Small artificial habitats to enhance the nursery function for juvenile fish in a large commercial port of the Mediterranean

Published source details Mercader M., Mercière A., Saragoni G., Cheminée A., Crec’hriou R., Pastor J., Rider M., Dubas R., Lecaillon G., Boissery P. & Lenfant P. (2017) Small artificial habitats to enhance the nursery function for juvenile fish in a large commercial port of the Mediterranean. Ecological Engineering, 105, 78-86.
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This study is summarised as evidence for the following.

	Action	Category
	Create small adjoining cavities or ‘swimthrough’ habitats (≤100 mm) on subtidal artificial structures Action Link

Create small adjoining cavities or ‘swimthrough’ habitats (≤100 mm) on subtidal artificial structures

A replicated, paired sites, controlled study in 2014 on three subtidal seawalls in a port in the Mediterranean Sea, France (Mercader et al. 2017) found that creating small swimthrough habitats on seawalls had mixed effects on juvenile fish species richness, abundance and community composition on and around the walls, depending on the site, survey month and species. Over four months, at two of three sites, juvenile fish species richness and total abundance was higher on and around seawall surfaces with swimthrough habitats (3–4 species and 13–18 individuals/10 m seawall) than those without (0–1 species and 3–12 individuals/10 m). At the third site, there were no significant differences (1 species and 3 individuals/10 m seawall with and without swimthroughs). Community composition (data reported as statistical model results) and individual species abundances varied on and around seawall surfaces with and without swimthroughs, depending on the site, survey month and species (see paper for results). Six species recorded on and around swimthroughs were absent from seawall surfaces without. Small swimthrough habitats were created in May 2014 by attaching steel cages containing oyster shells (Biohuts) to seawall surfaces (30 m long). Thirty-five Biohuts (height: 0.8 m; length: 0.5 m; width: 0.3 m; mesh size: 25–50 mm) were attached at 1 m depth on each of three vertical seawalls. Biohuts were compared with adjacent seawall surfaces (30 m long) on each wall. Juvenile fishes were counted on and around seawall surfaces with and without Biohuts over four months.

(Summarised by: Ally Evans)