Coral Reef Restoration
Koh Tao, Thailand

Earth’s coral reefs are vital to human beings and the planet’s wider ecosystem for many reasons:

• Habitat for a huge range of aquatic life; Estimates suggest over 800 species of hard coral exist, with more than 4000 species of fish living around coral reefs. Studies indicate that a quarter of all fish species live near coral reefs. Coral reefs provide habitat and shelter for near countless species of marine organisms.
• Food Source; The massive population of fish living in and near coral reefs is reported to feed over half a million people globally.
• Spawning Ground; It’s not only fish species which remain amongst the corals who are dependent on reefs. Coral reefs are also an important spawning habitat and/or feeding ground for countless oceanic species too.
• Epic Biodiversity; Scientists identify coral reefs as a rich environment for discovering new compounds and approaches to drive research, with much greater potential than land-based alternatives.
• Tourism; Scuba diving and snorkeling to explore coral reefs is a huge attraction for tourist destinations throughout the tropics.
• Employment; Tourism & fishing industries dependent on coral reefs provide jobs for hundreds of millions of people
• Critical role in Ocean Chemistry; Coral reefs perform a key function in carbon and nitrogen-fixing, nutrient recycling, and the oxygen production cycle. Without coral reefs, many processes would become severely disrupted or impossible.
• Prevention of Coastal Erosion & Flooding. Coral reefs form a natural barrier against wave action and storms. In 2014, the journal of Nature Communications published an article detailing the ‘effectiveness of coral reefs for coastal hazard risk’, in which corals are reported to be able to reduce wave energy by up to 97%!

The effects of humans, and our contribution to climate change have a significant impact on coral reefs in a variety of ways.

Ocean Warming

Greenhouse gas emissions and the warming of the oceans is the most obvious impact which results in coral bleaching. To date, 70% of global coral reefs have experienced these destructive bleaching events. Corals thrive in water between 23-31˚C much of the world’s coral currently exists in water right at the upper limit of this temperature range and in shallow water most susceptible to increases. An increase of just one degree can trigger a bleaching event here in the Gulf of Thailand.

Acidification

Increased levels of CO2 in our atmosphere also dissolve into the ocean lowering the overall pH. This results in what we call ocean acidification which results in corals building weaker structures and becoming more susceptible to damage from storms.

Dissolved Oxygen Content

A final significant factor is the results of runoff from human coastal settlement. Dense coastal population settlements often result in hypoxic “dead zones” where there is not enough dissolved oxygen to support life. Species such as clownfish are highly at risk as they require high levels of dissolved O2. If species that exist in the coral reef ecosystem are lost it can become unbalanced and ultimately result in its destruction.

Over 5,000 species of corals are known worldwide, supporting around 30% of all marine organisms. However, a 2019 paper published by Nature Journal reported that coral reefs cover only 0.5% of the ocean floor.

Coral reefs grow in warm waters, typically 23-30°C, with access to sunlight, away from areas of high sediment and pollution.

Alarmingly, human impact and global warming are causing coral reefs to decline rapidly. In the past 30 years, Earth has lost approximately 50% of all coral coverage. Scientists predict that up to 90% of all corals will die by 2050.

Drilling down to specific observations, as of 2022, the IUCN (International Union for Conservation of Nature) Red List of Threatened Species reports that 33% of all coral species face extinction. In a further illustration, Science Journal reported that between 1977 and 2001, coral coverage in the Caribbean sea is estimated to have dropped from 50% to just 10%.

Coral Reefs in Thailand

Today, Thailand is home to more than 4,000 species of fish and 700 categorized types of coral. The trend in Thailand is identical – coral reefs are disappearing fast.

Directly related to Koh Tao, Thailand’s Ramkhamhaeng University shared an academic paper stating that “Farther south to Suratthani, there are several islands which harbor well developed coral reefs. Koh Samui, Koh Pha-Ngan and Koh Tao Islands are the famous tourist places. They are undergoing severe degradation. Conservation activities and proper management plans for the coral reefs in this region are required.”

Following millennia of evolution, corals can recover from storm damage, bleaching periods, and other destructive events. Individual fragments or damaged colonies can recover through reproduction – both sexually and asexually – multiplying to form healthy coral reefs.

Earth’s spiraling human population is already causing wide-scale destruction to coral reefs.

As scuba divers, we can contribute to coral restoration projects to help rekindle nature’s balance.

Coral reef rehabilitation is possible using approaches including:

• Educating humans to avoid direct contact with corals (tourism, fishing industry, shipping)
• Eliminating or minimizing pollution
• Foraging for and saving damaged coral fragments
• Transplanting corals into environments that are favorable for growth
• Removal of invasive species (such as lionfish or crown-of-thorns starfish)
• Community-based education programs & initiatives
• Responding to emergencies (such as ship groundings, oil spills, disease, or coastal erosion)

Scuba divers can further assist by surveying coral reefs and sharing data with collaborations such as Coral Watch.

Gaining an accurate snapshot of the current health status & trends exhibited by coral reefs allows scientists to plan and implement viable coral restoration projects.

Coral reef damage can occur due to both natural and human influences.

Coral restoration is an effort to rehabilitate damaged coral reefs, usually by combining passive and active coral restoration strategies.

In most cases, passive restoration should come first. Removing or minimizing whatever is causing the initial coral damage. For example, this could be establishing a Marine Protected Area (MPA) to prevent fishing on an area of damaged coral reef.

Once any detrimental factors have been mitigated, active coral restoration can proceed. Active coral restoration means investing time and resources to rebuild and restore the coral reef.

Objectives could be:

• Increasing the amount of coral coverage in an area
• Improving the healthiness of coral colonies
• Broadening the biodiversity of species on the reef

Approaches to active coral restoration can include fragmenting a mature coral colony, then growing the resulting fragments in a coral nursery under ideal conditions. Once fragmented corals have grown to become adequately large and robust, they can be transplanted back into the reef. This fragmentation method offers several advantages in growth-rate and resilience of the restored reef.

Another method of active coral restoration uses divers to scour the seabed, searching for corals of opportunity. Fringing coral reefs can be battered by wave action or storms, causing coral fragments to be separated and fall to the ocean floor. Divers can save these tiny coral fragments, transplanting them back into a favorable environment on the reef to recover, grow and reproduce.

The first step in restoring a reef is setting up Marine Protected Areas (MPAs). Reefs are home to 1 in 3 known fish species. Eliminating fishing in these fragile ecosystems helps maintain balance and the future health of the reef.

While there are different approaches to restoring a reef, in the example of our ALotMeant project we use the technique of foraging for and rehabilitating fragments of opportunity:

1. Forage for damaged coral fragments of opportunity on the ocean floor
2. Transplant collected coral fragments onto substrates with favorable conditions for coral growth
3. Maintain and monitor coral health and growth over time

Corals are naturally adapted to reproduce through fragmentation to survive and regrow after destructive storms. However, this is an adaptation with a low survival rate as many fragments do not end up in a conducive location for growth. Many fragments end up buried in the sand, in a location without enough sunlight, or end up overrun by competing algae.

By foraging for coral fragments and then attaching them to underwater structures we ensure fragments have a better opportunity to recover with access to optimal conditions for healthy growth and begin creating new reefs.

We monitor a range of environmental factors to ensure our structure placement is optimized and to pinpoint times of the year best suited to planting. (Enroll in our ALotMeant Level 2 Coral Survey program to join our team in collecting this data!).

Coral can be transplanted, and provides a crucial technique in active coral restoration.

Coral reefs thrive when individual fragments and colonies enjoy favorable environmental conditions. Key environmental elements include:

• Sunlight
• Temperature
• Salinity
• Sediment
• Shelter from waves, weather, or human contact

By transplanting corals into optimal conditions, we give fragments a higher success rate of growth & reproduction.

Candidate corals for transplanting, methods of attachment, and target substrates vary depending on the project.

Good candidates to be transplanted can include:

• ‘Coral fragments of opportunity‘; Damaged coral fragments that have been separated from the reef and discovered by divers on the seabed.
• Coral fragmentation, deliberately fragmenting mature coral colonies into smaller pieces.

Coral fragments can be transplanted onto natural or manmade substrates. It is possible to transplant a coral into an existing reef by attaching it to a suitable rock or boulder. Alternatively, purpose-built structures can be deployed on the seabed. Manmade options include steel frames or concrete blocks.

Techniques to attach a coral fragment depend on the type of coral and target substrate. For example, branching corals species such as Acropora are easily attached to steel frames using a zip tie. Sub-massive coral fragments such as Porites can be attached to a concrete block using epoxy resin.

Passive coral restoration is a strategy to rehabilitate coral reefs by managing external issues which cause damage to coral reefs.

Approaches to passive coral restoration are wide-ranging and include:

• Setting up Marine Protected Areas (MPAs) or passing legislation to protect marine habitats.
• Removing or controlling predator species (for example, crown-of-thorns starfish)
• Fishing quotas & restrictions
• Educating local communities
• Tourism control (especially boating, scuba diving & snorkeling activities)
• Land use restrictions
• Establishing shipping/boating channels away from coral reefs
• Pollution control
• Removing invasive algae blooms

The amount of time needed to restore a damaged coral reef can range from several months to decades; Project timeframe depends on many factors:

Extent & Cause of Coral Reef Damage

The first step in any coral restoration plan should be to eliminate or reduce any cause(s) of reef damage.

For some instances, sources of damage have already been eliminated before a restoration project is launched (for example, responding to a ship grounding or tropical storm). In such cases, active coral restoration can proceed immediately.

More complex scenarios could require initiatives to educate local communities or the implementation of laws to govern land use or fishing industries. It may also be necessary to establish MPAs. Work could take months or years to complete.

Availability of Coral Fragments

If coral fragments to be transplanted are readily available, restoration work can proceed quickly.

Using dive teams to search for ‘coral fragments of opportunity’, if fragments are scarce, it will take longer for divers to locate suitable specimens. In some situations, there may be insufficient quantities of coral fragments available. Ultimately, this will cause a halt to restoration efforts.

Coral fragmentation is an alternate approach to sourcing coral fragments. Coral fragmentation is not permitted in some countries (such as Thailand), but when fragmentation is viable, it can be an excellent method for sourcing sufficient numbers of corals to transplant.

Duration of Transplanting Dives

How long does it take for teams of divers to transplant coral fragments onto a reef? Underwater work depends on several factors:

• Quantity of coral fragments to be transplanted
• Number of trained divers available to perform the coral transplanting work
• Access to dive site/transit times
• Dive profile and underwater considerations; Depth, waves, current, and visibility

Type of Coral Species & Environmental Conditions

After coral fragments have been transplanted into a reef, subsequent growth and reproduction rates are dependent on the coral species.

Branching corals such as Acropora have rapid growth rates of around 1-2cm per month. Massive or sub-massive corals such as Diploria or Porites grow gradually at approximately 2mm per month. Encrusting corals often mature even more slowly.

Favorable environmental conditions will also influence the health and growth of transplanted coral fragments. With enough sunlight, clean water, low sediment, and few predators, corals will be able to grow and reproduce more readily.

Summary

The amount of time required to restore an area of coral reef is dependent on the unique circumstances of that project.

Consider two scenarios:

A ship grounding on a fringing reef resulting in damage to branching corals. Clean water, calm sea conditions, shallow depth with good visibility, and an abundance of coral fragments of opportunity. In this scenario, the coral reef could be on its way to recovery in as little as six months.

Imagine an overfished and heavily polluted reef. The reef is already in bad shape suffering rampant algae blooms and invasions of predator species. Lack of governance of local land use, fishing industries, or wastewater management further accelerates the rate of decline. High sediment, and large amounts of pollutants provide further complications. The declining reef took thousands of years to form and is biodiverse, comprising branching, massive and encrusting corals. This situation is a lot more complex and may require many years to reverse. Coral restoration efforts may even fail.

The financial cost of restoring a coral reef depends on the methods used and scope of restoration work. Considerations include:

• Extent & cause of coral reef damage
• Availability of suitable coral fragments for transplant
• Ease of undertaking coral transplant dives
• Type of coral species and environmental conditions

Coral restoration projects which tackle a combination of complex issues will likely be more expensive to undertake than straightforward restoration assignments.

As an illustrative example, let’s examine the ‘Alotmeant’ reef restoration project on Koh Tao, Thailand.

Breaking down the project into key activities:

Planning Phase

• Making survey dives to put together a situation assessment
• Discussing potential coral restoration approaches & feasibility
• Project planning & budgeting
• Submitting a proposal to local authorities (the Department of Marine & Coastal Resources) & working through the approval process

Coral Restoration Work

• Sourcing construction materials, required to build underwater structures
• Building structures on land, ready for deployment. For Alotmeant we chose a combination of steel rebar pyramids with concrete feet, used for mounting branching type corals. Plus hollow concrete blocks to which we attach massive & sub-massive coral fragments
• Deploy and arrange structures on the seabed
• Teams of divers search the ocean floor to locate coral fragments of opportunity
• Coral fragments are moved to the restoration site underwater
• Transplant coral fragments onto the underwater structures. For branching corals, divers attach the coral fragments to rebar pyramids using zip ties. Or for massive and sub-massive corals epoxy resin is used to fix the corals to a concrete block.
• Transplanted coral fragments are tagged and photographed. Data is uploaded to a database to track the project

Ongoing Activities

• Teams of divers frequently check the ‘Alotmeant’ site to perform maintenance and monitoring actions
• Algae and sediment are cleared from fragments & structures
• The growth rate of coral fragments is measured and documented
• Periodic environmental measurements are taken from the Alotmeant site, including pH, dissolved oxygen content, underwater clarity & salinity
• Findings are uploaded to online collaborations including Coral Watch

For the AlotMeant reef restoration project in Koh Tao, Thailand, we estimate the cost of restoring the coral reef to be approximately 700THB ($21USD) per coral fragment.