By Andrew Bruckner, Georgia Coward, Coral Reef CPR

The most devastating coral bleaching event affecting reefs worldwide unfolded between 2015 and2017.  Over 80% of the world’s reefs bleached, triggering massive coral die-offs. In many locations bleaching was followed by outbreaks of coral disease and explosions of coral predators.  The Maldives was no exception.  Reefs here had rebounded after the last major bleaching event in 1998, and thriving communities of staghorn coral, table coral, boulder coral and foliaceous lettuce coral abounded.  Between March and June 2016, water temperatures climbed to 32-36° C, causing corals to turn stark white, and quickly dying. Catastrophic losses of the dominant branching and table corals (Acropora spp; Pocillopora spp.) and plating corals (e.g. Echinopora, Pachyseris, Pavona) left entire habitats devoid of coral and color with mortality extending to 30 m and deeper.

Typical shallow reef in the Maldives following the bleaching event. All of the table and staghorn corals died

Fortunately there were isolated survivors, and the slow-growing massive frame building corals (e.g. Porites) fared much better.   Our team also found bleaching refuges that still contained some of the table acroporids and thickets of staghorn coral that these reefs were most renowned for, and recovery is underway due to survival of juvenile corals and settlement and growth of new coral recruits. 

The rate at which these reefs rebound may depend on the time until the next severe El Niño event.  But right now what is most critical is the severity of localized impacts, as this may affect the ability of the reef to adapt to and resist future temperature disturbances. The recent, accelerating development boom in the Maldives has dramatically increased concentrations of coral predators (Drupella snails, and Culcita and Acanthaster sea stars), as well as run-off, sewage discharge and other land based pollutants may delay recovery and reduce the resilience of these reefs to climate change, unless drastic steps are taken to modify human behaviors and practices. 

Another key step undertaken by Coral Reef CPR is an expansion of coral gardening and restoration through development of coral nurseries and outplanting of nursery-reared corals onto damaged reefs.  Since August 2016, we’ve introduced new approaches for coral nurseries to the Maldives and have expanded our nurseries to three different atolls.  We currently have over 16,000 corals within our nurseries.  Our nurseries have exhibited over 95% survival, and thousands of these corals are ready to outplant onto reefs. 

During the pilot phase of this project, we evaluated the existing coral rehabilitation projects in the Maldives and elsewhere, and tested different approaches to grow corals. These include use of metal frames, securing corals to cement and other structures, attaching coral branches directly to the reef, and growing corals on elevated tables, ropes and floating PVC trees. These tests would enable us to identify the most effective, low cost, low tech and optimal technique for use in the Maldives. Our ultimate goal was to develop a coral nursery technique that would enable large scale replication throughout the country, on both resort and local islands.

One of our initial nursery techniques; a plastic mesh table used to grow coral fragments The same mesh table after eight months

The same mesh table after eight months

The same table after one year

We first tested the existing approach that is in widespread use by resorts throughout the country in “adopt a coral” programs.  We attached tiny coral fragments to metal (rebar) frames. Most resorts will sell these frames to guests as a reef conservation approach, and typically involve the resort operator or dive center staff attaching coral branches to the frame with cable ties.  The frames are usually placed in shallow, sandy lagoonal areas where guests snorkel (and often in areas that coral would not naturally grow).  In all of the areas that we worked, more than 98% of the corals on these frames died during 2016.  Sadly resorts continue to use these, and in numerous cases they attach entire colonies to the frames to “show” rapid growth, yet they are actually causing more damage by removing colonies from sensitive reef areas that are key to the recovery of the reefs.  Another issue involves the deterioration of the frames over time.  They tend to begin rusting after a few months and this promotes algal growth.

Our next method to test involved  collecting coral branches that had accumulated in sand patches adjacent to reef environments, and attached these directly to reef substrates in fore reef communities using cement nails and cable ties. The coral fragments grew over the nail and fused with the reef quite quickly, and they continued growing upright, forming small bushes over the next few months.  While this technique was feasible in some areas, they require weekly maintenance, as many of our corals succumbed to predation by Drupella gastropods.  These snails aggregated on the coral branches, as this was the only preferred available food source for the snails, and many were subsequently killed.  We had similar problems using cement structures that were placed in sandy and rubble areas, and some of these were even attacked by crown of thorns starfish (Acanthaster spp.).

To avoid issues with coral predators, we began growing corals on elevated tables and suspended in the water column on ropes.  We experimented with different locations and depths for our nurseries, both protected lagoonal areas and on outer fore reef communities from 1-20 m depth.  Regardless of location, we had exceptional rates of growth, but there were large differences depending on depth, habitat and species.  We were forced to abandon nurseries on the outer reefs in South Malé Atoll, as they were badly damaged during a severe monsoonal storm; entire tables were broken, overturned and carried into deeper water, while rope nurseries fared much better.

An example of our chosen nursery technique; a coral rope nursery when first established

The same ropes after four months

The same ropes after ten months

Maintenance of nurseries was our other key lesson.  On several outer reefs, our tables were infested with competing benthic animals, especially sponges and tunicates.  While these could be easily removed, some of our nurseries were not visited and cleaned for 3-4 months and tables became overgrown by tunicates.

After experimentation through the fall/winter of 2016, we selected coral rope nurseries as the optimal technique in the Maldives.  They are very inexpensive, can be fabricated with materials that are readily available in every small island nation, and are very efficient.  Two of us have been able to set up a coral nursery containing over 3,000 corals within a week, with most of the investment in non-destructive collection practices. We use coral branches that are rescued and would otherwise die, collecting fragments that were broken by snorkelers, located in construction and sand extraction sites, and affected by diseases and coral predators.  We never remove a coral colony that is attached to the reef, and when collecting branches from colonies that resisted bleaching, we only take the branch tips.  In this way, the remainder of the coral will survive and can continue growing.

A set of ropes with staghorn fragments when first established in October 2016

Same ropes in February 2016

Same ropes in August 2016. These were transplanted onto a reef at the end of 2017.

Once we have collected enough coral, we use common garden clippers to cut the corals into small fragments (2-8 cm in length) and attach these to ropes with a thin cable tie.  By suspending corals in the water column, we avoid burial by sand, the corals are exposed to higher water flow, and they are out of reach of coral predators.  They grow quickly, first cementing over the cable tie within just a few weeks and then beginning to branch.  Within three months, our corals are small 10 cm bushes and after 12-18 months they are large colonies, 20-30 cm in diameter and are ready to transplant to a reef. 

Using ropes also makes transplantation much easier.  We can simply cut the rope to separate the coral and then secure the coral to the bottom with a nail and cable tie or non-toxic epoxy, to glue it to the reef. 

The key step in outplanting our corals is to make sure the corals are in similar habitats and depths, and when moving to other depths to slowly acclimate the corals so they will survive.  There is also a need for continued monitoring, to avoid invasion by coral eating snails and sea stars and to remove algae if present.  The other important stage is to plant corals in clusters, placing different genetic clones of the same species in close proximity, so that your efforts will benefit other reefs, by increasing successful potential for reproduction and production of new coral larvae.

Close-up of two coral fragments when they were first attached to a rope

Same coral fragment after one year

Second coral fragment after one year

Having successfully expanded our coral nurseries and restoration efforts to three atolls, our goal is to grow our program throughout the Maldives and into other Indian and Pacific Ocean locations.  We have developed a very successful model partnering with resorts, through their Corporate Social Responsibility (CSR) programs.  This benefits both the reefs and the resort.  The resorts are responsible for managing and protecting reefs around the resort, their guests want the opportunity to snorkel and dive on beautiful reefs, and resorts are supposed to take steps to demonstrate they are environmentally friendly and have a sustainable business model.  We focus much of our work on education and training, working with resort staff, communities and students on these projects.  We conduct seminars and workshops to improve their awareness and understanding of reefs.  We teach them new techniques and strategies in coral gardening that can help them cope with changing circumstances due to climate change.  We empower them to make a difference by involving them in our in-water efforts to establish coral nurseries and turn ownership of these nurseries to them, helping them throughout the entire process, from growing the corals to outplanting them onto the reefs.

Through additional funding for our staff, we would be able to expand the spatial scale of this project, benefiting coral reefs and the humans that rely on these reefs worldwide, especially developing small island nations that house the majority of the world’s coral reefs, but lack capacity and finances to address conservation needs.  Help Coral Reef CPR achieve our goals through a donation to our coral gardening efforts. Find us on Facebook (@coralreefcpr) and check out our website for more information:  www.coralreefcpr.org

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This piece was edited and posted onto SEVENSEAS Media by: Giacomo Abrusci