Uncovering drivers of juvenile coral density following mass bleaching

Abstract

Thermally induced mass coral bleaching is globally responsible for major losses of coral cover. Coral recovery from mass coral disturbances like the 2016 bleaching event hinges on successful recruitment of new coral colonies to the existing population. Juvenile corals as a life history stage represent survival and growth of new recruits. As such, habitat preferences of juvenile corals and how environmental parameters interact to drive coral recovery following a mass bleaching disturbance are important research areas. To expand our knowledge on this topic, we compared juvenile coral densities from before the 2016 bleaching event with those after the disturbance and identified abiotic and biotic characteristics of 21 reefs in the inner Seychelles that predict juvenile coral densities. Our results show that following the 2016 bleaching event, juvenile coral densities were significantly reduced by about 70%, with a particularly large decline in juvenile Acropora. Macroalgae present a large obstacle to survival of juvenile corals in a post-bleaching setting, but their influence varies as a function of herbivore biomass, reef structure, and reef type. Higher biomass of herbivorous fish weakens the negative effect of macroalgae on juvenile corals, and structural complexity on granitic reefs is a strong positive predictor of juvenile coral density. However, structural complexity on carbonate or patch reefs was negatively related to juvenile coral density, highlighting the importance of considering interactive terms in analyses. Our study emphasises the importance of habitat for juvenile coral abundance at both fine and seascape scales, adding to the literature on drivers of reef rebound potential following severe coral bleaching. Keywords Coral reef recovery Á Recruitment Á Coral bleaching Á Coral reef ecology Á Macroalgae Á Seychelles Topic Editor Morgan S. Pratchett

Southwestern Atlantic reef-building corals Mussismilia spp. are able to spawn while fully bleached

“…used in this study. Coral spawning during or after bleaching recovery have been observed in the Indo-Pacific (Ward et al 2000;Cox 2007;Dajka et al 2019;Sakai et al 2020) and the Caribbean (Levitan et al 2014;Hagedorn et al 2016;Fisch et al 2019), however, this is the first report demonstrating the ability of corals to spawn and form viable larvae while fully bleached. The bleaching condition was assessed through the color reference chart and it did correspond to low symbiont concentrations.…”

Shaping coral traits: plasticity more than filtering

“…As a result, algal cover decreases possibly due to the increase of herbivores (49). Structural complexity also correlates with coral diversity and abundance (50) and with the reef ability of recovering faster after disturbance (51). Here we show that the shape of structure is highly responsive to shifting environmental conditions.…”

Abiotic and biotic controls on coral recovery 16 years after mass bleaching

“…In Seychelles, reef-level variation in coral recruitment appears to be driven by benthic habitat properties rather than larval supply. Survivorship of juvenile corals to adults is lower on unstable rubble reefs that are frequently disturbed by wave action (Chong-Seng et al 2014), and juvenile coral recovery from severe bleaching is moderated by habitat complexity (Dajka et al 2019). Nitrogen enrichment, however, may have had an additional, indirect influence on recovery times by stimulating algal growth.…”