Individual hard coral colonies from four representative reef sites around Little Cayman were surveyed yearly between 2010 and 2015, a period of non-disturbance between two elevated seawater temperature anomalies. Phot...Individual hard coral colonies from four representative reef sites around Little Cayman were surveyed yearly between 2010 and 2015, a period of non-disturbance between two elevated seawater temperature anomalies. Photographic censuses produced 7069 annual transitions that were used to describe the demographics (size class frequencies, abundance, area cover) and population dynamics under non-disturbance environmental conditions. Agariciids, Porites asteroides, and Siderastrea radians have replaced acroporids as the predominant massive corals. Recruitment rates were generally low (<1 colony per m2), except for a fourfold recruitment pulse of S. radians that occurred in 2011. On average, 42% of coral recruits survived their first year but only 10% lived longer than four years. Temporal comparisons allowed correction factors to be calculated for in-situ methods that overestimate recruitment of colonies ≤2 cm in diameter and overlook larger colonies. Size class transitions included growth (~33%), stasis (~33%), partial mortality (10% - 33%), and whole colony mortality, which decreased with increasing colony size (typically 30 cm2). Transition matrices indicated that Little Cayman assemblages have declining hard coral populations (λ < 1) but as stable size class distributions progress toward higher proportions of colonies with >150 cm2 surface areas, live area cover may remain relatively stable. Projection models indicated that downward population trends would be exacerbated even by mild disturbance (5% - 10% mortality) scenarios. The fate of hard corals on Little Cayman’s reefs was determined to be heavily dependent on the health and transitions of agariciid colonies. Conservation strategies that currently focus on restoration of Caribbean acroporids should be expanded to include agariciids, which were previously considered “weeds”.展开更多
This study describes the health status of Siderastrea siderea in Little Cayman before, during, and after the 2015 Caribbean-wide elevated temperature anomaly. Colony color was used as a proxy for health during snorkel...This study describes the health status of Siderastrea siderea in Little Cayman before, during, and after the 2015 Caribbean-wide elevated temperature anomaly. Colony color was used as a proxy for health during snorkel and scuba surveys of shallow (°C, S. siderea were early indicators of reef stress and among the first corals to bleach. Depth and site resilience did not significantly impact temperature susceptibility;however, smaller colonies (2 surface area) were more likely to change color than the larger size classes. Little Cayman’s S. siderea were capable of surviving large-scale (>80%) bleaching: mortality was observed for only one colony. Resilience rates varied considerably: one-third of the impacted population returned to the normal brown color within two months, one-third required 3 - 9 months to recover, and the fates of the remaining one-third remain to be determined. If the return to normal color is indicative of resistance to reef disturbances, S. siderea may be among the “winning” coral species following elevated temperature anomalies which are predicted to occur with increasing frequency and severity as a result of climate change.展开更多
文摘Individual hard coral colonies from four representative reef sites around Little Cayman were surveyed yearly between 2010 and 2015, a period of non-disturbance between two elevated seawater temperature anomalies. Photographic censuses produced 7069 annual transitions that were used to describe the demographics (size class frequencies, abundance, area cover) and population dynamics under non-disturbance environmental conditions. Agariciids, Porites asteroides, and Siderastrea radians have replaced acroporids as the predominant massive corals. Recruitment rates were generally low (<1 colony per m2), except for a fourfold recruitment pulse of S. radians that occurred in 2011. On average, 42% of coral recruits survived their first year but only 10% lived longer than four years. Temporal comparisons allowed correction factors to be calculated for in-situ methods that overestimate recruitment of colonies ≤2 cm in diameter and overlook larger colonies. Size class transitions included growth (~33%), stasis (~33%), partial mortality (10% - 33%), and whole colony mortality, which decreased with increasing colony size (typically 30 cm2). Transition matrices indicated that Little Cayman assemblages have declining hard coral populations (λ < 1) but as stable size class distributions progress toward higher proportions of colonies with >150 cm2 surface areas, live area cover may remain relatively stable. Projection models indicated that downward population trends would be exacerbated even by mild disturbance (5% - 10% mortality) scenarios. The fate of hard corals on Little Cayman’s reefs was determined to be heavily dependent on the health and transitions of agariciid colonies. Conservation strategies that currently focus on restoration of Caribbean acroporids should be expanded to include agariciids, which were previously considered “weeds”.
文摘This study describes the health status of Siderastrea siderea in Little Cayman before, during, and after the 2015 Caribbean-wide elevated temperature anomaly. Colony color was used as a proxy for health during snorkel and scuba surveys of shallow (°C, S. siderea were early indicators of reef stress and among the first corals to bleach. Depth and site resilience did not significantly impact temperature susceptibility;however, smaller colonies (2 surface area) were more likely to change color than the larger size classes. Little Cayman’s S. siderea were capable of surviving large-scale (>80%) bleaching: mortality was observed for only one colony. Resilience rates varied considerably: one-third of the impacted population returned to the normal brown color within two months, one-third required 3 - 9 months to recover, and the fates of the remaining one-third remain to be determined. If the return to normal color is indicative of resistance to reef disturbances, S. siderea may be among the “winning” coral species following elevated temperature anomalies which are predicted to occur with increasing frequency and severity as a result of climate change.
