Reefs made from sunken trees can help restore biodiversity in degraded marine habitats, scientists have found.  It is estimated that coral reefs support about 25% of all marine life. They provide housing, food and areas to spawn for millions of marine species and are the backbone of maintaining the aquatic life cycle.  Since the 1950s, more than half of natural coral reefs have been lost to climate change, which has had dire effects on marine biodiversity.  …A team of researchers built dozens of pyramid-shaped structures made out of felled pear trees, sank them to the seabed and monitored them for more than six months.  …Dickson and colleagues found that after six months the tree reefs were home to algae and more than 15 sessile organisms – species that are immobile and typically anchored to a surface, like barnacles on the hull of a ship.