Application of BMCs through encapsulation in biodegradable polymers to enhance coral health in the context of restoration

Coral reefs are crucial marine ecosystems that support a third of marine biodiversity and provide benefits and services to human populations that include coastal protection, sustenance, and commercial fisheries and tourism. However, coral reefs are under immense pressure due to local and global threats. Among local stresses are pollution, coastal development, and overfishing. The increase in average sea-surface temperature and ocean acidification caused by climate change are increasing the intensity of coral bleaching and mortality. The increase in the intensity and frequency of mass bleaching events led to the harsh decline in coral cover and ecosystem health, which calls for the development of urgent and innovative restoration solutions.Active restoration techniques such as the Mars Assisted Reef Restoration System (MARRS) provide stable substrates for coral growth and larval settlement. However, corals are variable in growth rate, and restoration projects take years to create a functioning coral reef ecosystem successfully. In addition, coral fragments are vulnerable in the early stage of transplanting due to stress related to fragmentation and environmental factors. Marine probiotics or Beneficial Microorganisms for Corals (BMCs) are administered to corals to enhance growth and resilience as the beneficial bacteria benefit their coral host.BMCs have been delivered to corals by directly administering bacteria in a saline solution. Encapsulation of bacteria is an alternative and viable option that can be used for the application of BMCs. Alginate beads are biodegradable polymers that are derived from algae. BMCs can be encapsulated in alginate beads and slowly release bacteria over a period of two to three weeks. In our recent experiment, we administered BMCs that are encapsulated in alginate beads to coral fragments in our MARRS. We put alginate beads in 3-D printed 15 cm cylindrical containers that have slit systems with a membrane on the slits that are opposite the coral side on the reef star bar to allow the flow of bacteria to one side only. We had three treatments in our experiment, which are: 1) control, where we attached empty containers on the bar where we had the corals, 2) alginate beads in the containers, and lastly, 3) BMCs encapsulated in alginate beads in the containers.  Our preliminary results showed an improvement of survivorship in the BMC-beads treated corals compared to control and empty bead treatments. These preliminary results suggest that using BMCs encapsulated in alginate beads can enhance coral survivorship during heat stress, positively impacting restoration efforts.