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Coral-reef ecosystems are experiencing frequent and severe disturbance events that are reducing global coral abundance and potentially overwhelming the natural capacity for reefs to recover. While mitigation strategies for climate warming and other anthropogenic disturbances are implemented, coral restoration programmes are being established worldwide as an additional conservation measure to minimise coral loss and enhance coral recovery. Current restoration efforts predominantly rely on asexually produced coral fragments—a process with inherent practical constraints on the genetic diversity conserved and the spatial scale achieved. Because the resilience of coral communities has hitherto relied on regular renewal with natural recruits, the scaling-up of restoration programmes would benefit from greater use of sexually produced corals, which is an approach that is gaining momentum. Here we review the present state of knowledge of scleractinian coral sexual reproduction in the context of reef restoration, with a focus on broadcast-spawning corals. We identify key knowledge gaps and bottlenecks that currently constrain the sexual production of corals and consider the feasibility of using sexually produced corals for scaling-up restoration to the reef- and reef-system scales.

Coral cover has declined markedly in the recent past in many regions of the world, including the Great Barrier Reef (GBR), Australia. The major causes of this decline are generally considered to be mortality associated with large-scale severe disturbances (i.e. catastrophic mortality), such as Acanthaster planci outbreaks, cyclones and bleaching. However, background rates of mortality (i.e. not associated with catastrophic disturbance), are rarely quantified, but without these it is difficult to assess the relative importance of these 2 types of mortality (catastrophic and background). We quantified spatial and temporal variation in catastrophic and background whole-colony mortality of the common reef coral Acropora millepora over 24 mo at 2 sites in 3 regions separated by 700 km along the GBR. The study period included 2 cyclones and a flood. Overall mortality rates were exceptionally high. Of 180 colonies tagged in April 2009, only 36 (20%) were alive in April 2011, and 68% of this mortality occurred in intervals following the 3 large disturbances. Background mortality rates were also high in the Palm Islands, where they approached 40% yr-1 compared to

This manuscript was improved by constructive comments from the Responsible Editor and 2 anonymous reviewers. This study was supported by the Endeavour International and JCU Postgraduate Research Scholarship to K.M.Q., the Australian Research Council grant, through the ARC Centre of Excellence for Coral Reef Studies, to B.L.W., and by funding from the Australian Institute of Marine Science to L.K.B.

Sexual reproduction is vital for population persistence, even in organisms that can reproduce asexually, such as corals. Yet, information on spatial and temporal variation in reproductive traits is surprisingly rare. Here, we examined spatial and temporal variation in fecundity, defined as the number of oocytes per polyp, in the staghorn coral Acropora millepora over 2 yr among 6 populations separated by over 700 km on inshore reefs on the Great Barrier Reef. Variation in fecundity was greatest at small spatial scales: there were pronounced differences in fecundity within and among colonies at each site but little variation at the site or regional scale. This suggests that fecundity is affected by environmental variables that also vary at small scales, such as light and water flow, rather than variables that vary on a regional scale, such as temperature. Colony fecundity in the first year was a good predictor of colony fecundity in the second year, suggesting that some genotypes are more fecund than others. This research suggests that factors operating at the scale of the individual, such as microhabitat differences in flow or light, or genetic identity, are the main cause of variation in fecundity among coral colonies.

The impact of a mass bleaching event on temporal and spatial population genetic struc- ture in 4 scleractinian coral species in the Acropora aspera group was studied around the Palm Islands in the central Great Barrier Reef. Species status of sympatric populations of 2 of the 4 species, A. millepora and A. spathulata, was confirmed by the population genetic data; these species have recently been separated based on morphological and breeding characters. Spatial analyses of popu- lation samples from 2004 detected differences in the level of gene flow among locations. No signifi- cant genetic differentiation was inferred between conspecific populations at Orpheus and Pelorus Islands, which are both located in the northern part of the island group and separated by ~1000 m. In contrast, all populations at Fantome Island were genetically differentiated, despite this island being located only 11 km south. Sampling of A. millepora and A. pulchra in the year prior to the 1998 mass bleaching event enabled a temporal comparison across this event. The genetic composition of these populations changed between 1997 and 2004, but patterns of genetic differentiation among locations were similar in 1997 and 2004. Extensive mortality of these species following the 1998 bleaching event did not cause an apparent reduction in genetic diversity and identical multi-locus genotypes were encountered in both temporal samples, suggesting that re-growth of surviving genotypes con- tributed to the recovery of these populations. Comparisons among the 4 study species revealed lower genetic diversity in A. papillare, consistent with its low abundance throughout its distributional range.