Ocean warming is driving an increase in the frequency and severity of marine heatwaves, causing untold damage to coral reefs. Tropical corals, which live in symbiosis with tiny single-celled algae, are sensitive to high temperatures, and exhibit a stress response called bleaching when the ocean gets too hot.In the last four decades, marine heatwaves have caused widespread bleaching, and have killed millions of corals. Because of this, a global search is underway for reefs that can withstand the heat stress, survive future warming, and act as sources of heat-tolerant coral larvae to replenish affected areas both naturally and through restoration.
Now, scientists studying reefs in Palau, an archipelago in the western tropical Pacific, have identified genetic subgroups of a common coral species that exhibit remarkable tolerance to the extreme heat associated with marine heatwaves. Further, the scientists have found evidence that larvae from these corals are traveling from their birthing grounds deep in Palau’s lagoons to the outer reef, where they survive and grow, and maintain their heat tolerance.
Understanding both the underlying mechanisms that facilitate heat tolerance of these corals, as well as the dispersal capabilities of their larvae will go a long way toward enhancing coral reef conservation and restoration efforts in the 21st-century ocean, according to scientists at the Woods Hole Oceanographic Institution (WHOI) who led the research.
In Palau’s main lagoon, a network of very ancient, fossilized reefs has been uplifted to form a series of mountains known as the Rock Islands. These formations slow water flow in and around them, creating localized environments in which the water temperatures are consistently higher than other areas of Palau’s reefs.
Scientists sampled the keystone coral species Porites lobata across Palau, including the Rock Islands. They took skeletal biopsies and examined the cores for stress bands, which are telltale signs of bleaching, a stress response corals have to high temperatures. They found corals from the Rock Islands bleached less during the intense 1998 heatwave than corals from other areas of the reef, indicating enhanced thermal tolerance.
Read the paper HERE
Image: Porites cf. lobata is a key reef-building coral that provides habitats for numerous species, including feather stars (comatulid crinoids) and fish. Credit: Kharis Schrage, Woods Hole Oceanographic Institution