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The structure of an ecosystem is usually determined by the shape of the organisms that build it, commonly known as ecosystem engineers. Understanding to what extent plasticity and environmental filtering determine variation in the physical structure of ecosystem engineers is necessary to predict how ecosystem structure may change. Here, we explored coral survival and the plasticity of morphological traits that are critical for habitat provision in coral reefs. We conducted a reciprocal clonal transplant experiment in which branching corals from the genera Porites and Acropora were moved to and from a deep and a shallow site within a lagoon in the Maldives. Survival and trait analyses revealed that transplant destination consistently induced the strongest changes, particularly among Acropora spp. The origin of the corals had only marginal effects on some of the traits. We also detected variation in the way individuals from the same species and site differentiate in their shape, showing that traits linked to habitat provision are phenotypically plastic. The results suggest that in the quite common lagoonal conditions studied here, coral phenotypic plasticity plays a stronger role than environmental filtering, in determining the zonation of coral morphologies, and consequently the habitats they provide for other organisms.

Le scogliere coralline, conosciute per essere uno degli ecosistemi più ricchi di biodiversità del pianeta, stanno diminuendo ad un ritmo allarmante. Per contrastare le minacce poste dai cambiamenti climatici e da altri impatti di origine antropica gli sforzi di conservazione attiva, come il ripristino della scogliera corallina, sono aumentati a livello globale. Il ripristino ecologico si pone come obiettivo principale quello di assistere il recupero naturale, aumentandone la resilienza, delle scogliere coralline nel tentativo di preservare le numerose funzioni e servizi ecosistemici che questi habitat iconici forniscono alla società. La vulnerabilità delle Maldive alle minacce globali e locali è più evidente in quanto rappresentata da isole coralline con un'economia basata sulle attività come la pesca e il turismo. Tuttavia, sono disponibili poche informazioni sulle tecniche migliori di ripristino dei coralli che potrebbero essere applicate a livello regionale alle Maldive. Il "Coral Gardening", una tecnica che comprende l'allevamento di frammenti di coralli in vivai sommersi seguito dal trapianto di quest’ultimi in un sito di restauro, sembra particolarmente adatta per una località remota come l’arcipelago maldiviano. Il metodo, infatti, può essere utilizzato dalle comunità locali o organizzazioni turistiche per accelerare il recupero locale della scogliera corallina, creando al contempo consapevolezza e permettendo una gestione mirata delle sue risorse. Questo studio valuta l'applicazione su larga scala del "Coral Gardening" per il ripristino dei coralli alle Maldive, fornendo per la prima volta la necessaria validazione a livello regionale di questa tecnica. Per stimare le prestazioni di questo approccio di ripristino in diverse regioni e habitat (ad es. laguna e scogliera corallina), sono stati valutati un totale di sei vivai sommersi di corallo presenti sia sull'isola locale di Magoodhoo nell'atollo di Faafu che sull'isola turistica di Athuruga nell'atollo di Alif Dhaal. Il prestazioni della tecnica del coral gardening è stato valutato per tre diversi generi di coralli, quali Acropora, Pocillopora e Porites, utilizzando un protocollo di monitoraggio standard. Tale analisi hanno fornito parametri di riferimento regionali per la crescita dei frammenti in funzione del tempo e della profondità, nonché in funzione dei tassi di sopravvivenza dei coralli, che in genere superavano abbondantemente il 90% in entrambi gli habitat utilizzati. Inoltre, sono state prese in considerazione le interazioni ecologiche quali la fauna associata ai coralli e la presenza di predatori nel confronto tra i coralli allevati e trapiantati. L’utilizzo e l’efficacia delle tecniche di ripristino dei coralli sono state ulteriormente riesaminate rispetto al recupero naturale della scogliera corallina nel sito di ripopolamento, nonché delle potenziali implicazioni ecologiche delle attività di ripristino eseguite. In questo caso, il trapianto di coralli ha fornito ottimi risultati e ha apportato benefici significativi all'ambiente degradato della scogliera corallina, attraverso l’aumento in termini di abbondanza e diversità della comunità ittica, così come della copertura naturale dei coralli. Sebbene i risultati complessivi dello studio siano incoraggianti, questa ricerca affronta anche potenziali rischi per il successo del ripristino delle scogliere coralline. In particolare sono stati valutati i rischi inerenti gli effetti negativi legati ad un’interruzione prolungata delle attività di monitoraggio e manutenzione e degli eventuali impatti di patologie in grado di colpire i coralli. Nel complesso, i risultati presentati e le implicazioni pratiche ottenute grazie a questo lavoro forniranno una base scientifica per i futuri studi riguardanti il restauro delle scogliere coralline con la speranza che possano rappresentare una guida verso una conservazione di questo habitat più efficiente. Coral reefs, which are among the most biodiverse ecosystems on the planet, are declining at an alarming rate. To counteract the threats posed by climate change and other anthropogenic impacts, conservation efforts such as active coral reef restoration have increased globally. Ecological restoration aims to assist natural recovery and increase coral reefs resilience in an effort to preserve the many functions and services these iconic ecosystems provide to society. Under current climate scenarios, coastal and island populations are the first to suffer from continued ecosystem degradation. For example, the Maldives’ vulnerability to global and local coral reef threats is evident for a nation that lives on shallow reef islands with an economy driven by fisheries and tourism. However, little information is available on suitable, regionally tested coral restoration techniques that could be applied at an ecological meaningful scale in the Maldives. ‘Coral gardening’, which comprises fragment farming in coral nurseries followed by the transplantation of these corals to a restoration site, appears particularly suitable for remote locations like the Maldives. The method can be applied by local communities or tourism stakeholders to assist local reef recovery, while creating awareness, stewardship and even income opportunities. This research assesses the application of ‘coral gardening’ for upscaled coral restoration efforts in the Maldives, providing the necessary regional validation and useful insights into the various aspects of this technique for the first time. To evaluate the suitability and performance of this restoration approach across different regions and farming habitats (i.e., lagoon and reef), a total of six mid-water coral rope nurseries were assessed on the local island of Magoodhoo in Faafu Atoll and on Athuruga resort island in Alif Dhaal Atoll. Coral gardening success was examined for three different coral genera, namely Acropora, Pocillopora and Porites, using a common monitoring protocol. This delivered regional benchmarks for fragment growth over time and at different depths as well as coral survival, which typically exceeded 90% in both farming habitats. In addition, ecological interactions were investigated by including mutualistic fauna and predator associations in the assessments of farmed and transplanted corals. For example, a positive correlation between Trapezia guard crabs and farming stock health was observed, while the corallivorous nudibranch Phestilla is newly reported on coral nursery stock. Coral restoration demand and success is further reviewed in the context of natural reef recovery on the restoration site as well as potential ecological implications of restoration activities. Here, coral outplanting was successful and significantly benefitted the degraded reef environment, increasing fish abundance and diversity along with natural coral cover While the overall study results are encouraging, this research also addresses potential risks to coral restoration success, in particular the negative effects of prolonged monitoring and maintenance disruptions and the impacts of coral disease occurrence. Using a number of real case studies, it is demonstrated how these factors can diminish coral gardening outcomes and project success, if not managed in time. Overall, the findings presented and the practical applications concluded from this work hope to provide a scientific baseline for future restoration efforts that can guides restoration practitioners towards efficient conservation work.

Small island nations like the Maldives are highly dependent on healthy coral reefs and the ecosystem services they provide. Lately, Maldivian reefs have experienced considerable degradation as a result of severe mass bleaching events and accumulating threats posed by pollution, human development, coral diseases, and outbreaks of corallivores. Coral restoration can be a useful mitigation tool in assisting natural recovery, especially when economically important reef areas such as resort reefs are in poor health with slow natural recovery. This study assesses the performance efficiency of lagoon mid-water rope nurseries for coral gardening in two different atolls in the Maldives for the first time. Three different coral genera, namely Acropora, Pocillopora, and Porites, were assessed applying a common monitoring protocol. Fragment survival was generally very high, exceeding 90% survivorship for the genus Acropora and Pocillopora, while nursing success for Porites was significantly lower (66%). We further report benchmark growth rates for these genera in mid-water rope nurseries in the Maldives. The study also identifies potential threats to coral nursing success, namely disease occurrence and predation, as we report the corallivorous nudibranch Phestilla on in situ nursing stock for the first time. Overall, our results suggest that the use of mid-water rope nurseries in lagoons is an efficient and widely applicable technique for rearing corals in the Maldives. We aim to provide useful insight into best practices for applying this coral gardening technique on a wider scale in the archipelago and highlight future research requirements.

Corallivory causes considerable damage to coral reefs and can exacerbate other disturbances. Among coral predators, Drupella spp. are considered as delayer of coral recovery in the Republic of Maldives, although little information is available on their ecology. Thus, we aimed to assess their population structure, feeding behaviour and spatial distribution around 2 years after a coral bleaching event in 2016. Biological and environmental data were collected using belt and line intercept transects in six shallow reefs in Maldives. The snails occurred in aggregations with a maximum of 62 individuals and exhibited a preference for branching corals. Yet, the gastropods showed a high plasticity in adapting feeding preferences to prey availability. Drupella spp. were homogenously distributed in the study area with an average of 9.04 ± 19.72 ind/200 m2. However, their occurrence was significantly different at the reef scale with the highest densities found in locations with higher coral cover. The impact of Drupella spp. appeared to be minimal with the population suffering from the loss of coral cover. We suggest that monitoring programs collect temporal- and spatial-scale data on non-outbreaking populations or non-aggregating populations to understand the dynamics of predation related to the co-occurrence of anthropogenic and natural impacts.

The need for comprehensive and effective coral restoration projects, as part of a broader conservation management strategy, is accelerating in the face of coral reef ecosystem decline. This study aims to expand the currently limited knowledge base for restoration techniques in the Maldives by testing the performance of mid-water rope nurseries in a lagoon and a reef habitat. We examined whether different coral farming habitats impacted fragment survival, health and growth of two coral genera and how the occurrence of mutualistic fauna, predation and disease influenced coral rearing success. Two nurseries were stocked with a total of 448 Pocillopora verrucosa and 96 Acropora spp. fragments, divided into different groups (four Pocillopora groups: lagoon nursery at 5 m; reef nursery at 5, 10 and 15 m; two Acropora groups: lagoon nursery at 5 m and reef nursery at 5 m). Eight fragment replicates from the same donor colony (Pocillopora genets: N = 14, Acropora genets N = 6) were used in each group and monitored for one year. Our results show that fragment survival was high in both farming habitats (>90%), with P. verrucosa surviving significantly better in the lagoon and Acropora spp. surviving and growing significantly faster in the reef nursery. P. verrucosa growth rates were similar between reef and lagoon habitat. Different rearing depths in the reef nursery had no impact on the survival of P. verrucosa but coral growth decreased considerably with depth, reducing fragments’ ecological volume augmentation and growth rates by almost half from 5 to 15 m depth. Further, higher fish predation rates on fragments were recorded on the reef, which did not impact overall nursery performance. Mutualistic fauna, which correlated positively with fragment survival, was more frequently observed in the lagoon nursery. The occurrence of disease was noted in both habitats, even though implications for fragment health were more severe in the lagoon. Overall, our study demonstrates that lagoon and reef nurseries are suitable for rearing large numbers of coral fragments for transplantation. Nevertheless, we recommend considering the specific environmental conditions of the farming habitat, in particular water quality and year-round accessibility, in each case and to adjust the coral farming strategy accordingly. We hope that this novel research encourages the increased application of mid-water rope nurseries for ‘coral gardening’ to advance coral reef recovery and climate resilience in the Maldives.

Although corallivory is recognized as a threat affecting the structure and integrity of coral reef habitats, ecological data on most species of coral consumers remain limited, slowing down the development of conservation and restoration strategies of the reef ecosystems. In this study, the population distribution and corallivorous behaviour of the cushion sea star Culcita sp. were investigated in the south region of Faafu Atoll, Maldives. Most sea stars were found on reef slopes within 0–10m depth and in areas characterized by low live coral cover. Several coral genera were preyed on by the sea star. Although most of the consumed corals belong to the genus Acropora, a feeding preference for the genera Pocillopora and Pavona and a consistent avoidance of the genus Porites were observed. Furthermore, the majority of the prey corals were small colonies (< 10cm diameter), even though Culcita sp. appeared to be capable of partially consuming larger colonies. Dietary preferences for specific coral colonies or genera have the potential to generate local shifts in coral community composition and structure and may affect reef recovery following natural and anthropogenic disturbance in an already impacted environment such as the Maldivian reefs.

Outbreaks of the corallivorous crown-of-thorns seastars have received increasing attention due to their negative impacts on coral reefs in the Indo-Pacific Ocean. However, outbreaks in remote and dislocated islands are still poorly understood. This study aims to begin filling informational gaps regarding outbreaks of Acanthaster planci in the remote islands of the central Ari Atoll, Republic of Maldives. The population of A. planci was monitored during three periods over 2 years (2015-2016) to evaluate variations in abundance and to characterise size structure and feeding behaviour. The outbreak appeared to be severe and active throughout the entire study period. The size structure analysis revealed a multimodal distribution dominated by individuals between 20 and 30 cm, suggesting that the outbreak may have resulted from a few nearby mass spawning events. Additionally, the most abundant live coral was Porites, which was also the most consumed genus; however, the electivity index showed a preference for corals of the genera Favites and Pavona. Finally, we also highlighted the need for more geographically extended surveys to better understand local patterns regarding outbreaks of A. planci in the Republic of Maldives.