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

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Four studies examined the effects of creating small adjoining cavities or ‘swimthrough’ habitats on subtidal artificial structures on the biodiversity of those structures. Two studies were in marinas in France and Morocco, while one was in each of a lagoon in Mayotte and a port in France.

COMMUNITY RESPONSE (1 STUDY)

  • Fish community composition (1 study): One replicated, paired sites, controlled study in France found that creating small swimthrough habitats on subtidal artificial structures had mixed effects on the juvenile fish community composition on and around structure surfaces, depending on the site and survey month. Swimthrough habitats supported six species that were absent from structure surfaces without swimthroughs.
  • Fish richness/diversity (1 study): One replicated, paired sites, controlled study in France found that creating small swimthrough habitats on subtidal artificial structures had mixed effects on juvenile fish species richness on and around structure surfaces, depending on the site.

POPULATION RESPONSE (2 STUDIES)

  • Fish abundance (2 studies): Two replicated, paired sites, controlled studies in France found that creating small swimthrough habitats on subtidal artificial structures had mixed effects on juvenile fish abundances on and around structure surfaces, depending on the species, site, survey month and/or juvenile development stage.

BEHAVIOUR (3 STUDIES)

  • Use (3 studies): One replicated, paired sites, controlled study in France found that creating small swimthrough habitats on subtidal artificial structures had mixed effects on juvenile seabream habitat use on and around structure surfaces, depending on the species and juvenile development stage. Two studies (including one replicated study) in Mayotte and Morocco reported that small swimthrough habitats, along with large swimthroughs and environmentally-sensitive material in one, were used by juvenile spiny lobsters, sea firs, adult fish and/or juvenile fish.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A study in 2009–2010 on a subtidal pipeline in a lagoon in the Mozambique Channel, Mayotte (Pioch et al. 2011) reported that small swimthrough habitats created on pipeline anchor-weights, along with large 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 swimthrough habitats and environmentally-sensitive material. Small swimthrough habitats were created by attaching basalt rocks or semi-cylindrical tiles to the horizontal surfaces of concrete anchor-weights placed over a seabed pipeline (400 mm diameter). Basalt may be considered an environmentally-sensitive material compared with concrete. Large swimthrough habitats were also created between the anchor-weights and pipeline. 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
  2. A replicated, paired sites, controlled study in 2013–2014 on subtidal seawalls and pontoons in five marinas in the Mediterranean Sea, France (Bouchoucha et al. 2016) found that creating small swimthrough habitats on seawalls and pontoons had mixed effects on juvenile seabream Diplodus spp. abundance and habitat usage on and around the structures, depending on the species, juvenile development stage, site and survey month. Over 17 months, juvenile seabream (four species) used swimthrough habitats created on seawalls as frequently as those created under pontoons, and in three of six comparisons, they used both more than seawall and pontoon surfaces without swimthroughs, but in the other three comparisons no significant difference was found (data reported as habitat preference index). Abundances on and around swimthroughs and seawall and pontoon surfaces varied depending on the species, development stage, site and survey month (swimthroughs: 0–6 individuals/survey for any one species; seawall and pontoon: both 0–2/survey; see paper for results). Small swimthrough habitats were created by attaching steel cages containing oyster shells (Biohuts: height: 0.8 m; length: 0.5 m; width: 0.3 m; mesh size: 25–50 mm) to seawalls and pontoons in March 2013. Eight Biohuts were attached to each of three vertical seawalls, and three were suspended under each of three pontoons, in each of five marinas (depth not reported). Biohuts were compared with seawall (height: 0.8 m; length: 5 m) and pontoon (4 m2) surfaces without swimthroughs. Juvenile seabreams were counted on and around Biohuts and seawall/pontoon surfaces over 17 months.

    Study and other actions tested
  3. 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.

    Study and other actions tested
  4. A replicated study in 2014–2015 on subtidal pontoons in a marina in the Alboran Sea, Morocco (Selfati et al. 2018) found that small swimthrough habitats created under pontoons were used by seven species of juvenile fishes. After 12 months, 34 juvenile mottled groupers (Mycteroperca rubra) and 28 juvenile dusky groupers (Epinephelus marginatus) were recorded on and around swimthrough habitats (Biohuts). Juveniles of three seabream species (Diplodus sargus, Diplodus cervinus, Sarpa salpa), European bass (Dicentrarchus labrax) and mullet (Mugilidae) were also recorded on and around swimthroughs. On average, there were 3 juveniles/Biohut. Small swimthrough habitats were created in June 2014 by attaching steel cages containing oyster shells (Biohuts) beneath pontoons. Fifty Biohuts (height: 0.8 m; length: 0.5 m; width: 0.3 m; mesh size: 25–50 mm) were attached at 1 m depth beneath pontoons (arrangement not reported). Juvenile fishes were counted on and around Biohuts after 12 months.

    Study and other actions tested
Please cite as:

Evans, A.J., Moore, P.J., Firth, L.B., Smith, R.K., and Sutherland, W.J. (2021) Enhancing the Biodiversity of Marine Artificial Structures: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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Biodiversity of Marine Artificial Structures

This Action forms part of the Action Synopsis:

Biodiversity of Marine Artificial Structures
Biodiversity of Marine Artificial Structures

Biodiversity of Marine Artificial Structures - Published 2021

Enhancing biodiversity of marine artificial structures synopsis

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