Energetic and reproductive costs of coral recovery in divergent bleaching responses

Abstract

Mass thermal bleaching events are a primary threat to coral reefs, yet the sublethal impacts, particularly on energetics and reproduction, are poorly characterized. Given that the persistence of coral populations is contingent upon the reproduction of individuals that survive disturbances, there is an urgent need to understand the sublethal effects of bleaching on reproductive output to accurately predict coral recovery rates. In 2019, the French Polynesian island of Mo’orea experienced a severe mass bleaching event accompanied by widespread coral mortality. At the most heavily impacted sites, we observed Acropora hyacinthus individuals that were resistant to bleaching, alongside colonies that bleached but showed signs of symbiont recovery shortly after the bleaching event. We collected fragments from A. hyacinthus colonies five months post-bleaching and, using energetic assays and histological measurements, examined the physiological and reproductive consequences of these two distinct heat stress responses. Despite healthy appearances in both resistant and recovered corals, we found that recovered colonies had significantly reduced energy reserves compared to resistant colonies. In addition, we detected compound effects of stress on reproduction: recovered colonies displayed both a lower probability of containing gametes and lower fecundity per polyp. Our results indicate that bleaching inflicts an energetic constraint on the concurrent re-accumulation of energy reserves and development of reproductive material, with decreased reproductive potential of survivors possibly hampering overall reef resilience. These findings highlight the presence of intraspecific responses to bleaching and the importance of considering multiple trajectories for individual species when predicting population recovery following disturbance.

Endosymbiont strategic shifts inhibit cooperation during coral bleaching recovery

“…Host lipids continued to deplete after heat stress abated (p = 0.027, Fig. 3I), which is consistent with prior evidence that corals remain energetically limited during bleaching recovery [60], and in particular that this population of M. capitata catabolizes lipids to survive bleaching [61] and takes at least 6 weeks to replenish energy reserves [62]. Given that M. capitata can also compensate for lost symbionts by increasing heterotrophy [63], the sluggish early recovery we observed may have been mitigated if we had fed corals during the experiment.…”

“…Such a strategic shift at the expense of the coral could explain why energetic losses from bleaching can persist for months (e.g. [60]), and why sexual reproduction can suffer even years after colonies regain normal symbiont populations (e.g. [79, 80]).…”

Green fluorescent protein-like pigments optimise the internal light environment in symbiotic reef-building corals

“…Aside from variability in skeletal morphology, tissue-level changes such as contraction and expansion are known to affect light penetration ( Wangpraseurt et al, 2014a ; Wangpraseurt et al, 2017b ). The thickness and composition of the tissue can be affected by a number of variables, including genotype, nutritional status, seasonality, and environmental history ( Harland et al, 1992 ; Jones et al, 2020 ; Leinbach et al, 2021 ; Lough and Barnes, 2000 ; Rocker et al, 2019 ). Changes in tissue composition (e.g.…”

Coral‐bleaching responses to climate change across biological scales

“…Consequently, calcification rates do not return to “normal” for months after bleaching (Rodrigues & Grottoli, 2006). Other post‐bleaching ramifications may include the following: (i) increased disease susceptibility (Muller et al, 2008), (ii) destabilization of the coral's bacterial and viral communities (Messyasz et al, 2020; Ziegler et al, 2017), (iii) reductions in antibiotic properties of coral mucus (Ritchie, 2006), (iv) prolonged dependence on heterotrophically derived carbon (Hughes & Grottoli, 2013), (v) suppression of the coral immune system (Pinzón et al, 2015), and (vi) reductions in reproductive output (Fisch et al, 2019; Leinbach et al, 2021; Ward et al, 2000) that can be suppressed years after bleaching (Johnston et al, 2020; Levitan et al, 2014; Figure 3).…”