The legacy of stress: Coral bleaching impacts reproduction years later

The extent to which populations persist under environmental stress depends on the reproductive output of individuals that survive the stress. In coral systems, corals bleach in response to stress from elevated water temperature. However, little is known of the extent to which thermal stress impairs the reproductive capacity of the survivors over the following years, limiting the capacity to predict how populations will persist in the Anthropocene. Using histology to quantify the abundance and size of oocytes and spermaries per polyp, we tested how bleaching impairs the reproductive response of the coral Pocillopora meandrina over two reproductive seasons following the 2015 mass bleaching event in the Hawaiian Islands. We found that smaller colonies not only had a greater probability of bleaching but also suffered greater reproductive impacts over a longer time. In contrast, larger colonies generated comparable reproductive output regardless of bleaching severity, although bleached colonies generated smaller oocytes the year after bleaching. These results show that reproductive impacts of bleaching are more complex and size‐specific than commonly assumed. Therefore, estimates of bleaching mortality may underestimate the true impact of thermal stress on populations, especially as populations lose larger individuals from repeated and co‐occurring stressors. A free Plain Language Summary can be found within the Supporting Information of this article.