In July, I introduced via The Nature Conservancy’s photo of the month what may then have been the world’s largest living table coral (pictured above).
I found it on a reef in Nusa Laut, Indonesia. I also indicated that the coral felt like an old friend to me and that I would develop a knot in my stomach on visiting the reef in anticipation of finding my “old friend” dead or damaged.
Table corals are not as long lived as some of their massive boulder forming community members.
The reason is that table corals grow by dividing horizontally away from the center after reaching a certain thickness.
The central polyps stop dividing vertically and eventually get old and die from natural senescence. The center of any very large table coral colony usually is dead.
Massive corals on the other hand, like some we’ve seen in our Indo-Pacific seas, may be hundreds to over a thousand years old. This one, for instance, is 350 years old.
These corals grow by dividing vertically and thus are constantly renewing themselves as they grow upwards and outwards.
Table corals are also vulnerable to toppling by storm surges and breakage of their narrow pedestals when shaken by earthquakes and tremors in seismically active areas like those in the West Pacific and Coral Triangle.
How these corals respond to the stress of being shaken and toppled is a great indicator of their resilience. Some simply give up and die. Other more resilient ones seem to shrug off the stress and reorient their plane of growth, contributing dramatic new architecture to the reef community.
I exhorted friends who visited the Nusa Laut reef in November last year to measure the majestic table coral precisely and report on its well-being.
The news wasn’t good.
The coral had collapsed into six pieces. The extended horizontal plate clearly became too heavy for the dead central portion to support, even though the surrounding living tissue was actively growing back over the dead area.
But it was too little too late. I learned that there was no evidence of any damage related to people, like anchoring or blast fishing that caused the breakage; it appeared that the coral colony just got too large and old and the table too heavy so it broke away into slabs under its own weight.
Looking on the bright side, we potentially now have five or six new tables instead of just one large and increasingly moribund one; the center stands proud on its base and is covered by calcareous coralline algae – an excellent surface to enhance recruitment and growth of young corals; the huge area covered by this coral (576 square feet) is now partly opened up for recruitment by a range of different coral species, enhancing the biodiversity; and the absence of any evidence of heat related coral bleaching bodes well for the survival of the entire community.
The fracturing of this colony has had an important story to tell.
Learning from the demise of this table coral and the picture painted by others across the region, it is clear that table corals do reach a maximum size, though I have never seen that documented. At 24.5 feet x 23.5 feet this table coral must have been at or close to the limit.
Nevertheless, it is sad to see it go even from natural causes.
It was the world’s largest table coral after all and more than 80 years old (not a bad age really).
Now that honor will fall to another table coral that itself is marching inexorably on to its demise as it slips down the slope of natural senescence.
I will miss the majesty and presence it carried, but can at least marvel at the succession it has enabled and the cycle of life, death and succession on coral reefs.
As we learn more about these natural cycles, we will appreciate how coral death is not all bad and, importantly, not all attributable to people as is our wont. Those visually satisfying stands of high cover of large corals and low diversity may look healthy but are the product of generally calm and stable conditions. This makes them vulnerable to anomalies in temperatures and weather, as well as to outbreaks of coral predators and disease.
Areas of periodic disturbance on the other hand look messier, yet maintain higher diversity by preventing dominance by few species and open up spaces for a range of different ones (well known in ecology as the intermediate disturbance hypothesis.
We all love to dive and snorkel over coral reefs that support healthy communities.
We may just need to discipline ourselves to accept that a little natural damage is beneficial for reef resilience and that an occasional big disturbance by an earthquake or storm surge might actually enable the reef community to reorganize in a way that retains the resistant or hardiest, culls the weakest, and enhances diversity by opening up space for recruitment by a range of opportunists.
Unraveling the story each reef has to tell about its condition, processes of natural change and succession, and its prospects for survival adds a new dimension to the experience. It is what makes every dive or snorkel different and exciting for me.
Thanks to Dr Ed Warner and Karl Klingeler for taking time to find the Nusa Laut table coral in November and their observations.
Photos by Rod Salm/TNC
Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.