Suspended sediment and reduced salinity decrease development success of early stages of Acropora tumida and Platygyra carnosa in a turbid coral habitat, Hong Kong

Suspended sediment and salinity stresses may escalate under climate change in inshore turbid habitats. We test whether fertilization and embryonic development of Acropora tumida and Platygyra carnosa are less prone to both stressors in turbid coral habitats compared to thresholds reported in literature for species found in clear water reefs. Under optimal sperm concentration (10⁶ sperm mL⁻¹), fertilization of A. tumida declined by 50 % when exposed to combined sediment (92 mg L⁻¹) and salinity stresses. However, these stressors had no significant impact on P. carnosa. We found ∼20- and ∼ 7-fold increases in abnormal embryos for A. tumida and P. carnosa, respectively, under combined stressors. Furthermore, silicon-rich terrestrial-originated sediment caused 50 % larval mortality for A. tumida at a lower concentration of 53 mg L⁻¹. We showed that climate change-related salinity and sediment stresses may hinder coral reproduction and challenge coral recovery, questioning the coral survival in nearshore turbid habitats.