Scleractinian corals are the main framework builders on coral reefs, creating much of the structural complexity needed to support species biodiversity (Moberg and Folke 1999). Coral reefs serve as breeding grounds, nurseries, habitat for reef-associated organisms, and protect shorelines (Sutton 1983, Sale 1991, Done et al. 1996, Sheppard et al. 2009, Beck et al 2018). High economic value of the reefs can be derived from these different functions and environmental services, making it one of the most important marine ecosystems (de Groot et al. 2012, Costanza et al. 2014, Woodhead et al. 2019). Despite the importance of coral reefs, global and local disturbances such as ocean warming, unregulated aquaculture resulting in eutrophication, and overfishing continue to threaten their persistence and survival (Hilomen and Jimenez 2001, Hoegh-Guldberg et al. 2007, San Diego-Mcglone et al. 2008, Hughes et al. 2018a, 2018b). Following disturbances, coral populations rely heavily on recruitment of juvenile corals derived from sexual reproduction to ensure natural recovery, and hence, recruitment success is in turn reliant on the abundance of reproductively mature colonies (Underwood and Fairweather 1989; Hughes et al. 2000). It is therefore important to determine the age and size at the onset of reproductive maturity of common scleractinian corals for the appropriate management of our reefs.

 

Corals reproduce either asexually through natural fragmentation or sexually through the production of gametes and larvae. Developed gametes are either brooded internally wherein fertilization takes place inside the polyp, releasing swimming larvae into the water column or broadcast spawned into the water column for external fertilization (Harrison and Wallace 1990, Baird et al. 2009, Schmidt-Roach et al. 2012). Corals have a biphasic life cycle having a shorter larval phase and longer benthic phase until sexual maturity (Harrison 2011). Larvae settle on the substrate approximately 1 to 4 days post-fertilization at the earliest which calcify and grow until and beyond sexual maturity (Miller and Mundy 2003; Nishikawa et al. 2003; Toh et al. 2012). Coral recruits undergo maturation from juvenile to adult before they are capable of sexual reproduction and finally completing the coral’s life cycle (Szmant-Froelich 1985).