Young Coral Reef Surprise: Extra-Deep with Little Sunlight, yet Quick-Growing

Young  Coral  Reef  Surprise:  Extra-Deep  with  Little  Sunlight,  yet  Quick-Growing

Dr. James J. S. Johnson

So is this great and wide sea, wherein are things creeping innumerable, both small and great beasts. (Psalm 104:25)

CORAL: L, with symbiotic Zooanthellate microalgae vs. R without symbiotic microalgae (“bleached”)

Recent research is surprising those who study coral reefs, especially those who assume that they grow slowly.(1),(2)  As a result of these empirical findings, coral reef growth reveal—to the surprise and chagrin of old-earth evolutionists—that reef ages do not conflict with relatively “young” Biblical chronology timeframes.

New research at the University of Hawaiʻi at Mānoa revealed unexpectedly high growth rates for deep water photosynthetic corals. The study published in the journal Coral Reefs, led by Samuel Kahng … alters the assumption that deep corals living on the brink of darkness grow extremely slowly.(1)

Actually, other overly-simplistic aging assumptions (about “ancient corals”) have been shown so unreliable, in prior years, that it is surprising that these Hawaii researchers were themselves surprised by their recent coral-aging findings.(3)

But why would marine biologists continually assume that coral reefs, grown large in mesophotic depths (i.e., so deep that sunlight is modest), must be so ancient?

In theory, the deeper the sea-water, the harder it is for underwater sunlight to power photosynthesis—in symbiotic microalgae that corals need to survive.(1),(2)  So, because the intensity of sunlight diminishes as sea-depth increases, decreased sunlight means decreased microalgae photosynthesis, which then means decreased food and oxygen for the symbiotic corals—ultimately resulting in decreased ability for the microalgae-dependent corals to grow.

Leptoseris is a group of zooxanthellate (symbiotic microalgae) coral species which dominate the coral community near the deepest reaches of the sun’s light throughout the Indo-Pacific. Symbiotic microalgae live within the transparent tissues of some coral—giving corals their primary color and providing the machinery for photosynthesis, and in turn, [food] energy. Deeper in the ocean, less light is available. At the lower end of their depth range, the sunlight available to the Leptoseris species examined in the recent study is less than 0.2 % of surface light levels. Less light dictates a general trend of slower growth among species that rely on light for photosynthesis.(1) [emphasis added]

Notice that the researchers started with the assumption that less-sunlit corals grew at very slow rates, which is an assumption that would suggest that those slow-growing corals—if large—must have large ages.

Previous studies suggested that photosynthetic corals at the bottom of the ocean’s sunlit layer grow extremely slowly—about 0.04 inch per year for one species of Leptoseris. Until recently, there were few data on growth rates of corals at depths greater than about 225 feet given the logistical challenges of performing traditional time series growth measurements at these depths.(1)

So, in light of “logistical challenges” of past investigations, the age of a coral reef was estimated by indexing it to some time-measuring rate that requires less “logistical challenge” difficulties. But what age-estimating methodology has been used for extrapolating, back into imagined timeframes that were unaccompanied by human eyewitnesses, for dating the age of mesophotic coral ecosystems?

The “clock” chosen, for the coral, was radiometric dating, based on uranium-to-thorium decay(1),(2)—an assumption-heavy decay process “rate” analysis that carries its own reliability/unreliability baggage.(3),(4)

Kahng, who is also an associate professor at Hawai‘i Pacific University, collaborated with SOEST’s Hawaiʻi Undersea Research Laboratory (HURL) …[and others,] to collect colonies of Leptoseris at depths between 225 and 360 feet in the Au‘au Channel, Hawai‘i using HURL’s Pisces IV/V submersibles. The research team used uranium-thorium radiometric dating to accurately [sic] determine the age of the coral skeletons at multiple points along its radial growth axis—much like one might determine the age of tree rings within a tree trunk (1)

238U—230Th disequilibrium (U-Th) dating, which utilizes the 238U—234U—230Th decay chain … [is often used] for determining the age of Pleistocene to Recent carbonate deposits. … However, the uncertainty in hydrogenous and detrital sources of 230Th – also termed ‘non-radiogenic’ (230Thnr), initial (230Th0) or secondary 230Th sources that were not generated in the in situ decay of U – incorporated into the coral skeleton during skeletogenesis and after death, respectively, can result in inaccurate age estimates [for review see Zhao et al. (2009)]. This is especially true for young coral samples where the proportion of 230Th0 is significantly greater than the radiogenic 230Th component, or from corals from inshore reef settings where non-carbonate terrestrial input is much greater compared offshore settings; the former having 232Th levels typically a few orders of magnitudes higher than the latter…(4)

But using uranium-thorium radiometric dating—to count coral ages—gets worse.

[Also[ the 230Th0 in a sample cannot be separated from the radiogenic 230Th during measurement, it can only be corrected for using the measured 232Th in conjunction with the initial 230Th/232Th ratio in the sample (expressed here as 230Th/232Th0). As 230Th/232Th0 may vary between sites or even between samples [from the same reef site], a bulk-Earth activity value of 0.82 (atomic value -4.4 x 10-6) with a large arbitrarily assigned uncertainty of ± 50—100% has been commonly assumed to correct for the 232Th0 contribution. Although this assumption was proven to be acceptable for most coral samples from inshore settings, the large associated uncertainty makes the age uncertainty of the corrected 230Th age for young corals too large to be meaningful.(4)  [citing the Zhao(5) study; emphasis added]

Of course, when error margins become “too large to be meaningful” it is time to reconsider just how speculative those non-forensic age estimates are.(4),(5),(6)

Some biologists like to say that massive coral reefs represent more than 100,000 years of growth, supposedly nullifying the Bible’s account of a world that is only thousands of years old. However, many known factors can affect coral reef growth rates. Now, a 50-year study of Caribbean coral reefs confirms the unpredictability of using such growth as a “clock.” Researchers in the past have assumed that by measuring the rate of growth of a coral reef, as well as the total size of the reef, they can estimate how long it took corals to build it. One big problem with this “natural clock” system is that the growth rate of corals is inconsistent and relies on a host of changing variables.(3)

In fact, young-earth creation scientists have, for decades, shown that coral reef formations are not a valid challenge to the chronology of the Bible.

Drs. John Whitcomb and Henry Morris noted this in 1961, citing a study that found 20 centimeters of coral reef growth in 5 years. They wrote, “This rate of growth could certainly account for most of the coral reef depths around the world even during the few thousand years since the Deluge.”  Like any process used as a natural clock, one must assume a constant rate for that process through history. But when it comes to using coral reefs as such a clock, their growth rates have proved to be less than reliable and therefore do not challenge the Genesis record of a young world.(3)

Likewise, the University of Hawaiʻi coral researchers compared their age-counting methodology to so-called “annual” tree ring counting, another unreliable “clock” that should raise yellow flags of caution.(1)  Yet, as a previous report (of mine) has recently reminded, counting tree growth rings does not prove how old a tree is, because weather fluctuations can cause trees to add “extra” growth rings inside a year’s time.(7)

And, to the surprise of many, even Carbon-14 dating has its reliability problems, as a previous report (of mine) has shown.(8) So, what is the basic underlying problem—with these speculations about coral reef ages, as they are linked to radiometric decay rates? This is yet another illustration of the uniformitarian fallacy.(6)

Meanwhile, coral reefs grow at (somewhat) predictable rates—at present.  But what can we conclude from that? Whenever there is a predictable pattern of some process—like growing coral—we can interpret that pattern two ways.

As one option, we can simplistically assume—without the benefit of having observed events in the past that are unlike what is happening today—that the presently predictable pattern is what it has always been, and always will be.(6)

Or, as a more conservative option, we can look at a presently predictable process and recognize that we cannot logically assume that this process represents what has always been happening.(6) Indeed, the apostle Peter taught that the second approach is the only realistic way to understand the world and its history, as Peter predicted that “scoffers” (in the “last days”) would fail to recognize truth due to their uniformitarian fallacy.(9)

Meanwhile, the world’s coral ecosystems should continually astonish and delight us, if we have eyes to see what wonderful works God is doing there.(3),(6)

Some call coral reefs “rainforests of the sea” because these reefs occupy less than 1% of oceanic waters, while they host almost ¼ of Earth’s oceans’ known biodiversity. Indeed, coral reefs are “home” to millions of different crustaceans (like crabs, shrimp), mollusks (like clams, squids, octopi), and fish (like snappers, parrot fish, clown fish, scorpion fish), as well as sponges, sea turtles, sea stars, sea horses, and more.

Even coral reef-dwelling flatworms can be admired, by some observers–such as creation biologist Frank Sherwin:

The Platyhelminthes, or flatworms, are soft, unsegmented animals and include some of the most beautiful invertebrates in the world … Snorkelers and divers delight in watching the lazy, colorful undulations of the three-inch divided flatworm (Pseudoceros) that lives in coral reefs.(10)

Regardless of whether you admire reef-dwelling flatworms, you can appreciate how zooxanthellate corals demonstrate God’s caring providence, quietly displaying mutual aid between coral polyps and their photosynthesizing microalgae helpers.

Even with minimal sunlight, it’s a beautiful day in the (coral reef) neighborhood.



  1. Staff writer. 2020. Surprising Growth Rates Discovered in Deepest Photosynthetic Corals. University of Hawaiʻi at Mānoa (June 15, 2020), posted at . Somewhat like oysters and clams, coral polyps are soft-bodied animals who live inside hard exoskeletons produced from hardened calcium carbon. Living inside a coral polyp’s body is a symbiotic zooxanthella, a tiny one-celled yellowish-brown dinoflagellate alga that photosynthetically uses available sunlight, to produce sugars and dissolved oxygen (which its host coral polyp needs to survive).
  2. “The ecology of phototrophic corals in the lower photic zone remains poorly understood. Studies to date indicate that growth rates generally decrease as available light attenuates with depth and are very slow at depths > 40 m. Here, we provide detailed evidence for moderate growth for obligate zooxanthellate corals at extreme depths.” Kahng, S. E., T. K. Watanabe, H. Hu, et al. Moderate Zooxanthellate Coral Growth Rates in the Lower Photic Zone. Coral Reefs (published June 15, 2020). .
  3. Thomas, B. 2011. 50-Year Study Shows Coral ‘Clocks’ Unreliable. Creation Science Update (January 28, 2011), posted at .
  4. Clark, T. R. Clark, G. Roff, J.-x. Zhao, et al. 2014. Testing the Precision and Accuracy of the U-Th Chronometer for Dating Coral Mortality Events in the Last 100 Years. Quaternary Geochronology. 23:35-45 (especially page 36).
  5. Zhao, J.-x., K. Yu, Y.-x. Feng, et al. 2009. High-precision 238U—234U—230Th Disequilibrium Dating of the Recent Past: A Review. Quaternary Geochronology. 4:423-433.
  6. Johnson, J. J. S. 2014. Is the Present the ‘Key’ to Our Past? Acts & Facts. 43(6):19, posted at . It was eventually learned that deeper-anchored coral reefs could grow faster than expected due to their calcified exoskeletons being thinner and better shaped for maximizing whatever sunlight reaches the lower (mesophotic) sea-depths. “The thin plate-like colonies of Leptoseris, which dominate the coral community in the lower photic zone throughout the Indo-Pacific, primarily grow radially and do not appear to appreciably thicken over time. In the lower photic zone, this growth strategy maximizes surface area with minimal calcification, thereby enabling Leptoseris to expand planar area more quickly than thickly calcified species. Photosynthetic and growth efficiencies may also be facilitated by the optical geometry of their skeletons, increased access to inorganic nutrients and cooler temperatures at depth. These robust growth rates have important implications on the recovery potential of MCE [mesophotic coral ecosystem] habitat in the event of disturbance.” (Quoting from Samuel E. Kahng et al., in Coral Reefs, 2020, supra, footnote 2.)
  7. Johnson, J. J. S. 2020. Children’s Tree Book Rings of Evolutionary Agenda. Creation Science Update (June 8, 2020), posted at .
  8. Decades of confusion were resolved when it was proven that Carbon-14 radiometric dating assumptions sometimes fail in the real world. Johnson, J. J. S. 2018. Viking Bones Contradict Carbon-14 Assumptions. Acts & Facts. 47(5):21, posted at . For an audio message on this topic, listen to Johnson, J. J. S. 2018. Why One-Size-Fits-All Radiocarbon Dating Doesn’t Work. ICR Podcast (August 24, 2018), posted at .
  9. The uniformitarian fallacy, which in scientific circles is quite popular nowadays, was predicted almost 2000 years ago. See 2 Peter 3:1-6.
  10. Sherwin, F. 2013. God’s Amazing Invertebrates: The Missing Links Are Still Missing.Acts & Facts. 42(2):12-15. See also Psalm 104:25; Job 12:8-9.

    [A condensed version of this study, q.v., edited for a less technical-learned readership, was posted on ICR’s website during June AD2020.]

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