Operation and Maintenance
Small adaptations of both texture and structure of concrete constructions within the intertidal zone of the marine environment were found to lead to better settlement and growth conditions for algae and macrobenthos to settle and grow. Thus primary and secondary production is enhanced, without decreasing the safety level of the port. Given the ‘scale-concept’, these small scale adaptations can provide benefits for groynes and revetments as sources of enhanced productivity and habitat diversity on the meso scale.
Analysis of the photographs taken of the sections on the slabs showed that the sections on the slabs with a fine or coarse surface were colonized more rapidly by small green algae (Ulothrix flacca and Urospora penicilliformis) than those with a smoother surface.
The geometric structures, cup and holes, which retained water longer during low tide favored the initial colonization by larger green algae (Ulva intestinalis). As succession proceeded, the differences in algal density between the sections on the slabs became less obvious.
All sections of the slabs in the mid and low tidal zone of both locations where rapidly overgrown by barnacles (Elminius modestus). Mussels (Mytilus edulis) were only found in the 9 sections with grooves, holes and cup, and developed best within the grooves. Both grooves and holes where used by periwinkles (Littorina littorea) for shelter at low tide. These results were in line with results found in the Azores (Martins et al. 2010), where pits with varying densities and sizes were drilled in a seawall, resulting in higher number of algae and macrobenthos within those pits.
The table below shows the flora (algae) and fauna that was found on the eco-slabs after well over a year of deployment. It was found that 9 algae species were growing on the eco-slabs.
|flora species||fauna species|
|1||Urospora penicilliformis||1||Elminius modestus|
|2||Ulothrix flacca||2||Littorina littorea|
|3||Blidingia minima||3||Mytilus edulis|
|4||Ulva intestinalis||4||Actinia equina|
The costs for the production of the eco-slabs for the pilot study were €60 per piece. The construction costs (of 10 slabs) were about €6000. For (possible future) large-scale production, it is recommended to apply the special textures and geometrical shapes directly on the concrete blocks instead of working with slabs. The estimated additional costs of such eco-blocks are expected to be about 2-3% of the costs of the normal concrete blocks.