Nature Healed by Nature—Eco-Friendly, Advanced Underwater Materials for Coral Reef Conservation and Restoration

Coral reefs are one of the most biodiverse ecosystems in the world and provide support for food, medicine, and tourism to the local population. Corals are animals that host several symbiotic microorganisms, including dinoflagellate algae (primarily Symbiodiniaceae) and bacteria, which supply their metabolism and homeostasis, and produce calcium carbonate to form their exoskeletons, which in turn build coral reefs. This fascinating ecosystem is threatened by decline due to climate changes, human-related activity, and the increase in seawater temperature. Massive events of coral disease outbreaks and coral bleaching are becoming more frequent every year, and it has been estimated that by the end of 2050, 50% of the reefs will be damaged.
Researchers are making several efforts in the direction of healing, restoring, and rescuing the reefs, but most of their approaches have been unsuccessful in arresting the progression of this ecological drama. For instance, corals are farmed in protected environments such as aquaria or outdoor structures called “nurseries” and then transplanted in the coral reefs to repopulate damaged reef areas. Probiotics, antibiotics, and active molecules have been proposed for managing coral diseases and bleaching; however, they have highlighted the lack of efficacy, scalability, and tools for proper underwater administration into corals. Moreover, the materials used in coral restoration actions and strategies are often plastic-based, improperly designed to be eco-friendly, compatible with corals and other marine species, and not biodegradable.
To increase the number of these actions massively, huge human resources efforts are required. Specifically, the working time of specialized divers is affected by oxygen consumption, limiting their actions to 1-2 hours and requiring a broad turnover of operators.
Finally, Sustainable Development Goals (SDGs) released by the United Nations highlight the need for more advanced actions that take into account keeping and protecting the biodiversity and life below water (SDG 14) while avoiding releasing toxic or not biodegradable compounds in the seawater (SDG 6) and using bio-based materials (SDG 12).
Here, natural, biodegradable, and eco-friendly materials to be used in coral restoration and to face coral disease and bleaching will be presented. The designed materials have physicochemical and mechanical features suitable for corals and to be used underwater, varying from responsive and controlled drug delivery systems to antifouling and conductive bio-cement. In addition, such materials can be used as potential materials for underwater robotics or as application tools for existing robots, which can support divers in enhancing coral restoration yields with the hope of giving a chance of survival for this millennial underwater paradise.