Dangerous demographics in post-bleach corals reveal boom-bust versus protracted declines

Abstract

Thermal-stress events have changed the structure, biodiversity, and functioning of coral reefs. But how these disturbances affect the dynamics of individual coral colonies remains unclear. By tracking the fate of 1069 individual Acropora and massive Porites coral colonies for up to 5 years, spanning three bleaching events, we reveal striking genus-level differences in their demographic response to bleaching (mortality, growth, and recruitment). Although Acropora colonies were locally extirpated, substantial local recruitment and fast growth revealed a marked capacity for apparent recovery. By contrast, almost all massive Porites colonies survived and the majority grew in area; yet no new colonies were detected over the 5 years. Our results highlight contrasting dynamics of boom-and-bust vs. protracted declines in two major coral groups. These dangerous demographics emphasise the need for caution when documenting the susceptibility and perceived resistance or recovery of corals to disturbances.

Prevalence and extent of coral diseases in shallow and mesophotic reefs of the Southwestern Atlantic

“…These results indicate that S. stellata and M. cavernosa are afflicted by disease to different extents. Although these two species have massive growth form and may have similar susceptibility strategy (Loya et al 2001;Morais et al 2021), M. cavernosa is usually classified as a stress-tolerant species, while S. stellata is reported as weedy species (Darling et al 2012). Our finding agrees with this classification and supports previous studies that have shown the genus Siderastrea to have up to four times more prevalence of disease than the genus Montastraea (Calnan et al 2007).…”

Highly variable response of hard coral taxa to successive coral bleaching events (2019-2020) and rising ocean temperatures in Northeast Peninsular Malaysia

“…Ultimately, mean seawater temperatures are perpetually rising around Pulau Lang Tengah (Figure 2), in addition to higher frequencies of thermal anomalies that surpass the thermal maxima of scleractinian taxa, causing repeated thermal stress. Regardless of differences in thermal tolerance and low mortality rates post bleaching events as those reported here (Figure 4 and Supplementary S5), such warming trends and resulting bleaching events selectively pressure scleractinian communities by altering scleractinian community assemblages (Loya et al, 2001; Baker et al, 2008, Hughes et al, 2018a), and likely influence demographic processes in surviving colonies who suffer high bleaching severity, such as massive Porites (Morais et al, 2021). Thus, severe annual coral bleaching will represent an imminent risk to coral reef survival and integrity (Van Hooidonk et al, 2017 (UNEP)).…”

“…We acknowledge that genetic and cellular process are underpinning heat stress response in hard corals and that these can only be investigated on species level (Grottoli et al, 2014;Schoepf et al, 2015;Guzman et al, 2018). However, there is strong evidence that certain functional traits required for establishing thermally tolerant populations after large scale disturbance events, are phylogenetically conserved on genus level (Darling et al, 2012;Morais et al, 2021). Such traits include growth, fecundity and reproductive mode, and further supporting evidence is presented by Alvarez-Noriega et al (2016), who suggest that fecundity can be predicted by coral colony morphology.…”

“…In contrast to the above, two taxa ( Acropora , and Montipora ) displayed contrasting bleaching hierarchies and improved thermal tolerance as compared historical records (McClanahan et al, 2004; Guest et al, 2012; Pratchett et al, 2013), suggesting thermal adaptation due to directional selection, rather than thermal acclimation. Whereas species-specific genetic and cellular process are underpinning heat stress response in hard corals (Grottoli et al, 2014; Schoepf et al, 2015; Guzman et al, 2018), there is strong evidence that certain functional traits required for establishing thermally tolerant populations after large scale disturbance events are phylogenetically conserved on genus level (Darling et al, 2012; Morais et al, 2021). Such traits include growth, fecundity and reproductive mode, and further supporting evidence is presented by Alvarez-Noriega et al (2016), who suggest that fecundity can be predicted by coral colony morphology.…”

“…Subsequently, successful reproduction and recruitment of the surviving genotypes and taxa with fast growth and reproduction (Darling et al, 2012), perchance resulted in a directional selection since 1998 and 2010 of thermally tolerant genotypes of taxa historically classified as thermally susceptible (Edmunds, 1994; Thompson and van Woesik, 2009). Dramatic short-term recovery (e.g., <5 years) of depleted Acropora populations after bleaching events in 2016 and 2017 has been evidently highlighted on the Great Barrier Reef, whereby genus-wide recovery was facilitated by traits such as quick growth and reproduction (Morais et al, 2021). Furthermore, recent studies suggest that thermal stress does not impede heritability of functional traits responsible for growth and survival (Bairos-Novak et al, 2021), and greater thermal plasticity in surviving offspring has been demonstrated (Wong et al, 2021).…”