges and gastropods (Firth et al., unpublished). In a larger (dm-m) scale, holes, pools and ditches may provide additional habitat for anemones, tunicates and sponges.
Add figures, references???
References missing from text
Add references to experimental cases
Referenties
- Ecological research Elastocoast - Dutch pilot locations Petten and the Zuidbout, M. Lock, 1 september 2009.
Zie ook
- The colonization by seaweed and fauna of different revetment types at Sint-Annaland, Tholen; RAAK-PRO Building for Nature final report
- Ecological potential of mastic asphalt for rich revetments
- Oesterdam sand nourishment - ecological and morphological development of a local sand nourishment
- Abiotic factors
- On the relationship between dike revetments and ecology: lessons learned for design and follow-up monitoring for asphalt covered locations
- Building with Nature; from concepts to practice
- Early colonization of algal communities on polyurethane bonded aggregate: a field and laboratory study
- Properties habitat
- Ecosystem recovery after hypoxia: what can foraminifera indicate?
- The Benthic Ecosystem Quality Index (BEQI), intercalibration and assessment of Dutch coastal and transitional waters for the Water Framework Directive. Final report
