Perspectives on Coral Reef Rehabilitation

Gregor Hodgson, PhD

Coral Reef Ecologist

May 4, 2021

1) Introduction

My perspective is quite unusual because both my parents were marine biologists and I had the chance to begin research on coral reefs as a young boy in the 1960s – working on reefs in 25 different countries in all tropical seas by the time I was 19 years old. Subsequently, while running a global NGO focused on coral reefs for 20 years, I worked on reefs in about 100 coral reef countries. As a result, I saw coral reefs in pristine condition throughout the world and have watched as they have declined or died ever since.

Sadly, as we all know, coral reefs have been in trouble for quite a while, and most look very different from the reefs I worked on as a kid. In the Caribbean, human impacts and a disease wiped out the two main species of branching Caribbean corals called staghorn and elkhorn (of the genus Acropora) starting in the 1980s. Back then, these two species typically occupied as much as 60% of each reef with elkhorn coral (A. palmata) often occupying some of the reef flat and reef crest and upper slope, and staghorn coral (A. cervicornis) often forming mono-specific stands that covered a wide swath of the upper to mid reef slope. Therefore, when these two species were killed off in a large part of the Caribbean, this impact alone resulted in as much as 60% of many Caribbean reefs dying.  In the former staghorn zones, the fragile dead branches were eroded into sand, and typically have not returned.  The much more sturdy elkhorn coral reefs became skeleton reefs covered with macro-algae. These skeletons are still found standing in place where they died, like dinosaur bones, from the Bahamas to Colombia. To make matters worse, the long-spined black sea urchins of the genus Diadema, that normally eat a lot of macro-algae, also died off due to a disease. This allowed macro-algae to overgrow, damage and kill corals and dominate more Caribbean reefs.

While neither of these problems affected Indo-pacific coral reefs, overfishing of reef fish started to become a problem almost everywhere during the 1980s, and this too eventually, began to help destabilize coral reefs. At the same time, as human populations grew, sewage, fertilizer and chemical pollution of coastal waters near river mouths and cities increased and damaged reefs located near those areas. Finally, by the late 1990s, global warming got to the point where it began to kill off vast areas of coral reef all over the world through bleaching. When I saw my first major bleaching event in 1997 at Con Dau Island in Vietnam, I remember thinking how the bleached and dying corals looked like tombstones in a giant cemetary. Some of the larger corals that died were about 1000 years old. During the 2000s, global warming has also increased the frequency and intensity of hurricanes and typhoons, thus leading to further reef damage.

In response to this reef damage, scientists, recreational scuba divers and reef lovers often decided that it would be a good idea to try to rehabilitate and/or restore damaged coral reefs. Below I very briefly summarize my views of the reality of reef rehabilitation and/or restoration today. My definition of rehabilitation is carrying out activities to try to bring back more live coral and other reef organisms on a reef. Restoration is defined as trying to recreate a coral reef with the same characteristics as a reef that was damaged or killed.

2) Perspectives

I built my first artificial reef near Caubian Island in the Philippines in 1979.  It attracted a few fish and was later washed away in a typhoon. Subsequently, I have monitored many reefs where rehabilitation has been attempted through application of many different technologies. Recent increased interest in reef rehabilitation has led to experiments with many new techniques. As more reefs are damaged, people who love reefs are getting desperate to repair them.

Let me start with the bottom line and then provide details. At this time, coral reefs cannot be restored to the completely natural state that they were in before being damaged. The reason is that even in the Caribbean, coral reefs are extremely complex biological systems involving thousands of species from bacteria to sharks. In the past, 99.99% of our efforts to repair damaged reefs have focused on the corals. It was generally assumed that if we could re-establish the corals – and recreate a coral reef habitat – then the other organisms would naturally return. In reality, there are very few examples of this occurring, and the effort to document this is hampered by actually monitoring every species originally found on the reef before damage occurs, and then documenting a restoration attempt and re-surveying all those same thousands of species to see if they have returned. I am not aware of any published case where this has been documented. Therefore, my view is that “reef restoration” is not yet possible and this term should only be reserved as a project objective for the distant future.

Coral reef rehabilitation is still limited to relatively few species and relatively small areas compared to the size and diversity of the reefs that have been damaged or killed. Unless the original cause of the damage to coral reefs is stopped, rehabilitated reefs could be damaged again by the same impacts that damaged them the first time.

Good examples of the scale of the problem are found in all oceans. One example, is from the US state of Florida where I learned to scuba dive in 1970. At that time, Looe Key was a favorite dive location with abundant fish and corals. One of the organizations promoting reef rehabilitation in Florida,, states that coral cover in Florida used to be as high as 45% on coral reefs and is now down to below 5%. Since 2007, the Coral Restoration Foundation has grown and transplanted over 130,000 corals onto Florida reefs. Each fragment of 11 species of coral is carefully selected to take into account genetic diversity, and grown by hand in the laboratory or on strings suspended in the water, and then planted on the reef by volunteers. This effort is relatively inexpensive but requires a lot of volunteer time. Studies have shown that most of these corals typically last less than five years after transplantation because the same stressors that killed them the first time are still there. In fact, there are more coral diseases killing corals now than were present 20 years ago. The Florida Keys National Marine Sanctuary covers 9,900 km2 and in the 1990s, it included 1,400 km2 of living coral reefs. Imagine the work required to hand plant one coral fragment per square meter on these reefs… this would require 14,000,000 colonies!  The FKNMS does not even cover all the reefs in the Florida Keys … so the point is that the scale of the problem is enormous.

If we look at the Indo-Pacific, the problems are even greater. Perhaps the worst-case scenario has already started on the Great Barrier Reef (GBR) in Australia. The GBR was hit by wide-scale, severe hot water events in 2016, 2017 and again in 2020. Scientists estimate that about 50% of the corals on GBR have been killed by these bleaching events over the 2000 km length of the GBR. The areat of coral reef on the GBR is 130,000 km2, so using human labor to replant even 10% of the damaged reefs would be a huge undertaking, taking many years and at immense cost. Given the repeated pattern of bleaching there, it would not be a long-term solution because the transplanted corals would be killed again unless they were genetically modified to be more heat resistant. This would require genetically altering perhaps 1000 species of hard corals, soft corals and anemones. The only long-term solution for coral reef survival is to stop and reverse global warming.

Mass bleaching events on the Great Barrier Reef in 2016, 2017 and 2020
Mass bleaching events on the Great Barrier Reef in 2016, 2017 and 2020. [Credit: ARC Centre of Excellence for Coral Reef Studies]

In fact, a major political problem associated with rehabilitation efforts is that they can divert public attention away from the need to fix the real problem – reversing climate change. Another problem arises when promises are made to restore or rehabilitate “x” kilometers of damaged coral reef. This can lead to disappointment when the project eventually fails and the corals die.  A number of technical solutions have been proposed that supposedly improve the survival and growth of corals. One that stands out for all the wrong reasons is using an electric current to stimulate the growth of transplanted corals. Many reef front hotels around the world have been so desperate to “fix” their reefs, and the sales people of this silly technique have been so skillful that many “house reefs” are now littered with discarded cables and metal trays.

The bottom line is that if we can reverse global warming, coral reefs will repair themselves and grow back. Even now, on coral reefs in areas that have not yet been too badly damaged by hot water or other impacts, coral reefs still recover following severe damage from natural causes such as storm damage. In other areas, corals have managed to adapt to hotter conditions for now.

So, given this pessimistic assessment of the status of reefs and rehabilitation possibilities, why would I support rehabilitation projects?

Some coral reef rehabilitation projects are really helpful and valuable. The most valuable projects are those that are relatively small, and involve an educational component involving lots of local community members, especially students. Just like a farmer has to learn what conditions are best to grow corn or other crops, when students are involved in trying to plant and grow corals, they are forced to think about the conditions needed to sustain corals. They also watch as corals grow and begin to form habitat for fish and all the other organisms found on healthy coral reefs. Even when their farmed corals die due to a myriad of possible reasons, this becomes a learning experience too.

The biggest problem facing coral reefs globally is a lack of demand from the public to save them from global warming. By involving lots of citizens in helping to grow coral reefs, this begins to create a love for coral reefs and increases the political constituency that demands governments to reverse policies such as fossil fuel subsidies that encourage global warming. Creating small reef rehab projects on “house reefs” near beach resorts, also exposes lots of tourists to the projects, educates them about coral reefs and the problems that they face, and thus increases the value of the projects. Projects such as these often attract press coverage and, with luck, can increase the understanding and support of fishermen, politicians, government staff and agencies, thus further increasing public demand for coral reef conservation and for reversing global warming.

I support the coral farming projects of Aquaculture Development for the Environment (ADE) in Fiji because each individual project is tied in with a local Fijian community where students, fishermen and other community members are trained and involved. ADE is also bridging a gap between coral farming knowledge gained over decades of commercial farming experience, and academic knowledge e.g. genetics available through collaboration with local and international marine biologists.