Artificial structures, such as seawalls, breakwaters, and bulkheads, are far less structurally complex than natural marine environments. They form homogenous seascapes in which there are few places for marine organisms to find shelter from the elements (desiccation stress, high temperatures, UV exposure, and other risks at low tide) and from predators. As a result, they are relatively depauperate (low in species diversity) and offer few ecosystem services compared with natural shorelines.
Over the past decade, scientists have been working hard to identify eco-engineering strategies for artificial structures that will improve biodiversity and native populations of bivalves and other important taxa.
Here, we highlight two key developments in the realm of eco-engineering: ecological enhancement “tiles” and textured concrete slabs. Both approaches increase the complexity of artificial shorelines, thus increasing their ecological value.
Enhancement tiles are precast concrete units that can be affixed to seawalls to enhance biodiversity or support valuable species such as native bivalves.
Tiles have been developed by research groups in Singapore, the UK, and Australia to meet two different objectives: (1) enhancing biodiversity, and (2) enhancing native bivalve assemblages.
Tiles for enhancing biodiversity
Tiles for enhancing biodiversity on seawalls were first developed by Dr. Lynette Loke and the Experimental Marine Ecology Lab at the National University of Singapore, led by Dr. Peter Todd. Studies in Singapore have consistently demonstrated higher biodiversity as a result of structurally complex concrete tiles. Dr. Loke and Dr. Todd have maximized this effect through an iterative process, whereby they have identifying the specific design features and scale that are most effective at biodiversity enhancement.
Methods for constructing tiles like those from Singapore are presented in published work by Dr. Loke et al:
- Ecology (2016) Vol. 97, Iss. 2, pp. 383–393
- Raffles Bulletin of Zoology (2016) Supplement No. 32, pp. 1–10
- Journal of Experimental Marine Biology and Ecology (2017) Vol. 492, pp. 133-120 (may require purchase; an “in press” version is available for download here)
Dr. Loke has also developed a software program for generating tile designs called Complexity for Artificial Substrates (CASU). It produces ouput files that can be used directly in AutoCAD or other programs to produce tiles. Here’s the link that will download CASU. The user manual can be found here. Development and testing of the program is reported in Dr. Loke’s 2014 publication in PLOS ONE. Additional background information about ecological definitions of complexity and their relationship to diversity can also be found in this 2015 publication in Ecological Engineering.
Biodiversity tiles have also been developed in the UK by Artecology, a collaboration between ecological consultant Arc Consulting and artist Eccleston George, and are now commercially available. Effects of Artecology’s tiles on biodiversity are currently being assessed by University of Glasgow researchers; Preliminary results from that study are available here.
Tiles for enhancing native bivalves
The World Harbour Project (WHP) has developed tiles aimed at enhancing native bivalve assemblages. This work was done in partnership with Reef Design Lab, a not for profit design studio and think tank based in Melbourne, Australia.
WHP/Reef Design Lab tiles are commercially available through the Reef Design Lab website: http://www.reefdesignlab.com/seawalls/.
In 2016 and 2017, WHP conducted an experiment in 15 cities around the world (!!!) to test whether the tiles effectively enhance bivalve assemblages and reduce non-indigenous species. Results from that experiment should be available soon. In the meantime, a synopsis of the project can be found here.
Monitoring and quantifying effectiveness
If you are planning to incorporate enhancement tiles into a project, it’s important to do so in a manner that objectively evaluates their effectiveness and impact.
Tiles are a relatively new technology, and their effects to date have been evaluated in relatively few locations and for limited periods. By deploying tiles as experiments (with proper controls and levels of replication), you can contribute to the growing body of science on seawall enhancements and help advance our understanding of factors that influence their effectiveness.
We are happy to discuss tile deployment and experimental design – please don’t hesitate to drop us a line!
Ongoing monitoring and fieldwork required to assess the effectiveness of tiles may be achieved through partnerships with researchers in your area (World Harbour Project provides an excellent network for establishing such partnerships), or can be incorporated into tasks of contracted environmental consultants.
For new seawalls or bulkheads and for major retrofits, textured concrete slabs provide an ideal alternative to the homogeneous surfaces from concrete poured in place.
Elliott Bay Seawall Project
The Elliott Bay Seawall Project (Parsons Corporation) in Seattle is the largest project to date employing textured slabs. Slabs were designed by Haddad|Drugan and informed by research from the University of Washington. They form 1.2 km of continuous textured substrata that mimic surfaces of local taxa, including barnacles,
mussels, anemones, sea stars, and rockweed. The slabs will be monitored over time to quantify settlement and diversity of intertidal organisms.
Pre-fabricated textured slabs
Pre-fabricated textured slabs are commercially available from ECOncrete, a small firm that has developed a proprietary concrete mix that is pH-neutral, which can facilitate recruitment and biogenic buildup (link). Ecological responses to ECOncrete’s formula have been assessed through field experiments led by the company’s CEO, who is also a scientist, Dr. Shimrit Perkol-Finkel, and are reported in peer-reviewed publications (listed on Dr. Perkol-Finkel’s ResearchGate page). Textured slabs produced by the company are called ECOncrete® Enhanced Seawall Panels. In a 2017 study, four panels affixed to a smooth, vertical seawall in Marina Herzliya, Israel were found to increase species diversity relative to adjacent seawall surfaces after 22 months.
Importance of monitoring
Textured concrete slabs are a relatively new technology. If you are planning to employ them in a project, an accompanying monitoring plan that characterizes species composition over time and records any settlement by non-indigenous species is essential. This may be done as part of contracted environmental consulting work for the project, or via partnerships with researchers in your area (World Harbour Project provides an excellent network for establishing such partnerships).
Ideally, slabs are installed experimentally with proper controls, or in a before-after-impact-control design, in which case monitoring data can contribute to the growing body of peer-reviewed literature on seawall enhancements. At minimum, presence and percent cover of non-indigenous species on textured slabs should be periodically assessed and compared with smooth vertical surfaces the same area.
If you have any questions, we’re happy to discuss – please don’t hesitate to drop us a line!