Mangroves reveal more robust coral species


Porites lutea coralliths with live, photosynthesising tissue on all sides were found growing upon loose, sandy sediment. Photo taken by Elsa Naumann

Studies into coral growth in extreme environments have revealed that some species are more robust than previously thought, and capable of withstanding light deprivation for many days.

Climate change and ocean acidification are global concerns, threatening to alter the conditions under which corals grow. Consequently, recent research has focused on identifying the environmental thresholds of coral growth, and whether certain ecological or physiological strategies allow some corals to exist over a wider range of conditions than others.

The coralliths are capable of withstanding periods of up to 30 days without photosynthesis

By studying coral assemblages growing under sub-optimal conditions, we can determine what species are better equipped to deal with environmental change and what strategies allow them to exist in these environments.

Studying sub-optimal environments

Mangrove habitats, such as those found in Lahoa, within the Wakatobi Marine National Park in Indonesia, are considered sub-optimal environments for coral growth due to extreme daily fluctuations in light, temperature, tides and rates of sedimentation.


Porites lutea coralliths within the Lahoa mangroves. Photo taken by Elsa Naumann

Despite this, coral assemblages are found to be thriving in the channels scattered across Lahoa. Here, Porites lutea colonies that have adopted an unusual free-living growth strategy, producing what we term ‘coralliths’.

Despite being half embedded in sandy sediment, these corallith colonies exhibited live, photosynthetically active tissue on all surfaces. We hypothesised that the flow within the Lahoa Mangrove is sufficient to overturn the coralliths from time to time, ensuring that all the tissue is exposed to light.

Photosynthetic capability

In lab experiments, we found that the coralliths are capable of withstanding periods of up to 30 days of extreme light deprivation (ie starvation) on unexposed sides.

The combination of this extreme tolerance and suitable environmental conditions, such as high flow oxygenating the sediments in which they are embedded, allows Porites lutea to occupy a highly specialised niche within a marginal environment.

This suggests that some coral species are able to withstand far more extreme conditions than is generally perceived.

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