Additive Negative Effects of Anthropogenic Sedimentation and Warming on the Survival of Coral Recruits

Corals worldwide are facing population declines due to global climate change and local anthropogenic impacts. Global climate change effects 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 stressor that most undermines energy acquisition is sedimentation because it impedes coral heterotrophic feeding and their ability to photosynthesize. To investigate if reducing local sedimentation will enable corals to better endure ocean warming, we quantitatively assessed the combined effects of increased temperature and sedimentation (concentration and turbidity) on the survival of coral recruits of the species, Porites astreoides. We used sediment from a reef and a boat basin to mimic natural sediment (coarse) and anthropogenic (fine) sediment (common in dredging), respectively. Natural sediment did not negatively impact coral survival, but anthropogenic sediment did. We found that the capacity of coral recruits to survive under warmer temperatures is less compromised when anthropogenic sedimentation is maintained at the lowest level (30 mg.cm−2). Our study suggests that a reduction of US-EPA allowable turbidity from 29 Nephelometric Turbidity Units (NTU) above background to less than 7 NTU near coral reefs would facilitate coral recruit survival under current and higher temperatures

Natural vs. Anthropogenic Sedimentation: Does Reducing a Local Stressor Increase Coral Resilience to Climate Change?

Corals face serious worldwide population declines due to global climate change in combination with direct anthropogenic impacts. Global climate change is difficult to manage locally, but policy makers can regulate the magnitude of local stressors affecting reefs. The objective of this experiment is to investigate if reducing sedimentation will enable reef corals to better endure global climate change. It has been shown that some coral species can handle climate change stress when provided with additional energy resources. Here I tested if the capacity of corals to cope with climate change can be improved when their ability to feed and photosynthesize was not compromised by increased sedimentation. Sedimentation can impede coral feeding and their ability to photosynthesize due to direct polyp blocking and increased turbidity, which reduces light availability. To evaluate the potential of enhancing coral ability to tolerate climate change by reducing a local stressor, I examined the survival and growth of brooding coral Porites astreoides juveniles when exposed to ambient and elevated water temperatures under differing sedimentation rates. I also assessed if sediment composition has significant impacts on these results. I used sediment from a reef and sediment from a boat basin within a port to mimic natural and anthropogenic sediment types and processes (e.g. dredging). Experiments were conducted to quantitatively assess the synergistic effects of sediment concentration and composition, along with increased temperature on the survival and growth of juvenile P. astreoides. The most detrimental effects were observed with anthropogenic sediment, when both sediment concentration and water temperatures were high. However, increased natural reef sediment was found to be beneficial to juvenile corals. More interestingly, I found that corals capacity to deal with higher temperatures is improved when anthropogenic sedimentation is maintained at minimal levels and turbidity resulting from sedimentation was low. Therefore, this information will aid managers in making decisions that regulate dredging and construction activities to minimize sedimentation, which will contribute to increase coral survival under climate change

Data from: Additive negative effects of anthropogenic sedimentation and warming on the survival of coral recruits

Corals worldwide are facing population declines due to global climate change and local anthropogenic impacts. Global climate change effects 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 stressor that most undermines energy acquisition is sedimentation because it impedes coral heterotrophic feeding and their ability to photosynthesize. To investigate if reducing local sedimentation will enable corals to better endure ocean warming, we quantitatively assessed the combined effects of increased temperature and sedimentation (concentration and turbidity) on the survival of coral recruits of the species, Porites astreoides. We used sediment from a reef and a boat basin to mimic natural sediment (coarse) and anthropogenic (fine) sediment (common in dredging), respectively. Natural sediment did not negatively impact coral survival, but anthropogenic sediment did. We found that the capacity of coral recruits to survive under warmer temperatures is less compromised when anthropogenic sedimentation is maintained at the lowest level (30 mg.cm−2). Our study suggests that a reduction of US-EPA allowable turbidity from 29 Nephelometric Turbidity Units (NTU) above background to less than 7 NTU near coral reefs would facilitate coral recruit survival under current and higher temperatures

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 (\u3e15 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

Survival of coral recruits at all combinations of temperature (26 and 30°C) and deposited sediment concentration (30, 60, 90 and 120 mg/cm2) using anthropogenic sediment

Data set arranged for survival analysis: Temperature (Celsius), Sediment (deposited natural sediment mg/cm2), Time (Weeks), Status (1- dead, 0 - alive)

Survival of coral recruits at all combinations of temperature (26 and 30°C) and deposited sediment concentration (30, 60, 90 and 120 mg/cm2) using natural sediment

Data set arranged for survival analysis: Temperature (Celsius), Sediment (deposited natural sediment mg/cm2), Time (Weeks), Status (1- dead, 0 - alive)