Evaluation of ecological engineering of “armoured” shorelines to improve their value as habitat

Published source details Chapman M.G. & Underwood A.J. (2011) Evaluation of ecological engineering of “armoured” shorelines to improve their value as habitat. Journal of Experimental Marine Biology and Ecology, 400, 302-313.
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This study is summarised as evidence for the following.

	Action	Category
	Create groove habitats (1–50 mm) on intertidal artificial structures Action Link
	Reduce the slope of intertidal artificial structures Action Link
	Create groove habitats (1–50 mm) on intertidal artificial structures Action Link
	Create hole habitats (>50 mm) on intertidal artificial structures Action Link
	Create 'rock pools' on intertidal artificial structures Action Link
	Create pit habitats (1–50 mm) on intertidal artificial structures Action Link

Create groove habitats (1–50 mm) on intertidal artificial structures

A replicated, randomized, controlled study in 2000–2003 on an intertidal seawall in Sydney Harbour estuary, Australia (Chapman & Underwood 2011a) found that creating groove habitats on the seawall did not alter the macroalgae and invertebrate community composition or increase limpet (Patellidae and/or Siphonariidae, Fissurellidae) species richness or abundance, or chiton (Polyplacophora) abundance on seawall surfaces. After three months, seawall surfaces with grooves supported similar macroalgae and invertebrate community composition to surfaces without (data reported as statistical model results). After 27 months, limpet species richness and abundance were similar in grooves (0 species and individuals/array) and on surfaces without (1 species/surface, 3 individuals/surface). The same was true for chiton abundance (grooves: 0 individuals/array; surfaces: 0/surface). Groove habitats were created in 2000 (month not reported) by drilling into a vertical sandstone seawall during reconstruction. Arrays of 16 grooves (length: 50 mm; width: 10 mm; depth: 5 mm; spacing/orientation not reported) were drilled on 1 × 0.4 m seawall surfaces. There were five surfaces with grooves and five without randomly arranged (shore level not reported). Macroalgae and invertebrates were counted on surfaces with and without grooves during low tide after three months. Mobile invertebrates were counted in grooves and on surfaces without after 27 months.

(Summarised by: Ally Evans)
Reduce the slope of intertidal artificial structures

A replicated, controlled study (year not reported) on an intertidal seawall in Sydney Harbour estuary, Australia (Chapman & Underwood 2011) found that reducing the slope of the seawall did not increase the abundance of macroalgae, oysters Saccostrea glomerata or mobile invertebrates on seawall surfaces. Over 24 months, the abundances of macroalgae, oysters and mobile invertebrates were similar on surfaces of a new sloping seawall and on remnants of the original vertical wall that it replaced (data not reported). The slope of a seawall was reduced by replacing a vertical concrete wall with a sloping wall of boulders. This increased the extent of the intertidal area from high to low shore by 2–3 m (timing and other details of the intervention not reported). Macroalgae and invertebrates were counted on 10 surfaces (dimensions not reported) in each of four sites on the new sloping wall, and 10 on a remnant of the original vertical wall, during low tide over 24 months.

(Summarised by: Ally Evans)
Create groove habitats (1–50 mm) on intertidal artificial structures

A replicated, paired sites, controlled study (year not reported) on two intertidal seawalls in Sydney Harbour estuary, Australia (Chapman & Underwood 2011b; same experimental set-up as Dugan et al. 2011) reported that creating groove habitats on the seawalls had mixed effects on invertebrate abundances depending on the species group and shore level, but data were not statistically tested. Over 12 months, both grooves and seawall surfaces without grooves supported mobile invertebrates (data not reported) and non-mobile invertebrates at midshore (mussels Mytilus galloprovincialis planulatis: recorded in grooves in 65% of surveys vs seawall surfaces in 27%; sponges (Porifera): 10 vs 4%; barnacles (Cirripedia): 26 vs 16%; tubeworms (Polychaeta): 34 vs 26%) and lowshore (mussels: 50 vs 33%; sponges: 20 vs 13%; sea squirts (Ascidiacea): 4 vs 3%; tubeworms: 44 vs 49%). Groove habitats were created by indenting wet mortar between blocks during maintenance of vertical sandstone seawalls (month/year not reported). Five grooves (width: 30–50 mm; depth: 20 mm; length/orientation/spacing not reported) were compared with five flat mortar surfaces (dimensions not reported) at both midshore and lowshore in each of two paired sites on each of two seawalls. Invertebrates were counted in grooves and on surfaces without during low tide over 12 months, on 10 occasions on one seawall and seven on the other.

(Summarised by: Ally Evans)
Create hole habitats (>50 mm) on intertidal artificial structures

A study (year not reported) on an intertidal seawall in Sydney Harbour estuary, Australia (Chapman & Underwood 2011) reported that hole habitats created on the seawall, along with rock pools, were used by mobile invertebrates from at least three species groups. Sea slugs (Opistobranchia), urchins (Echinoidea) and octopuses (Octopoda) were recorded in holes and pools. It is not clear whether these effects were the direct result of creating holes or rock pools. Hole habitats were created, along with rock pools, by replacing seawall blocks with sandbags during maintenance of a vertical sandstone seawall, then removing the sandbags to leave shaded water-retaining depressions in the wall. No other details were reported.

(Summarised by: Ally Evans)
Create 'rock pools' on intertidal artificial structures

A study (year not reported) on an intertidal seawall in Sydney Harbour estuary, Australia (Chapman & Underwood 2011) reported that rock pools created on the seawall, along with holes, were used by mobile invertebrates from at least three species groups. Sea slugs (Opistobranchia), urchins (Echinoidea) and octopuses (Octopoda) were recorded in pools and holes. It is not clear whether these effects were the direct result of creating rock pools or holes. Rock pools were created, along with holes, by replacing seawall blocks with sandbags during maintenance of a vertical sandstone seawall, then removing the sandbags to leave shaded water-retaining depressions in the wall. No other details were reported.

(Summarised by: Ally Evans)
Create pit habitats (1–50 mm) on intertidal artificial structures

A replicated, randomized, controlled study in 2000–2003 on an intertidal seawall in Sydney Harbour estuary, Australia (Chapman & Underwood 2011) found that creating pit habitats on the seawall did not alter the macroalgae and invertebrate community composition or increase limpet (Patellidae and/or Siphonariidae, Fissurellidae) species richness or abundance, or chiton (Polyplacophora) abundance on seawall surfaces. After three months, seawall surfaces with pits supported similar macroalgae and invertebrate community composition to surfaces without (data reported as statistical model results). After 27 months, limpet species richness and abundance were similar in large pits (0 species and individuals/array), small pits (1 species/array, 2 individuals/array) and on surfaces without pits (1 species/surface, 3 individuals/surface). The same was true for chiton abundance (large pits: 0 individuals/array; small pits: 2/array; no pits: 0/surface). Pit habitats were created in 2000 (month not reported) by drilling into a vertical sandstone seawall during reconstruction. Large (diameter: 50 mm) and small (25 mm) round pits (depth: 5 mm) were drilled in arrays of 16 (spacing/arrangement not reported) on 1 × 0.4 m seawall surfaces. There were five surfaces with each of large, small and no pits, randomly arranged (shore level not reported). Macroalgae and invertebrates were counted on surfaces with and without pits during low tide after three months. Mobile invertebrates were counted in pits and on surfaces without after 27 months.

(Summarised by: Ally Evans)