Create large adjoining cavities or ‘swimthrough’ habitats (>100 mm) on subtidal artificial structures
Overall effectiveness category Awaiting assessment
Number of studies: 2
Background information and definitions
Definition: ‘Large adjoining cavities or ‘swimthrough’ habitats’ are adjoining internal cavities sheltered from, but with access to/from, outside the structure. Dimensions can vary but are >100 mm in any direction.
Large adjoining cavities or ‘swimthrough’ habitats are not well-studied in subtidal rocky habitats. They may form through weathering of softer rocks, amongst loosely-consolidated boulders, or within three-dimensional structures created by organisms. They likely provide organisms refuge from predation, in the same way crevice and hole habitats do (Mercader et al. 2019; Nelson & Vance 1979). They could also serve as corridors, connecting adjacent refuge habitats. The size and density of cavities or swimthroughs is likely to affect the size, abundance and variety of organisms that can use them. Small habitats can provide refuge for small-bodied organisms but may exclude larger organisms, limit their growth and get rapidly filled-up (Firth et al. 2020). Large habitats can be used by larger-bodied organisms but may not provide sufficient refuge from predators for smaller organisms. By default, cavities and swimthroughs contain shaded surfaces, which can be associated with the presence of non-native species (Dafforn 2017).
Cavities/swimthroughs are sometimes present on marine artificial structures made of consolidated boulders or blocks (Sherrard et al. 2016) or gabion baskets (Firth et al. 2014), but are absent from many other structures. Large adjoining cavities or ‘swimthrough’ habitats can be created on subtidal artificial structures by adding or removing material, either during construction or retrospectively.
There is a body of literature investigating the effects of creating swimthrough habitats on artificial reefs (Brotto et al. 2006; Hylkema et al. 2020; Sherman et al. 2002). These studies are not included in this synopsis, which focusses on in situ conservation actions to enhance the biodiversity of structures that are engineered to fulfil a primary function other than providing artificial habitats.
See also: Create hole habitats (>50 mm) on subtidal artificial structures; Create crevice habitats (>50 mm) on subtidal artificial structures; Create small adjoining cavities or ‘swimthrough’ habitats (≤100 mm) on subtidal artificial structures.
Brotto D.S., Krohling W., Brum S. & Zalmon I.R. (2006) Usage patterns of an artificial reef by the fish community on the northern coast of Rio de Janeiro – Brazil. Journal of Coastal Research, 39, 1276–1280.
Dafforn K.A. (2017) Eco-engineering and management strategies for marine infrastructures to reduce establishment and dispersal of non-indigenous species. Management of Biological Invasions, 8, 153–161.
Firth L.B., Airoldi L., Bulleri F., Challinor S., Chee S.-Y., Evans A.J., Hanley M.E., Knights A.M., O’Shaughnessy K., Thompson R.C. & Hawkins S.J. (2020) Greening of grey infrastructure should not be used as a Trojan horse to facilitate coastal development. Journal of Applied Ecology, 57, 1762–1768.
Firth L.B., Thompson R.C., Bohn K., Abbiati M., Airoldi L., Bouma T.J., Bozzeda F., Ceccherelli V.U., Colangelo M.A., Evans A., Ferrario F., Hanley M.E., Hinz H., Hoggart S.P.G., Jackson J.E., Moore P., Morgan E.H., Perkol-Finkel S., Skov M.W., Strain E.M., van Belzen J. & Hawkins S.J. (2014) Between a rock and a hard place: environmental and engineering considerations when designing coastal defence structures. Coastal Engineering, 87, 122–135.
Hylkema A., Debrot A.O., Osinga R., Bron P.S., Heesink D.B., Izioka A.K., Reid C.B., Rippen J.C., Treibitz T., Yuval M. & Murk A.J. (2020) Fish assemblages of three common artificial reef designs during early colonization. Ecological Engineering, 157, 105994.
Mercader M., Blazy C., Di Pane J., Devissi C., Mercière A., Cheminée A., Thiriet P., Pastor J., Crec’hriou R., Verdoit-Jarraya M. & Lenfant P. (2019) Is artificial habitat diversity a key to restoring nurseries for juvenile coastal fish? Ex situ experiments on habitat selection and survival of juvenile seabreams. Restoration Ecology, 27, 1155–1165.
Nelson B.V. & Vance R.R. (1979) Diel foraging patterns of the sea urchin Centrostephanus coronatus as a predator avoidance strategy. Marine Biology, 51, 251–258.
Sherrard T.R.W., Hawkins S.J., Barfield P., Kitou M., Bray S. & Osborne P.E. (2016) Hidden biodiversity in cryptic habitats provided by porous coastal defence structures. Coastal Engineering, 118, 12–20.
Sherman R.L., Gilliam D.S. & Spieler R.E. (2002) Artificial reef design: void space, complexity, and attractants. ICES Journal of Marine Science, 59, S196–S200.
Supporting evidence from individual studies
A study in 2009–2010 on a subtidal pipeline in a lagoon in the Mozambique Channel, Mayotte (Pioch et al. 2011) reported that large swimthrough habitats created on pipeline anchor-weights, along with small swimthroughs and environmentally-sensitive material, were used by juvenile spiny lobster Panulirus versicolor, juvenile blue-and-yellow grouper Epinephelus flavocaeruleus, sea firs (Hydrozoa), and adult fishes from five families. After one month, juvenile spiny lobsters and blue-and-yellow groupers, sea firs, and adult damselfish/clownfish (Pomacentridae), wrasse (Labridae), butterflyfish (Chaetodontidae), squirrelfish/soldierfish (Holocentridae) and surgeonfish (Acanthuridae) were recorded on and around anchor-weights with swimthroughs and environmentally-sensitive material. Large swimthrough habitats were created by leaving gaps between concrete anchor-weights placed over a seabed pipeline (400 mm diameter). Anchor-weights also had basalt rocks or semi-cylindrical tiles attached to the top, creating small swimthrough habitats. Basalt may be considered an environmentally-sensitive material compared with concrete. Habitat dimensions/numbers were not reported. A total of 260 anchor-weights were placed with one every 10 m along the pipeline at 0–26 m depth during December 2009–March 2010. Fishes were counted on and around the pipeline from videos after 1 month.Study and other actions tested
A replicated, paired sites, controlled study in 2015–2016 on a seawall in a marina in Port Everglades, USA (Patranella et al. 2017) found that creating large swimthrough habitats in front of the seawall increased the fish species richness and abundance on and around seawall surfaces, but that effects varied depending on the species, size class and survey month. Over 14 months, total fish abundance was higher on and around seawall surfaces with swimthroughs (1,614 individuals) than those without (655 individuals). Fish species richness and average abundance (all size classes combined) was also higher (swimthroughs: 4 species and 10 individuals/survey; no swimthroughs: 2 species and 4 individuals/survey). This was also true for fishes in 20–300 mm size classes (swimthroughs: 0–2 species and 1–3 individuals/survey; no swimthroughs: 0–1 species and individuals/survey), but not for smaller or larger groups (both 0 species/survey; swimthroughs: 0–1 individuals/survey; no swimthroughs: 0 individuals/survey). Species abundances around seawall surfaces with and without swimthroughs varied depending on the species, size class and survey month (see paper for results). Sixteen species recorded on and around swimthroughs were absent from seawall surfaces without. Large swimthrough habitats (length: ~510 mm; width: ~250 mm; height: ~100 mm) were created by placing concrete bricks as spacers between four horizontally-stacked concrete paving slabs (510 × 510 mm). Twelve stacks of pavers with three swimthroughs/stack were placed at 1–3 m depth on silty seabed 0.5 m in front of a seawall in February 2015. Fishes were counted on and around sections of the seawall (1.5 × 1.5 m) with and without swimthroughs over 14 months.Study and other actions tested