Changes in coral reef ecosystems as an indication of climate and global change

Climate change poses significant threats to coral reefs through various mechanisms, including rising sea surface temperatures, ocean acidification, increased storm frequency and intensity, and sea level rise. This chapter focuses on the impact of rising sea temperatures on coral reef ecosystems, particularly the phenomenon of mass coral bleaching. Bleaching refers to the whitening of corals caused by the expulsion of algae, which not only provide corals with their vibrant colors but also supply most of their energy. This response is often triggered by elevated sea temperatures. Following major global scale bleaching events in 1982-83, 1987-88, 1994-95, 1997-98, 2014-17, and 2023-24, and regional events like those in 2002 (Great Barrier Reef) and 2005 (Caribbean), the link between climate change and mass bleaching of corals is now undeniable. Prolonged bleaching can also result in the death of the corals, with significant consequences for reef-associated species. The coral reef structure provides refuge to many species; however, once corals die, their skeletons are eroded, leading to the gradual collapse of the reef structure. Research suggests that a loss of reef structure may result in declines in the abundance, diversity, and productivity of reef fish populations. In addition, reef fish may be affected by the more direct impacts of climate change, with recent studies observing effects of increased temperature on physiology and behavior. While corals may have a natural ability to adapt to such changes, the increasing frequency and severity of bleaching events, combined with other human-induced pressures, such as fishing, pollution, and tourism, make coral reefs among the most vulnerable of the world’s ecosystems under current scenarios of future climate change. Recent studies are exploring innovative solutions, such as assisted evolution, to accelerate the natural adaptation processes of corals and help them survive rapidly changing environmental conditions. Additionally, mesophotic coral ecosystems, found at depths of 30-150 m, may play a critical role in sustaining coral reef biodiversity and ecological functions under future climate scenarios.