Maritechture™ screwable coral tiles have an internal thread that allows quick and tool free attachment to several other products outlined below in the following. Tiles are made from cement and shapes can be modified to cater for different propagation pathways, e.g. fragmentation, microfragmentation (Forsman et al., 2015) and recruitment ( Figures 1E, B, C ). We chose a hexagon shape for propagation of larger fragments, which allow easy screwing ( Figure 1D ). For propagation via micro-fragmentation, where a larger flatter surface is preferable, we developed a flatter hexagonal shape to promote the overgrowth of the surface ( Figure 1B ). For sexual propagation via larvae settlement, we developed a shape with multiple cavities to promote settlement. An RFID (radio frequency identification) chip can be embedded within the cement tiles, enabling long-term labelling of individual tiles ( Figure 1F ) and allowing for the identification and tracking of origin, performance and survival throughout restoration or enhancement efforts.

Maritechture™ coral crates ( Figure 2 ) are racks of durable, UV-resistant ABS plastic that allow coral tiles to be attached via threaded pins erected vertically from linear extrusions ( Figures 1A, B ). The design allows multiple tiles to be attached per frame, arranged in a uniform and equally spaced pattern. The crates are stackable and click into each other, creating a 10 cm gap between each level. Each row is pre-labelled, and the crates can be equipped with RFID tags or QR codes for organization of tiles. In their current design, each unit measures 50 x 50 x 15.5 cm and can hold up to 56 fragments. The crates have holes in their legs for horizontal connection of multiple crates, allowing, for example, the quick set-up of in situ nurseries.

The modular tile system allows for easy attachment and removal of propagated corals by screwing and provides great flexibility for different types of coral gardening and outplanting. Maritechture™ Reef Nails (patent pending) are threaded nuts that, when combined with a standard stainless-steel concrete/masonry nail, can be easily embedded in solid reef substrates and expose a thread that matches the coral tiles ( Figures 3A, B ). The nut fits tightly around the nail to avoid rotation but can be secured with additional adhesives if needed. Maritechture™ Reef Wall Plugs (patent pending) have the same function but are attached with a steel screw similar to a standard wall dowel ( Figures 3C, D ). They allow for quick and solid attachment of coral tiles to surfaces with predrilled holes, such as artificial structures.

To equip existing coral gardening infrastructures with our technology, we have developed several solutions (patents pending): Maritechture™ Clips for PVC pipe nurseries [e.g., coral tree nursery© (Nedimyer et al., 2011)( Figure 3E )], Maritechture™ adapters for steel rod/metal frame nurseries (e.g. Williams et al., 2019) that can be fastened with cable ties ( Figure 3F ), Maritechture™ adapters for aluminum frame/grid nurseries (e.g. Suggett et al., 2019) that can be fastened with cable ties ( Figure 3G ), and adapters for rope nurseries (e.g. Levy et al., 2010) that can be twisted into the rope and expose two sides for tile attachment ( Figure 3H ).

To provide a stable artificial substrate for coral outplants where this is lacking, we developed Maritechture™ Coral Pods, which are limestone structures consisting of two plates that can be assembled at 90-degree angles to form a quattro pod (four-legged stand) like structure ( Figure 4 ). Drilled holes along the top edge allow coral fragments to be attached with cable ties or Maritechture™ Reef Wall Plugs ( Figure 3C ). Additional holes in the center of the segments provide an ideal place for massive corals to be attached using our tile system. The shape and size (with individual panels approximately 145 cm long, 47 cm high, and 3 cm thick) aim to minimize waste during production and allow ergonomic handling, so the weight of each limestone segment is limited to approximately 20 kg ( Figure 4C ). The design provides stability in low to medium-energy environments. However, these dimensions and design (including number of stacked plates) can be adjusted depending on the available limestone slab sizes and the intended use.

With our technologies, corals may originate from sustainable harvesting (Rinkevich, 1995; Barton et al., 2017), fragments of hope (Garrison and Ward, 2012), coral relocation sites (Kenny et al., 2012), or nursery/growth operations (Rinkevich and Shafir, 2000; Barton et al., 2017). Propagation can be asexual by fragmentation (Rinkevich, 1995) or sexual by cultured (Petersen and Tollrian, 2001) or wild-caught larvae (Doropoulos et al., 2019) ( Figure 5 ). Regardless of origin, it is critical to collect as much metadata as possible on the corals to inform husbandry conditions and to direct downstream applications (Baums et al., 2011). This includes the GPS coordinates of the sample location in the case of wild-sourced corals or the origin of the donor/parental lineages in the case of husbandry. The sampling date, size, species, depth, temperature, light conditions, etc., should also be provided. These data should be recorded and stored in a central database ( Figure 5 ) to inform performance assessments and optimize future deployments.

Transplanting fragments or seeding larvae using trackable Maritechture™ Coral Tiles allows metadata to be associated with individuals via RFID tags. This information can guide culturing conditions during husbandry, for example, regarding light levels. Embedding the RFID tag into the transplant or seeding substrate allows for permanent long-term identification and efficient stock management (Schmidt-Roach et al., 2020). It will enable monitoring and tracking of individual colony performance, stress susceptibility, health and survival during culture and beyond, all of which can be related back to colony origin and history. If individuals die, the tiles can be cleaned and reused.

Tagged tiles are equipped with passive integrated transponders (PIT) based on radio frequency identification (RFID) with low-frequency operation (134.2 kHz) and 64-bit identification. The tags can be read with any PIT reader compatible with the ISO 11785 standard. When used in conjunction with inventory management software, this solution allows corals to be tracked as they are propagated or moved between tanks ex situ or sites/structures in situ to automatically update records. This enables real-time automated stock management to coordinate aquaculture and allocate harvestable colonies to outplanting efforts. We are currently prototyping software customized for this purpose.

For fragmentation, we use various standard cutting techniques such as bone cutters or a Gryphon Diamond Band Saw (AquaSaw). Adhesion of coral fragments to tiles or plugs is performed using various methods, including epoxy (e.g. Hein et al., 2020) or ultraviolet (UV)-curable oligomer-based adhesives (Takeuchi et al., 2019), or commercially available gel-based cyanoacrylate adhesives. It is important that the fragment’s tissue has grown over the tiles prior to outplanting, as the adhesion of the adhesive often wears off over time. It has been shown that coral fragments from branching species attached upside down grew significantly wider and faster over the tiles than corals attached right side up (Tagliafico et al., 2018), and we recommend this technique to promote rapid tile overgrowth.

The shape of the tile can be adjusted to the propagation pathway ( Figure 1 ). For fast-growing, branching species, we recommend small hexagonal tiles ( Figure 1E ). For slow-growing, massive species, we recommend larger tiles that allow the use of standard microfragmentation protocols ( Figure 1B ) (Forsman et al., 2015). For recruitment, we recommend structured tiles with small cavities, which have been shown to promote larval settlement (Nozawa et al., 2011; Randall et al., 2021).

Attachment of the tiles to the Maritechture™ Coral Crates supports the strategic organization of corals. The crates allow coral genotypes to be organized in rows divided into seven tiles per bar (labelled A-H on the crate) ( Figure 2A ). Secure attachment by the screw system avoids friction and damage to the colonies ( Video 1 ). The coral crate units facilitate easy handling in air and underwater and simplifies cleaning during aquaculture because of their smaller surface area compared to commonly used egg crate grids. The crates can also be tagged with RFID technology, allowing for automated inventory management. For transportation, the units can be safely stacked and transported directly to the outplanting site underwater. In addition, the horizontal connection of multiple crates and attachment to the seafloor enables the rapid establishment of in situ nurseries, e.g. for temporary storage.

We have developed several solutions for outplanting ( Figure 3 ). The advantage of our modular, screwable tile system is that coral crops can be quickly interchanged between crates and different structures or outplanted directly onto a natural or artificial substrate. We have developed adapters for the most common types of coral nursery structures including PVC pipes, metal rods, metal grids and ropes (Boström-Einarsson et al., 2020). This allows existing structures to be quickly modified and outfitted to accommodate our technologies.

Our Maritechture™ Reef Nails attach quickly (within seconds) to suitable reef substrate and create a solid bond that promotes attachment of the fragments to the reef substrate. A single dive buddy team can outplant over 50 fragments from a coral crate onto reef substrate in 30 minutes. For artificial structures that can be drilled with holes prior to deployment, we developed Maritechture™ Reef Wall Plugs. Similar in function to a conventional dowel, these allow for a solid connection of our tiles to artificial substrates such as Maritechture™ Reef Pods, jetty walls, floating villas or bridge piers.

We developed Maritechture™ Coral Pods as an environmentally friendly underwater landscaping tool to enhance reef landscapes and provide new substrate for coral outplanting and nursing where this is lacking. With our methods, we envision their use for the creation of artistically planned and curated underwater landscapes, whereby the structures can be arranged in geometric patterns for visual and orientation purposes. The units can be stacked flat on top of one another to minimize space requirements and ease transport and logistics costs. On-site, the coral pods can be quickly assembled either on board a vessel or underwater. The corals can be attached with Maritechture™ Reef Wall Plugs or cable ties.

In their current design, each assembled structure can accommodate up to 16 coral fragments. Given an area of 1.5 m² for coral growth per structure, we recommend a density of one structure per 3 m². With 14-16 corals per structure, this results in an outplanting density of approximately five corals per square meter, which may increase further with spontaneous natural recruitment, given that the material is highly suitable for coral settlement. By mounting the structures onboard a vessel, corals can be quickly attached before the pods are placed in the water, reducing dive time. In this way, a team of six can deploy up to 30 structures per dive, with four team members assembling the structures, stocking them with coral and lowering them with a crane, while two divers receive and position the structures on the seabed at the deployment depth. On rotation, a six-person construction team can place 90 structures in four hours, with each team member performing only a single dive. This allows for up to 250 square meters of reef landscape to be created in half a day.

To increase scalability and overcome time intensive adhesion during outplanting, Suggett et al. (2020) developed Coral Clips®, a fast solution to outplant fragments or tiles via a metal clip attached to a nail hammered into the reef. Similar in function to the Maritechture™ Coral Nails presented here, these work well on hard substrate and allow strategic placement of fragments during outplanting. While Coral Clips® are ideal to reattach so-called fragments of hope (lose fragments broken of larger colonies for example during storms), growing and attaching coral directly to their outplanting substrate via our Maritechture™ Coral Tiles minimizes the stress that may occur during detachment of corals after an intermediate gardening phase. Further, our tiles have the advantage of enabling long-term monitoring.

To avoid the need for dive operations at all during outplanting, Chamberland et al. (2017) proposed ceramic tetrapod structures seeded with coral recruits to be deployed from vessels into reefs. Although this permits the economic deployment of a large number of structures, tests need to be conducted to understand survival rates compared to recruitment tiles strategically placed using the Coral Clips® or Maritechture™ Reef Nail technology. Doropoulos et al. (2019) went a step further to propose industrial-scale harvesting of larvae via large vessels for relocation, whereby the mass of harvesting of coral larval slicks can be deported to foreign reefs to overcome the low survivorship of settlers. However, large scale pilot studies are still to be conducted.

Our Maritechture™ technologies provide the basis to enable the automation of coral reef restoration workflows in the future. Coral aquaculture can achieve higher production rates by optimizing conditions for increased growth, e.g. by adjusting light or temperature, or by co-culturing of beneficial biota and reducing algae growth (Craggs et al., 2019). However, optimal husbandry conditions can be species-specific (Merck et al., 2022). The organized placement of coral colonies on the coral crates allows quick and strategic performance assessments to ensure individuals are fostered under ideal conditions. Having coral fragments in fixed positions in the tanks may eventually facilitate AI-driven automated phenotyping, for example, via repeated structure from motion photometry using robotic solutions. Similar techniques are already in place in terrestrial systems to increase production rates and promote selective breeding (Humplík et al., 2015; Chawade et al., 2019). High-throughput phenotyping could enable big data analytics, which could dramatically increase production rates and the effectiveness of coral nursery efforts. Considering the current rise of applied use of robotic systems in fish farming (Wang et al., 2021) or even more distant sectors as part of the industry (Javaid et al., 2021), automatization of workflows is likely to play a significant role in reducing associated labor costs and achieving scale.

The ability to create detailed records and to trace performances over time using our trackable Maritechture™ Coral Tile technology enables unique information tools for stakeholder engagement. Creating cloud-based inventories and data records can not only guide coral restoration practitioners during their daily efforts, but it can also be used to inform stakeholders (e.g. governments or private entities investing into these efforts) about the success. Measuring and publishing performance can promote transparency and assist moderate expectations of the success of restoration efforts. Trust has been shown to significantly strengthen willingness to pay for restoration (Metcalf et al., 2015; Bakaki and Bernauer, 2016). In addition to building trust, communicating success as well as challenges on websites or social media may motivate public engagement and foster awareness. Projects could use this mechanism to transport positive messages of hope, which are important to gain public acceptance for government-funded restoration projects (Le et al., 2022).

For selective propagation efforts, it is vital to create detailed records to trace performances over time to permit adaptive management (Schmidt-Roach et al., 2020) and identify possible tradeoffs associated with the selected traits. Different pathways for thermal heat selection have been identified (Baums et al., 2019; Parkinson et al., 2019; Schmidt-Roach et al., 2020; Voolstra et al., 2020; Suggett et al., 2022). However, when comparing individuals from different environments, it should be considered that these may be phenotypically acclimated to different conditions, which may alter their performance in acute thermal stress assessments. Common-garden nurseries ex or in situ offer the advantage that individuals can be acclimated to similar conditions prior to testing, which may reduce acclimation biases during performance assessments. Although different strategies for selective breeding of corals for assisted evolution have been suggested (van Oppen et al., 2015; van Oppen et al., 2017) and partially tested (Humanes et al., 2021), the long-term effect and success of these strategies still remain uncertain. Our trackable tile system via RFID technology supports long-term monitoring efforts and permits informed adjustment of selective propagation strategies. In addition to RFID identification, the embedded stainless-steel nail in our reef nail solution can be detected using a metal detector similar to CoralClips® (Suggett et al., 2020).

Strategic outplanting can further increase genetic diversity and stress resilience, as restored corals have been observed to be reproductively active (Diraviya Raj et al., 2015). Coral pods and reef nails can be used to create coral seeding hubs (CSH), where different genotypes of conspecifics are planted in clusters strategically placed in the reef to promote reproduction and increase genetic diversity in the offspring (Schmidt-Roach et al., 2020). A portion of these transplants can be sourced from selected, higher stress resistant colonies to increase the frequency of favorable alleles in the population while maximizing genetic diversity (Schmidt-Roach et al., 2020). However, not all genotypes should be selected for increased single stress performance, and genetic diversity should be maximized to account for unforeseen stressors such as disease (Moriarty et al., 2020).

In contrast to present coastal developments that rarely extend beyond the shoreline, we advocate for a “blue architecture” and landscaping approach that extends landscaping of coastal developments into the sea. Community-conscious coastal developments that integrate the marine environment may secure natural capital (Cziesielski et al., 2021). Schmidt-Roach et al. (2020) stressed the mutual benefit of integrating coral restoration efforts in coastal developments to rehabilitate natural habitats and foster and secure blue natural capital as part of development assets. In addition to conventional restoration operations, the elements, tools and processes presented here allow easy and quick beautifications of jetty walls and other coastal structures with corals, turning these into meaningful resources to grow corals for restoration and to create or restore fully functional habitats.

A blue architecture and landscaping approach to coral restoration requires the contribution of a multidisciplinary team including marine ecologists, engineers, architects and artists, forming a community of practice that extends well beyond the competencies applied in conventional coral restoration projects. Applying a landscaping approach, our techniques allow the creation of scientifically and artistically curated underwater habitats resembling land-based botanical gardens. Architecture that extends into the sea connects coastal residents with their natural marine resources, engages citizens with restoration, raises awareness, promotes responsible stewardship, and boosts local economies. This may especially be of interest for ecotourism projects providing a dual benefit of attracting visitors and increasing resilience hence securing investments (Schmidt-Roach et al., 2020). Visionary plans for floating cities to address sea-level rise and overpopulation have become more concrete (Bolonkin, 2011; Wang, 2019) and offer unique opportunities for integrating marine landscape designs into marine urban projects. Massive tropical floating cities such as Oxagon envisioned by NEOM (https://www.neom.com/en-us/regions/oxagon) or Oceanix by BIG (https://big.dk/#projects-sfc) could be easily adjusted to harbor coral farming using the technologies presented here.

In conclusion, our platform aims to provide simple, eco-friendly and flexible infrastructure that caters towards a variety of different coral restoration and reefscaping efforts with a view of rendering coral restoration more cost-effective, scalable and sustainable. This is achieved by reducing workflow times as outlined above and ease of handling. Integrating novel monitoring tools, our approach delivers an intelligent solution to optimize and control stock management and enables adaptive management. The modularity of the tools aims to allow greater flexibility as different components can be added in the future to increase efficiency and effectiveness. We aim to make the above-described solutions available as the first modular off-the-shelf coral restoration technology, targeting production at scale to drive down costs, and to make them universally available.