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First 100 Corals Planted using Recycled Glass Sand

Our project sponsored by Medalla Light is officially underway! On June 11, our team successfully planted 100 Elkhorn coral (Acropora palmata) fragments using three different cement mixtures.

Elkhorn coral. Photo by Hector Ruiz

This is a scientific pilot project for us, so we are approaching this as scientists would - with a control and treatment groups. The first mix is our control mix and contains only cement and marmolina. This is the mixture we traditionally use to cement coral fragments to the reef. The cement is the hardening agent and the marmolina (or, crushed marble) slows the process slightly which gives us time to plant multiple fragments before the cement hardens beyond manipulation. Once planted, it takes about 45 minutes before the mixture is hard to the touch, but it requires at least 24 hours before it's fully cured. This is important because it highlights the level of planning that must go into a coral restoration event. For example, we generally need at least two great weather days - one day to plant and the next day to allow the cement to cure without hindrance from swell, strong currents or natural disturbances like storms and hurricanes.

The other two groups are our experimental, or treatment, mixes. The first mix is 2:1:1 cement/marmolina/recycled glass sand (RGS) and the second is 1:1:1 of the same components. The purpose is to see how much RGS we can incorporate before the integrity of the mix is compromised. In our land-based trials, we discovered that these mixtures worked great, but a mixture of 1:1:2, with RGS being the highest percentage component, was too much RGS to maintain a workable mix. So, now we will brainstorm a couple additional ideas but in the meantime, we took our working mixes to the field!

After clipping 100 fragments from the adjacent coral nursery, maintained by HJR Reefscaping, the team located a suitable area to evenly distribute our coral fragments in experimental plots. The photomosaics below show the area before and after the planting (use the slider to see the full photo).

There are 25 fragments per mix, except for the 2:1:1 mixture that has 50. Each fragment was measured so that we have the "starting size" in order to assess growth over time, which will be monitored for one year. Approximately 200 more coral fragments will be planted in the area nearby, using at least two additional experimental cement mixes and a combination of the current mixes. This will give us a good variety of mixtures among our plots to allow us to adequately assess if the RGS material has any affect on the growth rate of the corals. We hypothesize that the RGS mixes will not hinder coral growth and may even increase the growth rate due to the high concentration of silica present in the mix, which is a mineral that corals and other marine organisms use naturally.

After all the corals are planted, we will return to the location to monitor their growth every three months. We look forward to reporting what we find! You can follow along with the progress here on our News page.


Curious how the bottle crushing actually works? Take a look at this video where we describe the process!


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