On rural coastlines, rock pools form naturally over centuries or millennia and serve as refugia for marine life, offering protection from the elements and predators, and consequently support a high diversity of species.
By contrast, on human-engineered shorelines, which make up coastal cities, rock pools and complex habitat features are generally lacking.
Artificial rock pools are ecological enhancements that mimic natural rock pools and can be added to seawalls and breakwaters to increase biodiversity.
Approaches for building artificial rock pools differ depending on the type of project:
Rock pools for…
Masonary seawalls (new construction)
For new intertidal structures with masonry construction, an approach similar to the employed by Dr. Gee Chapman and Dr. David Blockley in a 2009 study may be ideal. Chapman and Blockley (2009) formed rock pools by omitting sandstone blocks during construction of a seawall in Sydney Harbor. Open spaces were then fitted spaces with sandstone shelves that extended horizontally from the wall.
Existing vertical seawalls
On existing vertical seawalls and bulkheads, rock pools of different sizes can be developed through:
(1) Drill coring: Small rock pools can be generated by drill coring directly into the structure, as described in a 2014 study by Dr. Louise Firth and colleagues. Firth et al. (2014) used a diamond-tipped drill corer to extract 15 cm diameter cores of two different depths (12 cm and 5 cm) from a granite seawall in Tywyn, UK. These dimensions were selected to mimic rock pools on nearby natural rocky shores (as discussed by Evans et al. 2016), but could be adjusted according to local conditions and particular species of interest. For instance, in a 2010 study, Dr. Gustavo Martins and colleagues selected a 12 mm diameter based on measurements of naturally-occurring pits on volcanic rocky shores in the Azores. Their study additionally focused on enhancing limpets, which used pits that closely match their shell dimensions (10-15 mm diameter).
(2) “Flower pots”: Larger rock pools can be integrated into existing vertical intertidal structures through the use of concrete structures that resemble flower pots. This approach was developed by Mark Browne and Gee Chapman and initially described in their 2011 study. Since natural rockpools of different sizes support different assemblages of organisms, “flower pots” constructed by Browne and Chapman (2011) were modified to be either 38 cm or 22 cm deep (all were 36 cm across at the top).
(3) Vertipools: Similar to “flower pot” pools in function, Vertipools are the creation of UK-based Artecology, a collaboration between ecological consultants Arc Consulting and public artists Eccleston George. Artecology offers several Vertipool models commercially, which you can peruse here.
Breakwaters (existing or new construction)
Rock pools can also be incorporated into breakwaters or other shoreline structures comprised of riprap using either commercially available or open-access (DIY) stand-alone enhancement unit.
(1) ECOncrete® Tide Pools are commercially available rock pools made of ECOncrete’s “bio-active” proprietary concrete mix (link). Projects utilizing ECOncrete® Tide Pools include Living Breakwaters on the south side of Staten Island that were designed by the landscape architectural firm, SCAPE.
(2) BIOBLOCKs are 1.5 m × 1.5 m × 1.1 m concrete blocks that include rock pools, among other enhancement features. BIOBLOCKs were designed by academics and their design is presented in Firth et al. (2014).
Importance of tidal height
While rock pool units are well established enhancement tools, care should be taken to ensure they are well positioned with respect to tidal height. Units placed too high in the intertidal zone, where they are only occasionally submerged by tides, will collect freshwater and have lower diversity. Accumulation of freshwater may be of particular concern in the tropics and in cities where mosquito-borne diseases pose a public health risk. Pools should be placed where the maximum amount of time between tidal submersion is less than the time required for mosquito larvae to develop (1-3 days in some areas). Units placed too low on the shoreline, particularly if just below the lowest low tide, will be of limited value.
As will all ecological enhancements, monitoring of rock pool units is essential to ensure they are effective and are not promoting establishment of non-indigenous species. This can be done by consulting with commercial providers of pre-fab units (where used), through partnerships with researchers (World Harbour Project provides an excellent network for establishing partnerships), or through contracted environmental consultants.
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