Lowered temperature and reduced salinity retarded development of early life history stages of Acropora valida from the marginal environment

To better understand the possible consequences of the co-occurrence of salinity and temperature stresses on reef building corals in subtropical marginal environment, laboratory based experiments were conducted on early embryonic developmental success of the newly fertilized eggs of Acropora valida from Hong Kong under different interactive temperature [24, 27 (ambient), 30 °C] and salinity [33 psu (ambient), 30, 28, 26 psu] treatments. Our results showed the effect of temperature to be comparatively stronger than that of salinity in affecting rate of embryonic development. There was a 4 h delay in embryonic development at lowered (24 °C) and slightly accelerated development at elevated (30 °C) temperatures. In addition, the interaction of temperature and salinity significantly affected the proportion of abnormal embryos. At 27 °C and 30 °C, the percentage of developmental abnormalities was generally low (<25 %) in salinities that ranged from 33 to 28 psu. A significant increase was observed at 26 psu treatment. Similar low level of abnormal embryonic development was observed at 24 °C except that increased abnormalities were already observed at a higher salinity of 28 psu. These results demonstrated that lowered temperature and reduced salinity (24 °C and 26 psu) have the potential to negatively impact the reproductive success of this coral species, and would ultimately lead to substantial decline in sexual recruitment. Such negative impact, however, could be alleviated under a warmer ocean, therefore allowing the persistence of this coral species in the long-term. These results are important for a better understanding of the possible consequences of climate change on reef building scleractinian corals in a subtropical marginal environment like Hong Kong.