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The increasing frequency and severity of coral bleaching underscores the need for effective coral reef restoration programs. These initiatives include deploying coral fragments or early recruits (spat), with large-scale coral seeding success dependent on improving coral survival by minimizing competition from algae and benthic invertebrates. This study presents a proof-of-concept field experiment assessing the effectiveness of two commercial non-biocidal fouling release coatings (FRCs) and an FRC wax coating in reducing fouling on coral seeding devices. Ceramic devices treated with FRCs were deployed with Acropora millepora microfragments and monitored over 46 weeks. Coated devices experienced significantly less fouling than uncoated controls, particularly during the critical early months when coral spat are most vulnerable. The best performing coating maintained over 10 times more clear surface area than uncoated devices, providing sustained protection without affecting coral survival. Corals also successfully overgrow the coatings by trial’s end. These findings suggest that FRCs could protect smaller coral spat from overgrowth, reducing early mortality until they reach a size escape threshold. Such coatings also hold promise for large-scale restoration projects, coral nurseries, and aquaculture. Future research should evaluate their efficacy across diverse habitats, particularly areas with high macroalgal cover, to optimize their application in restoration strategies. 

Developing an optimal heterotrophic feeding regime has the potential to improve captive coral growth and health. This study evaluated the efficacy of three exogenous diets: Artemia nauplii (ART), a commercially available coral diet (Reef Roids) (RR), and a novel, micro-bound diet (ATF), against a comparatively natural, unfiltered seawater treatment (RAW), and an unfed, ultra-filtered seawater treatment (CTL), in adult Acropora millepora and Pocillopora acuta nubbins. After 90 days, both species showed significantly positive weight gain in response to one treatment (A. millepora-RAW, P. acuta-ART), and comparatively low growth in response to another (A. millepora-ATF, P. acuta-RR). The results highlighted substantial differences in the nutritional requirements between species. The nutritional composition of A. millepora in the best performing treatment was dominated by high-energy materials such as storage lipids and saturated and monounsaturated fatty acids. In contrast, the P. acuta nutritional profile in the superior treatment showed a predominance of structural materials, including protein, phospholipids, and polyunsaturated fatty acids. This study demonstrates that Artemia nauplii can successfully replace a natural feeding regime for captive P. acuta, yet highlights the considerable work still required to optimise supplementary feeding regimes for A. millepora.

Heterotrophic feeding in newly-settled coral planulae can potentially improve survivorship and accelerate early development in some species; however, an optimal diet to facilitate this does not currently exist. This study evaluated the efficacy of three heterotrophic feeding regimes (enriched rotifers, unfiltered seawater, and a novel, particulate diet), against a wholly-phototrophic treatment on Acropora hyacinthus, A. loripes, A. millepora, and A. tenuis recruits, over 93 days post-settlement. The unfiltered seawater treatment recorded maximum survival for all species (A. hyacinthus 95.9±8.0%, A. loripes: 74.3±11.5%, A. millepora: 67±12.7%, A. tenuis: 53.2±11.3%), although not significant. Growth (% surface area gain) was also greatest in the unfiltered seawater, and this was significant for A. millepora (870±307%) and A. tenuis (693±91.8%) (p<0.05). Although total lipid concentration was relatively stable across treatments, the lipid class composition exhibited species-specific responses to each treatment. Lower saturated and higher polyunsaturated fatty acids appeared beneficial to recruit performance, particularly in the unfiltered seawater, which generally contained the highest levels of 20:5n-3 (EPA), 22:6n-3 (DHA), and 20:4n-6 (ARA). The present study demonstrates the capacity of a nutritionally adequate and readily accepted heterotrophic feeding regime to increase coral recruit survival, growth, and health, which can greatly reduce the time required in cost- and labour-intensive culture.

The corallivorous Crown-of-Thorns Starfish (CoTS, Acanthaster spp.) has been linked with the widespread loss of scleractinian coral cover on Indo-Pacific reefs during periodic population outbreaks. Here, we re-examine CoTS consumption by coral reef fish species by using new DNA technologies to detect Pacific Crown-of-Thorns Starfish ( Acanthaster cf. solaris ) in fish faecal and gut content samples. CoTS DNA was detected in samples from 18 different coral reef fish species collected on reefs at various stages of CoTS outbreaks in the Great Barrier Reef Marine Park, nine of which had not been previously reported to feed on CoTS. A comprehensive set of negative and positive control samples confirmed that our collection, processing and analysis procedures were robust, although food web transfer of CoTS DNA cannot be ruled out for some fish species. Our results, combined with the (i) presence of CoTS spines in some samples, (ii) reported predation on CoTS gametes, larvae and settled individuals, and (iii) known diet information for fish species examined, strongly indicate that direct fish predation on CoTS may well be more common than is currently appreciated. We provide recommendations for specific management approaches to enhance predation on CoTS by coral reef fishes, and to support the mitigation of CoTS outbreaks and reverse declines in hard coral cover.

Early post-settlement mortality is a major bottleneck in larval-based coral restoration, largely driven by competitive overgrowth from benthic fouling organisms. Non-biocidal fouling-release coatings (FRCs) may reduce fouling pressure and enhance spat survival, but their efficacy in situ remains poorly quantified. We evaluated whether a commercial FRC could reduce benthic fouling and improve survival of Acropora loripes spat on a mid-shelf Great Barrier Reef. Larvae were settled onto ceramic seeding devices containing either FRC-treated or untreated (control) cores. Devices were deployed on the reef and monitored for fouling cover and spat survival over 46 weeks (~12 months). Relationships between spat survival, fouling, and benthic community composition were assessed. Fouling was substantially lower on FRC-treated devices, with only 25% fouling cover, compared to near-total overgrowth on controls. Importantly, spat survival remained consistently higher on FRC devices (68%) compared to controls (59%) at 46 weeks. Spat survival was negatively associated with device fouling, independent of immediate benthic community composition. This study provides the first in situ mechanistic evidence that FRCs indirectly enhance coral spat survival by mitigating competitive fouling pressure during the critical early growth period. Although the greatest benefit occurred in the first six months, fouling protection persisted throughout the deployment, suggesting that FRCs could provide a scalable solution to improve restoration outcomes. Integration of FRCs into seeding device design represents a promising strategy to support large-scale coral reef restoration under ongoing climate stress.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Active restoration or intervention programs will be required in the future to support the resilience and adaptation of coral reef ecosystems in the face of climate change. Selective propagation of corals ex situ can help conserve keystone species and the ecosystems they underpin; cross-disciplinary research and communication between science and industry are essential to this success. Zoos and aquaria have a long history of managing ex situ breed-for-release programs and have led the establishment of wildlife biobanks (collections of cryopreserved living cells) along with the development of associated reproductive technologies for their application to wildlife conservation. Taronga Conservation Society Australia’s CryoDiversity Bank includes cryopreserved coral sperm from the Great Barrier Reef, which represents the largest repository from any reef system around the globe. This paper presents results from an inventory review of the current collection. The review highlighted the skew toward five Acropora species and the necessity to increase the taxonomic diversity of the collection. It also highlighted the need to increase geographic representation, even for the most well represented species. The inventory data will inform Taronga’s future research focus and sampling strategy to maximize genetic variation and biodiversity within the biobank and provide a test case for other practitioners implementing biobanking strategies for coral conservation around the world. Through co-investment and collaboration with research partners over the next decade, Taronga will prioritize and resource critical applied research and expand biobanking efforts to assist interventions for reef recovery and restoration.

Coral bleaching is occurring more frequently as the climate changes, with multiple mass mortality events recently recorded on the Great Barrier Reef. Thermal stress coupled with high irradiance have previously been shown to be primary causes for coral bleaching. Therefore, a reduction in either of these pressures could reduce coral stress and eventual bleaching. Herein, we report the early development of a novel technology capable of reducing the amount of light entering a water body by ~20% in open ocean conditions. This mono-particle “sun shield” consists of an ultra-thin monolayer material and reflective calcium carbonate particles. The monolayer enables spreading of the particles into a thin film across the water surface, with only small amounts of material needed: 7.1 g/m2. A numerical modelling case study of residence times and the build-up of reactive oxygen stress in corals showed that the successful application of a stable film over the Lizard Island reef flat could reduce the reactive oxygen stress to below bleaching levels across approximately 1.5 km2 of reef area. With further development, mono-particle films such as this have the potential to be deployed over at-risk coral reefs at relatively small scales during predicted heatwave conditions, potentially reducing the severity of bleaching on coral reefs.

Scleractinian corals are colonial organisms comprising multiple physiologically integrated polyps and branches. Colonialism in corals is highly beneficial, and allows a single colony to undergo several life processes at once through physiological integration and compartmentalised functioning. Elucidating differences in the biochemical composition of intra-colonial branch positions will provide valuable insight into the nutritional reserves underlying different regions in individual coral colonies. This will also ascertain prudent harvesting strategies of wild donor-colonies to generate coral stock with high survival and vigour prospects for reef-rehabilitation efforts and captive husbandry. This study examined the effects of colony branch position on the nutritional profile of two different colony sizes of the common scleractinian, Acropora millepora . For smaller colonies, branches were sampled at three locations: the colony centre (S-centre), 50% of the longitudinal radius length (LRL) (S-50), and the colony edge (S-edge). For larger colonies, four locations were sampled: the colony centre (L-centre), 33.3% of the LRL (L-33), 66.6% of the LRL (L-66), and the edge (L-edge). Results demonstrate significant branch position effects, with the edge regions containing higher protein, likely due to increased tissue synthesis and calcification. Meanwhile, storage lipid and total fatty acid concentrations were lower at the edges, possibly reflecting catabolism of high-energy nutrients to support proliferating cells. Results also showed a significant effect of colony size in the two classes examined. While the major protein and structural lipid sink was exhibited at the edge for both sizes, the major sink for high-energy lipids and fatty acids appeared to be the L-66 position of the larger colonies and the S-centre and S-50 positions for the smaller colonies. These results confirm that the scleractinian coral colony is not nutritionally homogeneous, and while different regions of the coral colony are functionally specialised, so too are their nutritional profiles geared toward meeting specific energetic demands.

Sexual propagation of corals is a promising strategy for coral restoration, but one of the main challenges is the high mortality of coral spat due to competitive interactions with macroalgae during the early life history stages. Optimising the properties of settlement substrates such as material types and surface roughness has the potential to improve the survival of spat by limiting the recruitment and growth of macroalgae. In this study, we assessed the effects of modifying surface roughness across three different tile materials (alumina-based ceramic, calcium carbonate (CaCO 3 ), and concrete) on the settlement success and post-settlement survivorship of Acropora kenti coral larvae in six mesocosm tanks, each with different established macroalgal communities. The macroalgal community compositions on the tiles were significantly different among material types, but not surface roughness, although the type and abundance of macroalgal species were heavily influenced by the established tank communities. Increasing surface roughness did not affect larval settlement success or spat survivorship. Substantially higher larval settlement density was found on concrete tiles (1.92 ± 0.10 larvae cm −2 ), but spat survival was the highest on CaCO 3 tiles (73.4 ± 4.2% survived). Very strong competitive interactions were observed between spat and macroalgae, with overgrowth by the crustose coralline alga Crustaphytum sp. and the brown alga Lobophora sp. being the primary cause of spat mortality. Overall, when taking into account both settlement and survival rates, concrete was the best performing among the tile types tested here.