#acropora millepora

Cluster coral (Acropora millepora)

COLORFUL CORALS PROTECT ALGAES IN THEIR INSIDE

Egologists have long time wondered how two coral reefs in the ocean seated next to each other can have drastically different shades of color. The answer, according to a new study, has to do with some mysteries of genetics. By sequencing three colonies of cluster coral (Acropora millepora) a branching stony coral obtained from the waters of Fiji, scientists at the University of Southampton, UK, have discovered the genetic basis that allows corals produce its impressive range of colors. They have found that instead of using a single gene to control pigment production, corals use multiple copies of the same gene. Depending on how many genes are active, the corals will become more or less colourful. Dr Jörg Wiedenmann, Professor of Biological Oceanography and Head of the University’s Coral Reef Laboratory, says: “It was one of the longstanding mysteries of coral reef biology – why sometimes individuals of the same coral species can show such dramatic differences in their colour, despite sitting side-by-side on the reef and being exposed to the same environmental conditions. The key finding is that these so-called ‘colour morphs’ do not use just one single gene to control the pigment production, but multiple identical copies thereof.” The research, which is published in Molecular Ecology, also explained how this strategy could help corals to survive in stressful environments. These fluorescent pigments that are primarily responsible about coral colors act as sunscreens for the symbiotic algae living in coral tissue.

Using the staghorn coral Acropora millepora as a model, the team found that the fluorescent pigments that are mostly responsible for coral colours act as sunscreens for the symbiotic algae that live in the coral tissue. These alga require light to produce sugars, which they can contribute to the nutrition of the corals in return for the shelter and the supply of nutrients that are provided by the coral host. However, the light intensities on coral reefs can, on occasions, exceed the levels that are healthy for the alga and the light becomes dangerous for the symbiotic partnership. This light stress can ultimately contribute to the loss of the symbiotic algae, a process known as coral bleaching. If the partnership cannot be re-established, the corals often die.

Photo: Colour polymorphism of Acropora millepora and variability in color.