Artificial reef structures and coral transplantation as potential tools for enhancing locally-managed inshore reefs: a case study from Wasini Island, Kenya

Abstract

Many severely degraded reefs in the western Indian Ocean region show no signs of natural recovery and have remained for decades as barren, unconsolidated coral rubble fields with depleted commercially important fish groups. Consequently, several restoration techniques have been designed and developed to mitigate the localized impacts on coral reefs. Evaluating the efficacy of combined use of artificial reef structures and coral transplantation in enhancing habitat and recovery of key functions in severely degraded reefs is key to improved conservation of coral reefs. In this study, the survivorship rate of corals transplanted on reef structures is assessed, and changes in coral and fish abundance on artificial reef units and nearby natural reefs over time are compared. Coral cover on artificial reef structures increased from a mean of 17 % one year after initial attachment of fragments to 41 % after two years, with Acropora corals providing the highest cover. The artificial reef structures were also rapidly colonized by reef fish, with fish densities of 18±13 indiv./100 m2 showing an increase of about three fold higher than on natural reefs after two years. Greater numbers of commercially important fish groups (e.g., Lutjanids and Acanthurids) were observed on artificial reefs while natural reefs harboured more small sized fish (Pomacentrids and Labrids). These findings provide insights for artificial reef projects that are capable of restoring the regenerative capacity of the human-induced coral rubble beds.

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

“…In addition, this material showed a more stable response than other tested materials, such as Bioferment (according to the author's observation in the field). This could be related to the physical-chemical stability of the material [20,23,24,50], which is an important aspect for the restoration of marine ecosystems as hard materials increase coral transplant survival [51]. Materials must be durable during submersion and removable from the sea bottom, as required by some legislation in European countries (i.e., Spain or Italy).…”

Examining the effectiveness of bored pile coral for coral rehabilitation

“…The algae easily attached to the BPC's surface, leading to more frequent grazing activities by a group of herbivore fish (Graham and Nash 2013;Knoester et al 2019;Wilson et al 2021). A previous study showed reef fish also quickly populated the artificial reef structures, which was three times greater than those observed on natural reefs after two years in Kenya (Mwaura et al 2022). Carnivorous fish slowly increased, albeit not too significantly, from 25 Kg/Ha in February 2022 to 74 Kg/Ha in January 2023.…”

“…This indicates coral rehabilitation effectively increases reef complexity (Hein et al 2020). The percentage of coral cover on artificial reef structures in Wasini Island, Kenya, rose significantly from 17% one year after fragments were first attached to 41% after two years (Mwaura et al 2022).…”