Restore biogenic habitats (other methods) - Restore oyster reefs

How is the evidence assessed?
  • Effectiveness
    60%
  • Certainty
    50%
  • Harms
    0%

Source countries

Key messages

  • Eight studies examined the effects of restoring oyster reefs (not by transplanting or translocating oysters) on oysters and oyster reef-associated subtidal benthic invertebrates. Two were in the Gulf of Mexico (USA), one was a global review, four were in the North Pacific Ocean (USA), and one was in the Mission-Aransas estuary (USA).

 

COMMUNITY RESPONSE (3 STUDIES)

  • Overall community composition (2 studies): One of two replicated, controlled studies in the Gulf of Mexico and the Mission-Aransas estuary found that after restoring eastern oyster reefs, the community composition of combined mobile decapod invertebrates and fish was similar on all types of restoration material used, but the other found that composition varied with the material used.
  • Overall species richness/diversity (3 studies): One replicated, site comparison study in the Gulf of Mexico found that diversity of reef-associated invertebrates was similar in reefs restored by laying rocks regardless of age, in young reefs restored by laying oyster shells, and in natural reefs, but lower in old shell-restored reefs. One replicated, controlled study in the Gulf of Mexico found that diversity of reef-associated invertebrates was higher in all restored reefs than on unrestored sediment, but that diversity varied between the restoration materials used. One replicated, controlled study in the Mission-Aransas estuary found that diversity of fish, crabs and shrimps varied with the restoration material used.

POPULATION RESPONSE (7 STUDIES)

  • Overall abundance (2 studies): One replicated, site comparison study in the Gulf of Mexico found that the effect of restoring eastern oyster reefs on the abundance of reef-associated invertebrates depended on the material used for restoration and the age of the reef. One replicated, controlled study in the Gulf of Mexico found that abundance of combined reef-associated mobile decapod invertebrate and fish was similar on all restored reefs regardless of the restoration material used, and higher than on unrestored sediment.
  • Crustacean abundance (1 study): One replicated, controlled study in the Mission-Aransas estuary found that after restoring eastern oyster reefs, crab abundance, but not biomass, and shrimp biomass, but not abundance, varied with the restoration material used.
  • Oyster abundance (6 studies): One replicated, site comparison study in the Gulf of Mexico found that oyster reefs restored by laying rocks had similar oyster abundance to natural reefs, and higher than reefs restored by laying oyster shells. One replicated, controlled study in the Mission-Aransas estuary found that oyster cover and abundance varied with the restoration material used. One replicated, controlled study in the Gulf of Mexico found that oyster spat abundance was similar on all types of restoration material used, and higher than on unrestored sediment. Three replicated, controlled studies in the North Pacific Ocean found that restoring oyster reefs by placing lines of clam shells below Mean Lower Low Water (MLLW) led to higher cover of clam shells by oysters than when placing the lines above MLLW, that for those placed below MLLW, keeping them there led to similar cover compared to moving them above MLLW halfway through the study, and that placing the lines on cobbly seabed led to similar cover compared to placing them on muddy seabed.
  • Oyster reproductive success (3 studies): Three replicated, controlled studies in the North Pacific Ocean found that restoring oyster reefs by placing lines of clam shells below Mean Lower Low Water (MLLW) led to higher recruitment of oyster spat on clam shells than by lacing lines above MLLW, that recruitment was higher on lines placed on cobbly seabed than on muddy seabed, and that recruitment was similar on lines placed near or far from the nearest adult oyster populations.
  • Oyster survival (5 studies): One global systematic review found that two of nine restoration techniques (restoring oyster reef by transplanting juveniles, and by creating no-harvest sanctuaries) assessed resulted in over 85% survival of restored oysters. Four replicated, controlled studies in the North Pacific Ocean found that restoring oyster reefs by placing lines of clam shells below Mean Lower Low Water (MLLW) led to similar survival of oysters than when placing the lines above MLLW, but that for those placed below MLLW, moving them above MLLW halfway through the study led to higher survival than keeping then below, that survival was similar on lines placed on cobbly seabed or muddy seabed, and that survival was similar on lines placed near or far from the nearest adult oyster populations.
  • Oyster condition (5 studies): One replicated, controlled study in the Gulf of Mexico found that the effect of restoring eastern oyster reefs on average spat size varied with the restoration material used. One replicated, controlled study in the North Pacific Ocean found that restoring oyster reefs by placing lines of clam shells below Mean Lower Low Water (MLLW) led to similar growth of oysters on the shells than placing lines above MLLW. Four replicated, controlled studies in the North Pacific Ocean found that restoring oyster reefs by placing lines of clam shells below Mean Lower Low Water (MLLW) led to higher cover of clam shells by non-native species than placing lines above MLLW, but that for those placed below MLLW, moving them above MLLW halfway through the study led to lower cover than keeping then below, that cover was similar on lines placed on cobbly seabed or muddy seabed, and that cover of clam shells by non-native species was higher on lines placed near compared to far from the nearest adult oyster populations.

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 replicated, site comparison study in 2011 of 20 oyster reefs in the northern Gulf of Mexico, from Texas to Florida, USA (Brown et al. 2014) found that the effect of restoring reefs of eastern oyster Crassostrea virginica on oysters and reef-associated invertebrates depended on the material used for restoration and the age of the reef. Reefs restored by laying rocks had similar oyster abundance (102–105 oyster/m2) to natural reefs (136 oyster/m2), while reefs restored by laying oyster shells had lower oyster abundance (3–22 oyster/m2) than any other reefs, regardless of the age of the restored reefs. In addition, diversity of reef-associated invertebrates (reported as diversity index) was similar in rock-restored reefs regardless of age, young shell-restored reefs (under five-year-old) and natural reefs, but significantly lower in old shell-restored reefs (over five-year-old). Overall abundance of reef-associated invertebrates was similar in young rock-restored reefs (106) and old shell-restored reefs (58) to natural reefs (182), but higher in old rock-restored reefs (345) and young shell-restored reefs (338) compared to natural reefs. Invertebrates were surveyed on 20 reefs (100 m offshore; approximately 2 m depth). Eight had been restored by laying rocks (six old; two young), five had been restored by laying shells (two old; three young), and seven were natural reefs. In October 2011, divers counted live eastern oysters in the top 10 cm of reef (five 0.25 m2 quadrats/reef). In May and again in July 2011, two 30 ×30 cm bags containing oyster shells were deployed at each reef to capture invertebrates and retrieved after one month (80 bags total). All four bags/reef were combined, and invertebrates (<1 mm) were identified and counted.

    Study and other actions tested
  2. A replicated, controlled study (year unspecified) of 10 soft seabed sites in the Gulf of Mexico, Texas, USA (George et al. 2015) found that the effect of restoring reefs of eastern oyster Crassostrea virginica on oysters and reef-associated mobile decapod invertebrates and fish depended on the material used for restoration. Average oyster spat abundance was similar on all types of restoration material used (840–1,390 spat/m2) and higher than at unrestored sediment (0 spat/m2). Average spat size was higher on concrete, river rock and oyster shell (15.5–15.8 mm) than on limestone (13.2 mm) and porcelain (11.8 mm). The community composition of combined mobile decapod invertebrates and fish was similar on all types of restoration material used (community data reported as graphical analyses). Average abundance of mobile decapod invertebrates and fish was similar on all types of restoration material used (310–550 individual/m2) and higher than on unrestored sediment (4.5 individual/m2). Diversity was higher on any restoration material than on unrestored sediment (data reported as a diversity index). Between restoration materials, diversity was higher on porcelain and oyster shell than concrete, which were all higher than on river rock and limestone. Five trays (0.75 m2) were deployed at each of 10 sites and filled with one of five types of restoration material (concrete, porcelain, limestone, river rock, oyster shell). After four months, all trays and one bare (unrestored) sediment patch were collected using a 1 m2 grab with a 1.6 mm mesh. One 0.09 m2 quadrat was deployed on each tray. Eastern oyster spat were counted in grab and quadrat samples. The shell height of up to 20 spat/tray was measured using callipers. Mobile decapod invertebrates and fish were identified and counted.

    Study and other actions tested
  3. A systematic review conducted in 2014 of studies from across the world (Bayraktarov et al. 2016) found that following oyster reef restoration projects, the survival of oysters varied with the restoration technique used. Comparing nine different techniques, the survival of oysters varied between 0% and 100% (survival for each technique not shown). Two of the nine restoration techniques (restoring oyster reef by transplanting juveniles, and by creating no-harvest sanctuaries) resulted in over 85% survival of restored oysters. A systematic review of the literature available by 21 November 2014 on the feasibility, survival, and costs of oyster reef restoration was conducted. Out of the 81 studies found on oyster reef restoration, 24 studies were included in the systematic review. Data on the restoration technique used and survival of “restored oysters” (exact definition not stated) were extracted and analysed.

    Study and other actions tested
  4. A replicated, controlled study in 2012–2014 of seven estuarine sites in Monterey Bay, North Pacific Ocean, USA (Zabin et al. 2016a) found that the effects on oysters and non-native species of restoring the reef-forming Olympia oyster Ostrea lurida by placing lines of clam shells (for oysters to settle on) varied with tidal elevation. After five months, oyster recruitment was higher on lines placed below Mean Lower Low Water (MLLW) (122 oysters/line) compared to lines placed above MLLW (70 oysters/line). Survival after five months was similar at both tidal elevation (below: 89%; above: 86%), leading to higher cover of clam shells by oysters below MLLW (20%) than above (12%). However, cover by non-native species was higher below MLLW (25%) than above (20%). In addition, after two years, oysters reached similar average maximum size below (60 mm) and above (59 mm) MLLW. In July 2012, six lines of clam shells were deployed at each of seven sites (at least 1 km apart): three lines above MLLW, three below. In December 2012, live and dead oysters were counted on each line, and the percentage cover of clam shells by oysters and non-native species (sponges, tunicates, bryozoans, and hydrozoans) was visually assessed. In May 2014, the five largest oysters on each line were measured.

     

    A replicated, controlled study in 2012–2014 of four estuarine sites in Monterey Bay, North Pacific Ocean, USA (Zabin et al. 2016b) found that the effects) on oysters and non-native species of restoring the reef-forming Olympia oyster Ostrea lurida by placing lines of clam shells (for oysters to settle on depended on if the lines were moved above or remained below Mean Lower Low Water (MLLW). After a year, cover of clam shells by oysters was similar on lines moved above (41%) and lines which had remained below (44%) MLLW. However, oyster survival after a year was higher on lines moved above (94%) than lines remained below (77%) MLLW, and clam shell cover by non-native species was lower (above: 4%; below: 43%). In July 2012, two lines of clam shells were deployed at each of four sites (at least 1 km apart) below MLLW. In June 2013, at each site, one line was moved above MLLW. In May 2014, live and dead oysters were counted on each line, and the percentage cover of clam shells by oysters and non-native species (sponges, tunicates, bryozoans, and hydrozoans) was visually assessed. No oyster recruitment occurred in 2013.

     

    A replicated, controlled study in 2012–2014 of four estuarine sites in Monterey Bay, North Pacific Ocean, USA (Zabin et al. 2016c) found that the effects on oysters and non-native species of restoring the reef-forming Olympia oyster Ostrea lurida by placing lines of clam shells (for oysters to settle on) varied with seabed type. After five months, oyster recruitment was higher on lines placed on cobbly seabed (138 oysters/line) compared to lines placed on muddy seabed (83 oysters/line). Survival after five months was lower on cobbly seabed (61%) than muddy seabed (99%). This led to similar cover of clam shells by oysters on cobbly (15%) and muddy seabed (18%). In addition, cover by non-native species was similar on both seabed type (cobble: 26%; mud: 31%). In July 2012, six lines of clam shells were deployed at each of four sites (at least 1 km apart): two cobbly sites and two muddy sites. In December 2012, live and dead oysters were counted on each line, and the percentage cover of clam shells by oysters and non-native species (sponges, tunicates, bryozoans, and hydrozoans) was visually assessed.

     

    A replicated, controlled study in 2012–2014 of five muddy estuarine sites in Monterey Bay, North Pacific Ocean, USA (Zabin et al. 2016d) found that the effects on oysters and non-native species of restoring the reef-forming Olympia oyster Ostrea lurida by placing lines of clam shells (for oysters to settle on) varied with distance to the nearest adult oyster populations. After five months, oyster recruitment and survival were similar on lines placed near (adjacent; 83 oysters/line; 14% survival) and far (over 300 m away; 77 oysters/line; 15%) from the nearest adult oyster populations. However, cover by non-native species was higher at sites near (31%) than far (14%) from the nearer adult populations. In July 2012, six lines of clam shells were deployed at each of five sites (at least 1 km apart): two sites “near” and three “far” from the nearest adult populations. In December 2012, live and dead oysters were counted on each line, and the percentage cover of clam shells by oysters and non-native species (sponges, tunicates, bryozoans, and hydrozoans) was visually assessed.

    Study and other actions tested
  5. A replicated, controlled study in 2013–2015 of 12 restored reefs in the Mission-Aransas estuary, southern coast of Texas, USA (Graham et al. 2017) found that the effects of restoring reefs of eastern oyster Crassostrea virginica on oysters and reef-associated organisms, after 21 months, depended on the material used. After 21 months, the community structure of combined invertebrates and fish differed with material (data presented as a graphical analysis). The diversity of mobile organisms (fish, crabs and shrimps) was similar across material (reported as a diversity index). Oysters dominated the cover of sessile organisms on all reefs, but cover was lower on river rock (41%) compared to all other material (68–53%). Oyster abundance was higher on concrete (1,020/m2), than limestone (940/m2), oyster shell (830/m2), and river rock (600/m2). Crabs (five species combined) dominated the mobile organisms across reefs, with no effect of material on their abundance (270–440/m2). Crab biomass was higher on oyster shell (53 g/m2) and concrete (38 g/m2) than river rock (24 g/m2), but not limestone (36 g/m2). Shrimps (five species combined) were more abundant on oyster shell (140/m2) than any other material (60–120/m2). Shrimp biomass was similar on all material (3–6 g/m2). In 2013, twelve oyster reefs (152 m3) were constructed with either concrete, river rocks, limestones, or oyster shells (3 reefs/material). After three months, six trays filled with 19 L of matching material were deployed at each reef. Quarterly, one tray/reef was retrieved and mobile organisms (> 4mm) identified, counted, and dry-weighed. Oysters were counted, and their percentage cover assessed. In addition, other sessile invertebrates were assessed, and a benefit-cost ratio for each material was calculated (see paper).

    Study and other actions tested
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.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Subtidal Benthic Invertebrate Conservation

This Action forms part of the Action Synopsis:

Subtidal Benthic Invertebrate Conservation
Subtidal Benthic Invertebrate Conservation

Subtidal Benthic Invertebrate Conservation - Published 2020

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, terrestrial mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 17

Go to the CE Journal

Subscribe to our newsletter

Please add your details if you are interested in receiving updates from the Conservation Evidence team about new papers, synopses and opportunities.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust