Understanding the influence of environmental factors on the development and dispersal of crown-of-thorns seastars is critical to predicting when and where outbreaks of these coral-eating seastars will occur. Outbreaks of the crown-of-thorns seastars are hypothesized to be driven by terrestrial runoff events that increase nutrients and the phytoplankton food for the larvae. In addition to increasing larval food supply, terrestrial runoff may also reduce salinity in the waters where seastars develop. We investigated the effects of reduced salinity on the fertilisation and early development of seastars, up to and including their hatching from the fertilisation envelope. We also tested the interactive effects of reduced salinity and reduced pH on the hatching of crown-of-thorns seastars. Overall, we found that reduced salinity has strong negative effects on fertilisation and early development, as has been shown in other echinoderm species. We also found that reduced salinity delays hatching but that reduced pH, in isolation or in combination with lower salinity, had no detectable effects on this developmental milestone. Models that assess the positive effects of terrestrial runoff on the development of crown-of-thorns seastars should also consider the strong negative effects of lower salinity on early development including lower levels of fertilisation, increased frequency of abnormal development and delayed time to hatching.
Allen, Jonathan D.; Schrage, Kharis R.; Foo, Shawna A.; Watson, Sue-Ann; and Byrne, Maria, The Effects of Salinity and pH on Fertilization, Early Development and Hatching in the Crown-of-Thorns Seastar (2017). Diversity, 9, 13.