Implications of high rates of sexual recruitment in driving rapid reef recovery in Mo’orea, French Polynesia

Abstract

Coral abundance continues to decline on tropical reefs around the world, and this trend suggests that coral reefs may not persist beyond the current century. In contrast, this study describes the near-complete mortality of corals on the outer reef (10 m and 17 m depth) of the north shore of Mo’orea, French Polynesia, from 2005 to 2010, followed by unprecedented recovery from 2011 to 2017. Intense corallivory and a cyclone drove coral cover from 33–48% to <3% by 2010, but over the following seven years, recovery occurred through rapid population growth (up to 12% cover y−1) to 25–74% cover by 2017. The thirteen-year, U-shape trajectory of coral cover over time created by the loss and replacement of millions of corals through sexual reproduction underscores the potential for beneficial genetic responses to environmental conditions for at least one genus, Pocillopora. The high ecological resilience of this coral community appears to have been enhanced by variation among genera in the susceptibility to declining cover, and the capacity for population growth (i.e., response diversity). These results suggest that the outer coral communities of Mo’orea may be poised for genetic changes that could affect their capacity to persistence.

Relative roles of biological and physical processes influencing coral recruitment during the lag phase of reef community recovery

“…Our findings show that, overall, processes driving recruitment success were hierarchal, often indirect, and occurred at different spatial scales. Coral settlement was found to be highly variable through time and space, as shown in previous studies [39][40][41] . Such variability highlights the common occurrence of recruitment pulses driven by larval supply in marine ecosystems, as settlement rates were only weakly explained by biophysical predictors at the scale of the tiles.…”

Deficits in functional trait diversity following recovery on coral reefs

“…In terrestrial landscapes, for example, loss of large, long-lived trees can lead to depleted states that are functionally compromised for decades or longer because of the limited capacity of these taxa to recruit and recover following elevated mortality [56]. Low levels of survival among corals in this analysis have led to limited response diversity, and has favoured taxa with smaller, shorter and simpler morphologies, with moderateto-fast growth rates, and 'weedy' life-history traits, such as high size-specific fecundity [57], and high rates of mortality and recruitment [50,58]. Such taxa are often more susceptible to storms [59], mass bleaching [48] and predator outbreaks [36], potentially limiting response diversity during future successive disturbance events.…”

“…In corals, response diversity can arise from various sources, including differences in recruitment rate [50], biomechanical stability [51] and bleaching tolerance [48]. As climate change progresses, differences in thermal tolerance among photosynthetic symbionts (Symbiodinium) may be a valuable source of response diversity, allowing some species or populations of corals to survive severe bouts of heat stress while others decline [52,53].…”

Coral bleaching susceptibility is predictive of subsequent mortality within but not between coral species

“…fish (Pratchett et al , 2011; Darling et al , 2017; Richardson et al , 2018). Coral mortality following bleaching can also alter the structure of the coral community itself, as bleaching-susceptible species are lost from the community (Loya et al , 2001; McClanahan, 2004; Baker et al , 2008; Bahr et al , 2017; Hughes et al , 2017) while stress-tolerant species remain (Edmunds, 2018; Hughes, Kerry, et al , 2018) and “weedy” genera that are better suited for rapid recovery following bleaching become dominant (Darling et al , 2012; Edmunds, 2018). These changes in community composition alter the ecological function of the reef (Alvarez-Filip et al , 2013), which alongside the structural degradation following bleaching leads to declines in ecosystem goods and services ranging from fisheries production to coastal protection and tourism (Munday et al 2008).…”

“…On a global scale, there is recent evidence that the temperature threshold for coral bleaching has risen in correspondence with global warming, suggesting widespread acclimatization and/or adaptation (Coles et al , 2018; DeCarlo et al , 2019). Alternatively, differences in the composition of coral communities between reefs can also influence bleaching extent due to species-specific differences in thermal tolerance (Rowan et al , 1997; Berkelmans and Van Oppen, 2006; Sampayo et al , 2008; Swain et al , 2016; Edmunds, 2018). Indeed, the global loss of many thermally sensitive coral species from reef communities (e.g.…”