The reproduction of the Red Sea coral Stylophora pistillata from Eilat: 4-decade perspective

Sexual reproduction characteristics of Stylophora pistillata, one of the most common coral species in the Gulf of Eilat, Red Sea, were extensively studied in the 1970s and 1980s. Four decades later, we examined possible changes in reproductive patterns in this species by placing planula traps over S. pistillata colonies during the 2015 and 2016 reproductive seasons. In total, 708 larval traps (222 traps in 2015 and 486 in 2016) were used, collecting 31,396 planulae overall (12,455 in 2015 and 18,852 in 2016). The results of this 2-year study indicated (a) lengthening of the reproductive season by up to 2 months (until mid-September 2015 and August 2016), (b) an extension of peaks in larval release from 2-3 to 5-6 months, (c) an increase in the percentage of colonies that release planula larvae, and (d) a high variability in larval release among different colonies and between consecutive collecting dates. All the above reflect decadal differences in the reproductive effort in S. pistillata. Furthermore, this study reveals that S. pistillata colonies stop releasing planulae after sea surface temperature (SST) reaches its annual peak, contrasting with the earlier finding that planula release ended before the annual SST peak. We propose that global change impacts and an increase in anthropogenic activities in the Gulf of Eilat are the culprit behind the reported changes in coral reproductive traits over the past 4 decades.