Abstract
Sexual reproduction is fundamental to the maintenance and recovery of coraldominated 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° 6.6’ S, 109° 25.5’W) 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.
Highlights
Reproductive pattern, timing and degree of spawning synchrony within and among scleractinian coral species can vary widely among coral assemblages in different regions (e.g. Wilson & Harrison 2003, Baird et al 2009, Harrison 2011, Glynn et al 2017, Romero-Torres et al 2017)
Fig. 1) on the northwest coast of Rapa Nui, which is light on potential proximate cues by which corals relatively more protected from severe waves gener- initiate gametogenesis and spawning, we examined ated by Antarctic ground swell originating from in situ temperature and wind data
Temporal progression in the proportional increase of mature (Stage IV) oocytes concurrently with mean ova size within a breeding season was clearly observed in P. lobata, but not P. verrucosa (Fig. 5B)
Summary
Reproductive pattern, timing and degree of spawning synchrony within and among scleractinian coral species can vary widely among coral assemblages in different regions Scleractinian coral and zooxanthellae assemblages here, which are best developed along the northern and western coast and extend below 60 m depth, are at their austral limit (Hubbard & Garcia 2003, Glynn et al 2017) They share closest compositional affinities with the Eastern Tropical Pacific, rather than westward Polynesia (Glynn et al 2007, 2017, Veron et al 2015), and the documented lack of gene flow and restricted dispersal potential suggest that isolation from the central Pacific is persistent, even under variable El Niño−Southern Oscillation and La Niña conditions
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