A research team at UC Berkeley has now answered a major question in coral biology: How are algae able to thrive inside the cells of coral? The finding could lead to new insights into why algae and coral are failing to thrive symbiotically and suggest ways to re-establish the connection and save the world's reefs.

The conclusions come from experiments conducted in the lab of Phillip Cleves, a Berkeley assistant professor of molecular and cell biology who has constructed a state-of-the-art saltwater nursery for coral.

On Australia's Great Barrier Reef, corals spawn once a year, releasing eggs and sperm in great clouds on a night in October or November around the full moon. This makes it hard to conduct genetic studies to understand the symbiotic relationship between algae and corals and their response to heat stress.

In their nursery, Cleves and his team have been able to raise different groups of corals to spawn throughout the year, giving researchers the opportunity to conduct genetic experiments every few months.

Based on genetic manipulations of these lab-grown corals and related anemones, which also incorporate algae into their cells, the researchers are challenging the assumption that coral long ago absorbed algae into specialized compartments inside their cells called symbiosomes.

Symbiosomes resemble mitochondria, the powerhouses of the cell, and chloroplasts, which harbor the photosynthetic machinery in plants. Both are thought to have been independent organisms that were long ago incorporated into cells and are now essential cellular components in all animals, plants and fungi.