Patterns in sexual reproduction of the dominant scleractinian corals at Rapa Nui (Easter Island): Pocillopora verrucosa and Porites lobata

Abstract

Sexual reproduction is fundamental to the maintenance and recovery of coral-dominated communities in high-latitude and isolated locations, where replenishment often depends on local reproductive activity rather than recruitment from distant reefs. Rapa Nui (Easter Island) is one of the most remote islands in the Pacific, lying at the southern, subtropical edge of the range of reef-building scleractinians. Here, we describe the sexual reproduction and timing of the 2 dominant corals, Pocillopora verrucosa and Porites lobata. Reproductive activity was inferred from the identification and staging of gametes via histological analyses of monthly samples collected from December 2012 to May 2014 at 12 m depth at Motu Tautara (27∞6.6íS, 109∞25.5íW) with in situ temperature records. In P. verrucosa, the observed hermaphroditic activity spanned from December to January, resulting in mature oocytes of 117 µm mean diameter. In P. lobata, observed gonochoric activity spanned from December to March, resulting in mature oocytes of 180 µm mean diameter. The observed initiation of gametogenic cycles coincided with the onset of spring warming in both species. Inferred spawning of P. verrucosa followed a relatively calm period of daily variance reduction in local in situ temperature and wind speed prior to the peak in thermal conditions, whereas inferred spawning of P. lobata coincided with peak temperatures in one year but not the other. We suggest temporal restrictions of disruptive coastal activities such as dredging during coral spawning periods and mitigation of land-based sources of pollution and watershed discharge that may reduce water quality.