Eco-engineering increases habitat availability and utilisation of seawalls by fish

Published source details Ushiama S., Mayer-Pinto M., Bugnot A.B., Johnston E.L. & Dafforn K.A. (2019) Eco-engineering increases habitat availability and utilisation of seawalls by fish. Ecological Engineering, 138, 403-411.
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This study is summarised as evidence for the following.

	Action	Category
	Transplant or seed organisms onto intertidal artificial structures Action Link
	*Create grooves and* small protrusions, ridges or ledges (1–50 mm) on intertidal artificial structures** Action Link

Transplant or seed organisms onto intertidal artificial structures

A replicated, randomized, controlled study in 2016–2017 on three intertidal seawalls in Sydney Harbour estuary, Australia (Ushiama et al. 2019) found that transplanting oysters Saccostrea glomerata, coralline algae Corallina officinalis, or both onto settlement plates did not increase the fish species richness or abundance or alter fish behaviour on and around plates, but benthic fish behaviour varied depending on the species transplanted. After 8–12 months, fish species richness and abundance were similar on and around settlement plates with and without transplanted coralline algae, oysters or both (data not reported). The same was true for the time fishes spent interacting with plates (with coralline algae: 1–21 minutes/60-minute survey; with oysters: 2–30 minutes/survey; both: 1–18/survey; neither: 1–27/survey). Benthic fishes took more bites from plates with oysters (10 bites/survey) than plates with both algae and oysters (2/survey), while both were similar to plates with algae only (6 bites/survey) and with neither (4/survey). There were no significant differences for pelagic fishes (with algae: 8 bites/survey; oysters: 21/survey; both: 5/survey; neither: 8/survey). Coralline algae collected from natural reefs and hatchery-reared juvenile oysters were attached to concrete settlement plates (250 × 250 mm) using epoxy glue and transplanted onto vertical sandstone seawalls. Algae, oysters (46 mm average length), both or neither were attached in eight patches/plate covering 125 cm². Plates had textured surfaces with or without grooves and small ledges (50 mm). Nine of each transplant-grooves/ledges combination were randomly arranged at midshore on each of three seawalls in March 2016. Fishes were counted on and around one of each plate design from 60-minute videos during each of three high tides after 8–12 months. The time fishes spent within 50 mm of plates and the number of bites they took was recorded.

(Summarised by: Ally Evans)
Create grooves and small protrusions, ridges or ledges (1–50 mm) on intertidal artificial structures

A replicated, randomized, controlled study in 2016–2017 on three intertidal seawalls in Sydney Harbour estuary, Australia (Ushiama et al. 2019) found that creating groove habitats and small ledges on settlement plates did not increase fish species richness or abundance or alter pelagic fish behaviour, but altered benthic fish behaviour on and around plates. After 8–12 months, fish species richness and abundance were similar on and around settlement plates with and without grooves and ledges (data not reported). Benthic fishes spent longer interacting with plates with grooves and ledges (30 minutes/60-minute survey) than without (17 minutes/survey), but took fewer bites from their surfaces (2 vs 8 bites/survey). There were no significant differences for pelagic fishes (2 vs 1 minutes/survey, 8 vs 13 bites/survey). Concrete settlement plates (250 × 250 mm) were moulded with and without groove habitats and small ledges. Plates with grooves and ledges had four horizontal grooves (length: 250 mm; width: 15–50 mm; depth: 50 mm) between five ledges (length: 250 mm; width: 17–65 mm; height: 50 mm). Plates had textured surfaces with or without juvenile oysters, coralline algae, or both attached. Nine plates of each grooves/ledges-transplant combination were randomly arranged at mid-lowshore on each of three vertical sandstone seawalls in March 2016. Fishes were counted on and around one of each plate design from 60-minute videos during each of three high tides after 8–12 months. The time fishes spent within 50 mm of plates and the number of bites they took was recorded.

(Summarised by: Ally Evans)