“Since microstructural and geochemical features are well preserved in giant clam fossils, it may now be possible to reconstruct the timing and occurrence of past typhoons to a level of accuracy that was previously impossible,” says Tsuyoshi Watanabe of Hokkaido University.

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Komagoe et al. had used the small giant clam Tridacna maxima to validate the usability of their shells as recorders of short-term environmental changes such as typhoons.

On the coral reefs, giant clams can be considered as one of the major carbonate contributors to reef frameworks due to their large shells, mostly made up of aragonite – a calcium carbonate polymorph. Shell carbonates generally come from ambient dissolved inorganic carbon, but also include carbon from metabolic respiration and zooxanthellae photosynthesis within the mantle tissues.

Since these sessile giant clam obtains dissolved inorganic chemicals from the natural environment, it can function as real-time bioindicators of coral reefs. This idea is not entirely new, as previous studies have used other species of giant clams, both fossil and fresh shells, to examine climate variability (e.g. light cycles, sea surface temperature). A research team, led by Dr. Tsuyoshi Watanabe of Hokkaido University, specifically showed that giant clams could record short-term environmental changes, such as those caused by typhoons, in their shells.

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Enlarged image of the shell edge showing a stripe pattern of growth increments. Geochemical analysis of increments reveals the clam’s paleoenvironment. Credit: Komagoe et al., Journal of Geophysical Research: Biogeosciences.

Living on the coral reefs, the giant clam ‘captures’ these environmental data within its intricate shell’s microstructures through depositing specific chemicals (such as carbon, nitrogen, metal ions, etc…) in their shells. Scientists could extract these chemicals and compare the chemical composition across different known environments, e.g. typhoon versus non-typhoon areas.

The giant clam shell growth pattern is also similar to tree rings; thus daily growth increments can be observed precisely and compared with the recent past environmental records that may include typhoon events, temperature fluctuations, etc…

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Giant clam produces these amazing shell architecture, which produces growth bands similar to that of tree rings. Credit: Dea/G. Cigolini, Getty Images.

Using live specimens of giant clams, the team found significant changes to the shell thickness and growth patterns after the animal had undergone a recent typhoon. This implies that we could possibly look back at past typhoons’ frequency and possibly, intensity of storms. Such information could help in alleviating the impacts of global warming, where the frequency of major tropical cyclones is expected to increase.

While some other researchers have raised scepticism on using the giant clam shells as a tool for examining past environments, they encourage further studies to validate the use of giant clam shells for this emerging area of research: paleotempestology—the study of past tropical cyclones using historical records and geological proxies.

The article can be found at: Komagoe et al., Geochemical and Microstructural Signals in Giant Clam Tridacna maxima Recorded Typhoon Events at Okinotori Island, JapanJournal of Geophysical Research: Biogeosciences, April 19, 2018. DOI: 10.1029/2017JG004082

Further reading list:

  • Tech Times, 19 June 2018: Giant clams can tell the history of typhoons and predict future storms
  • Earther, 18 June 2018: Giant clam shells may help predict future tropical storms
  • The Asian Scientist, 7 June 2018: Giant clams tell the history of typhoons
  • The Asian Scientist, 9 January 2015: Giant clams reveal the warmth of the middle age oceans
  • Neo ML, W Eckman, K Vicentuan-Cabaitan, SL-M Teo & PA Todd (2015) The ecological significance of giant clams in coral reef ecosystems. Biological Conservation 181: 111–123.
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