Climate Change Coral

Renewed hope for reef-building corals to combat climate change.

Paper: Liew, Y.J., Howells, E.J., Wang, X. et al. Intergenerational epigenetic inheritance in reef-building corals. Nat. Clim. Chang. (2020).

Challenge that corals face today

The beautiful expanses of colorful coral reefs are under threat from climate change. Two major causes include ocean warming and ocean acidification. High temperatures have caused profound damage to coral reefs due to bleaching.

A picture of Brain coral (Platygyra daedalea). This species was used as a model for experiments in this study.
Wikimedia commons

Corals possess a symbiotic relationship with photosynthetic algal species called zooxanthellae that reside in them. Symbiosis is a long-term interaction between two dissimilar organisms where both benefit from the relationship. The zooxanthellae provide corals their distinct color. Products of their photosynthesis such as sugars and oxygen are used by corals as food. In turn corals provide refuge, carbon dioxide and water from their respiration processes to the zooxanthellae. Thus, they depend on each other to survive. When corals are stressed by changes in their environmental conditions such as temperature they release the symbiotic algae living inside the coral tissues. The lack of algae causes corals to turn white, a process called as coral bleaching. This disturbs the symbioses and deprives corals of its food source. Bleached corals slowly die from starvation. This threat is extreme and has been recognized by scientists as a global phenomenon. The rapid rate of climate change is a greater concern as it overwhelms the rate of genetic adaptation required by the species to survive. However, the good news is that there is an increasing amount of research conducted by scientists all over the world to understand this phenomenon by means of a variety of research questions.

Why do we care?

Corals are one the most beautiful and intricate organisms with infinite structures and growth forms. As if that’s not enough, coral reefs perform diverse functions and affect the lives of several different species including humans. Corals are an integral part of the marine ecosystem providing refuge and serving as habitats for thousands of marine species. They play an important role in the food web. Their absence will lead to massive disruption of this ecosystem. These beautiful reef-building species also support the coastal economy by providing abundant fishing opportunities and multiple jobs associated with it. Compounds obtained from coral reefs are being used as medicines to treat cancer and other ailments. They also protect the shoreline by buffering the impacts of storms and large waves, acting as natural barriers against damaging events like hurricanes and even tsunamis. If you really want to put a dollar amount on the value of corals, the ecosystem services they provide are worth hundreds of billions of dollars. Loss of reefs will have troubling effects on many aspects of human and marine life.

Bleached brain coral showing lack of the vibrant color and turned white.
Image from flickr by NOAA

The study

This February we got some exciting news from a team of researchers led by Drs. Liew and Howells (Liew et al., 2020). Their experiments demonstrated that new generations of corals can be pre-adapted to warmer water temperatures by exposing their parents to similar environmental conditions.

This is possible through what scientists refer to as epigenetic conditioning. Genetics explains how children inherit characteristics from their parents. Scientists are showing that epigenetics also plays an important role in determining characteristics of offspring. Epigenetic mechanisms cause changes in the expression of genes rather than changing the genetic code itself. Think of it as an additional layer of control that does not actually edit the DNA code but controls activity of different genes. Most importantly these mechanisms are environmentally influenced and can cause changes that can be passed on to next generations.

In order to show epigenetic inheritance between generations in reef-building corals, the research group used the brain coral (Platygyra daedalea) as a model. They used two populations of this species exposed to starkly different environmental conditions. One of the population tested in this experiment, lives in extreme temperatures and salinities and has persisted through several bleaching events. Bleaching events are known as the bleaching of a large number of corals in a given time frame. The other test population lives in milder conditions and has not experienced bleaching events recently.

Through a cutting-edge technology, scientists compared epigenetic modifications in these two populations. Their data demonstrates transmission of epigenetic patterns from adults to sperm to subsequent larvae. This study showed corals can acclimatize to local environmental conditions that can be passed on to next generation using epigenetic conditioning. These pre-adapted coral colonies and larvae may help save dying reefs by heavily contributing to increase the resilience of the reef to thermal stress.

Brain coral, Mariana Islands, Guam
NOAA Photo Library

How does this help?

Corals like other living organisms possess the ability to adapt to environmental changes. But due to their long generation times, it is generally thought that corals may not adapt fast enough to keep up with the pace of climate change. But this research proves that epigenetic modifications are readily transmitted from parents to the offspring. Thus, if parents of reef-building corals are exposed to heat stress their offspring may have a better chance of coping with rising ocean temperatures. This provides an optimistic future for the corals battling climate change and for all of us who want to see these species flourish forever. The research team points out that while their study provides an optimistic result, more investigations into details such as functional advantages of epigenetic modifications need to be further studied. However, as of now this is a step forward in using science to understand these delicate relationships and provides hope for protecting corals from rapid climate change.

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