Coral Restoration Update: Spring 2022

In late April, we completed the outplanting for our pilot project using the experimental mixtures of recycled glass sand (RGS) and cement for coral reef restoration. We now have a total of 400 coral fragments in our project. Now we continue the monitoring phase where we revisit the coral fragments over time and document their growth and survivorship.


Elkhorn coral fragments that have started to fuse to the cement

The first monitoring expedition was last week. During this outing, our team visited the experimental plots to record a number of variables including:

  • size of the fragment (length, height)

  • fusion to the cement (had the fragment started to overgrow the cement?)

  • percent mortality (amount of the individual fragment that had died)

  • percent survivorship overall (number of fragments still living)

  • presence and percent of coral bleaching on the fragment

Using these metrics we can calculate and overall mean fragment size and survivorship estimate for each experimental plot by RGS mixture. The results?


Each plot had over 50% survivorship! In fact, no plot had less than 76%, which is amazing! Especially considering that in general most coral reef restoration initiatives are considered a success when at least 50% of the fragments survive. So we are doing better than the average restoration initiative - in fact, several plots had 100% survivorship!


There was also fusion already happening for many of the corals, which is great news that they have started to overgrow the RGS/cement mixtures. This was observed for corals in each of the experimental RGS ratios, so that means that at least our ratios are not inhibiting coral growth, which is what we anticipated. Additionally, every single coral was still secured to the substrate (no loose or missing fragments!) which proves the mixture is working as a strong adhesive!


The average size was 11 - 12 cm (4 inches) in length and 2-3 cm (1 inch) in height

One of our experimental plots with Elkhorn coral fragments

In terms of recycling, we have now used at least 14 cases of Medalla Light or roughly 344 beer bottles! This figure specifically refers to the number of bottles used in the actual cementation of the corals, and doesn't include the numerous other bottles we have used in the trials prior to the actual restoration.


These are promising results for the future use of RGS in marine conservation initiatives. This project will conclude next June 2023, and until then we will continue to monitor the growth and survivorship of these plots - and hopefully introduce some new corals to the area through continued restoration efforts as well. Stay tuned!