Community-managed coral reef restoration in southern Kenya initiates reef recovery using various artificial reef designs

Abstract

Monitoring of reef restoration efforts and artificial reefs (ARs) has typically been limited to coral fragment survival, hampering evaluation of broader objectives such as ecosystem recovery. This study aimed to determine to what extent AR design influences the ecological recovery of restored reefs by monitoring outplanted coral fragments, benthic cover, coral recruitment and fish and invertebrate communities for two years. Four AR designs (16 m2), unrestored controls and natural reef patches as reference (n = 10) were established in Mkwiro, Kenya. ARs consisted either of concrete disks with bottles, layered concrete disks, metal cages or a combination thereof. A mixture of 18 branching coral species (mainly Acropora spp.) was outplanted on ARs at a density of 7 corals m-2. After two years, 60% of all outplanted fragments had survived, already resulting in coral cover on most ARs comparable (though Acropora-dominated) to reference patches. Coral survival differed between ARs, with highest survival on cages due to the absence of crown-of-thorns sea star predation on this design. In total, 32 coral genera recruited on ARs and recruit densities were highest on reference patches, moderate on concrete ARs and low on cages. ARs and reference patches featured nearly twice the fish species richness and around an order of magnitude higher fish abundance and biomass compared to control patches. Fish abundance and biomass strongly correlated with coral cover on ARs. AR, reference and control patches all had distinct fish species compositions, but AR and reference patches were similar in terms of trophic structure of their fish communities. Motile invertebrates including gastropods, sea urchins, sea cucumbers and sea stars were present at ARs, but generally more abundant and diverse at natural reference patches. Taken together, all studied ecological parameters progressed towards reef ecosystem recovery, with varying influences of AR design and material. We recommend a combination of metal cages and layered concrete ARs to promote high fragment survival as well as natural coral recruitment. Ultimately, a longer period of monitoring is needed to fully determine the effectiveness reef restoration as conservation tool to support coral reef ecosystem recovery.

Benthic Colonization on New Materials for Marine Ecosystem Restoration in Porto Cesareo, Italy

“…Moreover, it has recently been determined that hard artificial reefs for transplantation are more effective in a couple of years than those without transplantation and other structures, despite being submerged for more than 100 years [53,54]. Hard artificial structures are usually made of concrete due to the availability and strength of this material when submerged.…”

Artificial Reefs around the World: A Review of the State of the Art and a Meta-Analysis of Its Effectiveness for the Restoration of Marine Ecosystems

“…The species similarity values between ARs and NRs sites were significantly lower than similarity values between reference NRs sites (Figure 10). Despite the total effect measure almost reaching the null effect line (light blue diamonds, Figure 10), as few articles supported similar metrics describing species composition between artificial and natural reefs with a considerable weight ( [35,36,41], both common and random effect models showed significant differences (total common effect p = 0.03, total random effect p = 0.05).…”

Habitat Enrichment Causes Changes in Fish Behavioural Characteristics: A Case Study of Sparus latus

“…Habitat restoration is a key way to restore fishery resources. Incorporating appropriate substrates, shelters, plants, and other structures into the habitat of aquatic organisms for habitat enrichment could enhance their environmental adaptability and increase their release survival rate [ 1 , 2 ]. However, the effect of habitat enrichment is influenced by the studied species, lifestyle, growth stage, and habitat structure [ 3 , 4 ].…”