A Coral Reef Recovers

I was hoping for the best, but expecting the worst, as I flew to the Caribbean—specifically, Cuba’s south coast—to see whether the coral reefs on one of my favourite diving spots had survived the past two years.

I had done several trips to this area, the last two separated by only a few months. In May 2023, the coral presented its usual spectacular display, in my opinion, one of the healthiest reefs left in the Caribbean. Three months later, as I described in my previous article, it looked “like some kind of aquatic battlefield, with the bones of the dead littering the bottom.” 

During dive after dive, and as far as visibility allowed, I could see vast expanses of bleached coral. By my estimate, almost half of it had been affected. I could not believe what I was seeing. I knew there had not been any major chemical spills in the area, and agricultural run-off was not an issue, as there is not much high-intensity farming in the area. I wondered whether this might be the most blatant example of global warming that I had ever encountered.

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Digging deeper

When I returned to Canada, I researched the mystery. After poring over a number of recent studies on corals and speaking with several scientists who work in the area, I learned that the die-off had probably been a direct result of a temperature change. NOAA scientists told me that temperatures increasing as little as one or two degrees above normal seasonal averages can start this kind of die-off. 

Curious, I went back to my dive computer and checked. Sure enough, temperatures during my first trip averaged 29°C. During the second trip, they were up by two degrees, to 31°C. Mystery solved. I also learned that the phenomenon was occurring across the Caribbean. 

But just as important to me was not just the question of why it happened, but the question of what the long-term consequences were. Could the corals come back?

Symbiotic algae

It was possible. Corals do not die in the same way many other species do. When corals bleach, they are not exactly dying; they are more likely being abandoned by the algae they depend on to survive. Healthy corals have a symbiotic relationship with microscopic algae that live in their tissues. These algae feed the corals and provide their colour. 

When the corals come under stress, the algae leave the corals. Without the algae, the corals turn white, or a very pale version of their original colour. Essentially, they start to starve. They can survive for a short time without the algae, but ultimately, they need these symbiotic creatures to return to thrive.

At the time I wrote my previous article, I had promised to return to this part of Cuba and do an update on this once-healthy stretch of reef, just south of Cienfuegos. I knew that if the corals got a break from the weather and if the water cooled down a degree or two, they might recover.

According to Derek Manzello, the director of NOAA’s Coral Reef Watch, “Corals can recover from bleaching if the heat stress subsides, but the corals that are able to recover will have impaired growth, reproduction, and be susceptible to disease for about two to four years after recovery.”

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Return to the scene

So, here I was, arriving on the bus from Santa Clara’s airport at Faro Luna on the south coast. It was mid-July, just six weeks short of two years since my last trip. After I checked into the hotel, I went down for dinner with the other diving guests, as this small hotel caters largely to divers. Right away, I asked about the health of the corals, but received only vague answers such as “yeah, it looks fine” or “looks the same to me.” Then, they went on to talk about the fish they had seen that day. Corals did not seem to be the focus of their attention.

Diving

So, it was still with some sense of dread that I carried my gear over to the dive shop for my first dive of the week. I asked the dive leader, Norbert Pietkiewicz, if he could take us to a site that might be a bit deeper than normal. There are a couple of great, deep walls in the area, and the cooler temperatures might present a better option. But he had a student in the group that day, and so we were heading for a site that allowed some of us to dive to around 20 or 30m (70 or 80ft), and still allowed Norbert and his student a chance to stay above 18m (60ft) to complete her training.

I rolled back into the water off the boat, popped back to the surface, let some air out of my wing and started a slow descent towards the bottom. Now, the weather had been a bit turbulent of late. Normally, 20m (65ft) of visibility is not unheard of in this area. But today, I could not see the bottom—at least, not until I was within about ten or 15m.

As soon as it came into view, I scanned anxiously for that field of white that I had seen last time. First impressions were encouraging, and I breathed a large sigh of relief.

There were a few spots of white here and there, dotting the reef, but most of the coral seemed to have bounced back. But let’s not be hasty, I thought to myself, “One swallow does not a spring make.” I started along the reef, making a careful inventory of the coral species. During the next six days, I would make a dozen dives, and during each, carefully inventory the coral species and how or if they had recovered. Here is what I found.

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Findings

The common sea fan coral seemed to be doing just fine, though many had not recovered all their brilliant blue colouring. On the whole, they were alive and doing passably well. Deep-water sea fans on the walls, on the other hand, were thriving. Sea whips had also come back at both shallow and deep locations. The brain coral had made a reasonable comeback but still needed to recover a little further. Even some pillar coral was showing some promise on a few select sections of the reef, although I was saddened to hear that one large growth—said to be nearly a century old—had died off during the summer of 2023 and not recovered.

On the downside, there was some evidence of stony coral tissue loss, particularly on the finger coral. But it had not spread in any serious way, and it did not seem worth panicking about. Also on the downside, I did not see one living piece of elkhorn coral. 

Now, let me stress that this is in no way a scientific study. This is just me covering parts of a reef that I have dived on multiple times over many years. 

Having said that, overall, I would have to conclude that the reef had made a remarkable recovery. I would estimate that only about 10 percent of the reef was suffering from some kind of bleaching or tissue loss. The rest was in relatively good shape. 

I would also like to note that, on the deeper parts of the wall, I saw massive growths of black coral along long stretches of the reef. And, as another aside, the sponge life was booming right across the reef. Barrel sponges and vase sponges seemed to be everywhere, along with tube and stove pipe sponges. They added a magnificent spark of colour to the recovering reef.

Final thoughts

At the end of the week, I had two final thoughts. Firstly, I will be back to dive this beautiful reef again, and secondly, as I headed back to the airport, I carried a small spark of optimism that maybe, just maybe, some coral reefs in the Caribbean might be around for a little longer. ■

^{Sources: NOAA, Wikipedia}