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Providing evidence to improve practice

Action: Restore biogenic habitats (other methods) - Restore mussel beds Subtidal Benthic Invertebrate Conservation

Key messages

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  • Two studies examined the effects of restoring mussel beds (not by transplanting or translocating mussels) on mussels and mussel bed-associated subtidal benthic invertebrates. Both were in Strangford Lough (UK).

 

COMMUNITY RESPONSE (2 STUDIES)

  • Overall community composition (2 studies): One replicated, controlled study in Strangford Lough found that after restoring beds of horse mussels by adding scallop shells to the seabed, overall invertebrate community composition in restored plots was different to that of unrestored plots. One replicated, controlled study in the same area found that after restoring beds of horse mussels by adding scallop shells to the seabed and translocating horse mussels, overall invertebrate community composition in plots restored with shells and mussels was different to plots restored without mussels (shells only), and both were different to unrestored plots and to nearby natural horse mussel beds.
  • Overall species richness/diversity (2 studies): One replicated, controlled study in Strangford Lough found that after restoring beds of horse mussels by adding scallop shells to the seabed, overall invertebrate species diversity was lower in restored plots compared to unrestored plots, but species richness was similar. One replicated, controlled study in the same area found that after restoring beds of horse mussels by adding scallop shells to the seabed and translocating horse mussels, species richness and diversity were higher in restored plots with mussels and shells compared to plots with shells only, and similar to nearby natural horse mussel beds.

POPULATION RESPONSE (1 STUDY)

  • Overall abundance (1 study): One replicated, controlled study in Strangford Lough found that after restoring beds of horse mussels by adding scallop shells to the seabed, overall invertebrate abundance was higher in restored plots compared to unrestored plots.

Supporting evidence from individual studies

1 

A replicated, controlled study in 2010–2011 of 12 plots in Strangford Lough, Northern Ireland, UK (Fariñas-Franco et al. 2013a – same experimental set-up as Fariñas-Franco et al. 2013b), found that one year after restoring horse mussel Modiolus modiolus habitat by adding scallop shells to the seabed, invertebrate community composition in restored plots was different to that of unrestored plots. Community data were reported as graphical analyses. In addition, while total invertebrate abundance was higher in restored plots (258–830 individuals) compared to unrestored plots (40–58 individuals), species diversity was lower in restored plots (data reported as diversity indices). Species richness was similar across plots (data reported as indices). Within restored plots, there were no differences between plots with elevated scallop shells and plots with flattened shells. In 2010 sixteen tonnes of scallop shells were deployed in bags at four sites (17–19 m depth) to recreate suitable habitat for horse mussel reefs. Each site was divided into an elevated plot (8 m2; shell rising 1 m above seabed) and a flattened plot (4 m2; 0.5 m above seabed). After 12 months, one quadrat (0.25 × 0.25 m) was deployed at each plot and at four adjacent unrestored plots. Sediment and shell were sampled for each quadrat to 10 cm depth. Organisms (>1 mm) were identified and recorded as either counts or presence/absence.

 

A replicated, controlled study in 2010–2011 of multiple plots in Strangford Lough, Northern Ireland, UK (Fariñas-Franco et al. 2013b – same experimental set-up as Fariñas-Franco et al. 2013a), found that one year after restoring horse mussel Modiolus modiolus biogenic habitat by adding scallop shells to the seabed and translocating horse mussels, overall invertebrate community composition in plots restored with shells and mussels was different to plots restored without mussels (shells only) and both were different to unrestored plots. Community data were presented as graphical analyses. In addition, species richness and diversity were higher in restored plots with mussels and shells compared to plots with shells only (data reported as indices). When compared with nearby natural horse mussel reefs, restored plots (with shells and mussels) had different community composition, despite having similar species richness and diversity. Within restored plots after a year, there were no differences between plots with elevated scallop shells and plots with flattened shells, apart for translocated mussel mortality which was lower in elevated plots (5%) compared to flattened plots or unrestored plots (19%). In 2010 sixteen tonnes of scallop shells were deployed in bags at four sites (17–19 m depth) to recreate suitable habitat for horse mussel reefs. Each site was divided into an elevated plot (8 m2; shell rising 1 m above seabed) and a flattened plot (4 m2; 0.5 m above seabed). Each plot was then sub-divided, and divers translocated live adult horse mussels from nearby natural mussel patches within the Lough into on half of each plot (500 mussels/subplot). After 12 months, one quadrat (0.25 × 0.25 m) was deployed at each subplot and at four adjacent unrestored plots. Sediment and shell were sampled for each quadrat to 10 cm depth. Organisms (>1 mm) were identified and recorded as either counts or presence/absence. Natural horse mussel communities from two nearby horse mussel reefs within the Lough were sampled in December 2010 using the same sampling methodology.

Referenced papers

Please cite as:

Lemasson, A.J., Pettit, L.R., Smith, R.K., and Sutherland, W.J. (2019) Subtidal Benthic Invertebrate Conservation: Global Evidence for the Effects of Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.