Synergistic Effects of Temperature and Sedimentation on Coral Recruits: Does Reducing a Local Stressor Increases Coral Resilience to Global Warming?

Corals face worldwide population declines due to global climate change and local anthropogenic impacts. The effects of global climate change are hard to tackle, but recent studies show that some coral species can better handle climate change stress when provided with additional energy resources. The local stress that most undermines energy acquisition is sedimentation because it impedes coral feeding and their ability to photosynthesize. To investigate if reducing local sedimentation will enable corals to better endure ocean warming, we quantitatively assessed the synergistic effects of increased temperature and sedimentation (rate, grain size composition, and turbidity) on the survival of coral recruits of the species Porites astreoides. Anthropogenic sedimentation (fine grain size, common in dredging) negatively impacted coral recruit survival, but natural sedimentation (coarse grain sizes) did not. When anthropogenic sedimentation rates and turbidity were kept at minimal levels (7 NTU), the survival of coral recruits reared at warmer temperatures was not significantly different from the survival of coral recruits reared at current day temperature and sedimentation (>15 NTU). These results suggest that a reduction of US-EPA allowable turbidity from 29 to 7 NTUs near coral reefs would facilitate coral recruit survival under global warming.